Radiation damage annealing effects at elevated temperatures in bipolar transistors for severe space environments

When bipolar and other silicon semiconductors are exposed to a reactor or to a space environment, it is possible to reduce radiation damage effects by operating the devices at elevated temperatures. If the energies of radiation at the location of the device are sufficiently low, permanent lattice displacements will not occur and annealing of the damage will take place. In general, reactor gamma photon energies fall below 1.5 MeV and the peak of neutron energies is below 1 MeV. Shielding usually reduces the energies of radiation reaching semiconductor devices below these values. Damage produced at ambient temperatures by such radiation can be annealed subsequently but few measurements have been made with irradiation at very high temperatures. The purpose of the present work was to determine ranges of dose and temperature in which annealing will allow continued operation of representative devices. A series of experiments was conducted on discrete epitaxial planar 2N2222A commercial transistors with environments of gamma radiation only (at 25/sup 0/C) and radiation with temperature at (125/sup 0/C). The devices were exposed to gamma radiation exceeding 200 Mrad (air). The transistors were Class A biased with the resistors selected to optimize the current stability over the temperature range ofmore » 25/sup 0/C to 125/sup 0/C. The gain of those devices operated at 1 milliamp and at ambient temperature decreased to about 2% of their original value. For transistors biased at a collector current of 10 milliamps and run at 125/sup 0/C, the gain dropped to only 48%. This work has demonstrated a number of important considerations. When working at elevated temperatures in situ measurements are a necessity. When designing circuits and enclosures, elevated temperature operation should be considered. These results and others are presented.« less