ERASING METHOD IN A FLASH MEMORY DEVICE

摘要

PURPOSE: An erasing method in a flash memory device is provided to have a cell have a normal erasing threshold voltage so that the cell may not be over-erased by carrying out an afterward program at regular intervals during an erasing operation. CONSTITUTION: The erasing method comprises the steps of: initializing(S300) an address; carrying out(S302) a previous program which programs in the case of an erased cell and leaves the cell as it is by changing the address of a desired sector; carrying out(S304) the previous program(S302) again if any one of overall cells is not programmed; comparing(S306) the sector address with a last sector address when the previous program is carried out normally; carrying out(S308) the previous program regarding other sectors by increasing the sector address if the sector address is the last one; initializing(S310) the address for an erasing operation if the previous program is carried out regarding the last sector; erasing(S312) by applying an erase bias to every cell of the first sector; carrying out(S314) an afterward programming which increases a threshold voltage of an over-erased cell to that of a normally erased cell by applying an afterward programming bias to cells of columns in a sector after a predetermined repetition of erasing; determining(S316) whether the cells are erased normally and carrying out(S312) the erasing operation when the cell erasion is not completed; finishing(S318) the erasing operation if the sector address is the last sector address when every cell of the sector is erased; and carrying out(S312) the erasing operation again for erasing the next sector by increasing a sector address if the sector address is not last one.