Endurance and memory decay of MNOS devices

Abstract

The endurance of MNOS EAROM‐type memory devices toward write/erase cycling is examined using the increase of the memory window decay rate as the criterion. Two decay regimes are identified: a short‐term decay in which the window decays linearly with log time, and a long‐term decay in which the rate is faster than log time. Beyond 10⁴ write/erase cycles the short‐term decay rate increases at a rate of 0.05 V per decade of decay per decade of write/erase cycling per volt of memory window being cycled, at room temperature. Cycling also results in a deeper stored charge centroid in the nitride. Increasing the temperature during writing increases the depth of the stored charge in the nitride at a rate of 1.6±0.3 Å/°C and decreases the short‐term decay rate. The degree of temperature dependence of the short‐term decay rate is a function of the write temperature and the number of accumulated write/erase cycles. The storage time t_B at which the long‐term decay commences is found to shift toward shorter times on cycling. These observations can be understood in terms of the back tunneling of stored charge into fast interface states in the short‐term decay region, and activated rearrangement of the stored charge within the nitride in the long‐term decay region.