Data recovery for defective word lines during programming of non-volatile memory arrays

• US 8,775,901 B2
• Filed: 07/28/2011
• Issued: 07/08/2014
• Est. Priority Date: 07/28/2011
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: Sandisk Technologies Incorporated (Western Digital Corporation)
• Inventors: Sharon, Eran, Alrod, Idan
• Primary Examiner(s): Chase, Shelly A
• Application Number:
  US13/193,148
• Publication Number:
  US 20130031429A1
• Time in Patent Office: 1,076 Days
• Field of Search: 714/746, 714/758, 714763-764, 714/773
• US Class Current: 714/763
• CPC Class Codes: G06F 11/1048 using arrangements adapted for a specific error detection or correction feature
• CPC Class Codes: G06F 11/1072 in multilevel memories
• CPC Class Codes: G11C 29/04 Detection or location of defective memory elements , e.g. cell constructio details, timing of test signals
• CPC Class Codes: G11C 29/82 for EEPROMs

Abstract

The recovery of data during programming, such as in the case of a broken word-line, is considered. The arrangement described assumes that k pages may be corrupted when the system finishes programming a block. Then these corrupted pages can be recovered using an erasure code. In order to recover any k pages, the system will compute and temporarily store k parity pages in the controller. These k parity pages may be computed on-the-fly as the data pages are received from the host. After programming the block if a problem is detected in a post-write read, and data in up to k pages is corrupt on some bad word-lines, then the missing data is recovered using the k parity pages that are stored in the controller and using the other non-corrupted pages that are read from the block of the memory array and decoded.

Claims

1. A method of operating a memory system including an array of flash memory cells formed along a plurality of word lines each capable of storing one or more pages of data, the method comprising:

receiving a first data page;

storing the received first data page in a first buffer;

writing the first data page from the first buffer into a corresponding word line of the flash memory;

generating a page of parity data for the received first page of data;

storing the page of parity data in a second buffer;

subsequent to receiving the first data page, sequentially receiving one or more additional pages of data, and for each of additional received page of data;

overwriting the preceding page of received data in the first buffer therewith;

writing the page of data from the first buffer into a corresponding word line of the flash memory; and

updating the page of parity data stored in the second buffer as a function of parity data as previously stored in the second buffer and the additional received page of data;

subsequently determining whether the first data page and the additional pages of data were written correctly; and

in response to determining that one of the data pages is written incorrectly, determining the correct data for the incorrectly written page based upon the page of parity data and the first and additional data pages as read from the array.

2. The method of claim 1, wherein overwriting the preceding page step is performed after verifying the completion of writing the first data page.

3. The method of claim 1, wherein the memory system includes a memory circuit, including the array, and a controller circuit, wherein the page of parity data is generated by logic circuitry on the controller circuit and the second buffer is formed on the controller circuit.

4. The method of claim 1, wherein determining whether the first data page and the additional pages of data were written correctly includes determining whether the pages individually have an acceptable amount of error.

5. The method of claim 4, whether each of the pages of data includes a user data portion and a corresponding error correction code (ECC) portion and wherein determining whether the pages individually have an acceptable amount of error comprises being able to read to read the user data portion using the corresponding ECC.

6. The method of claim 5, wherein the memory system includes a memory circuit, including the array, and a controller circuit, including ECC circuitry, and wherein the corresponding ECC is generated by the ECC circuitry.

7. The method of claim 1, wherein updating the page of parity data in the second buffer as a function of the previously stored parity data and the page comprises:

performing an exclusive OR operation of the contents of the second data buffer with the page; and

storing the result in the second buffer.

8. The method of claim 1, wherein updating the page of parity data in the second buffer as a function of the previously stored parity data and the page comprises:

computing an erasure correction code parity page from the contents of the second data buffer and the page; and

storing the result in the second buffer.

9. The method of claim 8, wherein the memory system includes a memory circuit, including the array, and a controller circuit, wherein the page of parity data is generate by logic circuitry on the controller circuit.

