Yeah, Va is related with W. And the Ron in spectre result is the Rds!
Added after 11 minutes:
I also wanna get help with the topic:
I'm designing a bandgap with subthreshold transistors. I find the Ids=W/L*Id0*exp(Vgs/(VT*n)) not accurately right for a mid-area exits between strong-inversion and weak invesion. So my bandgap has a poor PSRR(30db). Can any bro. give me a help. Thanks!
when Vgs < Vth, NMOS is in weak inversion & you will still get some current when you have a voltage difference between Drain and Source. Sub threshold currents flow in the weak inversion region.
You can calculate Vth easily for a known impurity concentration(Na) & Cox.
Vth = VFB + 2φf -(Qb/Cox) - (Qox/Cox)