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Performance and Reliability Characterization of 1200 V Silicon Carbide Power MOSFETs at High Temperatures
Keywords: Silicon Carbide power MOSFET, High temperature performance and reliability, Gate oxide
The low intrinsic carrier concentration and high thermal conductivity of the wide-bandgap semiconductor Silicon Carbide (SiC) make it a strong candidate for high-temperature power switching applications. In particular, the SiC power MOSFET is attractive due to the ability to thermally grow a Silicon Dioxide (SiO2) gate oxide on SiC, as is done for established Si technology. However, the small band offset between SiC and SiO2, coupled with a high density of electrically active bulk and interface states, results in threshold voltage (VT) instability and potentially unreliable device operation at high temperature. In this work, we have characterized commercially available, 1200 V SiC MOSFETs at high temperatures. Packaging technology for high-temperature operation is critical, and as such we have evaluated devices in both plastic and metal packages. Under forward blocking conditions, tested parts showed minimal drain leakage current up to the rated temperature of 125˚C, with leakage current monotonically increasing as the temperature increased further. For temperatures exceeding 125˚C, the metal-packaged parts showed approximately ten times less leakage current compared to the plastic-packaged parts. Moreover, a negative gate voltage could be used to reduce the leakage current for the metal-packaged parts, whereas for the plastic-packaged parts the leakage current was independent of gate voltage. This suggests the presence of a parasitic leakage path in the plastic-packaged parts, unrelated to the semiconductor die. The shift in threshold voltage (DeltaVT) was evaluated as function of temperature and gate voltage, and was shown to increase monotonically with both variables. Further, DeltaVT was independent of packaging type, suggesting that this degradation mechanism is inherent to the semiconductor device. The dependence of DeltaVT on gate voltage polarity was also examined and found to be larger for negative gate bias, suggesting that hole injection may result in greater VT instability than electron injection. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC0494AL85000. This work was performed under funding from the DOE Energy Storage Program managed by Dr. Imre Gyuk of the DOE Office of Electricity Delivery and Energy Reliability.
Robert Kaplar,
Sandia National Laboratories
Albuquerque, NM

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