10. The method of claim 1, further comprising:

re-writing the corrected data for the incorrectly written page to a new location.

11. The method of claim 10, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, the method further comprising:

re-writing the corrected data for the incorrectly written page and the other pages of data of the block to which the incorrectly written page was incorrectly written to a different block; and

marking the block to which the incorrectly written page was incorrectly written as defective in a memory management structure for the memory system.

12. The method of claim 1, wherein the memory cells are multistate cells storing N-bits per cell, N being an integer two or greater, and the word lines each capable of storing N logical pages arranged as an upper-most logical page to a lower-most logical page, wherein writing the first data page and the additional pages of data into corresponding word lines comprises:

writing each of the first data page and the additional pages of data into a first of the logical pages that is the same on each of the corresponding word lines.

13. The method of claim 12, further comprising:

receiving a second plurality of data pages, the second set having the same number of pages as the first data page and the additional pages of data;

generating a second page of parity data for the second set of data pages;

storing the second page of parity data in the second buffer, where the second buffer can hold the second page of parity data concurrently with the parity data generated as a function of the first data page and the additional pages of data;

writing each of the second set of data pages into a second of the logical pages that is the same on each of the corresponding word lines, the second of the logical pages being different than the first of the logical pages;

subsequently determining whether the second set of data pages was written correctly; and

in response to determining that a first page of the second set of data pages is written incorrectly, determining the correct data for the incorrectly written page based upon the second page of parity data and others of the pages of the second set of pages as read from the array.

14. The method of claim 13, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, and wherein the corresponding plurality of word lines are all of the word lines of a block.

15. The method of claim 13, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, and wherein the corresponding plurality of word lines are every other word line of a block.

16. The method of claim 15, further comprising:

receiving third and fourth sets of data pages, the third and fourth sets having the same number of pages;

generating a third and a fourth page of parity data respectively for each of the third and fourth sets of data pages;

storing the third and fourth pages of parity data in the second buffer, where the second buffer can hold the second, third and fourth pages of parity data concurrently with the generated as a function of the first data page and the additional pages of data;

writing each of the third and fourth set of data pages respectively into the first and second of the logical pages on each of the alternate word lines that are not written with the first and second sets of data;

subsequently determining whether the third or fourth set of data pages was written correctly; and

in response to determining that a first page of one or both of the third and fourth set of data pages is written incorrectly, determining the correct data thereof based upon the corresponding page of parity data and others of the pages of the corresponding set of pages as read from the array.

17. The method of claim 1, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, and wherein the corresponding plurality of word lines are from the same block.

18. The method of claim 1, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, and wherein the corresponding plurality of word lines are every other word line of a block.

19. The method of claim 18, further comprising:

receiving a second plurality of data pages;

generating a second page of parity data for the second set of data pages;

storing the second page of parity data in the second buffer, where the second buffer can hold the second page of parity data concurrently with the parity data generated as a function of the first data page and the additional pages of data;

writing the second set of data pages respectively into the alternate word lines that are not written with the first data page and the additional pages of data;

subsequently determining whether the second set of data pages was written correctly; and

in response to determining that a first page of the second set of data pages is written incorrectly, determining the correct data for the incorrectly written page based upon the second page of parity data and others of the pages of the second set of pages as read from the array.

20. In a non-volatile memory system including a memory circuit, the memory circuit having an array of non-volatile memory cells formed along a plurality of word lines each capable of storing one or more pages of data, and a controller circuit controlling the transfer of data between the memory system and a host and managing the storage of data on the memory circuit, a method of operating the memory system, comprising:

performing a write operation of a plurality of pages of data into the memory array, including;

receiving from a host the plurality of pages of data at the controller circuit;

computing a data check result from the plurality of pages of data wherein the data check result is a many to one transformation such that plurality of data pages cannot be reconstructed based solely upon the data check result;

transferring the plurality of pages of data from the controller circuit to the memory circuit;

writing the plurality of pages of data into array;

discarding by the controller of one or more of the pages; and

subsequent to writing the plurality of pages of data into the array, performing a post-write verify operation to determine whether the plurality of pages of data were correctly written, wherein the post-write verify operation is performed as part of the write operation independently of a separate host command therefor; and

in response to determining that a first of the plurality of pages of data is not written correctly, the determined incorrectly written page being one of the pages discarded by the controller, reading one or more of the other data pages from the memory array and reconstructing the first page from the data check result and the other data pages read from the memory array.

