A model of radiation induced leakage current (RILC) in ultra-thin gate oxides

An analytical model of Radiation Induced Leakage Current (RILC) has been developed for ultra-thin gate oxides submitted to high dose ionizing radiation. The model is based on the solution of the Schrödinger equation for a simplified oxide band structure, where RILC occurs through electron trap-assisted tunneling. The values of the model parameters have been calibrated by comparing the transmission probabilities obtained in this model with those obtained through the WKB method in the actual oxide band structure. No free fitting parameter has been introduced, and all physical constant values have been selected within the values found in literature. Different trap distributions have been considered as candidates, but the comparison between simulated and experimental curves have indicated that a double gaussian distribution in space and in energy grants the best fit of the experimental results for different ionizing particles, oxide fields during irradiation, radiation doses, and oxide thickness. Excellent matching has been found for both positive and negative RILC by using a single trap distribution. The trap density linearly increases with the radiation dose and decreases with the oxide field during irradiation. The trap distribution is spatially symmetrical in the oxide, centered in the middle of the oxide thickness, and is not modified as the cumulative dose increases.