Investigations of avalanche dynamics in IGBTs, bipolar GTOs and MCTs

A comprehensive investigation of the dynamic avalanche breakdown in insulated gate bipolar transistors (IGBT), bipolar gate turn off (GTO) thyristors and MOS controlled thyristors (MCT) is performed in this work. Based on analytical models of the failure mechanism due to dynamic avalanche, straightforward expressions of the effective dynamic forward blocking voltage fairly correctly predicting the decrease of sustaining voltage are deduced in this work. For the IGBT, two types of dynamic avalanche breakdown are identified: one during the unipolar phase of turn off; the second during the bipolar phase of the transient turn off. It is shown that for a gain of the active inner bipolar transistor less than 0.5, dynamic avalanche breakdown occurs only in the bipolar phase of turn off. The reduction of the gain below 0.4 greatly diminishes the chances for the dynamic breakdown of IGBTs. The phenomena leading to the dynamic avalanche breakdown of bipolar GTOs and MCTs with PMOS type turn off gate are rather similar. The design and drive conditions that might eliminate the dynamic avalanche breakdown are also presented in this work.