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