A Radiation Hard MNOS CCD for Low Temperature Applications

P-buried channel charge-coupled devices (CCDs) with a 100 Å sio2 and 1.2 Å Si3N4 dual gate insulator have been fabricated and radiation tested. The CCDs are 105-and 150-bit 4-phase linear shift registers with double-level polysilicon gates. Most of the experimental data is obtained on p-buried channel devices because design considerations suggest that the p-buried channel structure will have the greatest tolerance to ionizing radiation for devices with MNOS gates. Threshold shifts on the order of -1 volt/106 rad(Si) have been achieved at both 80°K and 300°K on CCDs which are operated continuously during the irradiation. The p-buried channel CCDs show essentially no degradation in pre-irradiation transfer efficiency up to doses of 106 rad(Si) without any change in the operating biases.