TEMPERATURE-DEPENDENCE OF HOT-ELECTRON DEGRADATION IN BIPOLAR-TRANSISTORS

Bipolar transistors were electrically stressed at -75, 175, and 240-de grees-C for 1000 h with a constant reverse-bias voltage applied to the emitter-base junction. Degradation of the base current and the curren t gain was observed. The rate of degradation was found to be temperatu re-dependent with a larger degradation occurring at the lower temperat ure. This temperature dependency is studied using an electron energy s imulation technique and experimental data on degradation and post-degr adation annealing. From the electron energy simulations, the number of hot electrons above a damage threshold energy was seen to increase wi th increasing ambient temperature at a constant reverse-bias voltage. This increase with temperature occurred because higher stress currents dominated over a reduction in the electron mean free path between col lisions at higher temperatures. However, an actual degradation rate re duction at higher temperatures occurs because of simultaneous annealin g of the states produced by hot electrons. A model is developed to des cribe the temperature dependence of degradation and post-degradation a nnealing.