SATURATION OF THE DOSE-RATE RESPONSE OF BIPOLAR-TRANSISTORS BELOW 10-RAD(SIO2) S - IMPLICATIONS FOR HARDNESS ASSURANCE/

The gain degradation of modern bipolar transistors was investigated fo r dose rates ranging from 0.01 similar to 2000 rad(SiO2)/s; Five diffe rent radiation sources were used for the exposures: three Co-60 source s, a 10-keV x-ray source, and a Cs-137, source. The C-137 exposures at 0.01 rad(SiO2)/s are two orders of magnitude lower in dose rate than any previous irradiations for this process and thus facilitate compari son to the device response in space. Low-dose-rate gain degradation ex ceeds high-dose-rate degradation for total doses less than 1 Mrad(SiO2 ), consistent with previous reports. For the first time, the gain degr adation is demonstrated to be equivalent for dose rates between 0.01 a nd 10 rad(SiO2)/s, suggesting that the dose-rate response saturates at similar to 10 rad(SiO2)/s for the devices studied in this work. On th e basis of a recent model, high-dose-rate irradiations at 60 degrees C were performed and found to be consistent with the room-temperature, low-dose-rate, saturated response. These results suggest several promi sing new approaches to bipolar space-qualification testing.