Breakdown voltages of base-collector junctions of medium- and low-voltage graded collector transistors

Abstract

Recent works on current mode second breakdown show that a substantial measure of protection against failure by avalanche injection can be built into a transistor by grading the impurity concentration of the collector. The breakdown voltage of the base-collector junction is an important parameter in designing the transistor. In this paper, the open emitter breakdown voltages of medium- and low-voltage epitaxial bipolar transistors with graded collectors are computed numerically. A general expression for the open emitter breakdown voltage as a function of initial collector doping (doping at the collector side of the base-collector interface) and collector impurity gradient has been obtained. Empirical expressions for collector parameters as a function of open base bulk breakdown voltage and common emitter current gain are also derived.