Positive oxide charge-enhanced read disturb in a localized trapping storage flash memory cell

Abstract

Read disturb-induced erase-state threshold voltage instability in a localized trapping storage Flash memory cell with a poly-silicon-oxide-nitride-oxide-silicon (SONOS) structure is investigated and reported. Our results show that positive trapped charge in bottom oxide generated during program/erase (P/E) cycles play a major role. Both gate voltage and drain voltage will accelerate the threshold voltage (V-t) drift. Hot-carrier caused disturb effect is more severe in a shorter gate length device at low temperature. A model of positive charge-assisted electron tunneling into a trapping nitride is proposed. Influence of channel doping on the V-t drift is studied. As the cell is in an "unbiased" storage mode, tunnel detrapping of positive oxide charges is responsible for the threshold voltage shift, which is insensitive to temperature.