Analytical modeling of the channel-charge in ion-implanted MOSFETs and MESFETs

Abstract

ABSTRACT Analytical modelling of implanted Buried Channel (BC) and Surface Channel (SC) MOSFETs and MESFETs is difficult since the highly non-uniform channel doping profile can not be integrated analyticallyto obtain the charge-voltage characteristics of the channel depletion layer. The present paper derives a general approximation to the non-uniform profile which gives simple and accurate closed form expressions directly in terms of device parameters for the variouscharacteristics of all the FETs under all implant and bias conditions (the implant may be shallow, deep or multiple, and it may be partially or fully depleted depending upon the bias conditions). The derivation does not make any a-priori assumptions about the shape of the approximate profile. Instead, the shape emerges from a new formulation of the analytical modelling problem. It is shown thatthe necessary condition for analytical modelling of all the threeFETs is the same, namely, expressing the depletion layer voltagedrop Vd as a polynomial of the depletion charge d' where the degreeof the polynomial can not exceed two. Next it is demonstrated that