Devlog #24

The 2D bipolar transistor now matches DEVSIM. The main current is within 0.8%, the small control current is within 3.4%, and the full output curve is within 2.7%. That closes the transistor phase.

Next I added two new kinds of physics. The first is the Schottky diode (something which people use everyday), a junction made by touching metal straight onto silicon instead of joining two kinds of silicon. I also added a small effect where the metal pulls the energy barrier down a bit, which lets more current through. The second is avalanche breakdown. Push enough reverse voltage onto a diode and electrons get going so fast they knock new electrons loose, those knock more loose, and the current shoots up. It matches DEVSIM too, and both got their own pages on the site explaining them.

Then I changed the shape of the mesh. Up to now the simulator could only split a device into rectangles. Now it can use triangles, which fit curved and oddly shaped devices much better. It can also read and write mesh files from Gmsh, a free meshing tool, and add triangles only where the answer changes quickly.

I also added round devices, where it simulates a thin slice of something cylindrical and treats the rest as spun around a center line. That showed me something cool: curved junctions break down at lower voltages than flat ones, because the electric field crowds together at the bend. I never told it that.