Trends in the total-dose response of modern bipolar transistors

The various phenomena occurring in bipolar transistors when they are exposed to ionizing radiation are discussed. NPN transistors are found to degrade more than PNP transistors. Devices with highly doped base rings will be less susceptible to total-dose damage than devices without base rings, especially in NPN devices. Devices with small emitter perimeter-to-area ratios will be less susceptible than devices with large perimeter-to-area ratios. Collector bias does not affect gain degradation. Reverse bias on the emitter is the worst-case irradiation bias condition. The increases in base current are larger at small base-emitter voltages than at large base-emitter voltages. Poly-emitter devices are initially harder than standard emitter devices, but may become worse than standard devices at large total doses. Degradation is worse at lower dose rates