Operation of SiGe bipolar technology at cryogenic temperatures

The recent introduction of silicon-germanium (SiGe) alloys has proven exceptionally promising for achieving excellent bipolar transistor performance at cryogenic temperatures, while maintaining the cost and yield advantages traditionally associated with silicon (Si) manufacturing. In this paper we review the features of silicon-germanium heterojunction bipolar transistors (SiGe HBTs) which make them particularly suitable for cryogenic operation. Using dc and ac experimental results, we also address the issues associated with profile optimization of SiGe HBTs for the cryogenic environment, the potential for cryogenic SiGe BiCMOS technologies, and present new results on liquid-helium temperature operation of SiGe HBTs. We conclude that SiGe HBT technology offers significant leverage for future cryogenic digital, analog and mixed-signal applications requiring the highest levels of perfomlance.