Temperature dependence and post-stress recovery of hot electron degradation effects in bipolar transistors

The authors present the results of a study of the BJT (bipolar junction transistor) degradation process due to hot electrons with the goal of better understanding the degradation rate of current gain and noise characteristics under various temperature and bias conditions. Degradation was produced by reverse biasing (-4 V) the base emitter junction of bipolar transistors at various temperatures (-75 to 240 C), with stress periods ranging from 1/60th of a second to over 1000 h. Post-stress recovery of the degradation was studied using both high-temperature annealing and base-emitter forward biases. Two mechanisms which decrease the rate of degradation at higher temperatures are the reduction in the number of hot electrons at higher temperatures and the simultaneous annealing of the states produced by hot electrons at higher temperatures. Experimental data are used to develop a model description of the hot-electron-induced gain degradation process which includes both the temperature dependence of the number of hot electrons and the temperature dependence of a simultaneous repassivation process which is observed at high ambient temperatures