21. The method of claim 20, wherein the controller discards said one or more pages subsequent to the transfer thereof to the memory circuit.

22. The method of claim 20, wherein the controller discards said one or more pages subsequent to the completion of the writing thereof.

23. The method of claim 20, wherein the controller discards said one or more pages subsequent to the completion of the writing and verification thereof.

24. The method of claim 20, wherein the data check result is generated by logic circuitry on the controller circuit and maintained in a buffer memory on the controller circuit.

25. The method of claim 20, wherein the data check result is computed using an erasure code encoder.

26. The method of claim 20, wherein the data check result is computed using an RS encoder.

27. The method of claim 20, wherein the data check result is computed as an exclusive OR operation of multiple ones of the plurality of pages of data.

28. The method of claim 20, further comprising:

re-writing the reconstructed first page to a new location on the memory circuit.

29. The method of claim 28, wherein the array is formed of a plurality of erase blocks each having a plurality of word lines, the method further comprising:

re-writing the reconstructed first page and the others of the plurality of pages of data of the block to which the first page was incorrectly written to a different block; and

marking the block to which the first page was incorrectly written as defective in a memory management structure for the memory system.

30. The method of claim 20, wherein the memory cells are multistate cells storing N-bits per cell, N being an integer two or greater, and the word-lines each capable of storing N logical pages, and wherein the plurality of pages of data includes first and second subsets each of multiple pages, wherein the first set of pages being written as lower logical pages on a corresponding set of multiple word-lines and the second set of pages begin written as upper logical pages the corresponding set of multiple word-lines, and wherein the data check result includes first and second data check results respectively computed from the first and second subsets, the method further including:

in response to determining that one of the pages of the first subset is not written correctly, the determined incorrectly written page being one of the pages discarded by the controller, reading one or more of the other data pages of the first subset from the memory array and reconstructing the incorrectly written page of the first subset from the first data check result and the other data pages of the first subset read from the memory array; and

in response to determining that one of the pages of the second subset is not written correctly, the determined incorrectly written page being one of the pages discarded by the controller, reading one or more of the other data pages of the second subset from the memory array and reconstructing the incorrectly written page of the second subset from the second data check result and the other data pages of the second subset read from the memory array.

31. The method of claim 30, wherein the first and second subsets are written into alternate ones of the word-lines, and wherein the plurality of pages of data further includes third and fourth subsets each of multiple pages, wherein the third set of pages being written as lower logical pages on a corresponding set of multiple word-lines and the fourth set of pages begin written as upper logical pages the corresponding set of multiple word-lines, the third and fourth subsets being written into the alternate ones of the word-lines not used for the first and second subsets, and wherein the data check result further includes third and fourth data check results respectively computed from the third and fourth subsets, the method including:

in response to determining that one of the pages of the third subset is not written correctly, the determined incorrectly written page being one of the pages discarded by the controller, reading one or more of the other data pages of the third subset from the memory array and reconstructing the incorrectly written page of the third subset from the third data check result and the other data pages of the third subset read from the memory array; and

in response to determining that one of the pages of the fourth subset is not written correctly, the determined incorrectly written page being one of the pages discarded by the controller, reading one or more of the other data pages of the fourth subset from the memory array and reconstructing the incorrectly written page of the fourth subset from the fourth data check result and the other data pages of the fourth subset read from the memory array.