Radiation Effects in Microwave Bipolar Transistors

The effects of gamma and neutron radiation on the high frequency characteristics of microwave transistors (HP-35821E) are explored. From theoretical and experimental results, it is determined that the major effect is a decrease in the forward transfer coefficient (S21) resulting from a neutron-enhanced decrease in cutoff frequency (fS) (i.e., increase in emitter-to-collector transit time). For the recommended operating conditions (VCE = 15V, IC = 15 mA) no change in S-parameters was noted after an ionizing dose of 107 rads (Si) in a Co60 source. By increasing the collector voltage so that the epitaxial collector is entirely depleted, these devices can be operated at fluence levels of 8 × 1015 n/cm2 (E> 10 keV).