Failure Modes of 15 kV SiC SGTO Thyristors during Repetitive Extreme Pulsed Overcurrent Conditions

Abstract

SiC SGTO thyristors are an advanced solution for increasing the power density of medium voltage power electronics. However, for these devices to replace Si thyristor technology in industrial applications their characteristics and failure modes must be understood. This letter presents the failure modes of two 15-kV SiC SGTO thyristors during repetitive overcurrent conditions. The devices were evaluated with 2-kA (3.85 kA/cm2) square pulses of 100 ${\boldsymbol \mu}$ s duration using a pulse forming network. Throughout testing, each devices’ static characteristics were analyzed for signs of degradation; upon degradation, testing was ceased and the physical failure mode was determined through imaging with a scanning electron microscope (SEM) in conjunction with a focused ion beam. The electrical results demonstrate the failure modes of both SiC SGTO thyristors during pulsed overcurrents electrically manifested themselves as a conductive path through the gate-anode junction and an increased device on-state voltage. SEM imaging revealed one SiC thyristor formed an approximately ${10\hbox{-}\mu{\rm m}}$ wide cylindrical void, and the second SiC thyristor formed an approximately ${200\hbox{-}\mu{\rm m}}$ long crack. However, the experimental results demonstrate these 15-kV SiC SGTO thyristors’ robust ability to repetitively switch at extreme high current density for tens of thousands of cycles.