Study of the impact of short-circuit conditions on the robustness of GaN power transistor for aeronautic and automotive applications

As part of the GANRET project led by the IRT Saint Exupery, this thesis investigates the short-circuit (SC) robustness of gallium nitride (GaN) high electron mobility transistors (HEMTs). Although these devices offer outstanding performances, their failure mechanisms under SC conditions remain insufficiently understood, which represents a major challenge for their integration into advanced power electronics converters.To provide new insights, a SC test bench was developed. It enables both single-event destructive SCs and repetitive SCs, at various drain-source voltage (VDS) levels. The bench was specifically designed to evaluate commercially available normally-off GaN HEMTs, 650 V/30 A, all sourced from the same manufacturer.A large-scale single-event destructive SC campaign on devices under test (DUTs) from different batches at 300 V, 400 V, and 500 V revealed a strong dependence of SC withstanding time (SCWT) on the applied voltage. The DUTs exhibited strong SC robustness at 300 V with SCWTs of several hundred microseconds, showed highly batch-dependent SCWT dispersion ranging from a few hundred nanoseconds to several hundred microseconds at 400 V, and failed almost immediately at 500 V (SCWTs ≤ 500 ns). No correlation was observed between SCWT and DUT static parameters characterized before the SC stress. No unique critical SC energy was identified, ruling out energy-driven failure mechanisms. An inverse relationship was observed between the SC current peak (ID-sat-max) and the SCWT: the higher the peak, the faster the failure occurs. It was also observed that the average power dissipated during the SC stress follows a square-root law with respect to SCWT, regardless of VDS, suggesting a thermal origin of the failure. Simplified thermal simulations based on the finite element method (FEM) showed that the DUTs fail within similar junction temperature ranges, although these simulation results should be interpreted as indicative. Repetitive SC testing at 400 V with very short pulses (≤ 500 ns) revealed that DUTs with the highest ID-sat-max survived the fewest SC cycles. Pre- and post-SC electrical characterization did not reveal reliable aging indicators, suggesting that damage likely occurs outside the DUT's active region. Thermal simulations again indicated failure at relatively similar junction temperatures, but the interplay between thermal and electrical degradation remains unclear.Overall, this thesis contributes to a better understanding of the short-circuit resistance of GaN HEMTs, the physical origin of the failure, and offers several possibilities for future investigations. It opens the way for further studies on the mechanisms distinguishing single-event destructive SC failures from repetitive SC events, on the improvement of electrothermal models, as well as on post-failure analysis to identify damaged areas and gain deeper insight into the underlying failure mechanisms.