Analytical Model for Subthreshold Swing and Threshold Voltage of Surrounding Gate Metal–Oxide–Semiconductor Field-Effect Transistors

Abstract

We investigate analytically the metal–oxide–semiconductor field-effect transistor (MOSFET) with a surrounding gate (SG). We develop and present an analytical model for subthreshold swing and threshold voltage. Poisson's equation is solved analytically. The analytical expressions for electrical potential, drain current in the subthreshold region, subthreshold swing, and threshold voltage are obtained. The analytical results are compared with simulated results, and the two agree very well. The subthreshold swing of an SG MOSFET can be improved either by reducing the silicon body radius or by reducing the oxide thickness. The threshold voltage decreases with reductions in the channel length, the silicon body radius, or the oxide thickness. Based on the threshold voltage model, drain induced barrier lowering (DIBL) effect is explored, and we find that DIBL effect is more severe for a device with a larger silicon body radius, and/or with a shorter channel length.