System for performing data pattern sensitivity compensation using different voltage

• US 7,310,272 B1
• Filed: 06/02/2006
• Issued: 12/18/2007
• 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): Zarabian, Amir
• Assistant Examiner(s): PHAM, LY D
• Application Number:
  US11/421,884
• Publication Number:
  US 20070279995A1
• Time in Patent Office: 564 Days
• Field of Search: 365/185.02, 365/185.18, 365/185.21, 365/185.22, 365/185.23, 365/185.24
• US Class Current: 365/185.22
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3454 Arrangements for verifying correct programming or for detecting overprogrammed cells
• CPC Class Codes: G11C 16/3459 Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 2211/5621 Multilevel programming verification

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 non-volatile storage system, comprising:

a group of connected non-volatile storage elements; and

a managing circuit in communication with said group of connected non-volatile storage elements, said managing circuit applies a particular voltage to a particular non-volatile storage element of said group, while applying said particular voltage said managing circuit applies a first voltage to a first set of one or more non-volatile storage elements of said group and a second voltage to a second 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 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, while applying said particular voltage said managing circuit applies a voltage that is different than said second voltage to a neighbor non-volatile storage element of said group, 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, said managing circuit verifies programming of said particular non-volatile storage element based on said particular voltage.

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

said second voltage is lower than said first voltage; and

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

3. A non-volatile storage system 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 managing circuit verifies programming of said particular non-volatile storage element as part of an iteration of a programming process.

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

said group of connected non-volatile storage elements is a NAND string.

5. A non-volatile storage system according to claim 4, 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.

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

said managing circuit reads 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.

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

said group of connected non-volatile storage elements is a 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.

8. A non-volatile storage system according to claim 7, 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 second voltage is lower than said first voltage;

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.

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

said managing circuit selects 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.