Reverse coupling effect with timing information for non-volatile memory

• US 7,289,344 B2
• Filed: 11/10/2005
• Issued: 10/30/2007
• Est. Priority Date: 11/10/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Chen, Jian
• Primary Examiner(s): Elms; Richard T.
• Assistant Examiner(s): NGUYEN, DANG T
• Application Number:
  US11/271,241
• Publication Number:
  US 20070103979A1
• Time in Patent Office: 719 Days
• Field of Search: 365/9, 365/185.33, 365/185.17, 365/185.09, 365/185.29
• US Class Current: 365/9
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3427 Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written

Abstract

Shifts in the apparent charge stored on a floating gate (or other charge storing element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in neighboring floating gates (or other neighboring charge storing elements). The problem occurs most pronouncedly between sets of adjacent memory cells that have been programmed at different times. To compensate for this coupling, the read process for a given memory cell will take into account the programmed state of a neighbor memory cell if the neighbor memory cell was programmed subsequent to the given memory cell. Techniques for determining whether the neighbor memory cell was programmed before or after the given memory cell are disclosed.

Claims

1. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements; and

one or more managing circuits in communication with said non-volatile storage elements, said one or more managing circuits access stored timing information that is customized for a set of data stored in said plurality of non-volatile storage elements and read said set of data from said plurality of non-volatile storage elements including selectively compensating for one or more potential errors in said set of data based on said timing information, said one or more potential errors are due to potential coupling between said one or more non-volatile storage elements and one or more neighboring non-volatile storage elements.

2. A non-volatile storage system according to claim 1, wherein:

said set of data is stored in a subset of said plurality of non-volatile storage elements, said subset has neighboring non-volatile storage elements;

said one or more managing circuits read first time data for a word line associated with said subset and read second time data for a word line associated with said neighboring non-volatile storage elements; and

said one or more managing circuits compare said first time data to said second time data and determine whether there is a potential for errors based on said comparing.

3. A non-volatile storage system according to claim 1, wherein:

said selectively compensating includes choosing whether or not to use a voltage offset and how much of said voltage offset to use during a read process based on said neighboring non-volatile storage elements.

4. A non-volatile storage system according to claim 1, wherein:

said set of data is stored in a subset of said plurality of non-volatile storage elements, said subset has a first set of neighbors and a second set of neighbors;

said one or more managing circuits read data from memory elements connected to a first word line, said memory elements include said subset and additional non-volatile storage elements storing said timing information, said timing information includes a first value and a second value, said first value indicates timing of programming said subset with respect to a first set of neighbors, said second value indicates timing of programming subset with respect to a second set of neighbors;

said one or more managing circuits report said data without compensating for one or more potential errors if said first value indicates that subset was programmed after said first set of neighbors and said second value indicates that said subset was programmed after said second set of neighbors; and

said one or more managing circuits report said data after compensating for one or more potential errors if said first value indicates that said subset was programmed potentially prior to said first set of neighbors or said second value indicates that said subset was programmed potentially prior to said second set of neighbors.

5. A non-volatile storage system according to claim 1, wherein:

said one or more managing circuits program said set of data to a subset of said plurality of non-volatile storage elements including programming said timing information; and

said programming said set of data includes reading neighbor timing information and determining said timing information that is customized for said set of data based on said neighbor timing information.

6. A non-volatile storage system according to claim 5, wherein:

said one or more non-volatile storage elements are multi-state non-volatile storage elements;

said reading neighbor timing information includes performing a read operation at one reference voltage level; and

said determining said timing information is based on said read operation at one reference voltage level.

7. A non-volatile storage system according to claim 1, wherein:

said set of data is stored in a subset of said plurality of non-volatile storage elements, said subset has neighboring non-volatile storage elements; and

said selectively compensating includes performing a first compensation process for coupling between said subset and said neighboring non-volatile storage elements if said timing information indicates that said subset was programmed prior to programming said neighboring non-volatile storage elements and reading without performing a first compensation process if said timing information indicates that said subset was not programmed prior to programming said neighboring non-volatile storage elements.

8. A non-volatile storage system according to claim 1, wherein:

said timing information can include any of an absolute time, a relative time, or an indication of order of programming.

9. A non-volatile storage system according to claim 1, wherein:

said set of data includes a page of data;

said set of data is stored in a subset of said plurality of non-volatile storage elements connected to a first word line; and

said one or more potential errors are due to coupling between said subset and one or more non-volatile storage elements connected to word lines that neighbor said first word line.

10. A non-volatile storage system according to claim 1, wherein:

said stored timing information is accessed concurrently while reading said set of data.

11. A non-volatile storage system according to claim 1, wherein:

said one or more managing circuits include one or more of a state machine, a decoder, sense circuits and a controller.

12. A non-volatile storage system according to claim 1, wherein:

said plurality of non-volatile storage elements are NAND flash memory devices.

13. A non-volatile storage system according to claim 1, wherein:

said plurality of non-volatile storage elements are multi-state flash memory devices.

14. A non-volatile storage system according to claim 1, wherein:

said plurality of non-volatile storage elements include floating gates.

15. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements;

a set of word lines connected to said non-volatile storage elements; and

one or more managing circuits in communication with said non-volatile storage elements and said set of wordlines, said one or more managing circuits program data to said non-volatile storage elements in a word line order that is not predefined, said programming includes storing timing information for said data, said one or more managing circuits read said data from said non-volatile storage system including selectively compensating for coupling between non-volatile storage elements if said stored timing information indicates that neighboring non-volatile storage elements were potentially programmed later in time than non-volatile storage elements storing said data.

16. A non-volatile storage system according to claim 15, wherein:

said programming includes reading a timing value for said neighboring non-volatile storage elements and determining said timing information based on said timing value for said neighboring non-volatile storage elements.

17. A non-volatile storage system according to claim 16, wherein:

said neighboring non-volatile storage elements are multi-state non-volatile storage elements; and

said reading said timing value for said neighboring non-volatile storage elements includes only needing to perform a read process at one read compare point to provide necessary data for said determining said timing information based on said timing value for said neighboring non-volatile storage elements.

18. A non-volatile storage system according to claim 15, wherein said one or more managing circuits program using a method comprising:

reading a first timing value for a first set of said neighboring non-volatile storage elements;

reading a second timing value for a second set of said neighboring non-volatile storage elements;

determining a third timing value based on said first timing value, said third timing value indicates programming order relative to said first set of said neighboring non-volatile storage elements;

determining a fourth timing value based on said second timing value, said fourth timing value indicates programming order relative to said second set of said neighboring non-volatile storage elements, said timing information includes said third timing value and said fourth timing value; and

programming a unit of information, said unit of formation includes said data and said third timing value and said fourth timing value.

19. A non-volatile storage system according to claim 15, wherein:

said plurality of non-volatile storage elements are NAND flash memory devices.

20. A non-volatile storage system according to claim 15, wherein:

said plurality of non-volatile storage elements are multi-state flash memory devices.

21. A non-volatile storage system, comprising:

non-volatile storage elements; and

one or more managing circuits in communication with said non-volatile storage elements, said one or more managing circuits capable of receiving a request to read data and accessing timing information that is customized for said data in response to said request, said one or more managing circuits determine whether there is a potential for coupling between non-volatile storage elements based on said timing information, a subset of said non-volatile storage elements store said data, said one or more managing circuits read said data including compensating for coupling between non-volatile storage elements if it is determined based on said timing information that there is potential for coupling between non-volatile storage elements.

22. A non-volatile storage system according to claim 21, wherein:

said data is stored in a subset of said non-volatile storage elements, said subset has neighboring non-volatile storage elements;

said one or more managing circuits read first time data for a word line associated with said subset and read second time data for a word line associated with said neighboring non-volatile storage elements; and

said one or more managing circuits compare said first time data to said second time data and determine whether there is a potential for coupling based on said comparing.

23. A non-volatile storage system according to claim 21, wherein:

said data is stored in a subset of said non-volatile storage elements, said subset has a first set of neighbors and a second set of neighbors;

said one or more managing circuits read data from memory elements connected to a first word line, said memory elements include said subset and additional non-volatile storage elements storing said timing information, said timing information includes a first value and a second value, said first value indicates timing of programming said subset with respect to a first set of neighbors, said second value indicates timing of programming subset with respect to a second set of neighbors;

said one or more managing circuits report said data without compensating for coupling if said first value indicates that subset was programmed after said first set of neighbors and said second value indicates that said subset was programmed after said second set of neighbors; and

said one or more managing circuits report said data after compensating for coupling if said first value indicates that said subset was programmed potentially prior to said first set of neighbors or said second value indicates that said subset was programmed potentially prior to said second set of neighbors.

24. A non-volatile storage system according to claim 21, wherein:

said one or more managing circuits program said data to said non-volatile storage elements including reading neighbor timing information associated with a set of neighboring non-volatile storage elements, determining said timing information that is customized for said data based on said neighbor timing information; and

storing said timing information that is customized for said data.

25. A non-volatile storage system according to claim 21, wherein:

said non-volatile storage elements are NAND flash memory devices.

26. A non-volatile storage system according to claim 21, wherein:

said non-volatile storage elements are multi-state flash memory devices.

27. A non-volatile storage system, comprising:

one or more non-volatile storage elements connected to a first word line;

one or more non-volatile storage elements connected to a second word line; and

means for receiving a request to read data stored in a predefined unit of data, said predefined unit of data is stored in said one or more non-volatile storage elements connected to said first word line, said predefined unit of data includes a first history data value that indicates order of programming of said unit of data with respect to said second word line;

means for reading said first history data value;

means for reading said data from said one or more non-volatile storage elements connected to said first word line including performing a first compensation process for coupling between said one or more non-volatile storage elements connected to said first word line and one or more non-volatile storage elements connected to said second word line if said first history data value indicates that said unit of data was programmed prior to potential programming of said second word line; and

means for reading said data from said one or more non-volatile storage elements connected to said first word line without performing a first compensation process if said first history data value does not indicate that said unit of data was programmed prior to said second word line.

28. A non-volatile storage system according to claim 27, wherein:

said unit of data is a page of data;

first history data value is a two bit value; and

said first compensation process includes performing read processes using offsets.

29. A non-volatile storage system according to claim 27, wherein:

said one or more non-volatile storage elements connected to said first word line and said one or more non-volatile storage elements connected to said second word line are multi-state flash memory elements.