The behavior of fixed and switching oxide traps of RADFETs during irradiation up to high absorbed doses

The behavior of radiation-induced fixed traps (FTs) in gate oxide and radiation-induced switching traps (STs) near and at the gate oxide/substrate interface during irradiation up to high absorbed doses has been considered. The zero-bias voltage regime, the simplest and most popular solution in practice, was chosen. Indeed, it is very difficult to predict the creation of radiation defects in the case of low electric fields, because there is a compromise between the external low electric fields induced by work function differences and the internal electrical fields induced by radiation-induced charged defects in the oxide. It was shown that the density of FTs is higher than the density of STs for lower absorbed doses, though the trend is reversed for doses greater than 700Gy. Although the number of FTs is much higher than the number of STs, many FTs are located in the bulk, far from the oxide/semiconductor interface and their influence on channel carriers is much smaller than the influence of STs that are located closer to the channel. The equation for fitting the threshold voltage components induced by FTs (ΔVft) and by STs (ΔVst) is proposed and very good fittings are obtained. It is shown that five experimental irradiation points are sufficient to draw a good conclusion about the values of the fitting parameters, i.e., the voltage saturation values and the degree of linearity.