Processes in radiation sensitive MOSFETs during irradiation and post irradiation annealing responsible for threshold voltage shift

The behavior of radiation-induced fixed oxide traps and radiation-induced switching traps near and at Si/SiO2 interface during gamma-ray irradiation up to 50 Gy and post-irradiation annealing at room temperature has been investigated. These processes lead to threshold voltage shift, ΔVT, which is dosimetric parameter employed in total absorbed radiation dose determination. Irradiation was performed with gate bias from 0 to 5 V and annealing was performed without gate bias. The midgap-subthreshold technique was used to separate fixed traps and switching traps which for p-channel MOSFETs contribute to ΔVT in the same direction. It was shown that the increase in gate bias lead to the increase in fixed oxide traps density and switching traps density, what further increases ΔVT for the same radiation dose. The density of fixed traps created during irradiation is higher than the switching traps density. Post irradiation annealing at room temperature without gate bias, for 100 days period, lead to relatively small decrease in ΔVT, what is a consequence of both, decrease in fixed oxide traps density and increase in switching traps density.