A stochastic model of gamma-ray induced oxide charge distribution and threshold voltage shift of MOS transistors

A stochastic model of gamma-ray radiation effects on the density of the induced charge in silicon dioxide films of MOS transistors is presented in this paper. It is assumed that both radiation induced charge generation and trapped charge recombination are stochastic processes. For estimating gamma-ray induced charges spatially distributed in silicon dioxide films, a procedure similar to the Monte Carlo method was used. The proposed model implemented in the programming language MATHEMATICA enables us, for the first time, to show the gamma-ray induced charge distribution as a function of gamma-ray doses. Using the developed model, we have also calculated the corresponding threshold voltage shifts of MOS transistors. These results were compared with the experimentally determined threshold voltage shift of MOS transistors with different voltages applied during irradiation vs. gamma radiation doses. Satisfactory agreements were obtained.