Multiple bad block flags for block quality classification and product diversity in tests on non-volatile memory

摘要

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 fuse ROM. For each block, a multi-bit flag indicates whether the block has few defects and is in the highest reliability category, has too many defects to use, or is in one of a number of recoverability categories. Multi-bit bad blocks values can be determined as part of a test process on fresh devices, and the test of the block can be stopped failing for critical category errors, but for recoverable categories, the test continues testing. and track the results to determine the recoverability category for the block, and write it on the die as a bad block flag for each block. These recoverability categories may be incorporated into wear leveling operations.