Data pattern sensitivity compensation using different voltage

• US 7,450,421 B2
• Filed: 06/02/2006
• Issued: 11/11/2008
• Est. Priority Date: 06/02/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima, Dong, Yingda
• Primary Examiner(s): LE, VU ANH
• Application Number:
  US11/421,871
• Publication Number:
  US 20070279994A1
• Time in Patent Office: 893 Days
• Field of Search: 365/185.17, 365/185.03, 365/185.11, 365/185.22
• US Class Current: 365/185.17
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data

Abstract

Errors can occur when reading the threshold voltage of a programmed non-volatile storage element due to at least two mechanisms: (1) capacitive coupling between neighboring floating gates and (2) changing conductivity of the channel area after programming (referred to as back pattern effect). To account for coupling between neighboring floating gates, the read process for a particular memory cell will provide compensation to an adjacent memory cell in order to reduce the coupling effect that the adjacent memory cell has on the particular memory cell. To account for the back pattern effect, a first voltage is used during a verify operation for unselected word lines that have been subjected to a programming operation and a second voltage is used for unselected word lines that have not been subjected to a programming operation. The combination of these two techniques provides for more accurate storage and retrieval of data.

Claims

1. A method for using non-volatile storage, comprising:

applying a particular voltage to a particular non-volatile storage element of a group of connected non-volatile storage elements;

applying a first voltage to a first set of one or more non-volatile storage elements of said group, said first set of one or more non-volatile storage elements are on a first side of said particular non-volatile storage element and have already been subjected to one or more programming processes since a last erase of said group, said first voltage is applied in coordination with said particular voltage;

applying a second voltage to a second set of one or more non-volatile storage elements of said group, said second set of one or more non-volatile storage elements are on a second side of said particular non-volatile storage element and have not already been subjected to a programming processes since said last erase of said group, said second voltage is applied in coordination with said particular voltage;

applying a voltage that is different than said second voltage to a neighbor non-volatile storage element of said group in coordination with applying said particular voltage, said neighbor non-volatile storage element is next to said particular non-volatile storage element on said second side of said particular non-volatile storage element, said neighbor of said particular non-volatile storage element has not been subjected to programming since erasing said group; and

verifying programming of said particular non-volatile storage element based on said particular voltage.

2. A method according to claim 1, wherein:

said second voltage is lower than said first voltage.

3. A method according to claim 2, wherein:

said voltage that is different than said second voltage is greater than said second voltage and less than said first voltage.

4. A method according to claim 2, wherein:

said voltage that is different than said second voltage is greater than said second voltage and equal to said first voltage.

5. A method according to claim 1, wherein:

said particular voltage is a verify reference voltage;

said first voltage is sufficiently high enough to turn on said first set of non-volatile storage elements;

said second voltage is sufficiently high enough to turn on said second set of non-volatile storage elements; and

said second voltage is lower than said first voltage; and

said verifying is performed as part of an iteration of a programming process.

6. A method according to claim 5, wherein:

said group of connected non-volatile storage elements are NAND flash memory devices that are part of a common NAND string.

7. A method according to claim 5, wherein:

said first set of non-volatile storage elements are on a source side of said particular non-volatile storage element;

said second set of non-volatile storage elements are on a drain side of said particular non-volatile storage element; and

said neighbor non-volatile storage elements is on said drain side of said particular non-volatile storage element.

8. A method according to claim 1, further comprising:

reading data from said particular non-volatile storage element including applying a common read voltage to said first set of non-volatile storage elements and said second set of non-volatile storage elements, said reading includes applying a data dependent voltage to said neighbor non-volatile storage element based on a condition of said neighbor non-volatile storage element.

9. A method according to claim 8, wherein:

said group of connected non-volatile storage elements are multi-state NAND flash memory devices that are part of a common NAND string;

said particular voltage is applied to a control gate for said particular non-volatile storage element;

said first voltage is applied to control gates for said first set of non-volatile storage elements;

said second voltage is applied to control gates for said second set of non-volatile storage elements; and

said voltage that is different than said second voltage is applied to a control gate for said neighbor non-volatile storage element.

10. A method according to claim 9, wherein:

said second voltage is lower than said first voltage;

said particular voltage is a verify reference voltage;

said first voltage is sufficiently high enough to turn on said first set of non-volatile storage elements;

said second voltage is sufficiently high enough to turn on said second set of non-volatile storage elements; and

said first set of non-volatile storage elements are on a source side of said particular non-volatile storage element;

said second set of non-volatile storage elements are on a drain side of said particular non-volatile storage element; and

said neighbor non-volatile storage elements is on said drain side of said particular non-volatile storage element.

