New approach for defining the threshold voltage of MOSFETs

The threshold voltage of MOSFETs has traditionally been defined as the gate voltage required to cause the surface potential to be equal to twice the Fermi potential in the bulk of semiconductor. Such a definition, although widely used for modeling long-channel MOSFET's, becomes increasingly questionable for modern devices with diminishing channel lengths. In this paper a new approach is proposed which defines the threshold voltage based on the intersection of the two asymptotes of the surface potential for the depletion and strong inversion regions. The approach is tested in a simulation environment for MOS devices having different channel lengths, oxide thicknesses, and substrate doping concentrations.