A 512-Gb 3-b/Cell 64-Stacked WL 3-D-NAND Flash Memory

A 64-word-line-stacked 512-Gb 3-b/cell 3-D NAND flash memory is presented. After briefly examining the challenges that occur to a stack, several technologies are suggested to resolve the issues. For performance enhancement, a novel program method hiding two-page data loading time is presented. This paper also discusses an electrical annealing improving reliability characteristic by removing holes in shallow traps. In addition, a valley tracking read for reducing timing overhead at a read retry is introduced by fast finding optimal read levels. Finally, a high-speed self-test mode for IO operation is presented. The chip, designed with the fourth generation of V-NAND technology, achieved an areal density of 3.98 Gb/mm
²
and operated up to 1 Gb/s at 1.2 V.