HCF4007U Dual Complementary Pair plus Inverter

Integrated circuits do not get any simpler than this. This is an HCF4007U made by ST with a week 27 1993 date code

ST HCF4007UAccording to the datasheet it can be, depending on the pin connections, either 3 inverters, a 3 input NOR or a 3 input NAND gate.

De-capping and you can see it is just 6 transistors! on a 1.47 mm x 1.35 mm die.ST HCF4007U die photo

(click on image for high resolution version)

It is barely an integrated circuit. Even with my lack of skills I can reverse engineer this part


And the pin-out





There is one mystery to me. The part is definitely CMOS as the datasheet specifies it, so they must be polysilicon gate MOSFETs.  Yet if you look at this high magnification image of a transistor edge, I cannot see the polysilicon??

Thanks to Jeremy for providing the part.

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Arduino CAN Bus Module

Last week I received an early xmas present! A reader, Jeremy kindly sent me a bunch of chips including some truly vintage devices that I will be analyzing over the next few weeks.  Included in the haul was a small CAN Bus controller board for Arduino.  Jeremy was interested in looking at a CAN transceiver chip so I am more than happy to oblige 🙂 CAN (Controller area network) was developed for automotive, and is used in all cars made today. It can communicate between the various ECU’s without the need for a central MCU.  I was not aware that it was being used outside of automotive, I guess with Arduino it is useful as a low cost control bus for home automation type projects.

This is the board containing two chips a timing crystal and four each of capacitors and resistors




The two chips are a Microchip MC2515 CAN bus controller, and the chip we are most interested in, the 8 pin NXP TJA1050 CAN bus transceiver.



The NXP TJA1050 has a datasheet that indicates it was first launched in 2003. The die is very interesting

(Click on image for high resolution version)

It’s a small die 1.54mm x 1.24mm (1.91 mm2) made on a two metal process. I spend a long time looking at the die trying to figure out what process technology is used. At first I thought it was a CMOS process as there is plenty of polysilicon visible, but the transistors do not look like MOSFETS.  I am now pretty confident that  this part is made on a double polysilicon Bipolar process.  This is a high speed Bipolar process that uses polysilicon to form base contacts and the emitters.  The CAN bus is relatively high speed interface up to 1Mbaud, so it makes sense to use a high speed Bipolar process.

Whilst I am not 100% sure I have it all figured out what layers you can see in the die photo, here is my take on the transistors

I think they have actually used 3 polysilicon layers, first they use an N++ polysilicon that contacts the low resistance collector regions, the second polysilicon is P-type (And the non-silicides regions of this show as pink/purple in my die photo).  This contacts the low doped implanted base doping layer and is a doughnut shape, with a hole that self-aligns the emitter.  The emitter poly (N++) covers the hole and is not directly visible, as it is itself covered with metal (And presumably silicide).

Why I think that three polysilicon layers are used, is that some strange resistor structures are present, that confused me and I can only reconcile with the extra poly.  I am pretty sure the pink layer is p-type polysilicon, but for many resistors like this one, it appears to be sitting on top of another polysilicon layer.  Thus I think they have put the collector polysilicon contact layer under the p-type resistors.  

I do not know why they have done that (Rather than the more conventional placement of resistors over the field oxide). It is possible that these are “pinched resistors” (Resistors where the p-type is used to pinch the n-epi to give a high resistance) but it would be odd to see a chain of pinched resistors, and the resistance value would be huge.

Here is a close-up (Focus stacked) image of another transistor design taken with my 80x objective

This is the block diagram from the datasheet


And here is the the pin-out annotated on the die photo




I did manage to trace the CANL and CANH pins to the two 25kΩ resistors, which are the resistors I showed earlier. Which also indicates the pink polysilicon layer has a ~75Ω/sq sheet resistance, to get the 25kΩ resistor value so confirming it is not a pinched resistorI think the driver is the two large transistors that have the part number over them, but I cannot resolve the block diagram to the die photo much further.

Since I de-capped the TJA1050 I also de-capped and took a die photo of the MCP2515 for completeness. It is a modern MCU die, probably made with a 90nm 6 or 8 metal CMOS process, so is not terribly interesting to look at.

