Actually diamond is a really good heat conductor. Dave's big idea was that the actual "thickness" of the chip that was needed to implement the transistors was a

Actually diamond is a really good heat conductor. Dave's big idea was that the actual "thickness" of the chip that was needed to implement the transistors was actually quite thin (think nanometers thin) and that if you put one of these on top of another one, you could use effects like electron tunneling to create links between the two, and even bisected transistors (where the gate was on one of the two and the channel was on the other). So here is an article from 4 years ago on diamond as a substrate: https://www.electronicdesign.com/power/applications-abound-synthetic-diamond-semiconductor-substrates https://www.electronicdesign.com/power/applications-abound-s... which talks about how great it is for spreading heat out. And one thought was that you would make a sandwich of interleaved chip slices and diamond slices, still thin enough to enable communication between the two semiconductor layers without having to solder balls between them. In that scenarios the package would have an outer ring that would clamp contact the diamond sheets to pull heat out of everything to the case. Of course the mass market adopted making chips really thin so that you can make a sleek phone or laptop. Not really conducive to stacks in the package. Perhaps that was the thing that killed it off.