Breakdown mechanism in short-channel MOS transistors

Abstract

In this paper a new breakdown mechanism in a short channel MOS transistor is proposed based on experimental measurements of substrate currents. We have observed a negative resistance in the substrate current followed by conductivity modulation, similar to the operation of a unijunction transistor during switching. By adding an external substrate resistance, saturation of the substrate current was observed in conjunction with the turn-on of the parasitic NPN (source-substrate-drain) bi-polar transistor. Breakdown of the device will occur when the drain bias reaches BVCEOof this parasitic bipolar transistor. The channel length dependence of the breakdown voltage of the short channel MOS transistor can then be explained by the dependence of BVCEOon the base width.