Degradation of avalanche ruggedness of power diodes by thermally induced local breakdown

The investigations into the failure mechanism of the power diode during the undamped inductive load switching (UIS) are presented using experiments and numerical simulations. During the avalanche event, the temperature rise due to the localized avalanche current increases breakdown voltage and as a result, the location of the peak impact ionization moves around in the device. This behavior alters the current distribution under the UIS condition, depending on the initial location of breakdown. When the avalanche event starts at the edge termination, the avalanche current redistribution into the active area is limited, resulting in weak avalanche capability. Therefore, for high avalanche ruggedness, the diode should have the uniformly distributed avalanche current, which can be observed when the breakdown starts at the bottom of anode junction. In this work, it is shown that the avalanche capability of the power diodes during the UIS conditions is strongly dependent on the location of the initial breakdown and the mismatch of the termination design and starting material can significantly degrade the avalanche capability. Therefore, the power diode with high avalanche capability should be designed by elaborately controlling the location of initial breakdown.