7.5 A 128Gb 2b/cell NAND flash memory in 14nm technology with tPROG=640µs and 800MB/s I/O rate

NAND flash memory is widely used as a cost-effective storage with high performance [1–2]. This paper presents a 128Gb multi-level cell (MLC) NAND flash memory with a 150 cells/string structure in 14nm CMOS that can be used as a cost-effective storage device. This paper also introduces several approaches to compensate for reliability and performance degradations caused by the 14nm transistors and the 150 cells/string structure. A technique was developed to suppress the background pattern dependency (BPD) by applying a low voltage to upper word lines (WLs) - the drain side(SSL side) WLs with respect to the location of the selected WL - during the verify sequence. Two techniques are also used to improve the program performance: equilibrium pulse scheme and smart start bias control scheme (SBC) in the MSB page. In addition, the first cycle recovery (FCR) of read enable (RE) and the bi-directional data strobe (DQS) is used to achieve a high speed I/O rate. As a result, a 640µs program time and a 800MB/s I/O rate is achieved.