Ionizing Radiation Effects in SOS Structures

The total ionizing radiation effects of n-channel enhancement mode silicon on sapphire MISFET's have been characterized up to a total dose of 107 rads (Si). The drain current versus drain voltage characteristics of the n-channel devices showing the "kink" effect were measured over a range of gate voltages and as a function of ionizing radiation. The effect of the ionizing radiation on the "kink" phenomenon was determined and the implications of this effect on the radiation hardness of n-channel MISFET's is discussed. The results show that the equivalent threshold voltage at the operating drain voltage must be defined and used in determining the radiation hardness of the n-channel device. The radiation induced back channel leakage currents of n-channel MISFET's are characterized in terms of device geometry and the amount of radiation induced trapped charge in the sapphire substrate. Results showing the leakage current plotted as a function of drain voltage suggest that the "kink" effect and related phenomena also enhance the radiation induced leakage current effects and lead to substantially increased values of leakage current.