Peaks in temperature distribution over the area of operating power semiconductor junctions related to the surface leakage current

The surface component of reverse current of operating power PN junctions at high temperature, is a source of power dissipation concentrated in a very thin layer at the junction periphery. The resulted heat in this thin layer is removed towards the heat sink only through the peripheral part of the semiconductor die area. Typical commercial rectifier diodes exhibiting surface leakage current are considered to illustrate non-uniform junction temperature distribution. At higher applied reverse voltage, the surface component of reverse current flows non-uniformly around the junction perimeter. It is shown that the thermal resistance for the heat transfer from the junction periphery is significant higher than the corresponding one for the heat removal from the junction bulk. A simple evaluation indicates that the temperature of local hot spots near the junction peripheral surface may be at least 10 °C higher than in the junction bulk. Junction temperature peaks were observed by infrared imaging microscopy. Influence on device reliability is possible.