Saturation of the dose-rate response of bipolar transistors below 10 rad(SiO/sub 2/)/s: implications for hardness assurance

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Abstract
The gain degradation of modern bipolar transistors was investigated for dose rates ranging from 0.01 to /spl sim/2000 rad(SiO/sub 2/)/s. Five different radiation sources were used for the exposures: three /sup 60/Co sources, a 10-keV X-ray source, and a /sup 137/Cs source. The /sup 137/Cs exposures at 0.01 rad(SiO/sub 2/)/s are two orders of magnitude lower in dose rate than any previous irradiations for this process and thus facilitate comparison to the device response in space. Low-dose-rate gain degradation exceeds high-dose-rate degradation for total doses less than 1 Mrad(SiO/sub 2/), consistent with previous reports. For the first time, the gain degradation is demonstrated to be equivalent for dose rates between 0.01 and 10 rad(SiO/sub 2/)/s, suggesting that the dose-rate response saturates at /spl sim/10 rad(SiO/sub 2/)/s for the devices studied in this work. On the basis of a recent model, high-dose-rate irradiations at 60/spl deg/C were performed and found to be consistent with the room-temperature, low-dose-rate, saturated response. These results suggest several promising new approaches to bipolar space-qualification testing.

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