Devlog #5

Since the license was added, all my time has gone into one stubborn thing, that is getting DEVSIM simulator, to produce trustworthy MOSFET curves.

It has been a long journey of small lies the application tells you. DEVSIM’s solve doesn’t take a device argument, so it solves everything you’ve ever built in that process at once. I was building one device per curve and leaving them around, so the second curve was dragging a finished device along with it and ruining the shared error check. Deleting each device when its curve finishes fixed a whole family of weird failures.

Then I found the equilibrium solve was starting from all zeros, which on this device is 0.6 V off. I supply it from charge neutrality now. Same final output but far less trouble getting there.

2 of my own ideas turned out wrong and got reverted, but I wrote the measurements rather than dropping them. Capping the solver’s pass budget moved the current by 0.4%. Pinning the math library to one thread made a four second step take three minutes. Big Ouch.

Currently, the 1 micron transfer curve at 50 mV of drain runs end to end and confirms with my simulator to within 0.23% above threshold. The 1 V curve still stalls at 0.4 V of gate, and I checked it properly rather than simply loosening the tolerance, because it turns out DEVSIM isn’t converging there at all.

My own code, for contrast, does the same curve in 4.6 seconds.