Neutron Irradiation Effects on Microwave Transistor Amplifiers

Studies are presented of neutron irradiation effects on microwave bipolar transistors in two applications--small signal, low noise amplifiers and large signal, power amplifiers. In both applications microwave transistors are found to be neutron tolerant. In the low noise case, the amplifier noise figure increases by less than 1 dB after a neutron fluence of 2 × 1015 n/cm2 (E > 10 keV). The observed degradation in noise figure is related both theoretically and experimentally to neutron-induced decreases in DC and low frequency current gain, and good agreement is found. In the power amplifier case, saturated output power and power gain decrease by 1.8 and 3 dB, respectively, after 2 × 1015 n/cm2. The change in saturated output power is related to increased high frequency Vce(sat), while the decreased gain is due to decreased high frequency current gain. Neutron effects on these transistor parameters are calculated from the power output and gain data, and compared with radiation effects on these parameters at low frequencies.