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US 2014/0157087 A1Published application
Bad Column Handling in Flash Memory
AssigneeSanDisk Technologies LLC
InventorsDamian Pablo Yurzola, Eran Sharon, Idan Alrod, Michael Altshuler, Madhuri Kotagiri, Rajeev Nagabhirava
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Abstract
In a flash memory, redundant columns are used alternatively as replacement columns for replacing bad columns or to provide additional redundancy for ECC encoding. Locations of bad columns are indicated to a soft-input ECC decoder so that data bits from bad columns are treated as having a lower reliability than data bits from other columns.
Claims16
A method of operating a memory array that includes at least one bad column, comprising:
- determining location information for the at least one bad column;
- compressing the location information;
- providing the compressed location information to a soft-input ECC decoder as a first soft data indicating low likelihood for hard data obtained from the at least one bad column;
- and
- decoding hard data in combination with the soft data indicating low likelihood for the hard data obtained from the at least one bad column.
2 more elements
A method of operating a memory array comprising:
- identifying a number of columns of the memory array as bad columns;
- ranking the identified bad columns;
- replacing high-ranked bad columns with redundant columns;
- recording low-ranked bad columns in a record;
- subsequently, storing data in the memory array including in the low-ranked bad columns;
- subsequently, reading the data from the memory array including from the low-ranked bad columns;
- identifying data from the low-ranked bad columns from the record;
- and
- performing soft-input Error Correction Code (ECC) decoding of the data, where data from the low-ranked bad columns is treated as having low likelihood in response to identifying the data as coming from the low-ranked bad columns.
6 more elements
A multi-plane flash memory array comprising:
- a first plane of flash memory cells in which bad columns are replaced with replacement columns and are not used for storage of data;
- and
- a second plane of flash memory cells in which bad columns are used for storage of data, replacement columns of the second plane used to store Error Correction Code (ECC) encoded data.
Dependencies are inferred from the claim text.