Total-Dose and Dose-Rate Dependence of Proton Damage in MOS Devices during and after Irradiation

Rad-hard CMOS/Bulk inverters with input gates high and low were irradiated by protons with a nominal energy of 8 MeV. The purpose of this study was to determine the total-dose and doserate dependence of threshold voltage shifts, both during and immediately after irradiation and over extended periods of time thereafter. Post-rad bias conditions were the same as during bombardment. The results suggest that previous measurements [1, 2], which indicated that post irradiation changes of voltage shifts depended on type of radiation source and on energy of particles, were essentially due to the unique combinations of total dose and dose rate applied in those experiments. It now appears, that all of the damage effects observed in the previous experiments for the various sources and energies, during and after irradiation, could be simulated by selected equivalent doses and dose rates with any radiation source or particle energy. The importance of this conclusion is that a key relationship of Co60 damage effects to those from any other radiation source could be experimentally determined in terms of total dose and dose rate alone. Consequently, a valid simulation of specific charged particle and energy effects of the space radiation environment may be accomplished on the ground with appropriately designed Co60 tests.