Parameter Extractions for a GaAs pHEMT Thermal Model Using a TFR-Heated Test Structure

The temperature-dependent thermal conductivities of a GaAs pseudomorphic high-electron mobility transistor's (pHEMT) substrate and epilayer regions are extracted to develop a 3-D finite-element-method thermal model. The thermal characterization is based on electrical gate-metal-finger temperature measurements of a customized GaAs pHEMT test structure. Heat flow from an integrated thin-film resistor is shown to be sensitive to the device's substrate thermal conductivity, while heat flow from the device's channel is most significantly affected by the epilayer region thermal conductivity. These observations are used in the formulation of the thermal parameter extraction technique, which serves as a useful and convenient device modeling tool that can be integrated into an engineering design flow. Specific knowledge about the semiconductor material fabrication process, which may be unavailable to the design engineer, is not required for accurate thermal characterization; this is the overriding advantage of the technique presented.