Localized Thermal Effects in Silicon Power Transistors

Abstract
This paper concerns effects observed in silicon power transistors. The first part deals with the appearance of thermally induced breakdown and the high local temperatures in a hot spot. By means of potential probing on the aluminum contact area of the transistor, two different types of behavior could be found. Usually the region carrying current in the breakdown condition occurs at about the center of the area developing a hot spot prior to breakdown. However, transistors have been observed in which the breakdown area did not coincide with the hot spot, indicating that a local defect is involved. In the second part of this paper some studies are presented on the nature of the damage caused by the breakdown. Generally the damage results in an ohmic path internally between emitter and collector. Continued operation in the breakdown region results in the resistance of the path becoming smaller until a short circuit is produced accompanied by evidence of local melting.

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