HIGH-INJECTION BARRIER EFFECTS IN SIGE HBTS OPERATING AT CRYOGENIC TEMPERATURES

We demonstrate that high-injection barrier effects associated with the collector-base silicon-germanium (SiGe) to silicon (Si) heterojunctio n are an important design constraint for SiGe heterojunction bipolar t ransistors (HBTs) operating at cryogenic temperatures. Due to its ther mally activated nature, these barrier effects can have important dc an d ac consequences at cryogenic temperatures even when undetectable und er room temperature operation. We use measured results from advanced S iGe HBTs and Si BJTs over a wide temperature range, in combination wit h simulation, to shed light on the design issues associated with these high-injection barrier phenomena.