College Student Details Making His Second Generation of ICs at Home
upstart writes:
In 2018 I made the first homemade integrated circuits in my garage fab. I was a senior in high school when I made the Z1 amplifier, and now I'm a senior in college so there are some long overdue improvements to the amateur silicon process.
The Z1 had 6 transistors and was a great test chip to develop all the processes and equipment. The Z2 has 100 transistors on a 10m polysilicon gate process - same technology as Intel's first processor. My chip is a simple 10*10 array of transistors to test, characterize, and tweak the process but this is a huge step closer to more advanced DIY computer chips. The Intel 4004 has 2,200 transistors and I've now made 1,200 on the same piece of silicon.Previously, I made chips with a metal gate process. The aluminum gate has a large work function difference with the silicon channel beneath it which results in a high threshold voltage (10V). I used these metal gate transistors in a few fun projects like a guitar distortion pedal and a ring oscillator LED blinker but both of these required one or two 9V batteries to run the circuit due to high Vth. By switching to a polysilicon gate process, I get a ton of performance benefits (self aligned gate means lower overlap capacitances) including a much lower Vth which makes these chips compatible with 2.5V and 3.3V logic levels. The new FETs have excellent characteristics:
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