Reverse-engineering a three-axis attitude indicator from the F-4 fighter plane

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).1 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?

The attitude indicator. The "W" forms a stylized aircraft. In this case, it indicates that the aircraft is climbing slightly. Photo from CuriousMarc.

The attitude indicator. The "W" forms a stylized aircraft. In this case, it indicates that the aircraft is climbing slightly. Photo from CuriousMarc.

We disassembled the indicator, reverse-engineered its 1960s-era circuitry, fixed some problems,2 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.)

The F-4 aircraft

The indicator was used in the F-4 Phantom II3 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.4

An F-4G Phantom II Wild Weasel aircraft. From National Archives.

An F-4G Phantom II Wild Weasel aircraft. From National Archives.

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.5 (The rear cockpit had a simpler two-axis attitude indicator.)

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.

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.

The attitude indicator mechanism

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.6

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.

The attitude indicator with the cover removed.

The attitude indicator with the cover removed.

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.

The components of the ball mechanism.

The components of the ball mechanism.

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.

The first set of slip rings. Yes, there is damage on one of the slip ring contacts.

The first set of slip rings. Yes, there is damage on one of the slip ring contacts.

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.

Connections for the second set of slip rings.

Connections for the second set of slip rings.

The servo loop

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.

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.)

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.

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.

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.

A synchro transmitter.

A synchro transmitter.

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.)

The schematic symbol for a synchro transmitter or receiver.

The schematic symbol for a synchro transmitter or receiver.

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.

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.

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.

A motor/tachometer similar (but not identical) to the one in the attitude indicator).

A motor/tachometer similar (but not identical) to the one in the attitude indicator).

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 180º out of phase, depending on the direction of rotation. For more information on how a motor/generator works, see my teardown.

The amplifier

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.

The amplifier assembly.

The amplifier assembly.

The amplifier assembly contains three amplifier boards (for roll, pitch, and azimuth), a DC power supply board, an AC transformer, and a trim potentiometer.7 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.8

The amplifier assembly mounted on the back of the instrument. We are feeding test signals to the connector in the upper left.

The amplifier assembly mounted on the back of the instrument. We are feeding test signals to the connector in the upper left.

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.

One of the three amplifier boards.

One of the three amplifier boards.

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.

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.

Schematic of one of the three amplifier boards. (Click for a larger version.)

Schematic of one of the three amplifier boards. (Click for a larger version.)

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.

The second type of amplifier board.

The second type of amplifier board.

The pitch trim circuit

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 90º climb. In this case, the attitude indicator should show the actual attitude and ignore the pitch trim adjustment.

I found a 1957 patent 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.

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.

The pitch trim circuit. Based on the patent.

The pitch trim circuit. Based on the patent.

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.

Conclusions

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.

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 panoramic touchscreen displaying the desired information in color. Nonetheless, mechanical instruments have a special charm, despite their impracticality.

For more, follow me on Mastodon as @[email protected] or RSS. (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.

Notes and references

Specifications9

  1. This three-axis attitude indicator is similar in many ways to the FDAI (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 (teardown), which rotates in two axes. Maybe someone will loan us an FDAI to examine...
     

  2. 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(!). 

  3. 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. Many people blame Boeing's current problems on this merger.) 

  4. 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 F-4 Weapons Delivery Manual discusses this switch briefly.

    The nuclear store consent switch, to the right of the Weapons System Officer in the rear cockpit. Photo from National Museum of the USAF.

    The nuclear store consent switch, to the right of the Weapons System Officer in the rear cockpit. Photo from National Museum of the USAF.

     

  5. 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 F-4E Flight Manual for details.

    A closeup of the indicator in the cockpit of the F-4 Phantom II. Photo from National Museum of the USAF.

    A closeup of the indicator in the cockpit of the F-4 Phantom II. Photo from National Museum of the USAF.

    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. 

  6. The diagram below shows the features of the indicator.

    The features of the Attitude Director Indicator (ADI). From F-4E Flight Manual TO 1F-4E-1.

    The features of the Attitude Director Indicator (ADI). From F-4E Flight Manual TO 1F-4E-1.

    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. 

  7. 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. 

  8. 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. 

  9. In this footnote, I'll link to some of the relevant military specifications.

    The attitude indicator is specified in military spec MIL-I-27619, 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 F-111A. (The ID-1144/AJB-7 indicator is probably the same as the ARU-11/A.) The ARU-21/A was used in the A-7D Corsair. The ARU-31/A was used in the RF-4C Phantom II, 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.

    Cockpit panel of the RF-4C. Photo from National Museum of the USAF.

    Cockpit panel of the RF-4C. Photo from National Museum of the USAF.

