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<h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2024/11/antenna-diodes-in-pentium-processor.html'>Antenna diodes in the Pentium processor</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-347521141499861916' itemprop='description articleBody'> <p>I was studying the silicon die of the Pentium processor and noticed some puzzling structures where signal lines were connected to the silicon substrate for no apparent reason. Two examples are in the photo below, where the metal wiring (orange) connects to small square regions of doped silicon (gray), isolated from the rest of the circuitry. I did some investigation and learned that these structures are "antenna diodes," special diodes that protect the circuitry from damage during manufacturing. In this blog post, I discuss the construction of the Pentium and explain how these antenna diodes work.</p> <p><a href="https://static.righto.com/images/pentium-antenna/diodes.jpg"><img alt="Closeup of the Pentium die showing the silicon and bottom metal layer. The arrows indicate connections to two antenna diodes. I removed the top two layers of metal for this photo." class="hilite" height="265" src="https://static.righto.com/images/pentium-antenna/diodes-w450.jpg" title="Closeup of the Pentium die showing the silicon and bottom metal layer. The arrows indicate connections to two antenna diodes. I removed the top two layers of metal for this photo." width="450" /></a><div class="cite">Closeup of the Pentium die showing the silicon and bottom metal layer. The arrows indicate connections to two antenna diodes. I removed the top two layers of metal for this photo.</div></p> <p>Intel released the Pentium processor in 1993, starting a long-running brand of high-performance processors: the Pentium Pro, Pentium II, and so on. In this post, I'm studying the original Pentium, which has 3.1 million transistors.<span id="fnref:versions"><a class="ref" href="#fn:versions">1</a></span> The die photo below shows the Pentium's fingernail-sized silicon die under a microscope. The chip has three layers of metal wiring on top of the silicon so the underlying silicon is almost entirely obscured.</p>  <p><a href="https://static.righto.com/images/pentium-antenna/pentium-labeled.jpg"><img alt="The Pentium die with the main functional blocks labeled. Click this photo (or any other) for a larger version." class="hilite" height="525" src="https://static.righto.com/images/pentium-antenna/pentium-labeled-w500.jpg" title="The Pentium die with the main functional blocks labeled. Click this photo (or any other) for a larger version." width="500" /></a><div class="cite">The Pentium die with the main functional blocks labeled. Click this photo (or any other) for a larger version.</div></p> <p>Modern processors are built from CMOS circuitry, which uses two types of transistors: NMOS and PMOS. The diagram below shows how an NMOS transistor is constructed. A transistor can be considered a switch between the source and drain, controlled by the gate. The source and drain regions (green) consist of silicon doped with impurities to change its semiconductor properties, forming N+ silicon. The gate consists of a layer of polysilicon (red), separated from the silicon by an absurdly thin insulating oxide layer. Since the oxide layer is just a few hundred atoms thick,<span id="fnref:gate"><a class="ref" href="#fn:gate">2</a></span> it is very fragile and easily damaged by excess voltage. (This is why CMOS chips are sensitive to static electricity.) As we will see, the oxide layer can also be damaged by voltage during manufacturing.</p> <p><a href="https://static.righto.com/images/pentium-antenna/mosfet-n.jpg"><img alt="Diagram showing the structure of an NMOS transistor." class="hilite" height="231" src="https://static.righto.com/images/pentium-antenna/mosfet-n-w400.jpg" title="Diagram showing the structure of an NMOS transistor." width="400" /></a><div class="cite">Diagram showing the structure of an NMOS transistor.</div></p> <p>The Pentium processor is constructed from multiple layers. Starting at the bottom, the Pentium has millions of transistors similar to the diagram above. Polysilicon wiring on top of the silicon not only forms the transistor gates but also provides short-range wiring. Above that, three layers of metal wiring connect the parts of the chip. Roughly speaking, the bottom layer of metal connects to the silicon and polysilicon to construct logic gates from the transistors, while the upper layers of wiring travel longer distances, with one layer for signals traveling horizontally and the other layer for signals traveling vertically. Tiny tungsten plugs called vias provide connections between the different layers of wiring. A key challenge of chip design is routing, directing signals through the multiple layers of wiring while packing the circuitry as densely as possible.</p> <p>The photo below shows a small region of the Pentium die with the three metal layers visible. The golden vertical lines are the top metal layer, formed from aluminum and copper. Underneath, you can see the horizontal wiring of the middle metal layer. The more complex wiring of the bottom metal layer can be seen, along with the silicon and polysilicon that form transistors. The small black dots are the tungsten vias that connect metal layers, while the larger dark circles are contacts with the underlying silicon or polysilicon. Near the bottom of the photo, the vertical gray bands are polysilicon lines, forming transistor gates. Although the chip appears flat, it has a three-dimensional structure with multiple layers of metal separated by insulating layers of silicon dioxide. This three-dimensional structure will be important in the discussion below. (The metal wiring is much denser over most of the chip; this region is one of the rare spots where all the layers are visible.)</p> <p><a href="https://static.righto.com/images/pentium-antenna/metal-layers.jpg"><img alt="Closeup of the Pentium die showing the metal layers. The L-shaped hook towards the lower left is a connection to an antenna diode. This photo shows a tiny part of the floating point unit. To show all the layers in focus, I combined multiple images with focus stacking." class="hilite" height="430" src="https://static.righto.com/images/pentium-antenna/metal-layers-w400.jpg" title="Closeup of the Pentium die showing the metal layers. The L-shaped hook towards the lower left is a connection to an antenna diode. This photo shows a tiny part of the floating point unit. To show all the layers in focus, I combined multiple images with focus stacking." width="400" /></a><div class="cite">Closeup of the Pentium die showing the metal layers. The L-shaped hook towards the lower left is a connection to an antenna diode. This photo shows a tiny part of the floating point unit. To show all the layers in focus, I combined multiple images with focus stacking.</div></p> <p>The manufacturing process for an integrated circuit is extraordinarily complicated but I'll skip over most of the details and focus on how each metal layer is constructed, layer by layer. First, a uniform metal layer is constructed over the silicon wafer. Next, the desired pattern is produced on the surface using a process called photolithography: a light-sensitive chemical called "resist" is applied to the wafer and exposed to light through a patterned mask. The light hardens the resist, creating a protective coating with the pattern of the desired wiring. Finally, the unprotected metal is etched away, leaving the wiring.</p> <p>In the early days of integrated circuits, the metal was removed with liquid acids, a process called wet etching. Inconveniently, wet etching tended to eat away metal underneath the edges of the mask, which became a problem as integrated circuits became denser and the wires needed to be thinner. The solution was dry etch, using a plasma to remove the metal. By applying a large voltage to plates above and below the chip, a gas such as HCl is ionized into a highly reactive plasma. This plasma attacks the surface (unless it is protected by the resist), removing the unwanted metal. The advantage of dry etching is that it can act vertically (anisotropically), providing more control over the line width.</p> <p>Although plasma etching improved the etching process, it caused another problem: plasma-induced oxide damage, also called (metaphorically) the "antenna effect."<span id="fnref:antenna"><a class="ref" href="#fn:antenna">3</a></span> The problem is that long metal wires on the chip could pick up an electrical charge from the plasma, producing a large voltage. As described earlier, the thin oxide layer under a transistor's gate is sensitive to voltage damage. The voltage induced by the plasma can destroy the transistor by blowing a hole through the gate oxide or it can degrade the transistor's performance by embedding charges inside the oxide layer.<span id="fnref:damage"><a class="ref" href="#fn:damage">4</a></span></p> <p>Several factors affect the risk of damage from the antenna effect. First, only the transistor's gate is sensitive to the induced voltage, due to the oxide layer. If the wire is also connected to a transistor's source or drain, the wire is "safe" since the source and drain provide connections to the chip's substrate, allowing the charge to dissipate harmlessly. Note that when the chip is completed, every transistor gate is connected to another transistor's source or drain (which provides the signal to the gate), so there is no risk of damage. Thus, the problem can only occur during manufacturing, with a metal line that is connected to a gate on one end but isn't connected on the other end. Moreover, the highest layer of metal is "safe" since everything is connected at that point. Another factor is that the induced voltage is proportional to the length of the metal wire, so short wires don't pose a risk. Finally, only the metal layer currently being etched poses a risk; since the lower layers are insulated by the thick oxide between layers, they won't pick up charge.</p> <p>These factors motivate several ways to prevent antenna problems.<span id="fnref:papers"><a class="ref" href="#fn:papers">5</a></span> First, a long wire can be broken into shorter segments, connected by jumpers on a higher layer. Second, moving long wires to the top metal layer eliminates problems.<span id="fnref:top-metal"><a class="ref" href="#fn:top-metal">6</a></span> Third, diodes can be added to drain the charge from the wire; these are called "antenna diodes". When the chip is in use, the antenna diodes are reverse-biased so they have no electrical effect. But during manufacturing, the antenna diodes let charge flow to the substrate before it causes problems.</p> <p>The third solution, the antenna diodes, explains the mysterious connections that I saw in the Pentium. In the diagram below, these diodes are visible on the die as square regions of doped silicon. The larger regions of doped silicon form PMOS transistors (upper) and NMOS transistors (lower). The polysilicon lines are faintly visible; they form transistor gates where they cross the doped silicon. (For this photo, I removed all the metal wiring.)</p> <p><a href="https://static.righto.com/images/pentium-antenna/silicon-diagram.jpg"><img alt="Closeup of the Pentium die showing transistors. The metal and polysilicon layers have been removed to show the silicon." class="hilite" height="574" src="https://static.righto.com/images/pentium-antenna/silicon-diagram-w450.jpg" title="Closeup of the Pentium die showing transistors. The metal and polysilicon layers have been removed to show the silicon." width="450" /></a><div class="cite">Closeup of the Pentium die showing transistors. The metal and polysilicon layers have been removed to show the silicon.</div></p> <p>Confusingly, the antenna diodes look almost identical to "well taps", connections from the substrate to the chip's positive voltage supply, but have a completely different purpose. In the Pentium, the PMOS transistors are constructed in "wells" of N-type silicon. These wells must be raised to the chip's positive voltage, so there are numerous well tap connections from the positive supply to the wells. The well taps consist of squares of N+ doped silicon in the the N-type silicon well, providing an electrical connection. On the other hand, the antenna diodes also consist of N+ doped silicon, but embedded in P-type silicon. This forms a P-N junction that creates the diode.</p> <p>In the Pentium, antenna diodes are used for only a small fraction of the wiring. The diodes require extra area on the die, so they are used only when necessary. Most of the antenna problems on the Pentium were apparently resolved through routing. Although the antenna diodes are relatively rare, they are still frequent enough that they caught my attention.</p> <p>Antenna effects are still an issue in modern integrated circuits. Integrated circuit fabricators provide rules on the maximum allowable size of antenna wires for a particular manufacturing process.<span id="fnref:rules"><a class="ref" href="#fn:rules">7</a></span> Software checks the design to ensure that the antenna rules are not violated, modifying the routing and inserting diodes as necessary. Violating the antenna rules can result in damaged chips and a very low yield, so it's more than just a theoretical issue.</p> <p>Thanks to <a href="https://www.reddit.com/r/chipdesign/comments/1gwkm65/pentium_why_are_signal_lines_connected_to_the/">/r/chipdesign</a> and Discord for discussion. If you're interested in the Pentium, I've written about <a href="https://www.righto.com/2024/07/pentium-standard-cells.html">standard cells</a> in the Pentium, and the Pentium as a <a href="https://www.righto.com/2024/08/pentium-navajo-fairchild-shiprock.html">Navajo rug</a>. Follow me on Mastodon (<a href="https://oldbytes.space/@kenshirriff">@<span class="__cf_email__" data-cfemail="3259575c415a5b40405b5454725d5e56504b4657411c4142535157">[email protected]</span></a>) or Bluesky (<a href="https://bsky.app/profile/righto.com">@righto.com</a>) or <a href="http://www.righto.com/feeds/posts/default">RSS</a> for updates.</p> <h2>Notes and references</h2> <div class="footnote"> <ol> <li id="fn:versions"> <p>In this post, I'm looking at the Pentium model 80501 (codenamed P5). This model was soon replaced with a faster, lower-power version called the 80502 (P54C). Both are considered original Pentiums. <a class="footnote-backref" href="#fnref:versions" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:gate"> <p><a href="https://www.ardent-tool.com/CPU/docs/MPR/19930531/070705.pdf">IC manufacturing drives CPU performance</a> states that gate oxide thickness was 100 to 300 angstroms in 1993. <a class="footnote-backref" href="#fnref:gate" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:antenna"> <p>The wires are acting metaphorically as antennas, not literally, as they collect charge, not picking up radio waves.</p> <p>Plasma-induced oxide damage gave rise to research and conferences in the 1990s to address this problem. The <a href="https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=715190">International Symposium on Plasma- and Process-Induced Damage</a> started in 1996 and continued until 2003. Numerous researchers from semiconductor companies and academia studied the causes and effects of plasma damage. <a class="footnote-backref" href="#fnref:antenna" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:damage"> <p>The damage is caused by "Fowler-Nordheim tunneling", where electrons tunnel through the oxide and cause damage. Flash memory uses this tunneling to erase the memory; the cumulative damage is why flash memory can only be written a limited number of times. <a class="footnote-backref" href="#fnref:damage" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:papers"> <p>Some relevant papers: <a href="https://doi.org/10.1116/1.585577">Magnetron etching of polysilicon: Electrical damage</a> (1991), <a href="https://doi.org/10.1109/55.145056">Thin-oxide damage from gate charging during plasma processing</a> (1992), <a href="https://doi.org/10.1109/RELPHY.1998.670660">Antenna protection strategy for ultra-thin gate MOSFETs</a> (1998), <a href="https://doi.org/10.1109/ISQED.2000.838883">Fixing antenna problem by dynamic diode dropping and jumper insertion</a> (2000). The Pentium uses the "dynamic diode dropping" approach, adding antenna diodes only as needed, rather than putting them in every circuit. I noticed that the Pentium uses extension wires to put the diode in a more distant site if there is no room for the diode under the existing wiring. As an aside, the third paper uses the curious length unit of k碌m; by calling 1000 碌m a k碌m, you can think in micrometers, even though this unit is normally called a mm. <a class="footnote-backref" href="#fnref:papers" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:top-metal"> <p>Sources say that routing signals on the top metal prevents antenna violations. However, I see several antenna diodes in the Pentium that are connected directly from the bottom metal (M1) through M2 to long lines on M3. These diodes seem redundant since the source/drain connections are in place by that time. So there are still a few mysteries... <a class="footnote-backref" href="#fnref:top-metal" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:rules"> <p>Foundries have antenna rules provided as part of the Process Design Kit (PDK). Here are the rules for <a href="https://www.southampton.ac.uk/~bim/notes/ice/DesignRules/guidelines.html">MOSIS</a> and <a href="https://skywater-pdk.readthedocs.io/en/main/rules/antenna.html">SkyWater</a>. I've focused on antenna effects from the metal wiring, but polysilicon and vias can also cause antenna damage. Thus, there are rules for these layers too. Polysilicon wiring is less likely to cause antenna problems, though, as it is usually restricted to short distances due to its higher resistance. <a class="footnote-backref" href="#fnref:rules" title="Jump back to footnote 7 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/347521141499861916' onclick=''> No comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=347521141499861916' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=347521141499861916&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=347521141499861916&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=347521141499861916&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=347521141499861916&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=347521141499861916&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=347521141499861916&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/electronics' rel='tag'>electronics</a>, <a href='http://www.righto.com/search/label/Pentium' rel='tag'>Pentium</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/wealth2024/wealth-graph2.png' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='1418194258206918136' itemprop='postId'/> <a name='1418194258206918136'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2024/10/wealth-distribution-in-united-states.html'>Wealth distribution in the United States</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-1418194258206918136' itemprop='description articleBody'> <p>Forbes recently published the <a href="https://www.forbes.com/forbes-400/">Forbes 400 List</a> for 2024, listing the 400 richest people in the United States. This inspired me to make a histogram to show the distribution of wealth in the United States. It turns out that if you put Elon Musk on the graph, almost the entire US population is crammed into a vertical bar, one pixel wide. Each pixel is $500 million wide, illustrating that $500 million essentially rounds to zero from the perspective of the wealthiest Americans.