Effect of P/E cycling on drain disturb in flash EEPROMs under CHE and CHISEL operation

Drain disturb is studied in NOR flash EEPROM cells under CHE and CHISEL programming operation, before and after repeated program/erase (P/E) cycling. Drain disturb is shown to originate from band-to-band tunneling under CHISEL operation, unlike under CHE operation where it originates from source-drain leakage. Under identical initial programming time, CHISEL operation always shows slightly lower program/disturb (P/D) margin before cycling but similar P/D margin after repetitive P/E cycling when compared to CHE operation. The degradation of gate coupling coefficient that affects source/drain leakage and the increase in trap-assisted band-to-band tunneling seems to explain well the behavior of CHE and CHISEL drain disturb after cycling.