Dose response, radiation sensitivity and signal fading of p-channel MOSFETs (RADFETs) irradiated up to 50 Gy with ⁶⁰Co

Abstract

This paper reports response of p-channel MOSFETs (RADFETs) to (60)Co gamma radiation in the 10-50 Gy dose range and signal fading (room temperature annealing) for 100 days after irradiation. RADFETs with three different thicknesses of the gate oxide layer were used. Irradiations were performed at gate biases ranging from 0 to 5 V. Threshold voltage shift was monitored during the irradiations and the subsequent fading. The dependence of the threshold voltage shift on the radiation dose is linear for the RADFETs with 100 nm- and 400 nm-thick gate oxide layers irradiated under the gate biases ranging from 1.25 to 5 V. Also, an exponential dependence of the radiation sensitivity on the gate bias during irradiation was found. The signal fades at room temperature without a gate bias. The results demonstrate that these RADFETs are suitable as sensors of gamma radiation. The threshold voltage shift of the RADFETs with 400 nm- and 1 μm-thick gate oxide layers decreases significantly during the first day after irradiation, which, unfortunately, makes these devices incapable of holding dosimetric information for long periods of time.

Keywords: Fading; Mosfet; Radfet; Sensitivity; Threshold voltage shift.