Die Size 1.95 mm x 1.66 mm (3,24mm2)

(Click on image for high resolution version)

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Maxim 785 Power Supply Controller

Another chip from the clamshell iBook from 2000.  Another Maxim power chip, this time it is from the main PCB.


Its a MAX785C which I am pretty sure is a dual (3.3V & 5V) PWM buck regulator for laptop computers.



I could not find a datasheet for the MAX785 but I did find one for the MAX786 which as you will see is almost certainly a minor change, or a slightly different version of the MAX785.

Here is the 4.6 mm x 2.8 mm dieMAX785 Die Photo (click on image for high resolution version)

For the MAX786 Maxim were once again kind enough to publish a chip topography 🙂 and you can see it matches the MAX785 die photo and pad layoutHere is my MAX785 die photo with the pads annotated, you can clearly see the symmetrical and  identical 3.3V & 5V PWM supply blocks with the 3.3V on the left.

Looking at the transistors zoomed in I can see a single Aluminum layer with 5 μm gate lengths and two polysilicon layers.

Referring to the Maxim Reliability Report I found whilst researching the earlier Maxim chip I can say with confidence the MAX785 was made on the Maxim SG5 process that looks something like this  (The transistors here are pretty drawn pretty ugly IMO)Its a CMOS process with a PNP transistor, zener diode and a Chrome/Si precision resistors. I have annotated the previous image with the layersThe layer 2 (PNP base drive) is/was unusual, they are making vertical PNP transistors.  In a standard CMOS process you can build lateral PNP transistors using the regular process.  However the gain of the lateral transistor is normally very low (As the base is defined lithographically you cannot make the base very narrow, unlike a diffused vertical base.)  Here is a large Bipolar transistor on this chip which is sandwiched between an two arrays of them to make  high current drive transistors.

Most of the large output transistors in the PWM blocks are I believe multi-finger MOSFET devices, here is a zoom image of one of them (It s hard to see the polysilicon gate as they have stitched metal lines along the gate, you can see the single gate contact at the very bottom right of the image.)


Update:  Laser trimmed resistors?

Frank commented that he could see some laser trimmed resistors, this was a very eagle eye observation! A bit of background, most silicon resistors are made with polysilicon or diffusions, and there are a number of variables that limit their accuracy such as thickness, width, dopant concentration, amount of dopant electrically activated during thermal processing.  It is typical that a resistor value is at best +/-10%.  For this reason most designs require only differential or ratio accuracy, and here the variables cancel out and you get very accurate matching.  Well over 90% (Perhaps 99%) of analog ic’s make do with these resistors. Occasionally a design needs an accurate absolute resistor, for these, a few processes (Like this Maxim SG5 process) offer a precision thin film resistor. These are made from thin (Typically 20nm-100nm) metal layer like Chrome used here.  I believe they can be made with +/-1-2 % accuracy. Sometimes a design needs even more absolute accuracy and for that they laser trim the thin film resistors, using a high power laser to ablate the metal track usually on a probe station where they measure the desired signal before and after trimming.

This is the section of the die where the thin film resistors have been cut.

It is a very complex serpentine that enables a wide variation in resistor value depending on where cuts are made.  After staring at this a bit and thinking some more, I don’t think they are laser trim cuts. The cut material looks too clean for laser ablation. What I think has happened is they designed the part with a un-cut serpentine resistor,  and then evaluated the initial prototypes making various laser cuts, and then used the results to change the resistor mask. In high volume, this would be much cheaper than trimming every die on a probe station.

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Texas Instruments TL494C PWM Control Circuit

The TL494C is a pulse width modulation control circuit, designed for power supply control, from the small power board on a clamshell iBook from 2000.

I have read the datasheet a few times and find it a quite complicated device.  I think is used to regulate the load when charging the battery, but I’m not very sure of that.

From the datasheet which was first published in January 1983 and revised March 2017, a 34 year old active document (And active part) that has to be some sort of record!

Onto the die photo which is really nice 🙂
TL494C die photo(As always click on image for high resolution version)

The die size is 2.08 mm x 1.9 mm (3.95 mm2) another single metal Bipolar process.


From this diagram in the datasheet I was able to identify the pins.  The output transistors are obvious and I can see the error amplifiers and some of the other functional blocks



Here is my annotated die photo

There are some interesting devices on this chip, look at this 6 terminal beast in the error amplifier – unfortunately I have no idea what it is.

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