Adaptive operation of three dimensional memory

摘要

When data from a portion of a three dimensional NAND memory array is determined to be uncorrectable by Error Correction Code (ECC), a determination is made as to whether data is uncorrectable by ECC throughout some unit that is larger than the portion. If modified read conditions provide ECC correctable data, the modified read conditions are recorded for subsequent reads of the larger unit.

主权项

1. A method of operating a three dimensional nonvolatile NAND memory comprising:
applying a first set of read conditions to a first portion of a block to obtain first data; performing Error Correction Code (ECC) decoding of the first data; determining that the first data is uncorrectable by ECC; in response to determining that the first data in the first portion of the block is uncorrectable by ECC, determining whether a larger unit within the three dimensional NAND memory, that is larger than the first portion of the block, is uncorrectable by ECC when read using the first set of read conditions, the larger unit consisting of: a set of strings within the block, the set of strings consisting of fewer than all strings of the block that are selected together by a common select line while other sets of strings within the block remain unselected and isolated by other select lines; if the stored data is uncorrectable by ECC throughout the larger unit, then applying modified read conditions to the first portion of the block to find a second set of read conditions that provide second data that is correctable by ECC; and returning corrected second data and recording the second set of read conditions for subsequent reads of data of the set of strings while continuing to use a default set of read conditions for the other sets of strings within the block.