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.