Collector-Base Junction Avalanche Effects in Advanced Double-Poly Self-Aligned Bipolar Transistors

Abstract

As bipolar devices are scaled down, the collector doping concentration needs to be increased in order to prevent base stretching, which causes performance degradation at high current density. The latter increases the electric field in the base-collector junction. In this paper, we report the observation of base current reversal induced by avalanche multiplication in advanced self-aligned bipolar devices at a collector junction reverse bias less than 3 V. Temperature measurements were carried out to verify the avalanche mechanism, and the dependence on the collector doping profile and high-level injection effects was investigated both experimentally and by numerical simulations. The avalanche effect, which is expected to aggravate with scaling, will eventually threaten normal circuit operation if certain criterion for base-collector reverse bias cannot be maintained. Therefore, future bipolar down-scaling to a thinner base and a higher current density needs to address this issue in an innovative way. © 1989 IEEE