Current gain degradation in SiGe HBTs by hot carriers

Abstract

The effects of open-collector and forward-collector reverse bias stressing on SiGe HBTs have been studied. Increases in the base current and degradation of the current gain, similar to those found in pure Si BJTs, were observed in the stressed devices. Short periods of severe reverse base-emitter bias stress cause random telegraph signals to occur in the base current. Damage is caused by hot holes, created by band-to-band tunneling in the base-emitter junction, during open-collector stressing and by hot holes and electrons, injected from the collector into the base, in forward-collector stressing. A comparison of the charge to failure as a function of stress voltage between the two hot carrier stressing methods suggests that, at a given kinetic energy, holes cause more damage than electrons.