Analysis of Avalanche UIS Ruggedness of Vertical Power Silicon and SiC NPN BJTs

In energy-dense power electronic applications such as electric vehicles, avalanche-induced failures represent a significant reliability risk that can impact system availability. This paper provides comprehensive measurements and modelings to investigate the robustness of high-voltage-rated Silicon and 4H-SiC bipolar junction transistors (BJTs) under unclamped inductive switching (UIS) conditions. The study employs a combination of experimental measurements and Technology Computer-Aided Design (TCAD) models to provide a comprehensive analysis of the failure mechanism of these devices under the intense electrothermal stress of avalanche mechanism. Measurements have been performed at 25 °C and 175 °C to assess the impact of elevated temperatures on the avalanche dynamics in Silicon and 4H-SiC NPN power BJTs. The UIS tests have been carried out by incrementally increase of either the DC-link voltage or the base pulse length till the device failure. It is seen that the Silicon device can tolerate higher UIS energy, due to its significantly larger die area. However, for the same UIS energy density per die area, the 4H-SiC NPN BJT clearly outperforms its Silicon counterpart.