Radiation and Oxide-Metal Interactions in MOS

Radiation stability of the MOS system is controlled by the oxide-silicon and oxide-metal barriers; oxide-metal interactions and certain dopants appear to affect the radiation sensitivity. It is shown that the OS system behaves differently from the MOS system. The effect of metals have been studied with the use of aluminum, molybdenum and chromium. Chromium appears to be a desirable metal; when this electrode is used other factors also assume importance. The best results obtained with chromium gate p-enhancement transistors are: a shift of only 1.5 V (~1011 charges/cm2) with a Co-60 source depositing 2 x 107 rad(Si) or 1.5 MeV electrons depositing 1014 electrons/cm2. The change in surface mobility is small. Isothermal relaxation experiments show a wide range of activation energies, some of which are characteristic of the metal used. Studies related to the "photocurrent" flowing during irradiation appear to indicate that the prevailing model for radiation "damage" must be altered.