13.5 A 512Gb 3-bit/Cell 3D Flash Memory on 128-Wordline-Layer with 132MB/s Write Performance Featuring Circuit-Under-Array Technology

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Abstract
Advancements in 3D-Flash memory-layer-stacking technology has enabled density scaling that circumvents the lithography limitations which have prevented 2D-NAND Flash memory from scaling [1]. Bit densities as high as 5.95Gb/mm 2 on a single die were recently reported [2], where a 512Gb NAND Flash was built on 96 layers of memory. As memory density increases, with memory layers increasing from 96 layers to 128 layers, higher bit density can be achieved by adopting larger capacity die; however, NAND performance per bit density is reducing with the 2-plane architecture. In this work, we propose a 512Gb 3b/cell 128WL-layer NAND Flash, with a bit density of 7.80Gb/mm 2 : a 31% improvement over the previously reported. Three key performance improving technologies have been implemented. (1) A 4-plane architecture with circuit under array (CUA) technology to improve performance per bit density. (2) A multi-die peak-power management (PPM) system to manage peak-power consumption in the system, via the ZQ pin. (3) A 4KB-page-read mode to reduce power consumption. Figure 13.5.1(a) summarized the key features and Fig. 13.5.1(b) shows the die photograph and the floorplan for this work. Figure 13.5.2 shows a table comparing this work to previous work.