vivkr
|
Hi,
The Vt is adjustable with doping, and that's what is used. Transistors with different Vt are made with different levels of doping as already observed in one reply.
The very same implant which is used for raising the Vt of FETs which would otherwise be formed depletion mode can also raise the Vt by a lower amount if administered in a smaller dose. By the way, I am not sure if one still gets normally ON FETs without an extra implant in the processes used nowadays. However, the principle remains the same.
The standard formula for computing the threshold contains terms related to work function and doping and you can find it in any device physics text. Try Tsividis for instance.
Vivek
|