Dynamic current localization during turn-off of high-power microgate bipolar switches

Abstract

The turn-off process of semiconductor switches with distributed microgates in the presence of small embedded technological inhomogeneities of their structure parameters is considered. The process dynamics is studied based on the analytical model of residual plasma displacement and the space charge region dynamics in the base, taking into account ionization in high electric fields. A spatially inhomogeneous switch structure is modeled by two groups of controlled cells with different parameters, i.e., emitter injection efficiencies or carrier lifetimes in n-type bases. Voltage coupling of all cells is complemented by the device interaction with the external circuit. The detrimental effect of current localization at the turn-off stage, which occurs even at a relatively small parameter variance, was studied within the proposed model. The results obtained allow quantitative characterization of the effect of technological inhomogeneities on safe operating area of high-power microgate bipolar switches.