# US 2014/0157087 A1 · Bad Column Handling in Flash Memory > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0157087 A1 - Document ID: US20140157087A1 - Status: Published application - Kind: A1 - Application number: 13/793,282 - Filed: 2013-03-11 - Published: 2014-06-05 - Earliest claimed: 2012-12-04 - Assignees: SanDisk Technologies LLC - Applicants: Sandisk Technologies, Inc. - Inventors: Damian Pablo Yurzola; Eran Sharon; Idan Alrod; Michael Altshuler; Madhuri Kotagiri; Rajeev Nagabhirava - Web page: https://patentgrep.com/patent/US20140157087A1 ## CPC - G06F 11/1068: {in sector programmable memories, e.g. flash disk (G06F11/1072 takes precedence)} - G06F 11/1012: {using codes or arrangements adapted for a specific type of error (G06F11/1048 takes precedence)} - G11C 29/52: Protection of memory contents; Detection of errors in memory contents - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - G11C: STATIC STORES (semiconductor memory devices H10B) ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The method of claim 1 wherein the providing step comprises: providing the compressed location information to a soft-input ECC decoder as soft data indicating low likelihood for hard data obtained from any column which shares the compressed location information of the at least one bad column. ### Claim 3 (depends on 1) The method of claim 1 further comprising performing a high resolution read to obtain a second soft read data, the second soft read data combined with the first soft data. ### Claim 4 (depends on 1) The method of claim 1 wherein compressing the location information includes dividing all columns into a plurality of sections and, in each section, treating a particular column as a bad column if the location information indicates that there is a bad column in any section of the plurality of sections at a location corresponding to the particular column. ### Claim 5 (depends on 1) The method of claim 1 wherein the memory array consists of a plurality of columns, each of the plurality of columns containing a plurality of bit lines, and wherein a column is considered as a bad column if it contains at least one defective bit line. ### Claim 6 (depends on 5) The method of claim 5 further comprising determining location information for at least one defective bit line in the at least one bad column, and wherein the compressed location information includes compressed bit line location information. ### Claim 7 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. ### Claim 8 (depends on 7) The method of claim 7 further comprising identifying one or more redundant columns that are not used for replacement of high-ranked bad columns and using the one or more redundant columns to provide additional redundancy for stored data. ### Claim 9 (depends on 7) The method of claim 7 wherein the identified bad columns are ranked according to the number of bad bit lines per column. ### Claim 10 (depends on 9) The method of claim 9 wherein high-ranked bad columns have a number of bad bit lines that is greater than a predetermined number and low-ranked bad columns have a number of bad bit lines that is less than or equal to the predetermined number. ### Claim 11 (depends on 7) The method of claim 7 wherein the identified bad columns are ranked according to ECC results from data stored in the bad columns. ### Claim 12 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. ### Claim 13 (depends on 12) The multi-plane flash memory array of claim 12 wherein the first plane has a first number of bad columns and the second plane has a second number of bad columns, the first number being less than the second number. ### Claim 14 (depends on 13) The multi-plane flash memory array of claim 13 wherein the first plane is on a first die and the second plane is on a second die. ### Claim 15 (depends on 14) The multi-plane flash memory array of claim 14 wherein the first die and the second die are selected for the multi-plane flash memory array based on the first number and the second number. ### Claim 16 (depends on 15) The multi-plane flash memory array of claim 15 further comprising a plurality of additional dies, each of the plurality of additional dies chosen based on respective numbers of bad columns in the dies.