</p> <p><img alt="Graph showing the wealth distribution in the United States." height="456" src="https://static.righto.com/images/wealth2024/wealth-graph2.png" width="614"></img></p> <p>The histogram above shows the wealth distribution in red. Note that the visible red line is one pixel wide at the left and disappears everywhere else—this is the important point: essentially the entire US population is in that first bar. The graph is drawn with the scale of 1 pixel = $500 million in the X axis, and 1 pixel = 1 million people in the Y axis. Away from the origin, the red line is invisible—a tiny fraction of a pixel tall since so few people have more than 500 million dollars.</p> <p>Since the median US household wealth is about $190,000, half the population would be crammed into a microscopic red line 1/2500 of a pixel wide using the scale above. (The line would be much narrower than the wavelength of light so it would be literally invisible). The very rich are so rich that you could take someone with a thousand times the median amount of money, and they would still have almost nothing compared to the richest Americans. If you increased their money by a factor of a thousand yet again, you'd be at Bezos' level, but still well short of Elon Musk.</p> <p>Another way to visualize the extreme distribution of wealth in the US is to imagine everyone in the US standing up while someone counts off millions of dollars, once per second. When your net worth is reached, you sit down. At the first count of $1 million, most people sit down, with 22 million people left standing. As the count continues—$2 million, $3 million, $4 million—more people sit down. After <a href="https://content.knightfrank.com/resources/knightfrank.com/wealthreport/the-wealth-report-2024.pdf#page=15">6 seconds</a>, everyone except the "1%" has taken their seat. As the counting approaches the 17-minute mark, only billionaires are left standing, but there are still days of counting ahead. Bill Gates sits down after a bit over one day, leaving 8 people, but the process is nowhere near the end. After about two days and 20 hours of counting, Elon Musk finally sits down.</p> <h1>Sources</h1> <p>The main source of data is the <a href="https://www.forbes.com/forbes-400/">Forbes 400 List</a> for 2024. Forbes claims there are 813 billionaires in the US <a href="https://www.forbes.com/billionaires/">here</a>. Median wealth data is from the <a href="https://www.federalreserve.gov/publications/files/scf23.pdf">Federal Reserve</a>; note that it is from 2022 and household rather than personal. The current US population estimate is from <a href="https://www.worldometers.info/world-population/us-population/">Worldometer</a>. I estimated wealth above $500 million, extrapolating from <a href="https://www.statista.com/statistics/1125846/us-millionaire-distribution-net-worth/">2019</a> data.</p> <p>I made a similar graph in 2013; you can see my post <a href="https://www.righto.com/2013/03/wealth-distribution-in-united-states.html">here</a> for comparison.</p> <p>Disclaimers: Wealth data has a lot of sources of error including people vs households, what gets counted, and changing time periods, but I've tried to make this graph as accurate as possible. I'm not making any prescriptive judgements here, just presenting the data. Obviously, if you want to see the details of the curve, a logarithmic scale makes more sense, but I want to show the "true" shape of the curve. I should also mention that wealth and income are very different things; this post looks strictly at wealth.</p> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/1418194258206918136' onclick=''> 21 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=1418194258206918136' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=1418194258206918136&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1418194258206918136&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1418194258206918136&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1418194258206918136&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1418194258206918136&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=1418194258206918136&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/random' rel='tag'>random</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/f4-attitude-indicator/indicator-w450.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='3021491939457609983' itemprop='postId'/> <a name='3021491939457609983'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2024/09/f4-attitude-indicator.html'>Reverse-engineering a three-axis attitude indicator from the F-4 fighter plane</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-3021491939457609983' itemprop='description articleBody'> <p>We recently received an attitude indicator for the F-4 fighter plane, an instrument that uses a rotating ball to show the aircraft's orientation and direction. In a normal aircraft, the artificial horizon shows the orientation in two axes (pitch and roll), but the F-4 indicator uses a rotating ball to show the orientation in three axes, adding azimuth (yaw).<span id="fnref:fdai"><a class="ref" href="#fn:fdai">1</a></span> It wasn't obvious to me how the ball could rotate in three axes: how could it turn in every direction and still remain attached to the instrument?</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/indicator.jpg"><img alt="The attitude indicator. The "W" forms a stylized aircraft. In this case, it indicates that the aircraft is climbing slightly. Photo from CuriousMarc." class="hilite" height="472" src="https://static.righto.com/images/f4-attitude-indicator/indicator-w450.jpg" title="The attitude indicator. The "W" forms a stylized aircraft. In this case, it indicates that the aircraft is climbing slightly. Photo from CuriousMarc." width="450" /></a><div class="cite">The attitude indicator. The "W" forms a stylized aircraft. In this case, it indicates that the aircraft is climbing slightly. Photo from CuriousMarc.</div></p> <p>We disassembled the indicator, reverse-engineered its 1960s-era circuitry, fixed some problems,<span id="fnref:problems"><a class="ref" href="#fn:problems">2</a></span> and got it spinning. The video clip below shows the indicator rotating around three axes. In this blog post, I discuss the mechanical and electrical construction of this indicator. (The quick explanation is that the ball is really two hollow half-shells attached to the internal mechanism at the "poles"; the shells rotate while the "equator" remains stationary.)</p> <iframe width="560" height="315" src="https://www.youtube.com/embed/uKzj5shVtlo?si=l9hPqevRy1niHm28" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe> <h2>The F-4 aircraft</h2> <p>The indicator was used in the F-4 Phantom II<span id="fnref:phantom-ii"><a class="ref" href="#fn:phantom-ii">3</a></span> so the pilot could keep track of the aircraft's orientation during high-speed maneuvers. The F-4 was a supersonic fighter manufactured from 1958 to 1981. Over 5000 were produced, making it the most-produced American supersonic aircraft ever. It was the main US fighter jet in the Vietnam War, operating from aircraft carriers. The F-4 was still used in the 1990s during the Gulf War, suppressing air defenses in the "Wild Weasel" role. The F-4 was capable of carrying nuclear bombs.<span id="fnref:nuclear"><a class="ref" href="#fn:nuclear">4</a></span></p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/phantom.jpg"><img alt="An F-4G Phantom II Wild Weasel aircraft. From National Archives." class="hilite" height="215" src="https://static.righto.com/images/f4-attitude-indicator/phantom-w500.jpg" title="An F-4G Phantom II Wild Weasel aircraft. From National Archives." width="500" /></a><div class="cite">An F-4G Phantom II Wild Weasel aircraft. From <a href="https://catalog.archives.gov/id/6346124">National Archives</a>.</div></p> <p>The F-4 was a two-seat aircraft, with the radar intercept officer controlling radar and weapons from a seat behind the pilot. Both cockpits had a panel crammed with instruments, with additional instruments and controls on the sides. As shown below, the pilot's panel had the three-axis attitude indicator in the central position, just below the reddish radar scope, reflecting its importance.<span id="fnref:standby"><a class="ref" href="#fn:standby">5</a></span> (The rear cockpit had a simpler two-axis attitude indicator.)</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/cockpit2.jpg"><img alt="The cockpit of the F-4C Phantom II, with the attitude indicator in the center of the panel. Click this photo (or any other) for a larger version. Photo from National Museum of the USAF." class="hilite" height="359" src="https://static.righto.com/images/f4-attitude-indicator/cockpit2-w500.jpg" title="The cockpit of the F-4C Phantom II, with the attitude indicator in the center of the panel. Click this photo (or any other) for a larger version. Photo from National Museum of the USAF." width="500" /></a><div class="cite">The cockpit of the F-4C Phantom II, with the attitude indicator in the center of the panel. Click this photo (or any other) for a larger version. Photo from <a href="https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196051/mcdonnell-douglas-f-4c-phantom-ii/">National Museum of the USAF</a>.</div></p> <h2>The attitude indicator mechanism</h2> <p>The ball inside the indicator shows the aircraft's position in three axes. The roll axis indicates the aircraft's angle if it rolls side-to-side along its axis of flight. The pitch axis indicates the aircraft's angle if it pitches up or down. Finally, the azimuth axis indicates the compass direction that the aircraft is heading, changed by the aircraft's turning left or right (yaw). The indicator also has moving needles and status flags, but in this post I'm focusing on the rotating ball.<span id="fnref:features"><a class="ref" href="#fn:features">6</a></span></p> <p>The indicator uses three motors to move the ball. The roll motor (below) is attached to the frame of the indicator, while the pitch and azimuth motors are inside the ball. The ball is held in place by the roll gimbal, which is attached to the ball mechanism at the top and bottom pivot points. The roll motor turns the roll gimbal and thus the ball, providing a clockwise/counterclockwise movement. The roll control transformer provides position feedback. Note the numerous wires on the roll gimbal, connected to the mechanism inside the ball.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/indicator-diagram.jpg"><img alt="The attitude indicator with the cover removed." class="hilite" height="572" src="https://static.righto.com/images/f4-attitude-indicator/indicator-diagram-w700.jpg" title="The attitude indicator with the cover removed." width="700" /></a><div class="cite">The attitude indicator with the cover removed.</div></p> <p>The diagram below shows the mechanism inside the ball, after removing the hemispherical shells of the ball. When the roll gimbal is rotated, this mechanism rotates with it. The pitch motor causes the entire mechanism to rotate around the pitch axis (horizontal here), which is attached along the "equator". The azimuth motor and control transformer are behind the pitch components, not visible in this photo. The azimuth motor turns the vertical shaft. The two hollow hemispheres of the ball attach to the top and bottom of the shaft. Thus, the azimuth motor rotates the ball shells around the azimuth axis, while the mechanism itself remains stationary.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/mechanism-diagram.jpg"><img alt="The components of the ball mechanism." class="hilite" height="537" src="https://static.righto.com/images/f4-attitude-indicator/mechanism-diagram-w700.jpg" title="The components of the ball mechanism." width="700" /></a><div class="cite">The components of the ball mechanism.</div></p> <p>Why doesn't the wiring get tangled up as the ball rotates? The solution is two sets of slip rings to implement the electrical connections. The photo below shows the first slip ring assembly, which handles rotation around the roll axis. These slip rings connect the stationary part of the instrument to the rotating roll gimbal. The black base and the vertical wires are attached to the instrument, while the striped shaft in the middle rotates with the ball assembly housing. Inside the shaft, wires go from the circular metal contacts to the roll gimbal.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/sliprings.jpg"><img alt="The first set of slip rings. Yes, there is damage on one of the slip ring contacts." class="hilite" height="339" src="https://static.righto.com/images/f4-attitude-indicator/sliprings-w500.jpg" title="The first set of slip rings. Yes, there is damage on one of the slip ring contacts." width="500" /></a><div class="cite">The first set of slip rings. Yes, there is damage on one of the slip ring contacts.</div></p> <p>Inside the ball, a second set of slip rings provides the electrical connection between the wiring on the roll gimbal and the ball mechanism. The photo below shows the connections to these slip rings, handling rotation around the pitch axis (horizontal in this photo). (The slip rings themselves are inside and are not visible.) The shaft sticking out of the assembly rotates around the azimuth (yaw) axis. The ball hemisphere is attached to the metal disk. The azimuth axis does not require slip rings since only the ball shells rotates; the electronics remain stationary.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/sliprings2.jpg"><img alt="Connections for the second set of slip rings." class="hilite" height="327" src="https://static.righto.com/images/f4-attitude-indicator/sliprings2-w350.jpg" title="Connections for the second set of slip rings." width="350" /></a><div class="cite">Connections for the second set of slip rings.</div></p> <h2>The servo loop</h2> <p>In this section, I'll explain how the motors are controlled by servo loops. The attitude indicator is driven by an external gyroscope, receiving electrical signals indicating the roll, pitch, and azimuth positions. As was common in 1960s avionics, the signals are transmitted from synchros, which use three wires to indicate an angle. The motors inside the attitude indicator rotate until the indicator's angles for the three axes match the input angles.</p> <p>Each motor is controlled by a servo loop, shown below. The goal is to rotate the output shaft to an angle that exactly matches the input angle, specified by the three synchro wires. The key is a device called a control transformer, which takes the three-wire input angle and a physical shaft rotation, and generates an error signal indicating the difference between the desired angle and the physical angle. The amplifier drives the motor in the appropriate direction until the error signal drops to zero. To improve the dynamic response of the servo loop, the tachometer signal is used as a negative feedback voltage. This ensures that the motor slows as the system gets closer to the right position, so the motor doesn't overshoot the position and oscillate. (This is sort of like a PID controller.)</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/servo-diagram.jpg"><img alt="This diagram shows the structure of the servo loop, with a feedback loop ensuring that the rotation angle of the output shaft matches the input angle." class="hilite" height="228" src="https://static.righto.com/images/f4-attitude-indicator/servo-diagram-w600.jpg" title="This diagram shows the structure of the servo loop, with a feedback loop ensuring that the rotation angle of the output shaft matches the input angle." width="600" /></a><div class="cite">This diagram shows the structure of the servo loop, with a feedback loop ensuring that the rotation angle of the output shaft matches the input angle.</div></p> <p>In more detail, the external gyroscope unit contains synchro transmitters, small devices that convert the angular position of a shaft into AC signals on three wires. The photo below shows a typical synchro, with the input shaft on the top and five wires at the bottom: two for power and three for the output.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/synchro.jpg"><img alt="A synchro transmitter." class="hilite" height="324" src="https://static.righto.com/images/f4-attitude-indicator/synchro-w200.jpg" title="A synchro transmitter." width="200" /></a><div class="cite">A synchro transmitter.</div></p> <p>Internally, the synchro has a rotating winding called the rotor that is driven with 400 Hz AC. Three fixed stator windings provide the three AC output signals. As the shaft rotates, the phase and voltage of the output signals changes, indicating the angle. (Synchros may seem bizarre, but they were extensively used in the 1950s and 1960s to transmit angular information in ships and aircraft.)</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/synchro-schematic.png"><img alt="The schematic symbol for a synchro transmitter or receiver." class="hilite" height="240" src="https://static.righto.com/images/f4-attitude-indicator/synchro-schematic-w250.png" title="The schematic symbol for a synchro transmitter or receiver." width="250" /></a><div class="cite">The schematic symbol for a synchro transmitter or receiver.</div></p> <p>The attitude indicator uses control transformers to process these input signals. A control transformer is similar to a synchro in appearance and construction, but it is wired differently. The three stator windings receive the inputs and the rotor winding provides the error output. If the rotor angle of the synchro transmitter and control transformer are the same, the signals cancel out and there is no error output. But as the difference between the two shaft angles increases, the rotor winding produces an error signal. The phase of the error signal indicates the direction of error.</p> <p>The next component is the motor/tachometer, a special motor that was often used in avionics servo loops. This motor is more complicated than a regular electric motor. The motor is powered by 115 volts AC, 400-Hertz, but this isn't sufficient to get the motor spinning. The motor also has two low-voltage AC control windings. Energizing a control winding will cause the motor to spin in one direction or the other.</p> <p>The motor/tachometer unit also contains a tachometer to measure its rotational speed, for use in a feedback loop. The tachometer is driven by another 115-volt AC winding and generates a low-voltage AC signal proportional to the rotational speed of the motor.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/motor-disassembled.jpg"><img alt="A motor/tachometer similar (but not identical) to the one in the attitude indicator)." class="hilite" height="262" src="https://static.righto.com/images/f4-attitude-indicator/motor-disassembled-w500.jpg" title="A motor/tachometer similar (but not identical) to the one in the attitude indicator)." width="500" /></a><div class="cite">A motor/tachometer similar (but not identical) to the one in the attitude indicator).