Charge Yield and Dose Effects in MOS Capacitors at 80 K

MOS devices, such as charge-coupled devices and MOSFET's, are being investigated for use in imaging, signal processing and detector preamplifier applications in which the detector and its immediately associated electronics are operated at low temperatures (less than or equal to 80 K). Recent experiments on MOS capacitors and devices at approximately 80 K have established that when hole-electron pairs are generated in the SiO/sub 2/ insulating layer by ionizing radiation the electrons are rapidly swept out of the oxide while the holes remain essentially immobile at or near their point of creation. As a result, the holes cause large flatband or threshold voltage shifts per unit dose in MOS structures. In contrast to the highly process-dependent ''permanent'' trapping of a small fraction of the radiation-generated holes observed at room temperature, the retention of the holes in SiO/sub 2/ at approximately 80 K is largely process-independent and is a consequence of a strongly temperature-dependent hole transport mechanism. The present paper discusses two related investigations of radiation-induced charge buildup in SiO/sub 2/ at approximately 80 K. In the first study, the retention of holes at low temperature is exploited to provide a direct measure of hole-electron pair yield per unit radiation dosemore » as a function of electric field for high-energy ionizing radiation. In the second study the response of MOS capacitors to short pulse high dose irradiation at approximately 80 K is investigated, and mechanisms which impose limits on the oxide charge buildup are examined.« less