Radiation-Induced Memory Loss in Thin-Oxide MNOS Devices

A theoretical model is proposed for the radiation-induced memory loss effect in thin-oxide MNOS memory devices. The model treats the stored charge as being located in the nitride, at an average distance from the silicon much larger than the oxide thickness. Under these conditions the radiation-induced conductivity in the nitride determines the decay of stored charge. It is proposed that the radiation-induced conductivity in the nitride is due to radiation-induced carriers drifting in the electric field during the slowing down process, and that the carriers become trapped before reaching thermal equilibrium. In calculating the radiation-induced nitride conductivity, a continuous slowing-down process is assumed. In addition, it is assumed that the radiation-induced carriers are generated according to a 1/(Energy) law. Although values for some of the parameters in the model are not known, it is shown that experimental values of the radiation-induced memory loss rate are consistent with physically reasonable values of the unknown parameters.