Systems and Methods to Avoid False Verify and False Read
AssigneeSanDisk Technologies LLC
InventorsChris Nga Yee Avila, Yingda Dong, Man Lung Mui
Life of this patent
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Abstract
In a nonvolatile NAND memory array, a NAND block may be falsely determined to be in an erased condition because of the effect of unwritten cells prior to the erase operation. Such cells may be programmed with dummy data prior to erase, or parameters used for a verify operation may be modified to compensate for such cells. Read operations may be similarly modified to compensate for unwritten cells.
Claims18
A method of performing an adaptive erase verification during erase of a block in a NAND memory, comprising:
- determining an amount of unwritten space remaining in the block;
- if the amount of unwritten space is less than a predetermined amount then performing erase verification using a default set of verification parameters;
- and
- if the amount of unwritten space exceeds the predetermined amount then performing erase verification using a modified set of verification parameters that is different to the default set of erase parameters.
A method of performing an adaptive read of a portion of data in a block in a NAND memory, comprising:
- determining an amount of unwritten space remaining in the block;
- if the amount of unwritten space is less than a predetermined amount then performing the read of the portion of data using a first set of read parameters;
- and
- if the amount of unwritten space exceeds the predetermined amount then performing the read of the portion of data using a second set of read parameters that is different to the first set of read parameters.
A method of operating a NAND memory comprising:
- identifying a block as being in condition for an erase operation;
- determining whether a number of unwritten memory cells in the block exceeds a predetermined number;
- subsequently, if the number of unwritten memory cells in the block exceeds the predetermined number, performing an unverified write operation that raises threshold voltages of unwritten memory cells from an unwritten state;
- and
- subsequently performing the erase operation.
Dependencies are inferred from the claim text.