Aplus Flash Technology, Inc.

Aplvs Flash Technology, Inc.

Mervyn Wong

Peter Wung Lee

Fu-Chang Hsu

Hsing-Ya Tsao

In the present invention a method is shown that uses three concurrent word line voltages in memory cell operations of an a NOR type EEPROM flash memory array. A first concurrent word line voltage controls the operation on a selected word line within a selected memory block. The second concurrent word line voltage inhibits cells on non selected word lines in the selected memory block, and the third concurrent word line voltage inhibits non-selected cells in non-selected blocks from disturb conditions. In addition the three consecutive word line voltages allow a block to be erased, pages within the block to be verified as erased, and pages within the block to be inhibited from further erasure. The three consecutive voltages also allow for the detection of over erasure of cells, correction on a page basis, and verification that the threshold voltage of the corrected cells are above an over erase value but below an erased value. The methods described herein produce a cell threshold voltage that has a narrow voltage distribution.

Set of three level concurrent word line bias conditions for a NOR type flash memory array

Set of three level concurrent word line bias conditions for a nor type flash memory array

In the present invention a three step write of a nonvolatile single transistor cell is disclosed. The three steps comprise erasing, reverse programming and programming which can be applied to a plurality of cell types to produce a symmetrical design and allowing shrinkage of the cell beyond that which is possible with other cells designed to use a two step write procedure. The methodology can be applied to either N-channel or P-channel devices and can be used on various type memory cells such as &ldquo;ETOX&rdquo;, &ldquo;NOR&rdquo; type, &ldquo;AND&rdquo; type, and &ldquo;OR&rdquo; type. Erasing and programming steps increase the Vt of the cell transistor, whereas reverse programming decreases the Vt of the cell transistor. Over-erase problems are eliminated using the three step write procedure.

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El Cerrito, CA, United States of America

Mervyn Wong