Wonderful work! Your articles are my favorite coffee reads

> Inconveniently, metal that contacts silicon, metal that crosses over silicon, and metal that forms a transistor all appear very similar in this chip. This makes it more difficult to determine the wiring.

I've heard that all diodes are LEDs, if one's vision extends to the infrared. Is it possible to fire up the chip and photograph it in the infrared, and would that make the transistors stand out?

Well, John McMaster was able to do some IR imaging of a chip: https://hackaday.com/2019/06/20/seeing-transistors-switch-in... But in this case, I think it's easier to squint at the die to distinguish the features by subtle differences in color. It's possible to tell them apart, but I wasted a lot of time before realizing "Oh, that's a transistor‽"

High resolution thermal imaging is tightly regulated

The emission from silicon referred to by myself248 is in the near infrared, not the thermal range. It's a commonly used diagnostic technique for silicon solar cells:

https://www.pveducation.org/pvcdrom/characterisation/electro...

I don't know if it could be used for the much smaller features found on integrated circuits, though.

As the restrictions are now blocking the IMPORT of such equipment it really is getting to be quite a joke. In the US we are only allowed to have expensive potato quality cameras with 9fps and even then that's not shitty enough -- they also have to have to inject artificial noise into it!

Thermal is not the same as near-red IR, which is what is being discussed here.

Why?

Because the government knows IR would be a pivotal tool in a civilian guerrilla uprising, and they want to keep such things out of the hands of the proletariat?

Got it. It was a genuine question asked out of ignorance on my part.

How would the extra resolution be useful in warfare?

Anti aircraft missiles (everything from plane launched to manpads), heat seeking weaponry capabilities, night vision, multispectrum sensors, optical gas imaging and a whole host of other dual use scientific applications. High resolution thermal vision is the lynchpin behind all of them. I am not sure why they are still tightly controlled since you can easily acquire them overseas.

The US government is terrified of its citizenry, as they are the only people that stand a chance of “fixing” it.

I've been successful at making many electronic parts light emitters even when they're not designed to be.

Some last longer than others under the conditions.

Since you mention it was a defective part, were you able to see the defect on the die?

We didn't see anything obviously wrong with the part. One bit of communication with the microprocessor was flaky, so it was probably a weak transistor. The consequence was that the Z80 attempted to look up a command in a lookup table, but the command wasn't there so it ended up looping through all of memory, hanging the floppy drive.

I'm not informed enough to come up with a good question, but I love your work! And I love the concept of chips built on sapphire, even if it didn't win in the marketplace. Could we get Ruby running on ruby? :P

Ruby (the gemstone) is just a red sapphire, in fact[1]. So maybe?

1: https://geology.com/gemstones/ruby-and-sapphire/

You mentioned that SOS still has a niche. What examples of current RF devices are using SOS?

Peregrine Semiconductor makes various SOS products. Here's a random example, an RF digital attenuator: https://www.psemi.com/pdf/datasheets/pe43205ds.pdf

Thoughts on distinguishing similar-looking things:

* take multiple pictures from slightly different angles

* take pictures using sensors for different frequencies (can be done with a colored transparent sheet, though simply using different cameras will have some effect)

* shine light from different angles

* shine different frequencies of light at it

Is a modern yield for SOS still as low as quoted?

I don't have figures for modern yields. I hope the yield is better. But I think there are fundamental difficulties with matching up the sapphire and silicon crystals that tends to produce faults.

I'm astounded HP made commercial products out of a process with such a low yield, I dont know how that was economical. (though none of the HP gear was exactly low margin)

The HP Journal article mentions the 9% yield as if they are perfectly fine with it. They were building these chips internally for high-margin gear (as you said), so it probably didn't matter if the chip cost $10 or $100, as long as it has the performance that they need. It's a completely different market from microprocessors such as the 6502 or the 8086, where customers are looking closely at the cost of the chip.

and RF components are still in that space to a greater or lesser extent too.

> I'm not sure what the oval stamp at the top is, maybe a turtle?

It's a teapot, on its head. How odd!

Perhaps https://en.m.wikipedia.org/wiki/Utah_teapot