Method and apparatus for management of over-erasure in NAND-based NOR-type flash memory
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United States of America Patent
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Nov 12, 2013
Grant Date -
Aug 2, 2012
app pub date -
Jan 31, 2011
filing date -
Jan 31, 2011
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Abstract
A method and apparatus for operating an array block of dual charge retaining transistor NOR flash memory cells by erasing the dual charge retaining transistor NOR flash memory cells to set their threshold voltage levels to prevent leakage current from corrupting data during a read operation. Erasure of the array block of NOR flash memory cells begins by selecting one of block section of the array block and strongly and deeply erasing, over-erase verifying, and programming iteratively until the charge retaining transistors have their threshold voltages between the lower voltage limit and the upper voltage limit of the first program state. Other block sections are iteratively selected and erased, over-erase verified, and programmed repeatedly until the charge retaining transistors have their threshold voltages between the lower voltage limit and the upper voltage limit of the first program state until the entire block has been erased and reprogrammed to a positive threshold level.
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