Data retention behavior of a SONOS type two-bit storage flash memory cell

Data retention loss mechanisms in a 2-bit SONOS type flash EEPROM cell with hot electron programming and hot hole erase are investigated. In erase (low-Vt) state, a threshold voltage drift with storage time is observed after P/E cycling stress. Positive trapped charge creation in the bottom oxide is found to be responsible for the drift. In program (high-Vt) state, data retention loss is attributed mostly to nitride charge escape by Frenkel-Poole emission and oxide trap assisted tunneling. A square-root dependence of the nitride charge loss on electric field is obtained. A Vg-acceleration method for retention lifetime measurement is proposed.