Cell characteristics investigation and failure analysis under different damage modes for the reverse blocking diode thyristor

Reverse blocking diode thyristor (RBDT) is a promising semiconductor switch for high-current pulsed power applications, but its reliability is limited by non-uniform cell turn-on, which may cause current concentration, blocking-voltage degradation, and device failure. This paper experimentally investigates the relationship between cell characteristics, current-sharing behavior, and failure modes of RBDT. A low-voltage turn-on-delay-based method is proposed to evaluate the process-determined cell uniformity. Under the same triggering condition and main voltage, one type of device shows a turn-on delay of about 1200 ns and a peak current of 136 A, whereas another type exhibits a shorter delay of about 700 ns and a higher peak current of 248 A, indicating better cell uniformity and a larger effective turn-on area. Increasing the main voltage is further shown to mitigate cell turn-on discrepancies, and this method is verified in a parallel-current-sharing application. Under an asymmetrical layout, the current distribution remains significantly unbalanced even after increasing the main voltage, with the best observed current-sharing ratio being about 6.294:1. After adopting a symmetrical layout and increasing the main voltage, the current-sharing ratio improves to nearly 1.064:1, and the output current capability approaches twice that of a single device. In addition, different failure modes are analyzed using electrical waveforms, blocking-voltage measurements, and external morphology observations. Localized thermal damage causes forward blocking-voltage degradation and reduces the peak current from 420 A to 240 A, while penetrating thermal breakdown leads to complete loss of forward and reverse blocking capabilities.