Block quality classification at testing for non-volatile memory, and multiple bad block flags for product diversity
For a non-volatile memory die formed of multiple blocks of memory cells, the memory die has a multi-bit bad block flag for each block stored on the memory die, such as in a fuse ROM. For each block, the multi-bit flag indicates if the block has few defects and is of the highest reliability category, is too defective to be used, or is in of one of multiple recoverability categories. The multi-bit bad blocks values can be determined as part a test process on fresh devices, where the test of a block can be fail stop for critical category errors, but, for recoverable categories, the test continues and tracks the test results to determine a recoverability category for the block and write this onto the die as a bad block flag for each block. These recoverability categories can be incorporated into wear leveling operations.
1. A method, comprising:
testing a non-volatile memory die comprising a plurality of blocks each having a plurality of memory cells, comprising:
performing a sequence of a plurality of test operations for each block, each of the test operations configured to determine a presence of a corresponding type of defect, including a plurality of defect categories, in the block on which the test operation is being performed; and
determining from the sequence of test operations a corresponding multi-bit flag value for each block, the multi-bit flag value indicating one of a plurality of recoverability categories for the corresponding block, the recoverability categories include a good block category, an unusable block category, and a plurality of intermediate recoverability level categories;
storing the multi-bit flag value for each of the blocks in non-volatile memory on the memory die;
grading the memory die into one of a plurality of groups of quality specifications based on the multi-bit flag values; and
assembling the memory die into a non-volatile memory package comprised of multiple memory die selected from a plurality of different groups of quality specifications.
2. The method of claim 1 , wherein:
the types of defects include a plurality of categories of error.
3. The method of claim 1 , wherein:
the types of defects include a plurality of degrees of error of a category of error.
4. The method of claim 1 , wherein performing the sequence of test operations for each block further includes:
determining whether a block fails a test operation of a critical category; and
in response to the to the block failing the test operation of the critical category, setting the recoverability category of the block failing the test operation as the unusable block category.
5. The method of claim 4 , wherein performing the sequence of test operations for each block further includes:
in response to the block failing the test operation of the critical category, discontinuing performing of the sequence of test operations for the block.
6. The method of claim 1 , wherein storing the multi-bit flag value for each of the blocks in non-volatile memory on the memory die includes:
writing the multi-bit flag values in a fuse ROM memory on the memory die.
7. The method of claim 1 , wherein storing the multi-bit flag value for each of the blocks in non-volatile memory on the memory die includes:
writing the multi-bit flag values in a block of the memory die.
8. The method of claim 1 , wherein performing a sequence of a plurality of test operations for each block includes:
performing each test operation of the sequence on all of the blocks prior to performing a subsequent test operation of the sequence on the blocks.
9. A non-volatile memory system, comprising:
a plurality of memory die, each comprising:
a plurality of blocks each comprising a plurality of non-volatile memory cells; and
a non-volatile system memory section storing, for each of the blocks, a multi-bit flag value indicating one of a plurality of recoverability categories of a corresponding block, the recoverability categories including a good block category, an unusable block category, and a plurality of recoverability level categories,
the plurality of memory die including memory die selected from a plurality of different groups of quality specifications based on the multi-bit flag values; and
a memory controller connected to the plurality of memory die and configured to:
perform a power on sequence for each of the memory die, the power on sequence including reading out the multi-bit flag values from the memory die and storing the multi-bit flag values in operating memory for the memory controller; and
select blocks of each of the memory die based upon a corresponding ordering of the blocks weighted by the recoverability category of each of the blocks in the ordering.
10. The non-volatile memory system of claim 9 , wherein the memory controller is further configured to:
maintain, for each of the blocks, a count for a number of program/erase cycles experienced by the block, wherein the ordering of the blocks is based upon the blocks' count of the number of program/erase cycles experienced by each block weighted by the block's recoverability category.
11. The non-volatile memory system of claim 9 , wherein:
when the memory controller selects blocks, blocks of an unusable block category are not selected.
12. The non-volatile memory system of claim 9 , wherein:
the ordering of the blocks is for use in a wear leveling operation.
13. The non-volatile memory system of claim 9 , wherein:
the memory controller selects the blocks for an internal data relocation operation initiated by the memory controller.
14. A method, comprising:
receiving a plurality of non-volatile memory die comprising a plurality of blocks each having a plurality of memory cells, each of the non-volatile memory die storing a multi-bit flag value for each of the blocks in non-volatile memory on the memory die indicating one of a plurality of recoverability categories for the corresponding block, the recoverability categories include a good block category, an unusable block category, and a plurality of intermediate recoverability level categories;
storing the multi-bit flag value for each of the blocks in non-volatile memory on the memory die;
grading the memory die into one of a plurality of groups of quality specifications based on the multi-bit flag values; and
assembling the memory die into a non-volatile memory package comprised of multiple memory die selected from a plurality of different groups of quality specifications.
15. The method of claim 14 , wherein:
the types of defects include a plurality of categories of error.
16. The method of claim 14 , wherein:
the types of defects include a plurality of degrees of error of a category of error.
17. The method of claim 14 , wherein the multi-bit flag values for each of the die are stored in a fuse ROM memory on the memory die.
18. The method of claim 14 , wherein the multi-bit flag value is stored in a block of the memory die.