GAIN DEGRADATION AND ENHANCED LOW-DOSE-RATE SENSITIVITY IN BIPOLAR JUNCTION TRANSISTORS

Abstract

The current gain of irradiated bipolar junction transistors decreases due to increased recombination current in the emitter-base depletion region and the neutral base. This recombination current depends on the interaction of two factors: (1) decreased minority-carrier lifetime at the Si / SiO 2 interface or in the bulk Si and (2) changes in surface potential caused by charge in the oxide. In npn transistors, these two factors both result in increased base current, while in pnp devices, positive charge in the oxide moderates the increase in base current due to surface recombination. In some technologies, the amount of degradation that occurs at a given total dose increases as the dose rate decreases. This enhanced low-dose-rate sensitivity results from space-charge effects produced by slowly transporting holes and protons in the oxide that covers the emitterbase junction.