Silicon-Germanium Heterojunction Bipolar Transistor

Abstract

Silicon (Si) bipolar transistor technology, despite its desirable features of fast switching speed, high transconductance, and excellent current-drive capability at room temperature (RT = 300 K), is often viewed as unsuitable for the cryogenic environment because its current gain (β = J_c/J_B), frequency response, and circuit speed typically degrade strongly with cooling [1,2]. Recent evidence [3–6] indicates, however, that careful profile design can be used to achieve respectable Si bipolar performance down to liquid-nitrogen temperature (LNT = 77 K). Even with these improvements, however, it is unlikely that conventionally designed Si bipolar technology will offer performance attractive enough to make it a serious contender to CMOS, a proven technology for cryogenic applications.