Analysis and characterization of the depletion-mode IGFET

Using simple charge-voltage relationships, a four-terminal model is developed for the depletion-mode IGFET. Various conditions which can coexist at the surface, such as accumulation, depletion, and inversion, are taken into account. The implanted channel is approximated by a box profile. The basic model elements, namely, the source-drain transport current and the various charging currents, are explicitly given in terms of known processing data and implanted channel parameters. Device threshold voltage, drain saturation voltage, and conditions for surface inversion are explicitly given as a function of these parameters.