RELIABILITY PHYSICS STUDIES ON TRANSISTORS.

The report describes work on the second breakdown phenomenon in transistors. Section 1 deals with a comparison of electrical test methods for observing the onset of the thermal instability which leads to second breakdown. Two types of pulsed emitter current measurements and one dc type measurement were used, with emitter-base junction voltage being the sensitive indicator in each case. The results of these methods are consistent, but would lead to different ratings of the safe operating area of the device. The stability index measurement is the most sensitive and conservative. Section 2 is preliminary treatment of breakdown at high collector voltage where avalanche multiplication cannot be ignored. The theoretical treatment shows that the effective base layer resistance between a hypothesized low breakdown region under the emitter and the base contact is an extremely critical parameter in determining the current at which the device goes into breakdown, and that the initial instability is an electrical one occurring much more rapidly than thermal instability. Section 3 describes work on a resistive emitter contact in order to stabilize transistors against second breakdown. Experiments reacting Al with SiO2 have produced resistive contacts which may be useful.