    The indicator was part of the AN/ASN-55 Attitude Heading Reference Set, specified in MIL-A-38329. I think that the indicator originally received its information from an MD-1 gyroscope (MIL-G-25597) and an ML-1 flux valve compass, but I haven't tracked down all the revisions and variants.

    Spec MIL-I-23524 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 MIL-S-23535 which contained the flight director computer MIL-S-23367.

    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.

     

Inside a ferroelectric RAM chip

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.

Die of the Ramtron FM24C64 FRAM chip. (Click this image (or any other) for a larger version.)

Die of the Ramtron FM24C64 FRAM chip. (Click this image (or any other) for a larger version.)

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.1 The logic circuitry at the left and right of the die implements the serial (I2C) interface for communication with the chip.2

The history of ferroelectric memory dates back to the early 1950s.3 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,4 limiting it to specialized applications, and development was mostly abandoned by the 1970s.

A 256-bit ferroelectric memory made by Bell Labs. Photo from Scientific American, June, 1955.

A 256-bit ferroelectric memory made by Bell Labs. Photo from Scientific American, June, 1955.

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 1984.5 Ramtron produced a tiny 256-bit memory chip in 1988, followed by much larger memories in the 1990s.

How FRAM works

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.)

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.

The ferroelectric effect in the PZT crystal. From Ramtron Catalog, cleaned up.

The ferroelectric effect in the PZT crystal. From Ramtron Catalog, cleaned up.

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.

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.

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.)6

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.7

A closer look at the die

The diagram below shows the main functional blocks of the chip.8 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.

The die with the main functional blocks labeled.

The die with the main functional blocks labeled.

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.)

Structure of the memory. The image is focus-stacked for clarity.

Structure of the memory. The image is focus-stacked for clarity.

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 footnote9 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.10 The additional fabrication steps and unusual materials significantly increase the cost of manufacturing FRAM.

Each top plate connection has an associated transistor, gated by a vertical word line.11 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 µm × 6.5 µm. The PZT cubes are spaced about 2.1 µm apart. The transistor gate length is roughly 700 nm. The 700 nm node 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.

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.

With the metal removed, the numbers are visible counting the columns.

With the metal removed, the numbers are visible counting the columns.

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.

The sense amplifiers.

The sense amplifiers.

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.

The plate driver circuitry.

The plate driver circuitry.

Finally, here's the part number and Ramtron logo on the die.

Closeup of the logo "FM24C64A Ramtron" on the die.

Closeup of the logo "FM24C64A Ramtron" on the die.

Conclusions

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 hoped 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 sells FRAM, but it is a niche product, for instance satellites that need radiation hardness. 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.

For more, follow me on Mastodon as @[email protected] or RSS. (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.

Notes and references

  1. The photo below shows the chip's 8-pin package.

    The chip is packaged in an 8-pin DIP. "RIC" stands for Ramtron International Corporation.

    The chip is packaged in an 8-pin DIP. "RIC" stands for Ramtron International Corporation.

     

  2. 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 I2C 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.

    Block diagram of the FRAM chip. From the datasheet.

    Block diagram of the FRAM chip. From the datasheet.

     

  3. 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. 

  4. A 1969 article in Electronics 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." 

  5. 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 patent. (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 here. A Popular Science article also provides information. 

  6. 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. 

  7. The reference cell approach is described in Ramtron patent 6028783A. 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. 

  8. Ramtron's 1987 patent describes the approximate structure of the memory. 

  9. 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.)

    Ramtron's process flow to create an FRAM die. From Patent 6613586.

    Ramtron's process flow to create an FRAM die. From Patent 6613586.

    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. 

  10. See the detailed article Ferroelectric Memories, Science, 1989, by Scott and Araujo (who is the "A" in "Ramtron"). 

  11. 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. 

The Pentium as a Navajo weaving

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.1 The weaver, Marilou Schultz, created the artwork in 1994 using traditional materials and techniques. The rug was commissioned by Intel as a gift to AISES (American Indian Science & Engineering Society) and is currently part of an art exhibition—Woven Histories: Textiles and Modern Abstraction—focusing on the intersection between abstract art and woven textiles.

"Replica of a Chip", created by Marilou Schultz, 1994. Wool. Photo taken at the National Gallery of Art, 2024.

"Replica of a Chip", created by Marilou Schultz, 1994. Wool. Photo taken at the National Gallery of Art, 2024.

I talked with Marilou Schultz, a Navajo/Diné 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.2 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".

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,3 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.

Comparison of the Pentium weaving (flipped vertically) with a Pentium die photo. Original die photo from Intel.

