Gregory's ServerA transparent IC? That's what we found inside a vintage HP floppy drive! The PHI chip (1977) is constructed from silicon-on-sapphire and you can see the gold "X" right through the die's sapphire substrate. 1/9
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HP made a lot of silicon-on-sapphire chips: processors, calculators, and this PHI interface chip. First was the MCΒ² 16-bit processor. This cover photo from HP Journal shows the transparency of that chip. 3/9 The package is unusual: the die is mounted on a flat ceramic substrate with a ceramic cap glued on. We heated the package to soften the glue. https://twitter.com/TubeTimeUS poked the cap with an X-Acto knife, but instead of sliding off, the cap violently flew off with a loud "pow"! 4/9  @kenshirriff Motorola experimented with that package design in the late 1980s, e.g. with their DSP56001, and called it the "SLAM" package. Maybe their's more than one reason for that name. photos of Motorola chip and a socket: @kenshirriff in the 90s, when i was working in chip design, SoS chips were primarily used for military and space applications as they are much more resilient to radiation than silicon substrates. however that seems a tad overkill for a floppy drive. ;-) |
Silicon-on-sapphire got its start in 1963. Instead of starting with a silicon wafer, silicon circuits are built on top of a synthetic sapphire base. The sapphire provides insulation between the transistors, improving performance and making the chip resistant to radiation. 2/9