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Managing the thermal behavior of GaN devices under test (DUT) poses significant challenges during accelerated thermal cycling (ATC) tests, particularly due to the compact packaging of small GaN devices (e.g., QFN package) and the sharp rise in the device's RDSon at high junction temperatures. This paper presents a framework for analyzing and modeling the thermal response performance of the ATC test setup and evaluating the impact of non-linear dissipated power on the GaN DUTs. It outlines the limitations of conventional thermal sensors in accurately estimating the DUT's junction temperature through case temperature measurements under ATC conditions. The analysis and modeling of the experimental junction temperature response function shows about 4 s time constant in the measurements using a thermistor placed near the DUT, highlighting the GaN DUT's susceptibility to thermal runaway under ATC conditions (Tj−max > 125 °C), where the thermal time constant significantly exceeds the DUT's thermal transient time. Consequently, an on-state resistance (RDSon)-based Tj estimation method is employed to monitor the Tj and control the thermal cycling window boundaries effectively. Experimental investigations of several e-mode GaN HEMTs under different ATC windows are conducted to validate the ATC testing framework. Moreover, the temperature coefficient of on-state resistance (α) is characterized and quantified - considering fully packaged individual GaN DUTs’ mechanical and electrical degradation mechanisms. 

This paper presents an improved on-state resistance (RDSon) measurement scheme for high and low-side GaN FETs, which is critical for reliable and precise assessment of GaN HEMT power devices’ lifetime and degradation patterns. The proposed circuit is based on an active voltage clamp using Si MOSFET and Schottky and Zener diodes. The proposed circuit features lower parasitic inductances and capacitances by replacing the Si MOSFET with e-mode GaN FET. This modification contributed to much lower ringing and spikes in the voltage and current waveform of both the measurement FET and the DUT. The absence of an embedded body diode in the GaN device in the measurement circuit allows zero reverse recovery operation, making it more viable in high-frequency power converters. This study also provides a detailed design analysis of a bootstrap GaN-based on-state voltage (VDSon) sensing scheme for high-side FETs, useful in multiple converter configurations for in-situ devices’ health monitoring and conditioning. Simulation and experimental results validate the performance and features of the proposed concepts.