Anomalously Large Threshold Voltage Fluctuation by Complex Random Telegraph Signal in Floating Gate Flash Memory

A threshold voltage fluctuation (DeltaV th ) due to random telegraph signal (RTS) in a floating-gate (FG) flash memory was investigated. From statistical analysis of the DeltaV th , we found an anomalously large DeltaV th at high percentage region of the DeltaV th distribution, which is caused by a complex RTS. Since the ratio of the complex RTS among the RTS is increased by charge injection to tunnel oxide, the dispersion of the DeltaV th distribution increases after program/erase (P/E) cycle. Since the DeltaV th due to the complex RTS is much larger than the simple RTS, the complex RTS become one of the reliability issues in larger capacity flash memory, especially after P/E cycle