Patent ID: 11978515

Abstract:
A semiconductor memory device capable of reducing failure caused by a source side effect after a large number of W/E cycles is provided. A reading method of a NAND flash memory includes: dividing multiple word lines connected to each memory cell of a NAND string into a group 1 of word lines WL0 to WLi−1, a group 2 of word lines WLi to WLj, . . . , a group y of word lines WLj+1 to WLk−1, and a group x of word lines WLk to WLn, presetting a relationship that each readout voltage (Vread1, Vread2, . . . , Vready, and Vreadx) corresponding to each group increases toward a bit line side, and applying a readout voltage to a selected word line according to the relationship.