Method for erasing flash electrically erasable programmable read-only memory (eeprom)

Abstract

A flash Electrically-Erasable Programmable Read-Only Memory (EEPROM) includes a plurality of field effect transistor memory cells, a power supply, and a controller which cooperates with the power supply to apply an erase pulse to the cells, and then erase verify a first byte of cells in each sector. If the first bytes in any sector has not passed erase verify, another erase pulse is applied to the cells of those sectors, and the first byte in each sector which did not pass erase verify the first time is erase verified again. This procedure is continued until the first byte in each sector has passed erase verify. Then, the sectors are processed in sequence to erase and erase verify every cell. First, an erase pulse is applied to all of the cells in the sector. Then, the first byte is erase verified. If the first byte passes erase verify (which it will because it did previously), the next byte is erase verified. Whenever a particular byte does not pass erase verify, another erase pulse is applied to all of the cells in the sector, and the particular cell is again erase verified. This procedure is sequentially performed on all of the bytes in the sector, or alternatively on the cells individually, until all of the cells have passed erase verify.