Method for optimizing distribution profile of cell threshold voltages in NAND-type flash memory device

摘要

A method is operable in a non-volatile memory device of a type having a plurality of blocks formed of a plurality of memory strings in which a plurality of memory cells are connected in series in which a programming operation is conducted after erasing memory cells. The method essentially including the steps of: erasing data held in the memory cells in a unit of the block; and applying a soft program voltage to word lines coupled with the erased memory cells in the unit of the block. The method improves a threshold voltage profile after an erasing cycle, whereby program stress can be minimized in a follow-up program operation.