Patent ID: 11972812
Assignee: SANDISK TECHNOLOGIES, INC.
Field: Computer technology (Electrical engineering)
Classification: CPC G | IPC G

Claim 19:
20. A non-volatile storage apparatus, comprising:
a plurality of NAND strings comprising non-volatile memory cells capable of being programmed to a plurality of data states, the plurality of data states includes low threshold voltage data states and a high threshold voltage data state, the low threshold voltage data states include lower threshold voltages than the high threshold voltage data state;
a plurality of word lines connected to the NAND strings;
a plurality of bit lines connected to the NAND strings; and
a control circuit connected to the plurality of word lines and the plurality of bit lines, the control circuit is configured to program data to the NAND strings and read data from the NAND strings;
in response to a read process failing for a plurality of memory cells of the NAND strings that are connected to a particular word line of the plurality of word lines, the control circuit is configured to:
perform a first sensing operation for each of the memory cells of the plurality of memory cells to determine whether the memory cells have respective threshold voltages above respective lower voltage limits, the respective lower voltage limits are respective read compare voltages for intended data states less a first set of one or more voltage magnitudes;
perform a second sensing operation for each of the memory cells of the plurality of memory cells to determine whether the memory cells have respective threshold voltages below respective upper voltage limits, the respective upper voltage limits are respective read compare voltages for intended data states plus a second set of one or more voltage magnitudes;
for memory cells of the plurality of memory cells that are part of the NAND strings and are connected to the particular word line, read both neighbor memory cells that are on word lines next to the particular word line to determine whether the neighbor memory cells are in the low threshold voltage data states; and
refresh data as originally intended for the memory cells of the plurality of memory cells of the NAND strings that are connected to the particular word line that are determined from the first sensing operation to have threshold voltages above respective lower voltage limits, determined from the second sensing operation to have threshold voltages below respective upper voltage limits and have both neighbor memory cells determined to be in low threshold voltage data states.