A model for EPROM intrinsic charge loss through oxide-nitride-oxide (ONO) interpoly dielectric

Intrinsic charge loss phenomena of an EPROM cell with an interpoly oxide-nitride-oxide (ONO) stacked film at elevated temperatures are discussed. There are three dominating charge loss mechanisms, which manifest themselves in three distinct phases in time evolution characteristics. The first phase is an initial fast threshold voltage shift which increases with nitride thickness and results from an intrinsic nitride property. The second phase is caused by electrons moving within the nitride. This electron transport follows a linear ohmic-like conduction. The third phase is a long-term charge loss due to electrons leaking through the top oxide. It can be minimized with a thick top oxide. Based on the above observations, a model to describe the intrinsic EPROM charge loss mechanisms is proposed. This model has been useful in developing a novel scaling methodology for an EPROM interpoly ONO films to improve charge retention capability.<
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