</div></p> <p>The photo above shows a motor/tachometer with the rotor removed. The unit has many wires because of its multiple windings. The rotor has two drums. The drum on the left, with the spiral stripes, is for the motor. This drum is a "squirrel-cage rotor", which spins due to induced currents. (There are no electrical connections to the rotor; the drums interact with the windings through magnetic fields.) The drum on the right is the tachometer rotor; it induces a signal in the output winding proportional to the speed due to eddy currents. The tachometer signal is at 400 Hz like the driving signal, either in phase or 180潞 out of phase, depending on the direction of rotation. For more information on how a motor/generator works, see my <a href="https://www.righto.com/2024/02/bendix-cadc-servomotor-tachometer.html">teardown</a>.</p> <h2>The amplifier</h2> <p>The motors are powered by an amplifier assembly that contains three separate error amplifiers, one for each axis. I had to reverse engineer the amplifier assembly in order to get the indicator working. The assembly mounts on the back of the attitude indicator and connects to one of the indicator's round connectors. Note the cutout in the lower left of the amplifier assembly to provide access to the second connector on the back of the indicator. The aircraft connects to the indicator through the second connector and the indicator passes the input signals to the amplifier through the connector shown above.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/amplifier-unit.jpg"><img alt="The amplifier assembly." class="hilite" height="451" src="https://static.righto.com/images/f4-attitude-indicator/amplifier-unit-w450.jpg" title="The amplifier assembly." width="450" /></a><div class="cite">The amplifier assembly.</div></p> <p>The amplifier assembly contains three amplifier boards (for roll, pitch, and azimuth), a DC power supply board, an AC transformer, and a trim potentiometer.<span id="fnref:supply"><a class="ref" href="#fn:supply">7</a></span> The photo below shows the amplifier assembly mounted on the back of the instrument. At the left, the AC transformer produces the motor control voltage and powers the power supply board, mounted vertically on the right. The assembly has three identical amplifier boards; the middle board has been unmounted to show the components. The amplifier connects to the instrument through a round connector below the transformer. The round connector at the upper left is on the instrument case (not the amplifier) and provides the connection between the aircraft and the instrument.<span id="fnref:case-connector"><a class="ref" href="#fn:case-connector">8</a></span></p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/amplifier-mounted.jpg"><img alt="The amplifier assembly mounted on the back of the instrument. We are feeding test signals to the connector in the upper left." class="hilite" height="600" src="https://static.righto.com/images/f4-attitude-indicator/amplifier-mounted-w450.jpg" title="The amplifier assembly mounted on the back of the instrument. We are feeding test signals to the connector in the upper left." width="450" /></a><div class="cite">The amplifier assembly mounted on the back of the instrument. We are feeding test signals to the connector in the upper left.</div></p> <p>The photo below shows one of the three amplifier boards. The construction is unusual, with some components stacked on top of other components to save space. Some of the component leads are long and protected with clear plastic sleeves. The board is connected to the rest of the amplifier assembly through a bundle of point-to-point wires, visible on the left. The round pulse transformer in the middle has five colorful wires coming out of it. At the right are the two transistors that drive the motor's control windings, with two capacitors between them. The transistors are mounted on a heat sink that is screwed down to the case of the amplifier assembly for cooling. The board is covered with a conformal coating to protect it from moisture or contaminants.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/amplifier-board.jpg"><img alt="One of the three amplifier boards." class="hilite" height="344" src="https://static.righto.com/images/f4-attitude-indicator/amplifier-board-w500.jpg" title="One of the three amplifier boards." width="500" /></a><div class="cite">One of the three amplifier boards.</div></p> <p>The function of each amplifier board is to generate the two control signals so the motor rotates in the appropriate direction based on the error signal fed into the amplifier. The amplifier also uses the tachometer output from the motor unit to slow the motor as the error signal decreases, preventing overshoot. The inputs to the amplifier are 400 hertz AC signals, with the phase indicating positive or negative error. The outputs drive the two control windings of the motor, determining which direction the motor rotates.</p> <p>The schematic for the amplifier board is below. The two transistors on the left amplify the error and tachometer signals, driving the pulse transformer. The outputs of the pulse transformer will have opposite phase, driving the output transistors for opposite halves of the 400 Hz cycle. One of the transistors will be in the right phase to turn on and pull the motor control AC to ground, while the other transistor will be in the wrong phase. Thus, the appropriate control winding will be activated (for half the cycle), causing the motor to spin in the desired direction.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/amplifier-schematic2.jpg"><img alt="Schematic of one of the three amplifier boards. (Click for a larger version.)" class="hilite" height="354" src="https://static.righto.com/images/f4-attitude-indicator/amplifier-schematic2-w600.jpg" title="Schematic of one of the three amplifier boards. (Click for a larger version.)" width="600" /></a><div class="cite">Schematic of one of the three amplifier boards. (Click for a larger version.)</div></p> <p>It turns out that there are two versions of the attitude indicator that use incompatible amplifiers. I think that the motors for the newer indicators have a single control winding rather than two. Fortunately, the connectors are keyed differently so you can't attach the wrong amplifier. The second amplifier (below) looks slightly more modern (1980s) with a double-sided circuit board and more components in place of the pulse transformer.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/amplifier2.jpg"><img alt="The second type of amplifier board." class="hilite" height="449" src="https://static.righto.com/images/f4-attitude-indicator/amplifier2-w500.jpg" title="The second type of amplifier board." width="500" /></a><div class="cite">The second type of amplifier board.</div></p> <h2>The pitch trim circuit</h2> <p>The attitude indicator has a pitch trim knob in the lower right, although the knob was missing from ours. The pitch trim adjustment turns out to be rather complicated. In level flight, an aircraft may have its nose angled up or down slightly to achieve the desired angle of attack. The pilot wants the attitude indicator to show level flight, even though the aircraft is slightly angled, so the indicator can be adjusted with the pitch trim knob. However, the problem is that a fighter plane may, for instance, do a vertical 90潞 climb. In this case, the attitude indicator should show the actual attitude and ignore the pitch trim adjustment.</p> <p>I found a <a href="https://patents.google.com/patent/US2941305A">1957 patent</a> that explained how this is implemented. The solution is to "fade out" the trim adjustment when the aircraft moves away from horizontal flight. This is implemented with a special multi-zone potentiometer that is controlled by the pitch angle.</p> <p>The schematic below shows how the pitch trim signal is generated from the special pitch angle potentiometer and the pilot's pitch trim adjustment. Like most signals in the attitude indicator, the pitch trim is a 400 Hz AC signal, with the phase indicating positive or negative. Ignoring the pitch angle for a moment, the drive signal into the transformer will be AC. The split windings of the transformer will generate a positive phase and a negative phase signal. Adjusting the pitch trim potentiometer lets the pilot vary the trim signal from positive to zero to negative, applying the desired correction to the indicator.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/pitch-trim.jpg"><img alt="The pitch trim circuit. Based on the patent." class="hilite" height="226" src="https://static.righto.com/images/f4-attitude-indicator/pitch-trim-w600.jpg" title="The pitch trim circuit. Based on the patent." width="600" /></a><div class="cite">The pitch trim circuit. Based on <a href="https://patents.google.com/patent/US2941305A">the patent</a>.</div></p> <p>Now, look at the complex pitch angle potentiometer. It has alternating resistive and conducting segments, with AC fed into opposite sides. (Note that +AC and -AC refer to the phase, not the voltage.) Because the resistances are equal, the AC signals will cancel out at the top and the bottom, yielding 0 volts on those segments. If the aircraft is roughly horizontal, the potentiometer wiper will pick up the positive-phase AC and feed it into the transformer, providing the desired trim adjustment as described previously. However, if the aircraft is climbing nearly vertically, the wiper will pick up the 0-volt signal, so there will be no pitch trim adjustment. For an angle range in between, the resistance of the potentiometer will cause the pitch trim signal to smoothly fade out. Likewise, if the aircraft is steeply diving, the wiper will pick up the 0 signal at the bottom, removing the pitch trim. And if the aircraft is inverted, the wiper will pick up the negative AC phase, causing the pitch trim adjustment to be applied in the opposite direction.</p> <h2>Conclusions</h2> <p>The attitude indicator is a key instrument in any aircraft, especially important when flying in low visibility. The F-4's attitude indicator goes beyond the artificial horizon indicator in a typical aircraft, adding a third axis to show the aircraft's heading. Supporting a third axis makes the instrument much more complicated, though. Looking inside the indicator reveals how the ball rotates in three axes while still remaining firmly attached.</p> <p>Modern fighter planes avoid complex electromechanical instruments. Instead, they provide a "glass cockpit" with most data provided digitally on screens. For instance, the F-35's console replaces all the instruments with a wide <a href="https://www.militaryaerospace.com/sensors/article/14276510/panoramic-display-f-35-cockpit-avionics">panoramic touchscreen</a> displaying the desired information in color. Nonetheless, mechanical instruments have a special charm, despite their impracticality.</p> <p>For more, follow me on Mastodon as <a href="https://oldbytes.space/@kenshirriff">@<span class="__cf_email__" data-cfemail="87ece2e9f4efeef5f5eee1e1c7e8ebe3e5fef3e2f4a9f4f7e6e4e2">[email protected]</span></a> or <a href="http://www.righto.com/feeds/posts/default">RSS</a>. (I've given up on Twitter.) I worked on this project with CuriousMarc and Eric Schlapfer, so expect a video at some point. Thanks to John Pumpkinhead and another collector for supplying the indicators and amplifiers.</p> <h2>Notes and references</h2> <p>Specifications<span id="fnref:specifications"><a class="ref" href="#fn:specifications">9</a></span></p>  <div class="footnote"> <ol> <li id="fn:fdai"> <p>This three-axis attitude indicator is similar in many ways to the <a href="https://www.nasa.gov/history/afj/ap16fj/01popup_fdai.html">FDAI</a> (Flight Director Attitude Indicator) that was used in the Apollo space flights, although the FDAI has more indicators and needles. It is more complex than the Soyus Globus, used for navigation (<a href="https://www.righto.com/2023/01/inside-globus-ink-mechanical-navigation.html">teardown</a>), which rotates in two axes. Maybe someone will loan us an FDAI to examine... <br/> <a class="footnote-backref" href="#fnref:fdai" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:problems"> <p>Our indicator has been used as a parts source, as it has cut wires inside and is missing the pitch trim knob, several needles, and internal adjustment potentiometers. We had to replace two failed capacitors in the power supply. There is still a short somewhere that we are tracking down; at one point it caused the bond wire inside a transistor to melt(!). <a class="footnote-backref" href="#fnref:problems" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:phantom-ii"> <p>The aircraft is the "Phantom II" because the original Phantom was a World War II fighter aircraft, the McDonnell FH Phantom. McDonnell Douglas reused the Phantom name for the F-4. (McDonnell became McDonnell Douglas in 1967 after merging with Douglas Aircraft. McDonnell Douglas merged into Boeing in 1997. <a href="https://www.nytimes.com/2024/01/23/opinion/boeing-737max-alaska-airlines.html">Many</a> <a href="https://www.newsweek.com/merger-that-brought-boeing-low-opinion-1867937">people</a> <a href="https://hbswk.hbs.edu/item/why-boeings-problems-with-737-max-began-more-than-25-years-ago">blame</a> <a href="https://qz.com/1776080/how-the-mcdonnell-douglas-boeing-merger-led-to-the-737-max-crisis">Boeing's</a> <a href="https://www.euronews.com/business/2024/02/07/boeings-tragedy-the-fall-of-an-american-icon">current</a> problems on this merger.) <a class="footnote-backref" href="#fnref:phantom-ii" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:nuclear"> <p>The F-4 could carry a variety of nuclear bombs such as the B28EX, B61, B43 and B57, referred to as "special weapons". The photo below shows the nuclear store consent switch, which armed a nuclear bomb for release. (Somehow I expected a more elaborate mechanism for nuclear bombs.) The switch labels are in the shadows, but say "REL/ARM", "SAFE", and "REL". The <a href="https://archive.org/details/f4cdennwdmanual">F-4 Weapons Delivery Manual</a> discusses this switch briefly.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/nuclear-store-consent.jpg"><img alt="The nuclear store consent switch, to the right of the Weapons System Officer in the rear cockpit. Photo from National Museum of the USAF." class="hilite" height="398" src="https://static.righto.com/images/f4-attitude-indicator/nuclear-store-consent-w500.jpg" title="The nuclear store consent switch, to the right of the Weapons System Officer in the rear cockpit. Photo from National Museum of the USAF." width="500" /></a><div class="cite">The nuclear store consent switch, to the right of the Weapons System Officer in the rear cockpit. Photo from <a href="https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196051/mcdonnell-douglas-f-4c-phantom-ii/">National Museum of the USAF</a>.</div></p> <p> <a class="footnote-backref" href="#fnref:nuclear" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:standby"> <p>The photo below is a closeup of the attitude indicator in the F-4 cockpit. Note the Primary/Standby toggle switch in the upper-left. Curiously, this switch is just screwed onto the console, with exposed wires. Based on other sources, this appears to be the standard mounting. This switch is the "reference system selector switch" that selects the data source for the indicator. In the primary setting, the gyroscopically-stabilized inertial navigation system (INS) provides the information. The INS normally gets azimuth information from the magnetic compass, but can use a directional gyro if the Earth's magnetic field is distorted, such as in polar regions. See the <a href="https://www.f4phantom.com/docs/F4Manual-1979-T-O-1F-4E-1-Flight-Manual-USAF-Series-F-4E-Aircraft.pdf#page=52">F-4E Flight Manual</a> for details.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/indicator-closeup.jpg"><img alt="A closeup of the indicator in the cockpit of the F-4 Phantom II. Photo from National Museum of the USAF." class="hilite" height="463" src="https://static.righto.com/images/f4-attitude-indicator/indicator-closeup-w450.jpg" title="A closeup of the indicator in the cockpit of the F-4 Phantom II. Photo from National Museum of the USAF." width="450" /></a><div class="cite">A closeup of the indicator in the cockpit of the F-4 Phantom II. Photo from <a href="https://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/196051/mcdonnell-douglas-f-4c-phantom-ii/">National Museum of the USAF</a>.</div></p> <p>The standby switch setting uses the bombing computer (the AN/AJB-7 Attitude-Reference Bombing Computer Set) as the information source; it has two independent gyroscopes. If the main attitude indicator fails entirely, the backup is the "emergency attitude reference system", a self-contained gyroscope and indicator below and to the right of the main attitude indicator; see the earlier cockpit photo. <a class="footnote-backref" href="#fnref:standby" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:features"> <p>The diagram below shows the features of the indicator.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/adi-diagram.jpg"><img alt="The features of the Attitude Director Indicator (ADI). From F-4E Flight Manual TO 1F-4E-1." class="hilite" height="401" src="https://static.righto.com/images/f4-attitude-indicator/adi-diagram-w700.jpg" title="The features of the Attitude Director Indicator (ADI). From F-4E Flight Manual TO 1F-4E-1." width="700" /></a><div class="cite">The features of the Attitude Director Indicator (ADI). From <a href="https://www.f4phantom.com/docs/F4Manual-1979-T-O-1F-4E-1-Flight-Manual-USAF-Series-F-4E-Aircraft.pdf#page=52">F-4E Flight Manual TO 1F-4E-1</a>.</div></p> <p>The pitch steering bar is used for an instrument (ILS) landing. The bank steering bar provides steering information from the navigation system for the desired course. <a class="footnote-backref" href="#fnref:features" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:supply"> <p>The roll, pitch, and azimuth inputs require different resistances, for instance, to handle the pitch trim input. These resistors are on the power supply board rather than an amplifier board. This allows the three amplifier boards to be identical, rather than having slightly different amplifier boards for each axis. <a class="footnote-backref" href="#fnref:supply" title="Jump back to footnote 7 in the text">↩</a></p> </li> <li id="fn:case-connector"> <p>The attitude indicator assembly has a round mil-spec connector and the case has a pass-through connector. That is, the aircraft wiring plugs into the outside of the case and the indicator internals plug into the inside of the case. The pin numbers on the outside of the case don't match the pin numbers on the internal connector, which is very annoying when reverse-engineering the system. <a class="footnote-backref" href="#fnref:case-connector" title="Jump back to footnote 8 in the text">↩</a></p> </li> <li id="fn:specifications"> <p>In this footnote, I'll link to some of the relevant military specifications.