High-Speed Multilevel NAND Flash Memory With Tight V-th Distribution Using an Engineered Potential Well and Forward-Bias Adjusted Programming

Abstract

This paper reports a high-speed multilevel-cell NAND Flash memory device using a Si-SiO2-TiN-TiO2-SiO2-TaN (SOTTOT) engineered potential well (EW). The SOTTOT EW Flash memory device has very fast cell programming speed and good data retention. A 16-kbit NAND memory block using SOTTOT cells was programmed using a forward-bias-adjusted programming scheme, which enables bit adjustability during page programming to suppress the development of fast bits. The SOTTOT memory block shows fast programming speed (similar to 40 mu s/page), tight threshold voltage (V-th) distribution (similar to 0.22 V/level), and clear V-th-level margins (similar to 0.9 V) for the eight-level programming. The SOTTOT memory block also shows good resistance against pass/read disturbances as well as good ten-year data retention at an ambient temperature of 75 degrees C throughout 10(5) programming/erasing cycling.