Variability of p-n Junctions and SiGe HBTs at Cryogenic Temperatures

This investigation examines the physical mechanisms that can increase the variability of both p-n junctions and silicon-germanium heterojunction bipolar transistors (SiGe HBTs) at cryogenic temperatures. The important operative mechanisms responsible for device parameter variability include bandgap narrowing due to heavy doping, mechanical stress, and the Ge profile. The impact of direct tunneling on cryogenic parameter variability in SiGe HBTs is also examined. Measurement results are compared with TCAD simulations to provide additional insights, and possible mitigation methods are discussed.