Channel Temperature Measurement of GaN HEMT Used in Kilowatt-Level Power Amplifier

This paper presents an electrical thermometry method designed for kilowatt(kW)-level Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs). The dependence of the drain current on the channel temperature in GaN HEMTs is utilized as a means to measure the transient channel temperature. However, in kW-class GaN HEMTs, the gate current can reach tens of milliamperes, and trap-induced capture resulting from high doping concentrations can both influence the drain current. Through modifications to the gate bias circuit, the gate voltage self-biasing phenomenon caused by the gate current is mitigated. A theoretical model is derived to express the relationship between the drain current and the channel temperature. Experimentally, amplifier modules equipped with kW-level HEMTs were placed on thermal stages set at 45 °C, 60 °C, and 80 °C. The transient drain current curves and the corresponding channel temperature profiles were measured. The measured drain current versus channel temperature curves at different ambient temperatures were fitted and compared with the theoretically derived formula. The relative error between the measured and calculated drain current values at the same channel temperature was found to be within 1%.