The effects of material interfaces on thermal resistance values for high-power microwave transistors

In this paper, we examine the effects that the thermal interface between materials has on the thermal resistance extracted from electrical measurements. We also examine the consequent degradation in electrical performance. We present the characterization of the transistor under various thermal environments: mounted in packages, using various die attachments, and on-wafer. A wide range of thermal resistances are extracted and we demonstrate the importance of proper characterization during on-wafer thermal measurements. Finite-element simulations show that we can account for various thermal interfaces by changing the coefficient of thermal transfer from the semiconductor device to the material beneath it. Simulations are shown to be in good agreement with measured results.