Bias dependence of ionizing radiation damage in SiGe HBTs at different dose rates

The influences of three different bias conditions on the ionizing radiation damage at different dose rates were investigated in discrete silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). Experiment results demonstrated that the bias configuration corresponding to the worst performance degradation depended on the dose rate. For the high dose rate irradiation, the case with all terminals floating shown an enhanced degradation, while during the low dose rate irradiation, the forward active mode suffered more irradiation damage. The underlying physical mechanisms were analyzed and investigated in detail. It was indicated that the varied bias dependences for the high and low dose rate irradiation might be attributed to different origins of hole and proton induced by gamma irradiation.