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

Abstract

A threshold voltage fluctuation (DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) due to random telegraph signal (RTS) in a floating-gate (FG) flash memory was investigated. From statistical analysis of the DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> , we found an anomalously large DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> at high percentage region of the DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> distribution increases after program/erase (P/E) cycle. Since the DeltaV <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> 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