Advanced Micro Devices Corporation

Vei-Han Chen

Sameer S Haddad

Colin Stewart Bill

Ravi S Sunkavalli

Ravi Prakash Gutala

Jonathan S Su

Wing Han Leung

John Chen

A flash Electrically-Erasable Programmable Read-Only Memory (EEPROM) includes a plurality of floating gate transistor memory cells, a plurality of wordlines connected to the cells and a power supply for generating erase pulses. A controller controls the power supply to apply an erase pulse to all wordlines which are not deselected. Then, an erase verify procedure is applied to the cells in sequence. If all cells connected to a wordline pass the erase verify test, the wordline is deselected such that subsequent erase pulses will not be applied to the wordline and possibly cause the cells to become overerased. In one embodiment of the invention, erase verify is performed on all of the cells after an erase pulse is applied. The erase operation is completed when all cells pass erase verify. In another embodiment, erase verify is applied to each cell in sequence, with erase pulses being applied until each current cell passes erase verify. The wordlines can be deselected individually or in groups. The invention results in a tightening of the threshold voltage distribution of the cells.

Method for erasing flash electrically erasable programmable read-only

A flash Electrically-Erasable Programmable Read-Only Memory (EEPROM) includes a plurality of field effect transistor memory cells each having a source, drain, floating gate and control gate, and a power source for supplying a plurality of voltages to the cells. A controller controls the power source to apply at least one erase pulse to the cells. Then, at least one overerase correction or 'soft programming' pulse is applied to the cells during which the source, drain and control gate voltages of the cells are such that the threshold voltages of overerased cells will be increased, but least erased cells will not be disturbed. The overerase correction pulses thereby tighten the threshold voltage distribution. A source to substrate bias voltage is applied for the duration of the overerase correction pulses which reduces the background leakage of the cells to a level at which the overerase correction operation can be effectively performed, even in applications with low supply voltages.

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Vei-Han Chen