Process variables which affect germanium transistor reliability

Investigations by the Bell Telephone Laboratories into the reliability characterization of PNP germanium alloy transistors produced by the Western Electric Company have resulted in dramatic improvement in the stability of their electrical properties. These studies have extended over about five million device hours of life testing, including about 600 transistors, some tests extending over two years. Early investigations were aimed at characterizing the stability of the emitter and collector junctions as well as the direct current gain of the transistor when subjected to various conditions of temperature, current, voltage and power. From these studies evolved a simple method for the early detection of instability which would eventually lead to failure. A need for improving the stability of this transistor was also established.