Comparison of local programming method for multi-bit/level 90nm SONOS memory

Three different programming methods, the conventional CHE injection, CHE with a positive substrate bias (CHE-P) and pulse agitated substrate hot electron injection (PASHEI) were compared to obtain the reliable multi-bit/level operations in 90nm SONOS memory. It is found that both CHE-P and PASHEI methods can improve the cycling endurance and retention characteristic for 2 bits operations. The CHE-P method further exhibits the superior P/E windows and reliability characteristic in 4-bit/4-level programming operations. Charge pumping measurement illustrates that the good characteristic is due to the suppressing of the secondary electron injection (SEI) in the CHE-P programming process. It results in less spatial mismatch between electrons and holes in the nitride layer.