</p> <p>The attitude indicator is specified in military spec <a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=18927">MIL-I-27619</a>, which covers three similar indicators, called ARU-11/A, ARU-21/A, and ARU-31/A. The three indicators are almost identical except the the ARU-21/A has the horizontal pointer alarm flag and the ARU-31/A has a bank angle command pointer and a bank scale at the bottom of the indicator, along with a bank angle command pointer adjustment knob in the lower left. The ARU-11/A was used in the <a href="https://archive.org/details/DTIC_ADA061494/page/n78/mode/1up">F-111A</a>. (The ID-1144/AJB-7 indicator is probably the same as the ARU-11/A.) The ARU-21/A was used in the <a href="https://archive.org/details/DTIC_ADA061494/page/n27/mode/1up">A-7D Corsair</a>. The ARU-31/A was used in the <a href="https://archive.org/details/DTIC_ADA061494/page/n279/mode/1up">RF-4C Phantom II</a>, the reconnaissance version of the F-4. The photo below shows the cockpit of the RF-4C; note that the attitude indicator in the center of the panel has two knobs.</p> <p><a href="https://static.righto.com/images/f4-attitude-indicator/rf-4c-cockpit.jpg"><img alt="Cockpit panel of the RF-4C. Photo from National Museum of the USAF." class="hilite" height="332" src="https://static.righto.com/images/f4-attitude-indicator/rf-4c-cockpit-w500.jpg" title="Cockpit panel of the RF-4C. Photo from National Museum of the USAF." width="500" /></a><div class="cite">Cockpit panel of the RF-4C. Photo from <a href="https://www.nationalmuseum.af.mil/Upcoming/Photos/igphoto/2000521427/">National Museum of the USAF</a>.</div></p> <p>The indicator was part of the AN/ASN-55 Attitude Heading Reference Set, specified in <a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=21973">MIL-A-38329</a>. I think that the indicator originally received its information from an MD-1 gyroscope (<a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=18055">MIL-G-25597</a>) and an ML-1 flux valve compass, but I haven't tracked down all the revisions and variants.</p> <p>Spec <a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=16409">MIL-I-23524</a> describes an indicator that is almost identical to the ARU-21/A but with white flags. This indicator was also used with the AJB-3A Bomb Release Computing Set, part of the A-4 Skyhawk. This indicator was used with the integrated flight information system <a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=16414">MIL-S-23535</a> which contained the flight director computer <a href="https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=16252">MIL-S-23367</a>.</p> <p>My indicator has no identifying markings, so I can't be sure of its exact model. Moreover, it has missing components, so it is hard to match up the features. Since my indicator has white flags it might be the ID-1329/A.</p> <p> <a class="footnote-backref" href="#fnref:specifications" title="Jump back to footnote 9 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/3021491939457609983' onclick=''> 7 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=3021491939457609983' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=3021491939457609983&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=3021491939457609983&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=3021491939457609983&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=3021491939457609983&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=3021491939457609983&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=3021491939457609983&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/electronics' rel='tag'>electronics</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a>, <a href='http://www.righto.com/search/label/teardown' rel='tag'>teardown</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/fm24c64/die-w600.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='2267371819270953626' itemprop='postId'/> <a name='2267371819270953626'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2024/09/ramtron-ferroelectric-fram-die.html'>Inside a ferroelectric RAM chip</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-2267371819270953626' itemprop='description articleBody'> <p>Ferroelectric memory (FRAM) is an interesting storage technique that stores bits in a special "ferroelectric" material. Ferroelectric memory is nonvolatile like flash memory, able to hold its data for decades. But, unlike flash, ferroelectric memory can write data rapidly. Moreover, FRAM is much more durable than flash and can be be written trillions of times. With these advantages, you might wonder why FRAM isn't more popular. The problem is that FRAM is much more expensive than flash, so it is only used in niche applications.</p> <p><a href="https://static.righto.com/images/fm24c64/die.jpg"><img alt="Die of the Ramtron FM24C64 FRAM chip. (Click this image (or any other) for a larger version.)" class="hilite" height="400" src="https://static.righto.com/images/fm24c64/die-w600.jpg" title="Die of the Ramtron FM24C64 FRAM chip. (Click this image (or any other) for a larger version.)" width="600" /></a><div class="cite">Die of the Ramtron FM24C64 FRAM chip. (Click this image (or any other) for a larger version.)</div></p> <p>This post takes a look inside an FRAM chip from 1999, designed by a company called Ramtron. The die photo above shows this 64-kilobit chip under a microscope; the four large dark stripes are the memory cells, containing tiny cubes of ferroelectric material. The horizontal greenish bands are the drivers to select a column of memory, while the vertical greenish band at the right holds the sense amplifiers that amplify the tiny signals from the memory cells. The eight whitish squares around the border of the die are the bond pads, which are connected to the chip's eight pins.<span id="fnref:package"><a class="ref" href="#fn:package">1</a></span> The logic circuitry at the left and right of the die implements the serial (I<sup>2</sup>C) interface for communication with the chip.<span id="fnref:block-diagram"><a class="ref" href="#fn:block-diagram">2</a></span></p> <p>The history of ferroelectric memory dates back to the early 1950s.<span id="fnref:ire"><a class="ref" href="#fn:ire">3</a></span> Many companies worked on FRAM from the 1950s to the 1970s, including Bell Labs, IBM, RCA, and Ford. The 1955 photo below shows a 256-bit ferroelectric memory built by Bell Labs. Unfortunately, ferroelectric memory had many problems,<span id="fnref:litton"><a class="ref" href="#fn:litton">4</a></span> limiting it to specialized applications, and development was mostly abandoned by the 1970s.</p> <p><a href="https://static.righto.com/images/fm24c64/bell-labs-fram.jpg"><img alt="A 256-bit ferroelectric memory made by Bell Labs. Photo from Scientific American, June, 1955." class="hilite" height="400" src="https://static.righto.com/images/fm24c64/bell-labs-fram-w400.jpg" title="A 256-bit ferroelectric memory made by Bell Labs. Photo from Scientific American, June, 1955." width="400" /></a><div class="cite">A 256-bit ferroelectric memory made by Bell Labs. Photo from Scientific American, June, 1955.</div></p> <p>Ferroelectric memory had a second chance, though. A major proponent of ferroelectric memory was George Rohrer, who started working on ferroelectric memory in 1968. He formed a memory company, Technovation, which was unsuccessful, and then cofounded Ramtron in 1984.<span id="fnref:rohrer"><a class="ref" href="#fn:rohrer">5</a></span> Ramtron produced a tiny <a href="https://ieeexplore.ieee.org/document/663665">256-bit memory chip</a> in 1988, followed by much larger memories in the 1990s.</p> <h2>How FRAM works</h2> <p>Ferroelectric memory uses a special material with the property of ferroelectricity. In a normal capacitor, applying an electric field causes the positive and negative charges to separate in the dielectric material, making it polarized. However, ferroelectric materials are special because they will retain this polarization even when the electric field is removed. By polarizing a ferroelectric material positively or negatively, a bit of data can be stored. (The name "ferroelectric" is in analogy to "ferromagnetic", even though ferroelectric materials are not ferrous.)</p> <p>This FRAM chip uses a ferroelectric material called lead zirconate titanate or PZT, containing lead, zirconium, titanium, and oxygen. The diagram below shows how an applied electric field causes the titanium or zirconium atom to physically move inside the crystal lattice, causing the ferroelectric effect. (Red atoms are lead, purple are oxygen, and yellow are zirconium or titanium.) Because the atoms physically change position, the polarization is stable for decades; in contrast, the capacitors in a DRAM chip lose their data in milliseconds unless refreshed. FRAM memory will eventually wear out, but it can be written trillions of times, much more than flash or EEPROM memory.</p> <p><a href="https://static.righto.com/images/fm24c64/pzt-diagram.jpg"><img alt="The ferroelectric effect in the PZT crystal. From Ramtron Catalog, cleaned up." class="hilite" height="359" src="https://static.righto.com/images/fm24c64/pzt-diagram-w500.jpg" title="The ferroelectric effect in the PZT crystal. From Ramtron Catalog, cleaned up." width="500" /></a><div class="cite">The ferroelectric effect in the PZT crystal. From <a href="https://www.cika.com/soporte/Information/Ramtron/Shortform-Catalog.pdf">Ramtron Catalog</a>, cleaned up.</div></p> <p>To store data, FRAM uses ferroelectric capacitors, capacitors with a ferroelectric material as the dielectric between the plates. Applying a voltage to the capacitor will create an electric field, polarizing the ferroelectric material. A positive voltage will store a 1, and a negative voltage will store a 0.</p> <p>Reading a bit from memory is a bit tricky. A positive voltage is applied, forcing the material into the 1 state. If the material was already in the 1 state, minimal current will flow. But if the material was in the 0 state, more current will flow as the capacitor changes state. This allows the 0 and 1 states to be distinguished.</p> <p>Note that reading the bit destroys the stored value. Thus, after a read, the 0 or 1 value must be written back to the capacitor to restore its previous state. (This is very similar to the magnetic core memory that was used in the 1960s.)<span id="fnref:core"><a class="ref" href="#fn:core">6</a></span></p> <p>The FRAM chip that I examined uses two capacitors per bit, storing opposite values. This approach makes it easier to distinguish a 1 from a 0: a sense amplifier compares the two tiny signals and generates a 1 or a 0 depending on which is larger. The downside of this approach is that using two capacitors per bit reduces the memory capacity. Later FRAMs increased the density by using one capacitor per bit, along with reference cells for comparison.<span id="fnref:reference"><a class="ref" href="#fn:reference">7</a></span></p> <h2>A closer look at the die</h2> <p>The diagram below shows the main functional blocks of the chip.<span id="fnref:patent"><a class="ref" href="#fn:patent">8</a></span> The memory itself is partitioned into four blocks. The word line decoders select the appropriate column for the address and the drivers generate the pulses on the word and plate lines. The signals from that column go to the sense amplifiers on the right, where the signals are converted to bits and written back to memory. On the left, the precharge circuitry charges the bit lines to a fixed voltage at the start of the memory cycle, while the decoders select the desired byte from the bit lines.</p> <p><a href="https://static.righto.com/images/fm24c64/die-labeled.jpg"><img alt="The die with the main functional blocks labeled." class="hilite" height="395" src="https://static.righto.com/images/fm24c64/die-labeled-w600.jpg" title="The die with the main functional blocks labeled." width="600" /></a><div class="cite">The die with the main functional blocks labeled.</div></p> <p>The diagram below shows a closeup of the memory. I removed the top metal layer and many of the memory cells to reveal the underlying structure. The structure is very three-dimensional compared to regular chips; the gray squares in the image are cubes of PZT, sitting on top of the plate lines. The brown rectangles labeled "top plate connection" are also three-dimensional; they are S-shaped brackets with the low end attached to the silicon and the high end contacting the top of the PZT cube. Thus, each PZT cube forms a capacitor with the plate line forming the bottom plate of the capacitor, the bracket forming the top plate connection, and the PZT cube sandwiched in between, providing the ferroelectric dielectric. (Some cubes have been knocked loose in this photo and are sitting at an angle; the cubes form a regular grid in the original chip.)</p> <p><a href="https://static.righto.com/images/fm24c64/memory-closeup.jpg"><img alt="Structure of the memory. The image is focus-stacked for clarity." class="hilite" height="461" src="https://static.righto.com/images/fm24c64/memory-closeup-w500.jpg" title="Structure of the memory. The image is focus-stacked for clarity." width="500" /></a><div class="cite">Structure of the memory. The image is focus-stacked for clarity.</div></p> <p>The physical design of the chip is complicated and quite different from a typical planar integrated circuit. Each capacitor requires a cube of PZT sandwiched between platinum electrodes, with the three-dimensional contact from the top of the capacitor to the silicon. Creating these structures requires numerous steps that aren't used in normal integrated circuit fabrication. (See the footnote<span id="fnref:process-flow"><a class="ref" href="#fn:process-flow">9</a></span> for details.) Moreover, the metal ions in the PZT material can contaminate the silicon production facility unless great care is taken, such as using a separate facility to apply the ferroelectric layer and all subsequent steps.<span id="fnref:science"><a class="ref" href="#fn:science">10</a></span> The additional fabrication steps and unusual materials significantly increase the cost of manufacturing FRAM.</p> <p>Each top plate connection has an associated transistor, gated by a vertical word line.<span id="fnref:transistors"><a class="ref" href="#fn:transistors">11</a></span> The transistors are connected to horizontal bit lines, metal lines that were removed for this photo. A memory cell, containing two capacitors, measures about 4.2 碌m × 6.5 碌m. The PZT cubes are spaced about 2.1 碌m apart. The transistor gate length is roughly 700 nm. The <a href="https://en.wikichip.org/wiki/700_nm_lithography_process">700 nm node</a> was introduced in 1993, while the die contains a 1999 copyright date, so the chip appears to be a few years behind the cutting edge as far as node.</p> <p>The memory is organized as 256 capacitors horizontally by 512 capacitors vertically, for a total of 64 kilobits (since each bit requires two capacitors). The memory is accessed as 8192 bytes. Curiously, the columns are numbered on the die, as shown below.</p> <p><a href="https://static.righto.com/images/fm24c64/top-numbers.jpg"><img alt="With the metal removed, the numbers are visible counting the columns." class="hilite" height="277" src="https://static.righto.com/images/fm24c64/top-numbers-w500.jpg" title="With the metal removed, the numbers are visible counting the columns." width="500" /></a><div class="cite">With the metal removed, the numbers are visible counting the columns.</div></p> <p>The photo below shows the sense amplifiers to the right of the memory, with some large transistors to boost the signal. Each sense amplifier receives two signals from the pair of capacitors holding a bit. The sense amplifier determines which signal is larger, deciding if the bit is a 0 or 1. Because the signals are very small, the sense amplifier must be very sensitive. The amplifier has two cross-connected transistors with each transistor trying to pull the other signal low. The signal that starts off larger will "win", creating a solid 0 or 1 signal. This value is rewritten to memory to restore the value, since reading the value erases the cells. In the photo, a few of the ferroelectric capacitors are visible at the far left. Part of the lower metal layer has come loose, causing the randomly strewn brown rectangles.</p> <p><a href="https://static.righto.com/images/fm24c64/sense-amps.jpg"><img alt="The sense amplifiers." class="hilite" height="164" src="https://static.righto.com/images/fm24c64/sense-amps-w500.jpg" title="The sense amplifiers." width="500" /></a><div class="cite">The sense amplifiers.</div></p> <p>The photo below shows eight of the plate drivers, below the memory cells. This circuit generates the pulse on the selected plate line. The plate lines are the thick white lines at the top of the image; they are platinum so they appear brighter in the photo than the other metal lines. Most of the capacitors are still present on the plate lines, but some capacitors have come loose and are scattered on the rest of the circuitry. Each plate line is connected to a metal line (brown), which connects the plate line to the drive transistors in the middle and bottom of the image. These transistors pull the appropriate plate line high or low as necessary. The columns of small black circles are connections between the metal line and the silicon of the transistor underneath.</p> <p><a href="https://static.righto.com/images/fm24c64/plate-drivers.jpg"><img alt="The plate driver circuitry." class="hilite" height="466" src="https://static.righto.com/images/fm24c64/plate-drivers-w400.jpg" title="The plate driver circuitry." width="400" /></a><div class="cite">The plate driver circuitry.</div></p> <p>Finally, here's the part number and Ramtron logo on the die.</p> <p><a href="https://static.righto.com/images/fm24c64/logo.jpg"><img alt="Closeup of the logo "FM24C64A Ramtron" on the die." class="hilite" height="57" src="https://static.righto.com/images/fm24c64/logo-w600.jpg" title="Closeup of the logo "FM24C64A Ramtron" on the die." width="600" /></a><div class="cite">Closeup of the logo "FM24C64A Ramtron" on the die.</div></p> <h2>Conclusions</h2> <p>Ferroelectric RAM is an example of a technology with many advantages that never achieved the hoped-for success. Many companies worked on FRAM from the 1950s to the 1970s but gave up on it. Ramtron tried again and produced products but they were not profitable. Ramtron had <a href="https://www.electronicsweekly.com/blogs/mannerisms/delusions/ramtron-bagged-up-by-cypress-2012-09/">hoped</a> that the density and cost of FRAM would be competitive with DRAM, but unfortunately that didn't pan out. Ramtron was acquired by Cypress Semiconductor in 2012 and then Cypress was acquired by Infineon in 2019. Infineon still <a href="https://www.infineon.com/cms/en/product/memories/f-ram-ferroelectric-ram/excelon-f-ram/">sells</a> FRAM, but it is a niche product, for instance satellites that need <a href="https://www.infineon.com/cms/en/product/promopages/1and2MbFRAM/">radiation hardness</a>. Currently, FRAM costs roughly $3/megabit, almost three orders of magnitude more expensive than flash memory, which is about $15/gigabit. Nonetheless, FRAM is a fascinating technology and the structures inside the chip are very interesting.</p> <p>For more, follow me on Mastodon as <a href="https://oldbytes.space/@kenshirriff">@<span class="__cf_email__" data-cfemail="2348464d504b4a51514a4545634c4f47415a5746500d5053424046">[email protected]</span></a> or <a href="http://www.righto.com/feeds/posts/default">RSS</a>. (I've given up on Twitter.) Thanks to CuriousMarc for providing the chip, which was used in a digital readout (DRO) for his CNC machine.