A 512Gb 3b/Cell 3D flash memory on a 96-word-line-layer technology

The first multi-layer stacked 3D Flash memory was proposed as BiCS FLASH in 2007 [1]. Since then, memory bit density has grown rapidly due to the increase in the number of stacked layers from continuous 3D technology innovations. On the other hand, the multi-level-cell technology, which was initially proposed for 2D Flash, has also been adopted to 3D Flash memories. The first 3b/cell 32-layer Flash was presented in 2015 [2], followed by a 48-layer one in 2016 [3], and a 64-layer one in 2017 [4,5]. This paper describes a 512Gb 3b/cell 3D Flash memory in a 96-word-line-layer BiCS FLASH technology. This work implements three key technologies to improve performance: (1) a string based start bias control scheme achieves a 7% shorter program time; (2) a smart V
t
-tracking read improves read retry performance by minimizing the tracking time and supporting a program suspend read function, and; (3) a low-pre-charge sense-amplifier bus scheme reduces both the power consumption and the data-transfer time between the sense amplifier (SA) and the data cache by half. Figure 20.1.1 shows the die micrograph and the summary of the key features of the chip.