Edge current induced failure of semiconductor PN junction during operation in the breakdown region of electrical characteristic

摘要

Typical blocking I-V characteristics are shown and analyzed for PN junctions exhibiting a breakdown region above 1000 V from commercial diodes and power MOSFETs. The leakage reverse current of PN junctions from commercial silicon devices available at this time has a flowing component at the semicon-ductor-passivant material interface around the junction edge.Part of the plotted experimental current-voltage characteristic fits to linear variation and deviation from this variation at higher applied voltage is attributed to non-controlled current flow in the interfacial layer, between the silicon and passivating material from the junction periphery. The thin interfacial layer including atomic layers both from the semiconductor and passivating dielectric material with fixed charges has imperfections resulted from the junction passivation process. For controlled-avalanche PN junctions no deviation from linear voltage dependence of the reverse current is possible until breakdown region practically at right knee appears. For other PN junctions deviation of the reverse current from linear variation results in a breakdown region with round knee and still with visible voltage dependence at current increase. Such soft breakdown region caused by the phenomena in the interfacial layer is exhibited at lower applied reverse voltage than the expected one for breakdown caused by charge carrier avalanche multiplication at the junction. Operation even for short in the soft breakdown region can lead to PN junction failure and for this reason, a maximum working permissible reverse voltage is specified in device data sheet with a value under the breakdown region. Junction failure consists in significantly lower reverse voltage than the initial one or even electrical short-circuit caused by a spot of material degradation in the interfacial layer from the junction periphery. Operation of the controlled-avalanche diode in the breakdown region is possible only for single pulse of short duration and at junction temperature not higher than 175 ℃. Above 150-175 ℃ even for controlled-avalanche diodes deviation from linear variation of the reverse current has been observed and soft breakdown region can appear before the expected avalanche breakdown. Device failure after operation in the breakdown region, caused by spot of material degradation at the junction periphery has occurred in such conditions. For high voltage commercial power MOSFETs operation in the avalanche breakdown region is limited to 150℃.