Transient Response of Junction Temperature in Power Heterojunction Bipolar Transistors

We present a theoretical analysis for calculating the transient device junction temperature as a function of position and time upon a stepwise increase of power dissipation. The derivation applies in particular to multifinger heterojunction bipolar transistors designed for microwave power application. It is determined that for a typical substrate thickness of 100 µm, the rise time of the junction temperature is roughly 3×10-7 s.