Comparison of the Pentium weaving (flipped vertically) with a Pentium die photo. Original die photo from Intel.

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.

The Pentium weaving, flipped and marked with the chip floorplan.

The Pentium weaving, flipped and marked with the chip floorplan.

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.

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.

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).

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.

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.

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 70% of Intel's profits. Intel steadily grew the New Mexico facility, adding Fab 9 and then Fab 11, which opened in September 1995, building Pentium and Pentium Pro chips in a 140-step manufacturing process. Intel's investment in Rio Rancho has continued with a $4 billion project underway for Fab 9 and Fab 11x. Intel has been criticized for environmental issues in New Mexico, detailed in the book Intel inside New Mexico: A case study of environmental and economic injustice. Intel, however, claims a sustainable future in New Mexico, restoring watersheds, using 100% renewable electricity, and recycling construction waste.

Fairchild and Shiprock

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.

Marilou Schultz's current weaving project. Photo provided by the artist.

Marilou Schultz's current weaving project. Photo provided by the artist.

In 1965, Fairchild started producing semiconductors in Shiprock, New Mexico, about 200 miles northwest of Intel's future facility. Fairchild produced a brochure 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.

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.

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.

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 the worst manager in the history of electronics, 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.

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.4 Navajo Tribal Chairman Raymond Nakai viewed industrialization as the only answer. Called "the first modern Navajo political leader", Nakai stated, "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.

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 366 Navajo workers.

Fairchild's manufacturing plant in Shiprock, NM, named after the Shiprock rock formation in the background. The formation is called Tsé Bitʼaʼí in Navajo.
    From The Industrialization of a 'Sleeping Giant', Commerce Today, January 25, 1971.

Fairchild's manufacturing plant in Shiprock, NM, named after the Shiprock rock formation in the background. The formation is called Tsé Bitʼaʼí in Navajo. From The Industrialization of a 'Sleeping Giant', Commerce Today, January 25, 1971.

By 1967, Robert Noyce, group vice-president of Fairchild, regarded the Shiprock plant as successful. He explained 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, stated, "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 Hogan's hogans.

Workers in Fairchild's Shiprock plan, 1966. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs.

Workers in Fairchild's Shiprock plan, 1966. Photo by Jack Grimes. Photo courtesy of Computer History Museum, Henry Mahler collection of Fairchild Semiconductor photographs.

In 1969, Fairchild opened its new facility at Shiprock and produced the commemorative brochure 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."7

However, in Indigenous Circuits: Navajo Women and the Racialization of Early Electronic Manufacture, 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".5 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."

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.

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.

At Shiprock, Fairchild employed 1200 workers,6 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 Shiprock7.

The Shiprock plant was considered a major success story at a meeting of the National Council on Indian Opportunity in 1971.7 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 code talker, 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.

Navajo workers using microscopes in Fairchild's Shiprock plant. From "The Navajo Nation Looks Ahead", National Geographic, December 1972.

Navajo workers using microscopes in Fairchild's Shiprock plant. From "The Navajo Nation Looks Ahead", National Geographic, December 1972.

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.

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, losing money on its integrated circuits, and it shed over 8000 employees between 1973 and 1975.8 At the Shiprock plant, Fairchild laid off9 140 Navajo employees in February 1975, angering the community. A group of 20 Indians armed with high-power rifles took over the plant, demanding that Fairchild rehire the employees. Fairchild portrayed the occupiers, part of the AIM (American Indian Movement), as an "outside group—representing neither employees, tribal authorities nor the community." 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" (source). MacDonald negotiated with the occupiers and the occupation ended peacefully a week later, with unconditional amnesty granted to the occupiers.10 However, concerned about future disruptions, Fairchild permanently closed the Shiprock plant and transferred production to Southeast Asia.

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.

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.

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" (link). 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."11 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."12

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."7

The role of women in fabricating and assembling electronics is often not recognized. A 1963 report 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.

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 1967 to make missiles for the Navy. At the plant's opening, Navajo Tribal Chairman Raymond Nakai pushed for industrialization, stating 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 slowdown in the electronics industry. General Dynamics opened another Navajo plant near Farmington NM in 1988. Due to the end of the Cold War, Hughes Aircraft (part of General Motors) acquired General Dynamics' missile business in 1992 and sold it to Raytheon in 1997. The Fort Defiance facility was closed in 2002 when its parent company, Delphi Automotive Systems, moved out of the military wiring business. The Farmington plant remains open, now Raytheon Diné, building components for Tomahawk, Javelin, and AMRAAM missiles.

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.

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.

Inside the Fairchild 9040 integrated circuit

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.

