Effects of Gamma Radiation on Trench Isolated CMOS

The gamma radiation hardness of trench isolated CMOS has been assessed with respect to the shift in threshold voltage of parasitic sidewall devices and minimum channel length NMOS and PMOS transistors. For parasitic devices, saturation of the threshold voltage shift is apparent after 20kRads. This is attributable to the low volume oxide films inherent to the device structure. Drifts in the parasitic threshold voltage over a 0 to 5OkRads range are significantly lower than for similar LOCOS field devices. Off-state leakage current is generated in NMOS transistors and has been characterised as a function of gamma ray dose; such leakage current levels also saturate with irradiation dose.