Parametric degradation in transistors

Understanding degradation of key transistor parameters is essential in addressing transistor reliability issues. What are some of the key aging kinetics that causes transistor degradation? Understanding device reliability issues through physics-of-failure analysis provides insights that often are unobtainable from experimental work alone. The more one is able to understand, the higher is the likelihood that improvements can be made in device design and in testing methods. Parametric degradation in transistors is described to help explain overall reliability, relationships to device junction aging, and to aid in predicting parameter drift. This work gives a number simple formulations that help provide insight into why key device transistor parameters age. This is provided in both the bipolar and FET (field-effect transistor) case. Although the formulations are simple, they illustrate the important role that leakage current plays in aging of key device parameters for bipolar and FET transistors. Aging of key transistor device parameter for the bipolar and FET case have been described. Leakage have been expressed as leaky capacitors and relationships established to aging. In the bipolar case for the common-emitter configuration, we find that transistor beta aging is directly proportional to the fractional change in the base-emitter leakage current. In the FET case, transconductance aging results from a change in the drain-source resistance and gate leakage. This modeling also helps explain their observed log (time) degradation of these parameters observed on life test. We presented simple formulations to help understand this degradation that links this aging to junction temperature dependent leakage current mechanisms. We presented life test data that is representative of typical aging on both HBTs and MESFETs. Additionally, we used a TAT model to link these results with experimentally observed log (time) degradation. Such formulations are important in the understanding of transistor reliability.