Experimental cryogenic modeling and noise of SiGe HBTs

SiGe devices are an exciting contender for extremely low noise, cryogenically cooled amplifiers. This paper begins with a procedure for extracting a simple equivalent circuit model capable of accurately describing SiGe HBT devices. Next, small-signal modeling results obtained for a 3×0.12×18um^2 SiGe HBT at 15, 40, 77, 120, 200, and 300K are presented along with discussion of performance enhancements due to cooling of the device. Finally, the modeled noise performance is presented as a function of temperature and frequency using the concept of minimum cascaded noise temperature, a figure of merit which incorporates both noise temperature and gain