MOS Hardening Approaches for Low-Temperature Applications

Abstract

Charge buildup in irradiated MOS devices is significantly more severe at low temperatures than at room temperature. Approaches for counteracting this problem are considered in this paper, including: (1) careful selection of the applied field; (2) ion implantation of the oxide; (3) use of a thin oxide. Experimental and analytical results are presented and it is demonstrated that the applied field dependence of flatband voltage shift in MOS capacitors irradiated at 77°K can be accounted for in terms of the field dependence of electron yield and the transport of holes at high fields. Analysis of ion implantation effects indicates that a significant improvement in radiation tolerance should be achievable by this method. A simultaneous consideration of the effects of oxide thickness and applied field on charge buildup in an unimplanted oxide suggests that reducing the thickness to ≼500 A° will largely eliminate low temperature problems in a steady-state ionizing radiation environment as long as the applied voltage is ≽ 10V.