Impact of threshold voltage shifting on junction temperature sensing in GaN HEMTs

Junction temperature sensing in GaN HEMTs has been identified as a critical challenge for condition monitoring especially under power cycling conditions. The use of temperature sensitive electrical parameters has been widely studied. In GaN devices, the ON-state resistance and gate leakage currents have been identified as TSEPs as both are junction temperature sensitive. Circuits capable of measuring the gate leakage currents in commercially available GaN HEMTs have previously been presented, however, the impact of variability in the threshold voltage on junction temperature sensing requires further investigation. In this paper, junction temperature measurements are implemented using the gate current as a TSEP and are compared with the junction temperature inferred from the ON-state resistance. The measured junction temperatures were verified against electrothermal simulations using manufacturer provided thermal networks. Threshold shift from charge trapping in Schottky GaN HEMTs has been shown to impact the temperature dependence of the gate leakage currents and ON-state resistance. It is important to account for these changes when using them as temperature sensitive electric parameters for real time junction temperature estimation in GaN HEMTs.