Interface states formation in a localized charge trapping nonvolatile memory device

Two NROM nonvolatile memory devices that are practically identical but exhibit different postcycling characteristics are investigated. Electrical characterizations combined with two-dimensional drift diffusion simulations were employed to quantify and differentiate the retention loss mechanisms. The comparison demonstrates the coexistence of two retention loss mechanisms, lateral charge transport in the nitride layer, and hot carrier induced interface states formation and anneal. The fabrication conditions in the various studies reported in the literature and the resultant impact on interface states formation are most likely the cause of the formally nonresolved debate regarding the origin of retention loss in NROM technology. The reduction in interface state formation during cycling is a key to achieving high reliability NROM cells and products.