Optimizing high voltage bipolar transistors in a smart-power complementary BiCMOS technology

The implementation of high voltage vertical bipolar transistors in a BiCMOS technology requires sufficient space for the extension of the collector-base depletion region. Assuming that layout design rules for high voltage devices are used, the open base breakdown voltage BVCEO is only defined by the one-dimensional vertical doping profile through the n(+)-emitter, the p-base, the n-intrinsic and the n(+)-extrinsic collector, i.e. lateral effects can be neglected for this type of breakdown. This paper describes the derivation of simple equations for optimizing the n(+)pn(-)n(+)-structure. Closed-form analytical equations based on the impact ionization model from Fulop ([1] Solid St. Electron. 10, 39 (1967)) yield the dependence of the open base breakdown voltage BVCEO on the transistor gain, doping level and width of the intrinsic collector. Copyright (C) 1996 Published by Elsevier Science Ltd