High-Speed Multilevel nand Flash Memory With Tight $V_{rm th}$ Distribution Using an Engineered Potential Well and Forward-Bias Adjusted Programming

摘要

This paper reports a high-speed multilevel-cell nand Flash memory device using a $hbox{Si}$– $hbox{SiO}_{2}$–$hbox{TiN}$– $hbox{TiO}_{2}$–$ hbox{SiO}_{2}$–$hbox{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 $(sim!hbox{40} muhbox{s}/hbox{page})$, tight threshold voltage $(V_{rm th})$ distribution ( $sim$0.22 V/level), and clear $V_{rm th}$-level margins ($sim$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 $^{circ} hbox{C}$ throughout $hbox{10}^{5}$ programming/erasing cycling.