Failure Analysis of 1200 V Trench IGBTs Under Repetitive Overcurrent Turn-off

The insulated gate bipolar transistor (IGBT) is supposed to repetitively turn-off overcurrent, which is promoted by the popular grid-forming strategies of converters. This paper investigates the failure mechanisms of trench IGBTs under repetitive overcurrent turn-off. First, an equivalent experimental circuit is established to conduct repetitive overcurrent turn-off tests on 1200 V IGBTs under different switching frequencies. Results indicate that the devices ultimately experience secondary breakdown failure. Furthermore, scanning electron microscope (SEM) analysis of the failed IGBTs reveals various microstructural features, such as current filament paths near ablation zones and shifted wavy patterns in the active region, indicating heat accumulation near the gate and curved heat diffusion from the gate to the N- drift region. These findings are validated by TCAD electrothermal simulations, which demonstrate degradation of the reverse bias safe operating area (RBSOA) during repetitive overcurrent turn-off. Moreover, RBSOA degradation is more severe at higher switching frequencies due to accelerated thermal accumulation.