The Impact of Temperature on GaN/Si HEMTs Under RF Operation Using Gate Resistance Thermometry

Several optical and electrical methods have been developed to thermally characterize GaN high-electron mobility transistors (HEMTs) under DC operation. Gate resistance thermometry (GRT) has proven to be an inexpensive and reliable method to estimate the peak temperature. The complex Joule heating profile of a HEMT, however, is highly bias dependent, and its temperature profile under RF conditions may vary compared to the profile generated under DC operation. Evaluating the thermal performance of HEMTs under RF operation is thus necessary to quantify any differences between these two modes of operation. Implementing a differential probe, this paper highlights the capability of using GRT to measure accurately the temperature of GaN/Si HEMTs under RF operation. A larger gate-to-gate spacing is shown to decrease the overall temperature rise, while a linear correlation is found between the power-added efficiency and the junction temperature. The effect of the baseplate temperature on the device's thermal performance both under steady-state and RF operations is presented. Overall, at a given power density and baseplate temperature, the RF temperature rise is shown to appear lower than its equivalent temperature under DC biasing.