Theory and simulation of combined mechanisms limiting the safe operating area of power semiconductor microelectronic switches

A generalized analytical model for the turn-off process of bipolar switches with microgates is developed taking into account the role of technological and design imperfections of real structures, which limit their safe operating area. Using a thyristor microchip with external field control, operating in a voltage inverter circuit, as an example, the boundary of the safe operating area with respect to the “turned-off current” is quantitatively determined. It is found that this boundary for a non-ideal structure in the low-voltage region is controlled by the effect of regenerative unlocking [triggering] of the cathode emitter; in the high-voltage region, this boundary is controlled by the onset of current localization in “perturbed” cells, involving dynamic breakdown. The possible applications of the developed model to indicate the directions of device-structure optimization to increase their maximum switching current are discussed. The adequacy of the results of model applications is validated using numerical simulation.