</p> <h2>Notes and references</h2> <div class="footnote"> <ol> <li id="fn:package"> <p>The photo below shows the chip's 8-pin package.</p> <p><a href="https://static.righto.com/images/fm24c64/package.jpg"><img alt="The chip is packaged in an 8-pin DIP. "RIC" stands for Ramtron International Corporation." class="hilite" height="227" src="https://static.righto.com/images/fm24c64/package-w250.jpg" title="The chip is packaged in an 8-pin DIP. "RIC" stands for Ramtron International Corporation." width="250" /></a><div class="cite">The chip is packaged in an 8-pin DIP. "RIC" stands for Ramtron International Corporation.</div></p> <p> <a class="footnote-backref" href="#fnref:package" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:block-diagram"> <p>The block diagram shows the structure of the chip, which is significantly different from a standard DRAM chip. The chip has logic to handle the I<sup>2</sup>C protocol, a serial protocol that uses a clock and a data line. (Note that the address lines A0-A2 are the address of the chip, not the memory address.) The WP (Write Protect) pin, protects one quarter of the chip from being modified. The chip allows an arbitrary number of bytes to be read or written sequentially in one operation. This is implemented by the counter and address latch.</p> <p><a href="https://static.righto.com/images/fm24c64/block-diagram.jpg"><img alt="Block diagram of the FRAM chip. From the datasheet." class="hilite" height="296" src="https://static.righto.com/images/fm24c64/block-diagram-w500.jpg" title="Block diagram of the FRAM chip. From the datasheet." width="500" /></a><div class="cite">Block diagram of the FRAM chip. From the <a href="https://www.infineon.com/dgdl/Infineon-FM24C64B_64-Kbit_(8_K_8)_Serial_(I2C)_F-RAM-DataSheet-v10_00-EN.pdf?fileId=8ac78c8c7d0d8da4017d0ebdee5b30f8">datasheet</a>.</div></p> <p> <a class="footnote-backref" href="#fnref:block-diagram" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:ire"> <p>An early description of ferroelectric memory is in the October 1953 Proceedings of the IRE. This issue focused on computers and had an article on computer memory systems by J. P. Eckert of ENIAC fame. In 1953, computer memory systems were primitive: mercury delay lines, electrostatic CRTs (Williams tubes), or rotating drums. The article describes experimental memory technologies including ferroelectric memory, magnetic core memory, neon-capacitor memory, phosphor drums, temperature-sensitive pigments, corona discharge, or electrolytic diodes. Within a couple of years, magnetic core memory became successful, dominating storage until semiconductor memory took over in the 1970s, and most of the other technologies were forgotten. <a class="footnote-backref" href="#fnref:ire" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:litton"> <p>A 1969 <a href="https://www.worldradiohistory.com/Archive-Electronics/60s/69/Electronics-1969-05-12.pdf#page=114">article</a> in <em>Electronics</em> discussed ferroelectric memories. At the time, ferroelectric memories were used for a few specialized applications. However, ferroelectric memories had many issues: slow write speed, high voltages (75 to 150 volts), and expensive logic to decode addresses. The article stated: "These considerations make the future of ferroelectric memories in computers rather bleak." <a class="footnote-backref" href="#fnref:litton" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:rohrer"> <p>Interestingly, the "Ram" in Ramtron comes from the initials of the cofounders: Rohrer, Araujo, and McMillan. Rohrer originally focused on potassium nitrate as the ferroelectric material, as described in his <a href="https://patents.google.com/patent/US3728694A">patent</a>. (I find it surprising that potassium nitrate is ferroelectric since it seems like such a simple, non-exotic chemical.) An extensive history of Ramtron is <a href="https://ieeexplore.ieee.org/document/663665">here</a>. A <a href="https://books.google.com/books?id=0e0F0zivk0gC&pg=PA88">Popular Science</a> article also provides information. <a class="footnote-backref" href="#fnref:rohrer" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:core"> <p>Like core memory, ferroelectric memory is based on a hysteresis loop. Because of the hysteresis loop, the material has two stable states, storing a 0 or 1. While core memory has a hysteresis loop for magnetization with respect to the magnetic field, ferroelectric memory The difference is that core memory has hysteresis of the magnetization with respect to the applied magnetic field, while ferroelectric memory has hysteresis of the polarization with respect to the applied electric field. <a class="footnote-backref" href="#fnref:core" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:reference"> <p>The reference cell approach is described in Ramtron patent <a href="https://patents.google.com/patent/US6028783A">6028783A</a>. The idea is to have a row of reference capacitors, but the reference capacitors are sized to generate a current midway between the 0 current and the 1 current. The reference capacitors provide the second input to the sense amplifiers, allowing the 0 and 1 bits to be distinguished. <a class="footnote-backref" href="#fnref:reference" title="Jump back to footnote 7 in the text">↩</a></p> </li> <li id="fn:patent"> <p>Ramtron's <a href="https://patents.google.com/patent/US4873664A">1987 patent</a> describes the approximate structure of the memory. <a class="footnote-backref" href="#fnref:patent" title="Jump back to footnote 8 in the text">↩</a></p> </li> <li id="fn:process-flow"> <p>The diagram below shows the complex process that Ramtron used to create an FRAM chip. (These steps are from a 2003 patent, so they may differ from the steps for the chip I examined.)</p> <p><a href="https://static.righto.com/images/fm24c64/process-flow.jpg"><img alt="Ramtron's process flow to create an FRAM die. From Patent 6613586." class="hilite" height="605" src="https://static.righto.com/images/fm24c64/process-flow-w450.jpg" title="Ramtron's process flow to create an FRAM die. From Patent 6613586." width="450" /></a><div class="cite">Ramtron's process flow to create an FRAM die. From <a href="https://patents.google.com/patent/US6613586B2">Patent 6613586</a>.</div></p> <p>Abbreviations: BPSG is borophosphosilicate glass. UTEOS is undoped tetraethylorthosilicate, a liquid used to deposit silicon dioxide on the surface. RTA is rapid thermal anneal. PTEOS is phosphorus-doped tetraethylorthosilicate, used to create a phosphorus-doped silicon dioxide layer. CMP is chemical mechanical planarization, polishing the die surface to be flat. TEC is the top electrode contact. ILD is interlevel dielectric, the insulating layer between conducting layers. <a class="footnote-backref" href="#fnref:process-flow" title="Jump back to footnote 9 in the text">↩</a></p> </li> <li id="fn:science"> <p>See the detailed article <a href="https://www.science.org/doi/10.1126/science.246.4936.1400">Ferroelectric Memories</a>, <em>Science</em>, 1989, by Scott and Araujo (who is the "A" in "Ramtron"). <a class="footnote-backref" href="#fnref:science" title="Jump back to footnote 10 in the text">↩</a></p> </li> <li id="fn:transistors"> <p>Early FRAM memories used an X-Y grid of wires without transistors. Although much simpler, this approach had the problem that current could flow through unwanted capacitors via "sneak" paths, causing noise in the signals and potentially corrupting data. High-density integrated circuits, however, made it practical to associate a transistor with each cell in modern FRAM chips. <a class="footnote-backref" href="#fnref:transistors" title="Jump back to footnote 11 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/2267371819270953626' onclick=''> 16 comments: </a> </span> <span class='post-icons'> <span class='item-action'> <a href='https://www.blogger.com/email-post.g?blogID=6264947694886887540&postID=2267371819270953626' title='Email Post'> <img alt='' class='icon-action' height='13' src='http://img1.blogblog.com/img/icon18_email.gif' width='18'/> </a> </span> <span class='item-control blog-admin pid-1138732533'> <a href='https://www.blogger.com/post-edit.g?blogID=6264947694886887540&postID=2267371819270953626&from=pencil' title='Edit Post'> <img alt='' class='icon-action' height='18' src='https://resources.blogblog.com/img/icon18_edit_allbkg.gif' width='18'/> </a> </span> </span> <span class='post-backlinks post-comment-link'> </span> <div class='post-share-buttons goog-inline-block'> <a class='goog-inline-block share-button sb-email' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=2267371819270953626&target=email' target='_blank' title='Email This'><span class='share-button-link-text'>Email This</span></a><a class='goog-inline-block share-button sb-blog' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=2267371819270953626&target=blog' onclick='window.open(this.href, "_blank", "height=270,width=475"); return false;' target='_blank' title='BlogThis!'><span class='share-button-link-text'>BlogThis!</span></a><a class='goog-inline-block share-button sb-twitter' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=2267371819270953626&target=twitter' target='_blank' title='Share to X'><span class='share-button-link-text'>Share to X</span></a><a class='goog-inline-block share-button sb-facebook' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=2267371819270953626&target=facebook' onclick='window.open(this.href, "_blank", "height=430,width=640"); return false;' target='_blank' title='Share to Facebook'><span class='share-button-link-text'>Share to Facebook</span></a><a class='goog-inline-block share-button sb-pinterest' href='https://www.blogger.com/share-post.g?blogID=6264947694886887540&postID=2267371819270953626&target=pinterest' target='_blank' title='Share to Pinterest'><span class='share-button-link-text'>Share to Pinterest</span></a> </div> </div> <div class='post-footer-line post-footer-line-2'><span class='post-labels'> Labels: <a href='http://www.righto.com/search/label/chips' rel='tag'>chips</a>, <a href='http://www.righto.com/search/label/electronics' rel='tag'>electronics</a>, <a href='http://www.righto.com/search/label/reverse-engineering' rel='tag'>reverse-engineering</a> </span> </div> <div class='post-footer-line post-footer-line-3'></div> </div> </div> </div> </div></div> <div class="date-outer"> <div class="date-posts"> <div class='post-outer'> <div class='post hentry' itemprop='blogPost' itemscope='itemscope' itemtype='http://schema.org/BlogPosting'> <meta content='https://static.righto.com/images/pentium-rug/pentium-rug-w500.jpg' itemprop='image_url'/> <meta content='6264947694886887540' itemprop='blogId'/> <meta content='1847189222202375114' itemprop='postId'/> <a name='1847189222202375114'></a> <h3 class='post-title entry-title' itemprop='name'> <a href='http://www.righto.com/2024/08/pentium-navajo-fairchild-shiprock.html'>The Pentium as a Navajo weaving</a> </h3> <div class='post-header'> <div class='post-header-line-1'></div> </div> <div class='post-body entry-content' id='post-body-1847189222202375114' itemprop='description articleBody'> <p>Hurrying through the National Gallery of Art five minutes before closing, I passed a Navajo weaving with a complex abstract pattern. Suddenly, I realized the pattern was strangely familiar, so I stopped and looked closely. The design turned out to be an image of Intel's Pentium chip, the start of the long-lived Pentium family.<span id="fnref:pentium"><a class="ref" href="#fn:pentium">1</a></span> The weaver, Marilou Schultz, created the artwork in 1994 using traditional materials and techniques. The rug was commissioned by Intel as a gift to <a href="https://archive.org/details/ERIC_ED409127/page/n2/mode/1up">AISES</a> (American Indian Science & Engineering Society) and is currently part of an art exhibition—<a href="https://www.nga.gov/exhibitions/2024/woven-histories-textiles-modern-abstraction.html">Woven Histories: Textiles and Modern Abstraction</a>—focusing on the intersection between abstract art and woven textiles.</p> <p><a href="https://static.righto.com/images/pentium-rug/pentium-rug.jpg"><img alt=""Replica of a Chip", created by Marilou Schultz, 1994. Wool. Photo taken at the National Gallery of Art, 2024." class="hilite" height="560" src="https://static.righto.com/images/pentium-rug/pentium-rug-w500.jpg" title=""Replica of a Chip", created by Marilou Schultz, 1994. Wool. Photo taken at the National Gallery of Art, 2024." width="500" /></a><div class="cite">"Replica of a Chip", created by Marilou Schultz, 1994. Wool. Photo taken at the National Gallery of Art, 2024.</div></p> <p>I talked with Marilou Schultz, a Navajo/Din茅 weaver and math teacher, to learn more about the artwork. Schultz learned weaving as a child—part of four generations of weavers—carding the wool, spinning it into yarn, and then weaving it. For the Intel project, she worked from a photograph of the die, marking it into 64 sections along each side so the die pattern could be accurately transferred to the weaving. Schultz used the "raised outline" technique, which gives a three-dimensional effect along borders. One of the interesting characteristics of the Pentium from the weaving perspective is its lack of symmetry, unlike traditional rugs. The Pentium weaving was colored with traditional plant dyes; the cream regions are the natural color of the wool from the long-horned Navajo-Churro sheep.<span id="fnref:sheep"><a class="ref" href="#fn:sheep">2</a></span> The yarn in the weaving is a bit finer than the yarn typically used for knitting. Weaving was a slow process, with a day's work extending the rug by 1" to 1.5".</p> <p>The Pentium die photo below shows the patterns and structures on the surface of the fingernail-sized silicon die, over three million tiny transistors. The weaving is a remarkably accurate representation of the die, reproducing the processor's complex designs. However, I noticed that the weaving was a mirror image of the physical Pentium die; I had to flip the rug image below to make them match. I asked Ms. Schultz if this was an artistic decision and she explained that she wove the rug to match the photograph. There is no specific front or back to a Navajo weaving because the design is similar on both sides,<span id="fnref:sides"><a class="ref" href="#fn:sides">3</a></span> so the gallery picked an arbitrary side to display. Unfortunately, they picked the wrong side, resulting in a backward die image. This probably bothers nobody but me, but I hope the gallery will correct this in future exhibits. For the remainder of this article, I will mirror the rug to match the physical die.</p> <p><a href="https://static.righto.com/images/pentium-rug/comparison.jpg"><img alt="Comparison of the Pentium weaving (flipped vertically) with a Pentium die photo. Original die photo from Intel." class="hilite" height="330" src="https://static.righto.com/images/pentium-rug/comparison-w600.jpg" title="Comparison of the Pentium weaving (flipped vertically) with a Pentium die photo. Original die photo from Intel." width="600" /></a><div class="cite">Comparison of the Pentium weaving (flipped vertically) with a Pentium die photo. Original die photo from <a href="https://en.wikichip.org/wiki/File:pentium_die_shot.png">Intel</a>.</div></p> <p>The rug is accurate enough that each region can be marked with its corresponding function in the real chip, as shown below. Starting in the center, the section labeled "integer execution units" is the heart of the processor, performing arithmetic operations and other functions on integer numbers. The Pentium is a 32-bit processor, so the integer execution unit is a vertical rectangle, 32 bits wide. The horizontal lines correspond to different types of circuitry such as adders, multipliers, shifters, and registers. To the right, the "floating point unit" performs more complex arithmetic operations on floating-point numbers, numbers with a fractional part that are used in applications such as spreadsheets and CAD drawings. Like the integer execution unit, the floating point unit has horizontal stripes corresponding to different functions. Floating-point numbers are represented with more bits, so the stripes are wider.</p> <p><a href="https://static.righto.com/images/pentium-rug/p54c-rug-floorplan2.jpg"><img alt="The Pentium weaving, flipped and marked with the chip floorplan." class="hilite" height="640" src="https://static.righto.com/images/pentium-rug/p54c-rug-floorplan2-w600.jpg" title="The Pentium weaving, flipped and marked with the chip floorplan." width="600" /></a><div class="cite">The Pentium weaving, flipped and marked with the chip floorplan.</div></p> <p>At the top, the "instruction fetch" section fetches the machine instructions that make up the software. The "instruction decode" section analyzes each instruction to determine what operations to perform. Simple operations, such as addition, are performed directly by the integer execution unit. Complicated instructions (a hallmark of Intel's processors) are broken down into smaller steps by the "complex instruction support" circuitry, with the steps held in the "microcode ROM". The "branch prediction logic" improves performance when the processor must make a decision for a branch instruction.</p> <p>The code and data caches provide a substantial performance boost. The problem is that the processor is considerably faster than the computer's RAM memory, so the processor can end up sitting idle until program code or data is provided by memory. The solution is the cache, a small, fast memory that holds bytes that the processor is likely to need. The Pentium processor had a small cache by modern standards, holding 8 kilobytes of code and 8 kilobytes of data. (In comparison, modern processors have multiple caches, with hundreds of kilobytes in the fastest cache and megabytes in a slower cache.) Cache memories are built from an array of memory storage elements in a structured grid, visible in the rug as uniform pink rectangles. The TLB (Translation Lookaside Buffer) assists the cache. Finally, the "bus interface logic" connects the processor to the computer's bus, providing access to memory and peripheral devices. Around the edges of the physical chip, tiny bond pads provide the connections between the silicon chip and the integrated circuit package. In the weaving, these tiny pads have been abstracted into small black rectangles.</p> <p>The weaving is accurate enough to determine that it represents a specific Pentium variant, called P54C. The motivation for the P54C was that the original Pentium chips (called P5) were not as fast as hoped and ran hot. Intel fixed this by using a more advanced manufacturing process, reducing the feature size from 800 to 600 nanometers and running the chip at 3.3 volts instead of 5 volts. Intel also modified the chip so that when parts of the chip were idle, the clock signal could be stopped to save power. (This is the "clock driver" circuitry at the top of the weaving.) Finally, Intel added multiprocessor logic (adding 200,000 more transistors), allowing two processors to work together more easily. The improved Pentium chip was smaller, faster, and used less power. This variant was called the P54C (for reasons I haven't been able to determine). The "multiprocessor logic" is visible in the Pentium rug, showing that it is the P54C Pentium (right) and not the P5 Pentium (left).