A Correlation Between Beta Degradation at Room Temperature versus Beta Degradation at Stress Temperature for Determining the Reliability of HBTs
E. Sabin, J. Scarpulla, E. Kaneshiro, W. Kim, D. Eng, D. Leung
TRW, Inc.
The reliability of TRW's HBT devices has been measured using a highly accelerated WLR (wafer level reliability) technique, and results agree with less-highly accelerated oven reliability tests of HBT's and MIMC circuits. This paper compares the projected activation energy and MTTF derived from WLR tests where the current gain (ß) is measured either at room temperature or at the stressing temperature. The latter is preferred from a test efficiency standpoint, but the former is more common. The results show that with a proper selection of a failure criterion for each, equivalent activation energies and MTTF's can be obtained. Unfortunately it is currently not possible to measure the emitter resistance or the low current turn on voltage while keeping the wafer at the stressing temperature. So if the reliability is needed for these parameters then it is suggested that the wafer be periodically cooled to room temperature for measurement.