11. A method according to claim 1, further comprising:

selecting a value of said voltage that is different than said second voltage based on how many non-volatile storage elements are in said second set.

12. A method for using non-volatile storage, comprising:

applying a particular voltage to a particular non-volatile storage element of a group of connected non-volatile storage elements;

applying a first voltage to a first set of one or more non-volatile storage elements of said group, said first set of one or more non-volatile storage elements have already been subjected to one or more programming processes since a last erase of said group, said first voltage is applied in coordination with said particular voltage;

applying a second voltage to a second set of one or more non-volatile storage elements of said group, said second set of one or more non-volatile storage elements have not already been subjected to a programming processes since said last erase of said group, said second voltage is applied in coordination with said particular voltage;

applying a voltage that is different than said second voltage to a neighbor non-volatile storage element of said group in coordination with applying said particular voltage, said neighbor non-volatile storage element is next to said particular non-volatile storage element;

verifying programming of said particular non-volatile storage element based on said particular voltage; and

reading data from said particular non-volatile storage element including applying a data dependent voltage to said neighbor non-volatile storage element based on a condition of said neighbor non-volatile storage element.

13. A method according to claim 12, wherein said reading data comprises:

(a) applying a read reference voltage to a control gate for said particular non-volatile storage element;

(b) applying a read pass voltage to control gates for said first set of one or more non-volatile storage elements and said second set of one or more non-volatile storage elements;

(b) applying said data dependent voltage to a control gate for said neighbor non-volatile storage element; and

(d) sensing a condition of said particular non-volatile storage element.

14. A method according to claim 13, wherein:

said steps (a), (b), (c) and (d) are performed for each programmed state.

15. A method according to claim 13, further comprising:

reading said condition of said neighbor non-volatile storage element prior to said applying a read reference voltage.

16. A method according to claim 12, wherein said reading data comprises:

applying multiple voltages to said neighbor non-volatile storage element and storing a sensed condition for one of said multiple voltages associated with said condition of said neighbor non-volatile storage element.

17. A method according to claim 12, wherein:

said second voltage is lower than said first voltage.

18. A method according to claim 12, wherein:

said voltage that is different than said second voltage is greater than said second voltage and less than said first voltage.

19. A method according to claim 12, wherein:

said group of connected non-volatile storage elements are NAND flash memory devices that are part of a common NAND string.

20. A method according to claim 19, wherein:

said particular voltage is applied to a control gate for said particular non-volatile storage element;

said first voltage is applied to control gates for said first set of non-volatile storage elements;

said second voltage is applied to control gates for said second set of non-volatile storage elements; and

said voltage that is different than said second voltage is applied to a control gate for said neighbor non-volatile storage element.

21. A method according to claim 20, wherein:

said first set of non-volatile storage elements are on a source side of said particular non-volatile storage element;

said second set of non-volatile storage elements are on a drain side of said particular non-volatile storage element; and

said neighbor non-volatile storage elements is on said drain side of said particular non-volatile storage element.

22. A method for using non-volatile storage, comprising:

applying a particular voltage to a particular non-volatile storage element of a group of connected non-volatile storage elements;

applying a first voltage to one or more non-volatile storage elements of said group that have already been subjected to one or more programming processes since a last erase of said group, said first voltage is applied in coordination with said particular voltage;

applying a second voltage to a set of one or more non-volatile storage elements of said group that have not already been subjected to a programming processes since erasing said group, said second voltage is applied in coordination with said particular voltage;

determining a dependent voltage based on a number of non-volatile storage elements in said set;

applying said dependent voltage to a non-volatile storage element that is a neighbor of said particular non-volatile storage element, said dependent voltage is applied in coordination with said particular voltage; and

sensing a condition related to said particular non-volatile storage element and said particular voltage.

23. A method according to claim 22, wherein:

said second voltage is lower than said first voltage.

24. A method according to claim 22, wherein:

said one or more non-volatile storage elements of said group that have already been subjected to one or more programming processes since a last erase of said group are on a source side of said particular non-volatile storage element;

said set of non-volatile storage elements are on a drain side of said particular non-volatile storage element; and

said non-volatile storage element that is said neighbor of said particular non-volatile storage element is on said drain side of said particular non-volatile storage element.

25. A method according to claim 22, wherein:

said group of connected non-volatile storage elements are NAND flash memory devices that are part of a common NAND string.

26. A method according to claim 22, further comprising:

reading data from said particular non-volatile storage element including applying a common read voltage to said one or more non-volatile storage elements of said group that have already been subjected to one or more programming processes and said set of non-volatile storage elements, said reading includes applying a data dependent signal to said non-volatile storage element that is said neighbor based on a condition of said neighbor non-volatile storage element.