Sapphire Photocurrent Sources and Their Impact on RAM Upset

This paper reports on the transient photocurrent measurements made with test structures fabricated on sapphire substrates, and the computer simulation model which was developed to use the test results. Predictions of logic upset for a 4K RAM CMOS/SOS compared with measured upset rates showed agreement within a factor of two. The test structure results indicate that the sapphire photoconductance is 6.3 × 10-19 mhos/ (rads/s)-¿m. The use of this value in the present simulation model will increase the predicted upset rate, and thus, increase the disagreement by more than a factor of two.