Effect of Operating Conditions and Transistor Parameters on Gain Degradation

Data for predicting transistor gain degradation in a neutron radiation environment were obtained from experimental studies of the variation of the radiation damage constant KT as a function of temperature and current during both measurement and irradiation. Relatively small spreads in the values of KT were obtained when the individual base transit times were measured and the radiation exposures were precisely determined. Radiation damage effect data from 20 different n-p-n silicon transistor types were obtained and normalized to the same minority carrier concentration in the base region, using the transit time and the VBE-Ic characteristics of the specific transistors. The resulting relative dispersions of the damage constant for minority carrier densities of 1015/cm3 and 1016/cm3 were typically 15 to 20 percent. These dispersions indicate that electrical measurements of transistor physical parameters can provide reasonably accurate predictions of the gain degradation for a wide variety of transistors without additional radiation testing of specific transistor types.