</p> <p><a href="https://static.righto.com/images/pentium-rug/pentiums.jpg"><img alt="The Pentium P5 on the left and the P54C on the right, showing the difference in die and package sizes. If you look closely, the P5 die on the left lacks the "multiprocessor logic" in the weaving, showing that the weaving is the P54C. I clipped the pins on the P5 to fit it under a microscope." class="hilite" height="270" src="https://static.righto.com/images/pentium-rug/pentiums-w600.jpg" title="The Pentium P5 on the left and the P54C on the right, showing the difference in die and package sizes. If you look closely, the P5 die on the left lacks the "multiprocessor logic" in the weaving, showing that the weaving is the P54C. I clipped the pins on the P5 to fit it under a microscope." width="600" /></a><div class="cite">The Pentium P5 on the left and the P54C on the right, showing the difference in die and package sizes. If you look closely, the P5 die on the left lacks the "multiprocessor logic" in the weaving, showing that the weaving is the P54C. I clipped the pins on the P5 to fit it under a microscope.</div></p> <p>Intel's connection with New Mexico started in 1980 when Intel opened a chip fabrication plant (fab) in Rio Rancho, a suburb north of Albuquerque. At the time, this plant, Fab 7, was Intel's largest and produced <a href="https://archive.org/details/intelinsidenewme0000unse/page/11/mode/1up">70%</a> of Intel's profits. Intel steadily grew the New Mexico facility, adding Fab 9 and then Fab 11, which <a href="https://www.nytimes.com/1995/12/03/business/suiting-up-for-america-s-high-tech-future.html">opened</a> in September 1995, building Pentium and Pentium Pro chips in a <a href="https://www.nytimes.com/1995/12/03/business/suiting-up-for-america-s-high-tech-future.html">140-step</a> manufacturing process. Intel's investment in Rio Rancho has continued with a $4 billion project <a href="https://www.intel.com/content/www/us/en/newsroom/news/updates-intel-10-largest-construction-projects.html#gs.di125l">underway</a> for Fab 9 and Fab 11x. Intel has been criticized for environmental issues in New Mexico, detailed in the book <a href="https://archive.org/details/intelinsidenewme0000unse">Intel inside New Mexico: A case study of environmental and economic injustice</a>. Intel, however, claims a <a href="https://download.intel.com/newsroom/2024/manufacturing/Intel-in-NM-Sustainability-Fact-Sheet.pdf">sustainable future</a> in New Mexico, restoring watersheds, using 100% renewable electricity, and recycling construction waste.</p>  <h2>Fairchild and Shiprock</h2> <p>Marilou Schultz is currently creating another weaving based on an integrated circuit, shown below. Although this chip, the Fairchild 9040, is much more obscure than the Pentium, it has important historical symbolism, as it was built by Navajo workers at a plant on Navajo land.</p> <p><a href="https://static.righto.com/images/pentium-rug/fairchild-rug.jpg"><img alt="Marilou Schultz's current weaving project. Photo provided by the artist." class="hilite" height="558" src="https://static.righto.com/images/pentium-rug/fairchild-rug-w400.jpg" title="Marilou Schultz's current weaving project. Photo provided by the artist." width="400" /></a><div class="cite">Marilou Schultz's current weaving project. Photo provided by the artist.</div></p> <p>In 1965, Fairchild started producing semiconductors in Shiprock, New Mexico, about 200 miles northwest of Intel's future facility. Fairchild produced a <a href="https://archive.computerhistory.org/resources/access/text/2017/01/102770254-05-01-acc.pdf">brochure</a> in 1969 to commemorate the opening of a new plant. Two of the photos in that brochure compared a traditional Navajo weaving to the pattern of a chip, which happened to be the 9040. Although Fairchild's Shiprock project started optimistically, it was suddenly shut down a decade later after an armed takeover. I'll discuss the complicated history of Fairchild in Shiprock and then describe the 9040 chip in more detail.</p> <p><a href="https://static.righto.com/images/pentium-rug/rug-ic.jpg"><img alt="A Navajo rug and the die of a Fairchild 9040 integrated circuit. Images from Fairchild's commemorative brochure on the opening of a new plant at Shiprock." class="hilite" height="347" src="https://static.righto.com/images/pentium-rug/rug-ic-w600.jpg" title="A Navajo rug and the die of a Fairchild 9040 integrated circuit. Images from Fairchild's commemorative brochure on the opening of a new plant at Shiprock." width="600" /></a><div class="cite">A Navajo rug and the die of a Fairchild 9040 integrated circuit. Images from Fairchild's <a href="https://archive.computerhistory.org/resources/access/text/2017/01/102770254-05-01-acc.pdf">commemorative brochure</a> on the opening of a new plant at Shiprock.</div></p> <p>The story of Fairchild starts with William Shockley, who invented the junction transistor at Bell Labs, won the Nobel prize, and founded Shockley Semiconductor Laboratory in 1957 to build transistors. Unfortunately, although Shockley was brilliant, he was said to be <a href="https://www.npr.org/2006/07/21/5573656/electronics-pioneer-william-shockleys-legacy">the worst manager in the history of electronics</a>, not to mention a notorious eugenicist and racist later in life. Eight of his top employees—called the "traitorous eight"—left Shockley's company in 1957 to found Fairchild Semiconductor. (The traitorous eight included Gordon Moore and Robert Noyce who ended up founding Intel in 1968). Noyce (co-)invented the integrated circuit in 1959 and Fairchild soon became a top semiconductor manufacturer, famous for its foundational role in Silicon Valley.</p> <p>The Shiprock project was part of an attempt in the 1960s to improve the economic situation of the Navajo through industrial development. The Navajo had suffered a century of oppression including forced deportation from their land through the Long Walk (1864-1866). The Navajo were suffering from 65% unemployment, a per-capita income of $300, and a lack of basics such as roads, electricity, running water, and health care. The Bureau of Indian Affairs was now trying to encourage economic self-sufficiency by funding industrial projects on Indian land.<span id="fnref:economy"><a class="ref" href="#fn:economy">4</a></span> Navajo Tribal Chairman Raymond Nakai viewed industrialization as the only answer. Called "<a href="https://books.google.com/books?id=aP4QyAXsnmkC&lpg=PP1&pg=PA228#v=onepage&q&f=false">the first modern Navajo political leader</a>", Nakai <a href="https://books.google.com/books?id=0y-8OOtshbAC&pg=PA7#v=onepage&q&f=false">stated</a>, "There are some would-be leaders of the tribe calling for the banishment of industry from the reservation and a return to the life of a century ago! But, it would not solve the problems. There is not sufficient grazing land on the reservation to support the population so industry must be brought in." Finally, Fairchild was trying to escape the high cost of Silicon Valley labor by opening plants in low-cost locations such as Maine, Australia, and Hong Kong. </p> <p>These factors led Fairchild to open a manufacturing facility on Navajo land in Shiprock, New Mexico. The project started in 1965 with 50 Navajo workers in the Shiprock Community Center manufacturing transistors, rapidly increasing to <a href="https://www.bia.gov/as-ia/opa/online-press-release/electronics-industry-expanding-navajo-reservation">366 Navajo workers</a>.</p> <p><a href="https://static.righto.com/images/pentium-rug/shiprock.jpg"><img alt="Fairchild's manufacturing plant in Shiprock, NM, named after the Shiprock rock formation in the background. The formation is called Ts茅 Bit始a始铆 in Navajo. From The Industrialization of a 'Sleeping Giant', Commerce Today, January 25, 1971." class="hilite" height="283" src="https://static.righto.com/images/pentium-rug/shiprock-w500.jpg" title="Fairchild's manufacturing plant in Shiprock, NM, named after the Shiprock rock formation in the background. The formation is called Ts茅 Bit始a始铆 in Navajo. From The Industrialization of a 'Sleeping Giant', Commerce Today, January 25, 1971." width="500" /></a><div class="cite">Fairchild's manufacturing plant in Shiprock, NM, named after the Shiprock rock formation in the background. The formation is called <i>Ts茅 Bit始a始铆</i> in Navajo. From <a href="https://books.google.com/books?id=GddHAQAAIAAJ&newbks=1&newbks_redir=0&pg=RA7-PA17#v=onepage&q&f=false">The Industrialization of a 'Sleeping Giant'</a>, Commerce Today, January 25, 1971.</div></p> <p>By 1967, Robert Noyce, group vice-president of Fairchild, regarded the Shiprock plant as successful. He <a href="https://bitsavers.org/magazines/Computers_And_Automation/196704.pdf">explained</a> that Fairchild was motivated both by low labor costs and by social benefits, saying, "Probably nobody would ever admit it, but I feel sure the Indians are the most underprivileged ethnic group in the United States." Two years later, Lester Hogan, Fairchild's president, <a href="https://www.worldradiohistory.com/Archive-Electronics/60s/69/Electronics-1969-03-17.pdf#page=55">stated</a>, "I thought the Shiprock plant was one of Bob Noyce's philanthropies until I went there," but he was so impressed that he decided to expand the plant. Hogan also directed Fairchild to help build hundreds of houses for workers; since a traditional Navajo dwelling is called a hogan, the houses were dubbed <a href="https://archive.computerhistory.org/resources/access/text/2021/08/102710155-05-01-acc.pdf">Hogan's hogans</a>.</p> <p><a href="https://static.righto.com/images/pentium-rug/102785007-03-15-acc.jpg"><img alt="Workers in Fairchild's Shiprock plan, 1966. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs." class="hilite" height="399" src="https://static.righto.com/images/pentium-rug/102785007-03-15-acc-w500.jpg" title="Workers in Fairchild's Shiprock plan, 1966. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs." width="500" /></a><div class="cite">Workers in Fairchild's Shiprock plan, 1966. Photo by Jack Grimes. Photo courtesy of Computer History Museum, <a href="https://www.computerhistory.org/collections/catalog/102785007">Henry Mahler collection of Fairchild Semiconductor photographs</a>.</div></p> <p>In 1969, Fairchild opened its new facility at Shiprock and produced the <a href="https://www.computerhistory.org/collections/catalog/102770254">commemorative brochure</a> mentioned earlier. As well as showing the striking visual similarity between the designs of traditional Navajo weavings and modern integrated circuits, it stated that "Weaving, like all Navajo arts, is done with unique imagination and craftsmanship" and described the "blending of innate Navajo skill and [Fairchild] Semiconductor's precision assembly techniques." Fairchild later said that "rug weaving, for instance, provides an inherent ability to recognize complex patterns, a skill which makes memorizing integrated circuit patterns a minimal problem."<span id="fnref:ncio"><a class="ref" href="#fn:ncio">7</a></span></p> <p>However, in <a href="https://lisanakamura.net/wp-content/uploads/2011/01/indigenous-circuits-nakamura-aq.pdf">Indigenous Circuits: Navajo Women and the Racialization of Early Electronic Manufacture</a>, digital media theorist Lisa Nakamura critiques this language as a process by which "electronics assembly work became both gendered and identified with specific racialized qualities".<span id="fnref:racialization"><a class="ref" href="#fn:racialization">5</a></span> Nakamura points out how "Navajo women’s affinity for electronics manufacture [was described] as both reflecting and satisfying an intrinsic gendered and racialized drive toward intricacy, detail, and quality."</p> <p><a href="https://static.righto.com/images/pentium-rug/shiprock-plant.jpg"><img alt="Fairchild's Shiprock plant, 1966. From the patterns on the floor, this photo may show the time period when Fairchild set up manufacturing in the school gymnasium. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs." class="hilite" height="400" src="https://static.righto.com/images/pentium-rug/shiprock-plant-w500.jpg" title="Fairchild's Shiprock plant, 1966. From the patterns on the floor, this photo may show the time period when Fairchild set up manufacturing in the school gymnasium. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs." width="500" /></a><div class="cite">Fairchild's Shiprock plant, 1966. From the patterns on the floor, this photo may show the time period when Fairchild set up manufacturing in the school gymnasium. Photo by Jack Grimes. Photo courtesy of Computer History Museum, <a href="https://www.computerhistory.org/collections/catalog/102785007">Henry Mahler collection of Fairchild Semiconductor photographs</a>.</div></p> <p>At Shiprock, Fairchild employed 1200 workers,<span id="fnref:workers"><a class="ref" href="#fn:workers">6</a></span> and all but 24 were Navajo, making Fairchild the nation's largest non-government employer of American Indians. Of the 33 production supervisors, 30 were Navajo. This project had extensive government involvement from the Bureau of Indian Affairs and the U.S. Public Health Service, while the Economic Development Administration made business loans to Fairchild, the Labor Department had job training programs, and Housing and Urban Development built housing at Shiprock<span id="fnref2:ncio"><a class="ref" href="#fn:ncio">7</a></span>.</p> <p>The Shiprock plant was considered a major success story at a meeting of the National Council on Indian Opportunity in 1971.<span id="fnref3:ncio"><a class="ref" href="#fn:ncio">7</a></span> US Vice President Agnew called the economic deprivation and 40-80% unemployment on Indian reservations "a problem of staggering magnitude" and encouraged more industrial development. Fairchild President Hogan stated that "Fairchild's program at Shiprock has been one of the most rewarding in the history of our company, from the standpoint of a sound business as well as social responsibility." He said that at first the plant was considered the "Shiprock experiment", but the plant was "now among the most productive and efficient of any Fairchild operation in the world." Peter MacDonald, Chairman of the Navajo Tribal Council and a World War II Navajo <a href="https://en.wikipedia.org/wiki/Code_talker">code talker</a>, discussed the extreme poverty and unemployment on the Navajo reservation, along with "inadequate housing, inadequate health care and the lack of viable economic activities." He referred to Fairchild as "one of the best arrangements we have ever had" providing not only employment but also supporting housing through a non-profit.</p> <p><a href="https://static.righto.com/images/pentium-rug/national-geographic.jpg"><img alt="Navajo workers using microscopes in Fairchild's Shiprock plant. From "The Navajo Nation Looks Ahead", National Geographic, December 1972." class="hilite" height="407" src="https://static.righto.com/images/pentium-rug/national-geographic-w500.jpg" title="Navajo workers using microscopes in Fairchild's Shiprock plant. From "The Navajo Nation Looks Ahead", National Geographic, December 1972." width="500" /></a><div class="cite">Navajo workers using microscopes in Fairchild's Shiprock plant. From "The Navajo Nation Looks Ahead", National Geographic, December 1972.</div></p> <p>In December 1972, National Geographic highlighted the Shiprock plant as "weaving for the Space Age", stating that the Fairchild plant was the tribe's most successful economic project with Shiprock booming due to the 4.5-million-dollar annual payroll. The article states: "Though the plant runs happily today, it was at first a battleground of warring cultures." A new manager, Paul Driscoll, realized that strict "white man's rules" were counterproductive. For instance, many employees couldn't phone in if they would be absent, as they didn't have telephones. Another issue was the language barrier since many workers spoke only Navajo, not English. So when technical words didn't exist in Navajo, substitutes were found: "aluminum" became "shiny metal". Driscoll also realized that Fairchild needed to adapt to traditional nine-day religious ceremonies. Soon the monthly turnover rate dropped from 12% to under 1%, better than Fairchild's other plants.</p> <p>Unfortunately, the Fairchild-Navajo manufacturing partnership soon met a dramatic end. In 1975, the semiconductor industry was suffering from the ongoing US recession. Fairchild was especially hard hit, <a href="https://archive.computerhistory.org/resources/access/text/2023/07/102710181-05-01-acc.pdf#page=24">losing money</a> on its integrated circuits, and it shed over <a href="https://archive.computerhistory.org/resources/access/text/2023/07/102710181-05-01-acc.pdf#page=21">8000 employees</a> between 1973 and 1975.<span id="fnref:fairchild"><a class="ref" href="#fn:fairchild">8</a></span> At the Shiprock plant, Fairchild laid off<span id="fnref:laid-off"><a class="ref" href="#fn:laid-off">9</a></span> 140 Navajo employees in February 1975, angering the community. A group of 20 Indians armed with high-power rifles <a href="https://www.nytimes.com/1975/03/02/archives/indians-vow-to-stay-in-fairchild-plant.html">took over</a> the plant, demanding that Fairchild rehire the employees. Fairchild portrayed the occupiers, part of the AIM (American Indian Movement), as an "<a href="https://archive.computerhistory.org/resources/access/text/2017/02/102770538-05-01-acc.pdf">outside group—representing neither employees, tribal authorities nor the community</a>." Peter MacDonald, chairman of the Navajo Nation, agreed with the AIM on many points but viewed the AIM occupiers as "foolish" with "little sense of Navajo history" and "no sense of the need for an Indian nation to grow" (<a href="https://archive.org/details/lastwarriorpeter0000macd/page/320/mode/1up">source</a>). MacDonald negotiated with the occupiers and the occupation <a href="https://www.nytimes.com/1975/03/04/archives/40-indians-accept-amnesty-and-end-plant-occupation.html">ended</a> peacefully a week later, with <a href="https://www.nytimes.com/1975/03/04/archives/40-indians-accept-amnesty-and-end-plant-occupation.html">unconditional amnesty</a> granted to the occupiers.<span id="fnref:aim"><a class="ref" href="#fn:aim">10</a></span> However, concerned about future disruptions, Fairchild <a href="https://www.nytimes.com/1975/03/13/archives/plant-that-indians-seized-is-now-shut.html">permanently closed</a> the Shiprock plant and <a href="https://archive.computerhistory.org/resources/access/text/2015/07/102658280-05-01-acc.pdf#page=6">transferred</a> production to Southeast Asia.</p> <p><a href="https://static.righto.com/images/pentium-rug/occupy.jpg"><img alt="An article entitled "Navajos Occupy Plant". Contrary to the title, MacDonald stated that many of the occupiers were from other tribes and were not acting in the best interest of the Navajo. From Workers' Power, the biweekly newspaper of the International Socialists, March 13-26, 1975." class="hilite" height="481" src="https://static.righto.com/images/pentium-rug/occupy-w500.jpg" title="An article entitled "Navajos Occupy Plant". Contrary to the title, MacDonald stated that many of the occupiers were from other tribes and were not acting in the best interest of the Navajo. From Workers' Power, the biweekly newspaper of the International Socialists, March 13-26, 1975." width="500" /></a><div class="cite">An article entitled "Navajos Occupy Plant". Contrary to the title, MacDonald stated that many of the occupiers were from other tribes and were not acting in the best interest of the Navajo. From <a href="https://www.marxists.org/history/etol/newspape/workerspower/wp116.pdf">Workers' Power</a>, the biweekly newspaper of the International Socialists, March 13-26, 1975.