The influence of body effect on the short-circuit ruggedness of emitter ballasted IGBTs

In this paper, we show that a dynamic increase in threshold voltage due to the high body effect coefficient in IGBTs contributes significantly to the improved short-circuit ruggedness in emitter ballasted IGBTs. We find that due to the nonlinear doping concentration in the DMOS channel, the body effect coefficient is high. Using analytical modeling and through numerical simulations, we show that the high body effect leads to a dynamic increase in V_th at high currents. Thus, a very small (50-100 mV) drop in the ballast resistor under normal operating currents will produce a 2-4 V increase in threshold voltage under short-circuit fault conditions. This greatly reduces the peak current through the device, increasing the short-circuit withstand time (SCWT). Experimental devices fabricated according to these principles demonstrate high short-circuit robustness with only minimal degradation of conduction drop