Gregory's ServerMost chips are formed on a silicon wafer, but this RCA telecommunications chip is constructed from sapphire. It is a silicon-on-sapphire CMOS chip, with silicon circuits sitting on top of a thin sapphire substrate. 1/11
Ken Shirriff
7 comments
Ken Shirriff
Regions of silicon sit on top of the sapphire substrate. NMOS transistors are green, PMOS are purple. White metal lines connect the circuitry, as well as reddish polysilicon. Polysilicon also forms the gates of the transistors. 3/11
Ken Shirriff
Here's an inverter; if you've studied CMOS it should look familiar. A PMOS transistor on the top, and an NMOS transistor on the bottom. Input is the red polysilicon, forming the transistor gates. Output is the metal on the right. 4/11
SLeiBt
@kenshirriff Fascinating ! 2 questions, if I may: 1) is that some type of input protection? 2) the datasheet states HDB3 outputs can source 10mA, whereas all other output currents are 1.6mA. So I went looking for larger drivers, but all outputs look similar. Am I missing something (maybe it's just that the design got revised?). Thanks for all those nerdily interesting posts 🙂  |
Because sapphire is an insulator, silicon-on-sapphire has many benefits. It is faster, denser, radiation-resistant, and performs better. As one RCA engineer said: "SOS was the future technology choice for RCA. Unfortunately, it turned out it was not the future." 2/11