Study of Thermal Coupling Effect in GaAs Heterojunction Bipolar Transistors by Using Simple Current Mirror Circuit

Peter Dai, Pete Zampardi, Kai Kwok, Cristian Cismaru and Ravi Ramanathan 
Skyworks Solutions Inc., 2427 W. Hillcrest Drive., Newbury Park, CA  913120 
Email: peter.dai@skyworksinc.com   Phone (805) 480-4313

A simple method for determining the mutual thermal coupling resistance between adjacent heterojunction bipolar transistors (HBTs) in a GaAs integrated circuit (IC) is presented.  It utilizes a simple current mirror (CM) configuration as a test vehicle to evaluate the electro-thermal interaction between two HBTs by comparing measured IV curves of the current mirror with circuit simulations that include the thermal coupling.  By changing the distance between the two HBTs, the spatial dependence of the thermal coupling resistance is also determined.  Comparing the measured data to theoretical calculations demonstrates that the interconnecting gold metal layers play an important role in thermal coupling.  

Keywords:  GaAs, HBT, current mirror, thermal coupling, thermal resistance

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