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 in-vestigated and reported. Our results show that positive trapped charge in bottom oxide generated during program/erase (P/E) cy-cles play a major role. Both gate voltage and drain voltage will ac-celerate the threshold voltage ( ) drift. Hot-carrier caused disturb effect is more severe in a shorter gate length device at low temper-ature. A model of positive charge-assisted electron tunneling into a trapping nitride is proposed. Influence of channel doping on the 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. Index Terms—Cycling-induced oxide charges, Flash EEPROM, hot-carrier effect, MXVAND, NROM, PHINES, positive charge