Hardware enthusiast Ken Shirriff se he boasted on his blog an unconventional chip find from 1977. While repairing an eight-inch floppy disk drive, he discovered a chip using sapphire as a substrate instead of ordinary silicon. Thanks to this, the chip is transparent with a perfectly visible structure of all connections.
The white circuits are metallic, on the contrary, the gray structure is silicon. Everything else is transparent sapphire as a substrate
The chip was manufactured by HP for its device and was responsible for the connection between the HP-IB bus and the Z80 chip in the floppy drive controller. In the HP archive, Shirriff discovered a more detailed description of the chip, so we can see, for example, a cross-section.
A thin silicon layer is formed on the sapphire substrate, which, through subsequent plating, creates individual metallic connections and gates. Because sapphire is an insulator, all silicon regions are separated, reducing the likelihood of stray currents among other things. At the time of its creation, it was one of the ways to increase performance. You can read much more about the parameters and design of the chip in exhaustive blogpost.
Although it might seem that this is a historical curiosity, we could also encounter transparent substrates in the future. Intel this fall issued a report, according to which he is working on more efficient chips that use glass. Among other things, it talks about better heat resistance. Intel’s potential processors with glass won’t be as impressive as the chip from 1977, but it’s an interesting technological return.
2023-12-26 11:45:21
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