Second breakdown in power transistors due to avalanche injection

Second breakdown in power transistors continues to be an actively discussed subject. Although there is general agreement that the lateral thermal instability model adequately explains forward bias second breakdown, it fails to explain the reverse bias failure mechanism. The thermal initiation and electrical initiation processes have been successful in explaining only some aspects of this phenomena. This paper studies the subject of reverse bias second breakdown both experimentally and analytically. It is seen that there is excellent correlation between theory and experiment. The conclusion of this investigation is that avalanche injection is the triggering mechanism. Further, the filamentary currents that result from this can in most cases result in device failure. It is also concluded that under fixed circuit conditions, the reverse bias second breakdown potential of a transistor is completely specified by the single parameter Vpwhich is the voltage necessary for avalanche injection.