Is the source-to-channel junction always a fixed 1e-20? Wouldn't it be better to have a parameter (with a default of 1e-20)?
x_jun_s = 1e-20; // x-position defining the source-to-channel junction
Is the 1e-20 in this equation always 1e-20, or is it actually equal to x_jun_s?
x_jun_d = lch_lim - 1e-20; // x-position defining the drain-to-channel junction