Thinking MOSFETs

The equations typically taught and used to estimate the threshold voltage for MOSFETs, based on the band bending in the MOSFET channel, are simple and easy to develop. However, they work well only for a subset of MOSFET types that do not include the MOSFETs of greatest interest today, including finFETs, nanosheet FETs, and most thin-film transistors (TFTs). This note provides an alternative, where threshold voltage is understood as moving the Fermi level to near the relevant band edge (conduction band minimum for n-channel MOSFETs or valence band maximum for p-channel MOSFETs).