The Selection of Transistors for Use in Ionizing Radiation Fields

The principal effects on transistors subjected to prolonged ionizing radiation fields are the reduction of the forward current gain and the increase of the collector-base leakage current. Thin base, high frequency transistors are more resistant to gain degradation than low frequency units. Leakage current increases arise from direct generation of carriers by the ionizing radiation, by the formation of surface channels, and damage to the lattice structure. The useful life of equipment can be increased by the selection of transistors which minimize surface channeling. The extent to which channeling will take place is strongly determined by the presence of surface defects and hence can be predicted by a microplasma noise test. Mechanical positioning problems can frequently be disclosed through a brief radiation screening test. In addition, units having abnormally high initial Icbo are subject to rapid failure.