Predicting CMOS Inverter Response in Nuclear and Space Environments

Linear system theory techniques were used to predict threshold-voltage shifts for 4007 inverters at dose rates of 270, 49.7, and 0.19 rad(Si)/s, from a transient annealing curve determined following a 5-rad(Si)/s 60Co irradiation. These predictions were compared with threshold-voltage shifts obtained following 60Co irradiations actually performed at these dose rates, and the agreement is excellent. We observed a wide range of annealing rates for commercial and military 4007 inverters--some Al-gate inverters exhibited very little annealing following irradiation, while an Si-gate inverter completely annealed back to its preirradiation threshold voltage in ~5 × 105 s. The radiation responses of 4007's from a specific manufacturer with different packaging (i.e., plastic or ceramic) and/or electrical characterization (i.e., high-reliability or JAN) were found to vary significantly. Maintaining bias following irradiation was determined to be important in characterizing the anneal of both Al-and Si-gate inverters. Finally, dose-enhancement effects on the threshold-voltage shift were observed for 60Co inpool irradiations where the source and sample were separated by 20 in. of water.