Elevated temperature microwave characteristics of heterojunction bipolar transistors

An analysis of the heterojunction bipolar transistor (HBT) temperature effect has been performed directly at microwave frequencies using a combination of measurements and physical modeling. The most temperature sensitive elements, the base-emitter resistance and capacitance, and the transconductance, were extracted from S-parameter data at 28 bias points for five temperatures from 23/spl deg/C to 225/spl deg/C. The element values were compared to a physical model showing excellent agreement. The magnitude and direction of change for the element values is shown versus temperature and bias which, along with the physical model, describes the HBT behavior with a strong bias on device physics. The cutoff frequencies f/sub T/ and f/sub MAX/ were also measured and calculated, both showing a monotonic decrease with temperature. Over the 200/spl deg/C range f/sub T/ and f/sub MAX/ decreased by a total of 40% and 60%, respectively.<>