</div></p> <p>For the most part, the Fairchild plant was viewed as a success prior to its occupation and closure. Navajo leader MacDonald looked back on the Fairchild plant as "a cooperative effort that was succeeding for everyone" (<a href="https://archive.org/details/lastwarriorpeter0000macd/page/318/mode/1up">link</a>). Alice Funston, a Navajo forewoman at Shiprock said, "Fairchild has not only helped women get ahead, it has been good for the entire Indian community in Shiprock."<span id="fnref:funston"><a class="ref" href="#fn:funston">11</a></span> On the other hand, Fairchild general manager Charles Sporck had a negative view looking back: "It [Shiprock] never worked out. We were really screwing up the whole societal structure of the Indian tribe. You know, the women were making money and the guys were drinking it up. We had a very major negative impact upon the Navajo tribe."<span id="fnref:sporck"><a class="ref" href="#fn:sporck">12</a></span></p> <p>Despite the stereotypes in Sporck's comments, he touches on important gender issues, both at Fairchild and in the electronics industry as a whole. Fairchild had long recognized the lack of jobs for men at Shiprock, despite attempts to create roles for men. In 1971, Fairchild President Hogan stated that since "semiconductor assembly operation require a great amount of detail work with tiny components, [it] lends itself to female workers. As a result, there are nearly three times as many Navajo women employed by Fairchild as men."<span id="fnref4:ncio"><a class="ref" href="#fn:ncio">7</a></span></p> <p>The role of women in fabricating and assembling electronics is often not recognized. A <a href="https://fraser.stlouisfed.org/files/docs/publications/bls/bls_1363_1963.pdf#page=43">1963 report</a> on electronics manufacturing estimated that women workers made up 41 percent of total employment in electronics manufacturing, largely in gendered roles. The report suggested that microminiaturization of semiconductors gave women an advantage over men in assembly and production-line work; women made up over 70% of semiconductor production-line workers, with 90-99% of inspecting and testing jobs. and 90-100% of assembler jobs. Women were largely locked out of non-production jobs; although women held a few technician and drafting roles, the percentage of woman engineers was too low to measure.</p> <p>The defense contractor General Dynamics also had Navajo plants, but with more success than Fairchild. General Dynamics opened a Navajo Nation plant in Fort Defiance, Arizona in <a href="https://www.andrews.edu/~tidwell/bsad560/Navajo">1967</a> to make <a href="https://www.bia.gov/as-ia/opa/online-press-release/missile-parts-plant-set-navajo-area">missiles for the Navy</a>. At the plant's opening, Navajo Tribal Chairman Raymond Nakai pushed for industrialization, <a href="https://archive.library.nau.edu/digital/collection/cpa/id/37191">stating</a> that it was in "industrialization and the money and the jobs engendered thereby that the future of the Navajo people will lie." The plant started with 30 employees, growing to 224 by the end of 1969, but then dropping to 99 in 1971 due to a <a href="https://books.google.com/books?id=0y-8OOtshbAC&pg=PA196#v=onepage&q&f=false">slowdown in the electronics industry</a>. General Dynamics opened another Navajo plant near Farmington NM in <a href="https://www.nytimes.com/1988/06/09/business/company-news-navajos-to-build-plant-for-dynamics.html">1988</a>. Due to the <a href="https://books.google.com/books?id=DkIrAQAAIAAJ&pg=PA231">end of the Cold War</a>, Hughes Aircraft (part of General Motors) acquired General Dynamics' missile business in 1992 and <a href="https://www.nytimes.com/1997/01/17/business/gm-to-sell-a-hughes-unit-to-raytheon.html">sold it to Raytheon in 1997</a>. The Fort Defiance facility was <a href="https://www.nhonews.com/opinion/ft-defiance-factory-to-close/article_4690c724-8082-5627-bdac-c001940e160b.html">closed in 2002</a> when its parent company, Delphi Automotive Systems, moved out of the military wiring business. The Farmington plant remains open, now <a href="https://www.dws.state.nm.us/Portals/0/DM/Raytheon_Dine_Facility.pdf">Raytheon Din茅</a>, building components for <a href="https://raytheon.mediaroom.com/2017-04-24-Raytheon-completes-new-5-million-warehouse-at-Dine-facility-near-Farmington">Tomahawk, Javelin, and AMRAAM missiles</a>.</p>  <p><a href="https://static.righto.com/images/pentium-rug/general-dynamics.jpg"><img alt="Navajo workers at the General Dynamics plant in Fort Defiance, AZ. From the 1965 General Dynamics film "The Navajo moves into the electronic age". From American Indian Film Gallery." class="hilite" height="446" src="https://static.righto.com/images/pentium-rug/general-dynamics-w500.jpg" title="Navajo workers at the General Dynamics plant in Fort Defiance, AZ. From the 1965 General Dynamics film "The Navajo moves into the electronic age". From American Indian Film Gallery." width="500" /></a><div class="cite">Navajo workers at the General Dynamics plant in Fort Defiance, AZ. From the 1965 General Dynamics film "The Navajo moves into the electronic age". From <a href="https://aifg.arizona.edu/film/navajo-moves-electronic-age">American Indian Film Gallery</a>.</div></p> <h2>Inside the Fairchild 9040 integrated circuit</h2> <p>The integrated circuit die image in Fairchild's commemorative brochure has an exceptionally striking design and color scheme. It's clear why this chip brings weaving to mind. Studying the die photo of the 9040 carefully reveals some interesting characteristics of integrated circuit design, so I will go into some detail.</p> <p><a href="https://static.righto.com/images/pentium-rug/9040.jpg"><img alt="Die photo of the Fairchild 9040 flip-flop. From the commemorative brochure." class="hilite" height="500" src="https://static.righto.com/images/pentium-rug/9040-w500.jpg" title="Die photo of the Fairchild 9040 flip-flop. From the commemorative brochure." width="500" /></a><div class="cite">Die photo of the Fairchild 9040 flip-flop. From the commemorative brochure.</div></p> <p>The chip was fabricated from a tiny square of silicon, which appears purple in the photograph. Different regions of the silicon die were treated (doped) with impurities to change the properties of the silicon and thus create electronic devices. These doped regions appear as green or blue lines. The white lines are the metal layer on top of the silicon, connecting the components. The 13 metal rectangles around the border are the bond pads. The chip was packaged in an unusual 13-pin flat-pack, as shown below. Each of the 13 bond pads above was connected by a tiny wire to one of the 13 external pins.</p> <p><a href="https://static.righto.com/images/pentium-rug/flatpack.jpg"><img alt="The Fairchild 9040 packaged in a 13-pin flatpack integrated circuit. The chip was also available in a 14-pin DIP, a standard way of packaging chips. Photo from the commemorative brochure." class="hilite" height="97" src="https://static.righto.com/images/pentium-rug/flatpack-w250.jpg" title="The Fairchild 9040 packaged in a 13-pin flatpack integrated circuit. The chip was also available in a 14-pin DIP, a standard way of packaging chips. Photo from the commemorative brochure." width="250" /></a><div class="cite">The Fairchild 9040 packaged in a 13-pin flatpack integrated circuit. The chip was also available in a 14-pin DIP, a standard way of packaging chips. Photo from the commemorative brochure.</div></p> <p>The Fairchild 9040 was introduced in the mid-1960s as part of Fairchild's Micrologic family, a set of high-performance integrated circuits that were designed to work together.<span id="fnref:dtl"><a class="ref" href="#fn:dtl">13</a></span> The 9040 chip was a "flip-flop", a circuit capable of storing a single bit, a 0 or 1. Flip-flops can be combined to form counters, counting the number of pulses, for instance.</p> <p>The most dramatic patterns on the chip are the intricate serpentine blue lines. Each line forms a resistor, controlling the flow of electricity by impeding its path. The lines must be long to provide the desired resistance, so they wind back and forth to fit into the available space. Each end of a resistor is connected to the metal layer, wiring it to another part of the circuit. Most of the die is occupied by resistors, which is a disadvantage of this type of circuit. Modern integrated circuits use a different type of circuitry (CMOS), which is much more compact, partly because it doesn't need bulky resistors.</p> <p><a href="https://static.righto.com/images/pentium-rug/resistors.jpg"><img alt="Resistors in the 9040 die." class="hilite" height="241" src="https://static.righto.com/images/pentium-rug/resistors-w500.jpg" title="Resistors in the 9040 die." width="500" /></a><div class="cite">Resistors in the 9040 die.</div></p> <p>Transistors are the main component of an integrated circuit. These tiny devices act as switches, turning signals on and off. The photo below shows one of the transistors in the 9040. It consists of three layers of silicon, with metal wiring connected to each layer. Note the blue region in the middle, surrounded by a slightly darker purple region; these color changes indicate that the silicon has been doped to change its properties. The green region surrounding the transistor provides isolation between this transistor and the other circuitry, so the transistors don't interfere with each other. The chip also has many diodes, which look similar to transistors except a diode has two connections.</p> <p><a href="https://static.righto.com/images/pentium-rug/transistor.jpg"><img alt="A transistor in the 9040 die. The three contacts are called the base, emitter, and collector." class="hilite" height="135" src="https://static.righto.com/images/pentium-rug/transistor-w200.jpg" title="A transistor in the 9040 die. The three contacts are called the base, emitter, and collector." width="200" /></a><div class="cite">A transistor in the 9040 die. The three contacts are called the base, emitter, and collector.</div></p> <p>These transistors with their three layers of silicon are a type known as bipolar. Modern computers use a different type of transistor, metal-oxide-semiconductor (MOS), which is much more compact and efficient. One of Fairchild's major failures was staying with bipolar transistors too long, rather than moving to MOS.<span id="fnref:mos"><a class="ref" href="#fn:mos">14</a></span> In a sense, the photo of the 9040 die shows the seeds of Fairchild's failure.</p> <p>The 9040 chip was constructed on a completely different scale from the Pentium, showing the rapid progress of the IC industry. The 9040 contains just 16 transistors, while the Pentium contains 3.3 million transistors. Thus, individual transistors can be seen in the 9040 image, while only large-scale functional blocks are visible in the Pentium. This increasing transistor count illustrates the exponential growth in integrated circuit capacity between the 9040 in the mid-1960s and the Pentium in 1993. This growth pattern, with the number of transistors doubling about every two years, is known as Moore's law, since it was first observed in 1965 by Gordon Moore (one of Fairchild's "traitorous eight", who later started Intel).</p> <p>The schematic below shows the circuitry inside the 9040 chip, with its 16 transistors, 16 diodes, and 22 resistors. The symmetry of the 9040 die photo makes it appealing, and that symmetry is reflected in the circuit below, with the left side and the right side mirror images. The idea behind a flip-flop is that it can hold either a 0 or a 1. In the chip, this is implemented by turning on the right side of the chip to hold a 0, or the left side to hold a 1. If one side of the chip is on, it forces the other side off, accomplished by the X-like crossings of signals in the center.<span id="fnref:schematic"><a class="ref" href="#fn:schematic">15</a></span> Thus, the symmetry is not arbitrary, but is critical to the operation of the circuit.</p> <p><a href="https://static.righto.com/images/pentium-rug/schematic.jpg"><img alt="Schematic of the Fairchild 9040 flip-flop chip. From Fairchild 1970 Data Catalog." class="hilite" height="498" src="https://static.righto.com/images/pentium-rug/schematic-w600.jpg" title="Schematic of the Fairchild 9040 flip-flop chip. From Fairchild 1970 Data Catalog." width="600" /></a><div class="cite">Schematic of the Fairchild 9040 flip-flop chip. From <a href="http://www.bitsavers.org/components/fairchild/_dataBooks/1970_Fairchild_Semiconductor_Integrated_Circuit_Data_Catalog.pdf">Fairchild 1970 Data Catalog</a>.</div></p> <p>Despite the obscurity of the 9040, multiple 9040 chips are currently on the Moon. The chip was used in the Apollo Lunar Surface Experiments Package (ALSEP),<span id="fnref:apollo"><a class="ref" href="#fn:apollo">16</a></span> in particular, the Active Seismic Experiment on Apollo 14 and 16. This experiment detonated small explosives on the Moon and measured the resulting seismic waves. The photo below is a detail from a blueprint<span id="fnref:alsep"><a class="ref" href="#fn:alsep">17</a></span> that shows three of the nineteen 9040 flip-flops (labeled "FF") as well as two 9041 logic gates, a chip in the same family as the 9040.</p> <p><a href="https://static.righto.com/images/pentium-rug/ase.jpg"><img alt="Detail from Logic Schematic Type B Board No.4 ASE." class="hilite" height="261" src="https://static.righto.com/images/pentium-rug/ase-w400.jpg" title="Detail from Logic Schematic Type B Board No.4 ASE." width="400" /></a><div class="cite">Detail from Logic Schematic Type B Board No.4 ASE.</div></p> <h2>Conclusions</h2> <p>The similarities between Navajo weavings and the patterns in integrated circuits have been described since the 1960s. Marilou Schultz's weavings of integrated circuits make these visual metaphors into concrete works of art. Although the Woven Histories exhibit at the National Gallery of Art is no longer on display, the exhibit will be at the National Gallery of Canada (Ottawa) starting November 8, 2024, and the Museum of Modern Art (New York) starting April 20, 2025 (full dates <a href="https://www.nga.gov/press/exhibitions/exhibitions-2024/5415.html">here</a>). If you're in the area, I recommend viewing the exhibit, but don't make my mistake: leave more than five minutes to see it!</p> <p>Many thanks to Marilou Schultz for discussing her art with me. For more on her art, see <a href="https://www.youtube.com/watch?v=lyVDvYURpqo">A Conversation with Marilou Schultz</a> on YouTube.<span id="fnref:amd"><a class="ref" href="#fn:amd">18</a></span> Follow me on Mastodon as <a href="https://oldbytes.space/@kenshirriff">@<span class="__cf_email__" data-cfemail="4d2628233e25243f3f242b2b0d2221292f3439283e633e3d2c2e28">[email protected]</span></a> or <a href="http://www.righto.com/feeds/posts/default">RSS</a> for updates.</p> <h2>Notes and references</h2> <div class="footnote"> <ol> <li id="fn:pentium"> <p>The original Pentium was followed by the Pentium Pro, the Pentium II, and others, forming a long-running brand of high-performance processors. Pentium was Intel's flagship line until the Core processors took over in 2006. <a class="footnote-backref" href="#fnref:pentium" title="Jump back to footnote 1 in the text">↩</a></p> </li> <li id="fn:sheep"> <p>Sheep hold a key role in Navajo culture and economy, which I'll briefly summarize here. Domestic sheep were brought to the Americas during the Spanish colonization, reaching the Navajo in the late 1500s. Since sheep were able to graze on semi-arid land unsuitable for crops, sheep became very important to the Navajo. Although the Navajo had used cotton for weaving in the past, the availability of wool made weaving a fundamental industry; the production and trading of woven Navajo blankets became an important economic factor in New Mexico by the 1750s (<a href="https://archive.org/details/motherearthfathe0000reno/page/15/mode/1up?view=theater">details</a>).</p> <p>Navajo leader Peter MacDonald <a href="https://archive.org/details/lastwarriorpeter0000macd/page/37/mode/1up?">described</a> the role of sheep: "Sheep were like money in the bank: the more you had, the better your life, your future, and your family's future." The number of sheep <a href="https://en.wikipedia.org/wiki/Navajo_Livestock_Reduction#/media/File:LivestockReductionNV.svg">grew exponentially</a> in the early 1900s, resulting in overgrazing of the land. The drought and Dust Bowl of the 1930s led the government to restrict the number of sheep on Navajo land, imposing the Navajo Livestock Reduction. This heavy-handed program purchased and slaughtered over half the livestock, which was catastrophic to the Navajo, both economically and culturally, destroying the Navajo's wealth and self-sufficiency.</p> <p>The <a href="https://en.wikipedia.org/wiki/Navajo-Churro">Navajo-Churro</a> sheep is a breed that the Navajo developed from the Churra sheep brought from Spain during the Spanish colonization of the Americas. These sheep have a long, lustrous fleece that is excellent for weaving. The Navajo-Churro is also called the Navajo Four-Horned Sheep as some rams have four horns, a rare trait. The Navajo-Churro breed was severely depleted when American troops killed livestock during the Navajo Wars (1863) and then brought close to extinction by the Livestock Reduction of the 1930s to 1950s. In the 1970s, the <a href="https://www.navajosheepproject.org/nsp-history">Navajo Sheep Project</a> started efforts to preserve and revitalize the Navajo-Churro. The breed is still rare, but currently numbers in the thousands. Now, <a href="https://apnews.com/article/climate-change-drought-sheep-wool-navajo-shepherds-90de90e2fd59651d6a447ace5086076e">climate change</a> and water shortages are putting more pressure on sheep grazing.  <a class="footnote-backref" href="#fnref:sheep" title="Jump back to footnote 2 in the text">↩</a></p> </li> <li id="fn:sides"> <p>A photo of the rug was published in <a href="https://archive.org/details/ERIC_ED409127/page/n1/mode/1up">American Indian Science & Engineering Society 1994 Annual Report</a>. This photo shows the "physically accurate" side of the rug, not the side that is currently on display.</p> <p><a href="https://static.righto.com/images/pentium-rug/aises.jpg"><img alt="A photo of the rug from 1994." class="hilite" height="455" src="https://static.righto.com/images/pentium-rug/aises-w500.jpg" title="A photo of the rug from 1994." width="500" /></a><div class="cite">A photo of the rug from 1994.