Temperature dependence of hot-electron degradation in bipolar transistors

Degradation of the base current and current gain observed in bipolar transistors that were electrically stressed at-75, 175, and 240°C for 1000 h with a constant reverse-bias voltage applied to the emitter-base junctions is discussed. The rate of degradation was found to be temperature-dependent with a larger degradation occurring at the lower temperature. This temperature dependency is studied using an electron energy simulation technique and experimental data on degradation and postdegradation annealing. From the electron energy simulations, the number of hot electrons above a damage threshold energy was seen to increase with 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 collisions at higher temperatures. However, an actual degradation rate reduction at higher temperatures occurs because of simultaneous annealing of the states produced by hot electrons. A model that describes the temperature dependence of degradation and postdegradation annealing is described