Cross temperature nand read

A method for reading memory cells, the method comprising:

• programming NAND memory cells to a plurality of data states including establishing a charge on each NAND memory cell, each data state associated with a threshold voltage distribution of a plurality of threshold voltage distributions;
• determining a cross-temperature factor based on sensing a group of the NAND memory cells at a first threshold voltage distribution of the plurality of threshold voltage distributions, the cross-temperature factor related to a difference in temperature between programming the group and reading the group;
• determining a data retention factor based on sensing the group of the NAND memory cells at a second threshold voltage distribution of the plurality of threshold voltage distributions, the data retention factor related to a difference in the charge between programming the group and reading the group;
• determining one or more read level offsets based on the cross-temperature factor and the data retention factor;
• and
• sensing the group of the NAND memory cells at a read reference voltage that is based on the one or more read level offsets.

A non-volatile memory system, comprising:

• a NAND memory structure having NAND memory cells;
• and
• one or more control circuits configured to communicate with the NAND memory structure, the one or more control circuits configured to:
• program a group of the NAND memory cells to a plurality of data states including establishing a charge on each NAND memory cell, each data state associated with a threshold voltage distribution of a plurality of threshold voltage distributions;
• determine a first count of a first number of memory cells within a first threshold voltage range associated with a first threshold voltage distribution of the plurality of threshold voltage distributions, the first threshold voltage distribution exhibits a greater threshold voltage shift due to change in temperature between programming and reading than due to change in the charge between programming and reading;
• determine a second count of a second number of memory cells within a second threshold voltage range associated with a second threshold voltage distribution of the plurality of threshold voltage distributions, the second threshold voltage distribution exhibits a greater threshold voltage shift due to change in the charge between programming and reading than due to change in the temperature between programming and reading;
• determine one or more read level offsets based on the first count and the second count;
• and
• sense the group of the NAND memory cells at a read reference voltage that is based on the one or more read level offsets.