</div></p> <p>Which side of a die image is the top is mostly arbitrary. Intel usually presents die photos with the tiny text on the die right side up, so I will use that convention. For the Pentium die, this text is in the lower right corner and says "80P54C (m) (c) intel '92,'93". Of course, this text is much too small to be part of the woven rug. <a class="footnote-backref" href="#fnref:sides" title="Jump back to footnote 3 in the text">↩</a></p> </li> <li id="fn:economy"> <p><a href="https://books.google.com/books?id=jYMfZ32kyhcC&pg=RA1-PA11">Strengthening the Indian Economy</a> (<i>Indian Affairs</i>, 1966) discusses various industrial development projects, of which Fairchild was the largest. Other projects included a plant at Rolla, ND to produce sapphire and ruby bearings, a Seminole project with Amphenol to produce electronic connectors, and a Hopi project with BVD to produce garments. Other economic development projects included timber and mining; extractive industries provided over half of Navajo income. <a class="footnote-backref" href="#fnref:economy" title="Jump back to footnote 4 in the text">↩</a></p> </li> <li id="fn:racialization"> <p>Racialization is defined by Nakamura as "the understanding of a specific population as possessing traits and behaviors that belong to a race, not an individual." <a class="footnote-backref" href="#fnref:racialization" title="Jump back to footnote 5 in the text">↩</a></p> </li> <li id="fn:workers"> <p>Many photos of workers at the Shiprock plant are in <a href="https://archive.computerhistory.org/resources/access/text/2021/08/102710153-05-01-acc.pdf#page=24">Fairchild VIEWS</a>, March 1969. Fairchild deserves credit for referring to the workers by name rather than viewing them as anonymous props for photos. Fairchild followed the same practice in its <a href="https://archive.computerhistory.org/resources/access/text/2023/07/102710181-05-01-acc.pdf">annual reports</a>. <a class="footnote-backref" href="#fnref:workers" title="Jump back to footnote 6 in the text">↩</a></p> </li> <li id="fn:ncio"> <p><a href="https://books.google.com/books?id=yzlIeEIlg4wC">NCIO (National Council on Indian Opportunity) News</a>, Oct/Nov 1971 described a high-level meeting with industry to discuss "new development on Indian reservations" with industry. US Vice President Spiro Agnew ran the meeting, with Attorney General John Mitchell a speaker along with Navajo Tribal Council chairman Peter MacDonald. Bizarrely, all three ended up convicted of felonies for different reasons. Within a few years, Mitchell was imprisoned for Watergate crimes and Agnew pled guilty to federal tax evasion. In 1990, MacDonald was convicted of fraud, riot, extortion, racketeering, and conspiracy by a Navajo tribal judge and then a federal judge, spending eight years in prison until pardoned by Bill Clinton (<a href="https://www.tucsonweekly.com/tucson/the-price-of-doing-business/Content?oid=1068359">details</a>). The story of Peter MacDonald is complex and many view his prosecution as politically motivated; <a href="https://amzn.to/4g2cfHr">MacDonald's memoir</a> provides his perspective. <a class="footnote-backref" href="#fnref:ncio" title="Jump back to footnote 7 in the text">↩</a><a class="footnote-backref" href="#fnref2:ncio" title="Jump back to footnote 7 in the text">↩</a><a class="footnote-backref" href="#fnref3:ncio" title="Jump back to footnote 7 in the text">↩</a><a class="footnote-backref" href="#fnref4:ncio" title="Jump back to footnote 7 in the text">↩</a></p> </li> <li id="fn:fairchild"> <p>Although Fairchild was highly successful at first, it suffered from chaotic management and economic decline. Fairchild steadily lost key employees, many of whom started competing companies. Most important was Intel, started in 1968 by Moore and Noyce, two of the "Traitorous Eight". Eventually, hundreds of companies (called the <a href="https://computerhistory.org/blog/fairchild-and-the-fairchildren/">Fairchildren</a>) could be traced back to Fairchild. Economic factors also battered Fairchild; the semiconductor industry had barely recovered from the <a href="https://www.nytimes.com/1975/03/10/archives/semiconductor-group-is-still-profitable-most-semiconductor.html">1970-1971 recession</a> when it was hit by the <a href="https://www.sjsu.edu/faculty/watkins/rec1974.htm">severe 1975 recession</a>. As a result, Fairchild had large layoffs, of which the Shiprock layoffs were a small part. Fairchild's business continued to decline; it was purchased by Schlumberger in 1979 and went through various acquisitions, mergers, and spinoffs until it finally ended in 2016, acquired by ON Semiconductor. <a class="footnote-backref" href="#fnref:fairchild" title="Jump back to footnote 8 in the text">↩</a></p> </li> <li id="fn:laid-off"> <p>Were the employees "laid off" or "layed off"? Curiously, the New York Times <a href="https://www.nytimes.com/1975/03/02/archives/indians-vow-to-stay-in-fairchild-plant.html">article</a> said "layed off" but <a href="https://www.google.com/search?q=%22laid+off%22+or+%22layed+off%22">sources</a> uniformly state that "layed off" is grammatically wrong. The New York Times has <a href="https://www.google.com/search?q=site:nytimes.com+%22layed+off%22">extensively used</a> "layed off" so this isn't a one-time typo. I hypothesized that usage had changed since the 1970s but Google Ngram Viewer shows <a href="https://books.google.com/ngrams/graph?content=layed+off%2C+laid+off&year_start=1800&year_end=2022&corpus=en&smoothing=3">laid off</a> as the consistent and overwhelming winner. Maybe "layed off" was a stylistic quirk of the New York Times? <a class="footnote-backref" href="#fnref:laid-off" title="Jump back to footnote 9 in the text">↩</a></p> </li> <li id="fn:aim"> <p>Looking back, MacDonald <a href="https://archive.org/details/lastwarriorpeter0000macd/page/234/mode/1up">questioned</a> his decision to let the occupation of Fairchild's plant continue rather than ordering the tribal police to forcibly remove the occupiers from the plant. In his view, his decision to let the occupation led to the closing of the plant and the loss of 1200 jobs. On the other hand, forcibly removing the occupiers risked violence and loss of life: "I would have become the chairman who killed his own people instead of the chairman who allowed Navajo to lose their jobs."</p> <p>The risk of bloodshed was not theoretical. In 1989, a <a href="https://navajotimes.com/news/2009/0709/071609riot.php">riot</a> between MacDonald's supporters and the police resulted in two Navajos being shot and killed by the police. MacDonald pressed for a federal investigation into police brutality, but instead MacDonald and Benally (a council delegate) received long prison sentences for inciting the riot even though they were not present at the time. <a class="footnote-backref" href="#fnref:aim" title="Jump back to footnote 10 in the text">↩</a></p> </li> <li id="fn:funston"> <p>Alice Funston was Forewoman for the Reliability and Quality Assurance Section at Shiprock. In a <a href="https://archive.computerhistory.org/resources/access/text/2023/07/102799380-05-01-acc.pdf#page=34">Fairchild employee newsletter</a>, she said, "Fairchild has not only helped women get ahead, it has been good for the entire Indian community in Shiprock. Before the plant was built here, there weren't many jobs available. You could work for the Bureau of Indian Affairs, the Navajo Tribe or other government agencies, but there just weren't enough jobs to go around. I started in assembly in 1965 and was recently promoted to Production Supervisor in R & Q.A. Since the beginning of the year, a number of women have been promoted into supervisory positions. When I joined Fairchild, most of the members of management were non-Indian. Today, almost all of our supervisors and managers are Indian." </p> <p>I quote this at length, since it was the only example I could find of an employee discussing Shiprock in their own words. It must be recognized, of course, that this is a company publication, so the comments may not be completely candid. See "Affirmative Action: A growing consciousness of the needs of the individual" in <a href="https://archive.computerhistory.org/resources/access/text/2023/07/102799380-05-01-acc.pdf#page=34">Fairchild HORIZONS</a>, May-June, 1973. <a class="footnote-backref" href="#fnref:funston" title="Jump back to footnote 11 in the text">↩</a></p> </li> <li id="fn:sporck"> <p>See <a href="https://purl.stanford.edu/fj299ww8737">Interview with Charlie Sporck</a>, 2000 February 21, timestamp 0:27. From "Silicon Genesis: oral history interviews of Silicon Valley scientists, 1995-2024," Stanford Digital Repository.</p> <p>I view Sporck's comments on the failure of Shiprock as highly questionable. First, Sporck left Fairchild in 1967, so he was not present for most of the Shiprock project. Moreover, he implies that Fairchild's closing of Shiprock was in the best interest of the Navajo, which is a morally convenient justification for Fairchild's decision, but contradicted by most other sources. <a class="footnote-backref" href="#fnref:sporck" title="Jump back to footnote 12 in the text">↩</a></p> </li> <li id="fn:dtl"> <p>Fairchild's 9040 logic family was called LPDT渭L for "low-power diode-transistor Micrologic". <a href="https://www.worldradiohistory.com/Archive-Electronics/60s/68/Electronics-1968-07-08.pdf#page3=35">Some sources</a> label this family as TTL (Transistor-Transistor Logic), probably confusing it with the 9000-family, which was TTL. <a class="footnote-backref" href="#fnref:dtl" title="Jump back to footnote 13 in the text">↩</a></p> </li> <li id="fn:mos"> <p>Fairchild's failure to recognize the importance of MOS transistors and transition from bipolar transistors is described in <a href="https://amzn.to/3yWRwUT">History of Semiconductor Engineering</a>, page 170. <a class="footnote-backref" href="#fnref:mos" title="Jump back to footnote 14 in the text">↩</a></p> </li> <li id="fn:schematic"> <p>I'll provide more details of the 9040 schematic in this footnote. The 9040 is a flexible flip-flop. It can be wired as an R-S (reset-set) flip-flop, set to 1 or reset to 0 as needed. It can also be wired as a J-K flip-flop, a flexible circuit that can store a value, hold a value, or toggle, based on the settings of the J and K inputs.</p> <p>The 9040 is a "dual-rank" flip-flop, meaning it holds its value in two latches: a primary latch and a secondary latch. (This type of flip flop was generally called "master-slave", a name that is <a href="https://en.wikipedia.org/wiki/Master%E2%80%93slave_(technology)#Controversy">now controversial</a>). Looking at the schematic, the primary latch at the bottom of the schematic passes its value to the secondary latch at the top under the control of the clock. This structure makes the flip-flop "edge-triggered", changing its value at the moment when the clock signal changes.</p> <p>This circuit uses diode-transistor logic. Diodes perform most of the logic operations by combining input signals, while the transistors provide amplification. Diodes play a different role in the "push-pull" output circuit, raising the level of the high-side transistor. Because the output circuit has a transistor, diode, and transistor stacked vertically, it is often called a <a href="https://en.wikipedia.org/wiki/Push%E2%80%93pull_output#Totem_pole_push%E2%80%93pull_output_stages">totem pole output</a>, a name that seems questionable in this context.</p> <p>One curious feature of the 9040 is that it contains two pull-up resistors that are not assigned any role. The user of the chip can attach them to unused inputs to keep the input at the desired value.</p> <p>Looking at the schematic shows 13 pins, corresponding to the 13 pins of the flat-pack integrated circuit. All but three of these pins are symmetrical; power (Vcc), ground, and the clock (CP) have single connections. The ground pad is in the bottom-center of the die, which maintains symmetry. The clock and power pads are side-by-side in the top-center of the die. If you study the die photograph closely, you will see that they subtlely break the chip's symmetry as the clock signal runs down the center of the die while the power connection runs down both sides. There are a few other subtle violations of symmetry when signals cross from one side of the chip to the other, as well as the obviously asymmetrical text. <a class="footnote-backref" href="#fnref:schematic" title="Jump back to footnote 15 in the text">↩</a></p> </li> <li id="fn:apollo"> <p>I haven't been able to prove that the Apollo program used chips from the Shiprock plant rather than a different facility. Fairchild President Hogan <a href="https://books.google.com/books?id=yzlIeEIlg4wC">stated</a> that workers at Shiprock assembled guidance, communications, and gyro systems that were used on Apollo rockets. <a class="footnote-backref" href="#fnref:apollo" title="Jump back to footnote 16 in the text">↩</a></p> </li> <li id="fn:alsep"> <p>The ALSEP schematic is from Miller, K. <a href="https://texashistory.unt.edu/ark:/67531/metapth1679471/m1/1/">Logic Schematic Type B Board No.4 ASE, A4, technical drawing, January 27, 1967</a>, University of North Texas Libraries, <a href="https://texashistory.unt.edu">The Portal to Texas History</a>; crediting Lunar Planetary Institute Library. <a class="footnote-backref" href="#fnref:alsep" title="Jump back to footnote 17 in the text">↩</a></p> </li> <li id="fn:amd"> <p>Marilou Schultz had another chip weaving on display at the National Gallery of Art. It is labeled "Untitled (Unknown Chip), 2008", but Antoine Bercovici identified it for me as the AMD K6 III processor, released in 1999 and comparable to the Pentium III.</p> <p><a href="https://static.righto.com/images/pentium-rug/amd.jpg"><img alt="A weaving created by Marilou Schultz, "Untitled (Unknown Chip)"." class="hilite" height="629" src="https://static.righto.com/images/pentium-rug/amd-w400.jpg" title="A weaving created by Marilou Schultz, "Untitled (Unknown Chip)"." width="400" /></a><div class="cite">A weaving created by Marilou Schultz, "Untitled (Unknown Chip)".</div></p> <p>If you're interested in computer-related weaving, the exhibition also had "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)" by Argentinian artist Analia Saban, created on a computer-automated Jacquard loom. This weaving represents a PC graphics card, specifically, the STB Velocity 128, which uses the Nvidia <a href="https://www.computer.org/publications/tech-news/chasing-pixels/famous-graphics-chips-nvidias-riva128">Riva 128</a> GPU chip. This chip was released in 1997, at a point when Nvidia was in a dire financial position, thirty days from going out of business. The Riva 128 saved Nvidia and now Nvidia is the world's third most valuable company.</p> <p><a href="https://static.righto.com/images/pentium-rug/saban.jpg"><img alt="A tapestry created by Analia Saban, "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)"." class="hilite" height="551" src="https://static.righto.com/images/pentium-rug/saban-w400.jpg" title="A tapestry created by Analia Saban, "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)"." width="400" /></a><div class="cite">A tapestry created by Analia Saban, "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)".</div></p> <p> <a class="footnote-backref" href="#fnref:amd" title="Jump back to footnote 18 in the text">↩</a></p> </li> </ol> </div> <div style='clear: both;'></div> </div> <div class='post-footer'> <div class='post-footer-line post-footer-line-1'><span class='post-comment-link'> <a class='comment-link' href='https://www.blogger.com/comment/fullpage/post/6264947694886887540/1847189222202375114' onclick=''> 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class='post-count-link' href='http://www.righto.com/2020/'> 2020 </a> <span class='post-count' dir='ltr'>(33)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate 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<span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/05/'> May </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/03/'> March </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2020/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/'> 2019 </a> <span class='post-count' dir='ltr'>(18)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/11/'> November </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/10/'> October </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/07/'> July </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2019/01/'> January </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/'> 2018 </a> <span class='post-count' dir='ltr'>(17)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/06/'> June </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/03/'> March </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2018/01/'> January </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/'> 2017 </a> <span class='post-count' dir='ltr'>(21)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/12/'> December </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/07/'> July </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/04/'> April </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2017/01/'> January </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/'> 2016 </a> <span class='post-count' dir='ltr'>(34)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/10/'> October </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/09/'> September </a> <span class='post-count' dir='ltr'>(8)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/08/'> August </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/07/'> July </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/06/'> June </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/05/'> May </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/02/'> February </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2016/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/'> 2015 </a> <span class='post-count' dir='ltr'>(12)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/12/'> December </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/11/'> November </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/10/'> October </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/08/'> August </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2015/02/'> February </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/'> 2014 </a> <span class='post-count' dir='ltr'>(13)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/12/'> December </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/10/'> October </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/09/'> September </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/05/'> May </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/03/'> March </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2014/02/'> February </a> <span class='post-count' dir='ltr'>(5)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/'> 2013 </a> <span class='post-count' dir='ltr'>(24)</span> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/11/'> November </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/09/'> September </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/08/'> August </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/07/'> July </a> <span class='post-count' dir='ltr'>(4)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/06/'> June </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/04/'> April </a> <span class='post-count' dir='ltr'>(1)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/03/'> March </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/02/'> February </a> <span class='post-count' dir='ltr'>(2)</span> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2013/01/'> January </a> <span class='post-count' dir='ltr'>(3)</span> </li> </ul> </li> </ul> <ul class='hierarchy'> <li class='archivedate collapsed'> <a class='toggle' href='javascript:void(0)'> <span class='zippy'> ►  </span> </a> <a class='post-count-link' href='http://www.righto.com/2012/'> 2012 </a> <span 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