Investigation of Oxide and Interface Trapped Charge on Threshold Voltage Shift in Gamma Irradiated NMOSFET by Subthreshold Method

In this paper, the oxide trapped charge density (NOT) and interface trapped charge density (NIT) on the threshold voltage shift with the total dose under gamma irradiation of NMOSFET are investigated. The subthreshold technique (mV/dec) is used to separate the irradiation induced threshold voltage shifts into voltage shifts due to the interface trapped charge. The linear extrapolation method is used to extract the threshold voltage from $I_{DS}-V_{GS}$ curve at low VDS of typically 100 mV. The results showed that the threshold voltage was shifted from 0.69 V to 0.45 V, the threshold swing was increased from 95 to 107 mV/dec, the oxide charge and interface charge density were found to be increase almost by 1 order in magnitude for a total gamma dose of 10 kGy.