SiGe HBTs junction temperature decrease in pulsed operating mode through an optimized topological structure coupled with a capacitive radiator

This paper focuses on the improvement of the thermal management of power transistor based on the SiGe BiCMOS9MW technology of STMicroelectronics. First, considering the possibilities compatible with the BiCMOS9MW manufacturing process, different topological structures enabling to optimize the junction temperature of such power transistors are proposed and studied. Then, for radar applications, approaches to take benefit of transient dynamic behavior in pulse wave operating mode are studied. In particular, the concept of “thermal sponge” brazed at the surface of the HBT transistors and acting as an efficient thermal capacitance increasing the overall thermal characteristic time of temperature rising is proposed and studied. Considering diamond thermal sponges and radar pulses of 50 μs, a 30% decrease of the junction temperature is demonstrated at the chip level. Finally, the proposed solution is studied at the package level. Due to technology constraints, the decrease of junction temperature is about 15% for the packaged chip.