Operation method of flash memory device capable of down-shifting a threshold voltage distribution of memory cells in a post-program verify operation

Abstract

In a driving method of a flash memory device including a selected first bit line and an unselected second bit line, a program voltage of a pulse is applied to word lines of all memory cells in a block passing an erase verify operation. After the first and second bit lines are precharged to a predetermined level, a ground voltage is applied to the word lines of all the memory cells in the block. The memory cells are evaluated for a predetermined time shorter than an evaluation time of a read operation. Whether or not a memory cell passing a verify operation exists among the memory cells is sensed. Resultantly, when the memory cell passing the verify operation exists, the memory cells in the block are programmed to a desired level using a predetermined program voltage and a step voltage.