Investigation of total dose effects in SiGe HBTs under different exposure conditions

This paper presents the total dose effects of gamma ray and swift heavy ion irradiation on silicon-germanium heterojunction bipolar transistors (SiGe HBTs). The direct current (DC) characteristics, such as forward-Gummel, reverse-Gummel and current ideality factors before and after irradiation are analyzed and used to quantify the dose tolerance. Experiment results show that the performance degradation depends on the dose rate and bias condition during gamma ray irradiation. Compared to gamma ray irradiation, more serious base current degradation exists in the transistors exposed to 25 MeV Si ion. The base current in forward- and reverse-Gummel mode are found to show a distinct sensitivity to gamma ray and swift heavy ion irradiation. An increase in emitter current appears in the reverse-Gummel test after heavy ion irradiation. The underlying physical mechanisms are analyzed and investigated in detail.