Die photo of the Fairchild 9040 flip-flop. From the commemorative brochure.

Die photo of the Fairchild 9040 flip-flop. From the commemorative brochure.

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.

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.

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.

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.13 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.

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.

Resistors in the 9040 die.

Resistors in the 9040 die.

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.

A transistor in the 9040 die. The three contacts are called the base, emitter, and collector.

A transistor in the 9040 die. The three contacts are called the base, emitter, and collector.

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.14 In a sense, the photo of the 9040 die shows the seeds of Fairchild's failure.

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).

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.15 Thus, the symmetry is not arbitrary, but is critical to the operation of the circuit.

Schematic of the Fairchild 9040 flip-flop chip. From Fairchild 1970 Data Catalog.

Schematic of the Fairchild 9040 flip-flop chip. From Fairchild 1970 Data Catalog.

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),16 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 blueprint17 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.

Detail from Logic Schematic Type B Board No.4 ASE.

Detail from Logic Schematic Type B Board No.4 ASE.

Conclusions

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 here). 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!

Many thanks to Marilou Schultz for discussing her art with me. For more on her art, see A Conversation with Marilou Schultz on YouTube.18 Follow me on Mastodon as @[email protected] or RSS for updates.

Notes and references

  1. 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. 

  2. 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 (details).

    Navajo leader Peter MacDonald described 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 grew exponentially 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.

    The Navajo-Churro 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 Navajo Sheep Project started efforts to preserve and revitalize the Navajo-Churro. The breed is still rare, but currently numbers in the thousands. Now, climate change and water shortages are putting more pressure on sheep grazing.  

  3. A photo of the rug was published in American Indian Science & Engineering Society 1994 Annual Report. This photo shows the "physically accurate" side of the rug, not the side that is currently on display.

    A photo of the rug from 1994.

    A photo of the rug from 1994.

    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. 

  4. Strengthening the Indian Economy (Indian Affairs, 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. 

  5. 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." 

  6. Many photos of workers at the Shiprock plant are in Fairchild VIEWS, 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 annual reports

  7. NCIO (National Council on Indian Opportunity) News, 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 (details). The story of Peter MacDonald is complex and many view his prosecution as politically motivated; MacDonald's memoir provides his perspective. 

  8. 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 Fairchildren) could be traced back to Fairchild. Economic factors also battered Fairchild; the semiconductor industry had barely recovered from the 1970-1971 recession when it was hit by the severe 1975 recession. 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. 

  9. Were the employees "laid off" or "layed off"? Curiously, the New York Times article said "layed off" but sources uniformly state that "layed off" is grammatically wrong. The New York Times has extensively used "layed off" so this isn't a one-time typo. I hypothesized that usage had changed since the 1970s but Google Ngram Viewer shows laid off as the consistent and overwhelming winner. Maybe "layed off" was a stylistic quirk of the New York Times? 

  10. Looking back, MacDonald questioned 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."

    The risk of bloodshed was not theoretical. In 1989, a riot 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. 

  11. Alice Funston was Forewoman for the Reliability and Quality Assurance Section at Shiprock. In a Fairchild employee newsletter, 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."

    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 Fairchild HORIZONS, May-June, 1973. 

  12. See Interview with Charlie Sporck, 2000 February 21, timestamp 0:27. From "Silicon Genesis: oral history interviews of Silicon Valley scientists, 1995-2024," Stanford Digital Repository.

    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. 

  13. Fairchild's 9040 logic family was called LPDTμL for "low-power diode-transistor Micrologic". Some sources label this family as TTL (Transistor-Transistor Logic), probably confusing it with the 9000-family, which was TTL. 

  14. Fairchild's failure to recognize the importance of MOS transistors and transition from bipolar transistors is described in History of Semiconductor Engineering, page 170. 

  15. 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.

    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 now controversial). 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.

    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 totem pole output, a name that seems questionable in this context.

    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.

    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. 

  16. 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 stated that workers at Shiprock assembled guidance, communications, and gyro systems that were used on Apollo rockets. 

  17. The ALSEP schematic is from Miller, K. Logic Schematic Type B Board No.4 ASE, A4, technical drawing, January 27, 1967, University of North Texas Libraries, The Portal to Texas History; crediting Lunar Planetary Institute Library. 

  18. 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.

    A weaving created by Marilou Schultz, "Untitled (Unknown Chip)".

    A weaving created by Marilou Schultz, "Untitled (Unknown Chip)".

    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 Riva 128 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.

    A tapestry created by Analia Saban, "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)".

    A tapestry created by Analia Saban, "Copper Tapestry (Riva 128 Graphics Card, Nvidia, 1997)".