SThM Temperature Mapping and Nonlinear Thermal Resistance Evolution With Bias on AlGaN/GaN HEMT Devices

Channel temperature has a strong impact on the performance of a microwave power transistor. In particular, it has a strong influence on the power gain, energetic efficiency, and reliability of the device. The thermal optimization of device geometry is therefore a key issue, together with precise measurements of temperature within the channel area. In this paper, we have used scanning thermal microscopy to perform temperature mapping, at variable dc bias points, on an AlGaN/GaN high-electron mobility transistor made on epilayers grown on silicon carbide substrate. We have analyzed the variation of the thermal resistance values, which are deduced from these measurements, with bias conditions $V_{\rm GS}$ and $V_{\rm DS}$. The observed nonlinear behavior is found to be in excellent agreement with physical simulations, strongly pointing out the large variability of the extension of the dissipation area with the dc bias conditions.