Apparatus with alternating read mode

• US 7,440,324 B2
• Filed: 12/29/2006
• Issued: 10/21/2008
• Est. Priority Date: 12/29/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima
• Primary Examiner(s): Lam; David
• Application Number:
  US11/618,578
• Publication Number:
  US 20080158974A1
• Time in Patent Office: 662 Days
• Field of Search: 365/185.17, 365/185.18, 365/185.21, 365/185.23, 365/185.24, 365/201
• US Class Current: 365/185.17
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/04 using variable threshold transistors, e.g. FAMOS
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• 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 29/52 Protection of memory contents; Detection of errors in memory contents

Abstract

Shifts in the apparent charge stored on a floating gate (or other charge storage element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates (or other charge storing elements). To account for this coupling, the read process for a targeted memory cell will provide compensation to an adjacent memory cell (or other memory cell) in order to reduce the coupling effect that the adjacent memory cell has on the targeted memory cell. The compensation applied is based on a condition of the adjacent memory cell. To apply the correct compensation, the read process will at least partially intermix read operations for the adjacent memory cell with read operations for the targeted memory cell.

Claims

1. A non-volatile storage system, comprising:

a set of non-volatile storage elements including a target non-volatile storage element and a neighbor non-volatile storage element, the neighbor non-volatile storage element is next to the target non-volatile storage element; and

one or more managing circuits in communication with the set of non-volatile storage elements, as part of an attempt to read data from the target non-volatile storage element the one or more managing circuits perform a set of read operations on the target non-volatile storage element and performs a group of read operations on the neighbor non-volatile storage element, one or more of the group of read operations are temporally intermixed with at least a portion of the set of read operations, the set of read operations include applying different voltages to the neighbor non-volatile storage element, the one or more managing circuits choose a subset of the set of read operations based on the group of read operations and identifies the data stored in the target non-volatile storage element based on the chosen subset.

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

each of the different voltages is associated with a different condition of the neighbor non-volatile storage element.

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

the set of read operations includes a first subset of read operations and a second subset of read operations;

the first subset of read operations includes multiple read operations that apply a first voltage to the neighbor non-volatile storage element; and

the second subset of read operations includes multiple read operations that apply a second voltage to the neighbor non-volatile storage element.

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

the target non-volatile storage element and the neighbor non-volatile storage element are part of a NAND string that includes other non-volatile storage elements;

at least one read operation of the set of read operations applies a read compare voltage to the target non-volatile storage element, a first voltage to the neighbor non-volatile storage element and an other voltage to the other non-volatile storage elements;

at least another read operation of the set of read operations applies the read compare voltage to the target non-volatile storage element, a second voltage to the neighbor non-volatile storage element and the other voltage to the other non-volatile storage elements; and

the other voltage is different than the first voltage.

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

a set of latches shared by the target non-volatile storage element and the neighbor non-volatile storage element, the one or more managing circuits choose the subset of the set of read operations by storing data in one of the latches for the subset because the subset is associated with a particular condition of the neighbor non-volatile storage element, the group of read operations identifies the particular condition.

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

the one or more managing circuits identify data by providing the data to a host that is in communication with the non-volatile storage system.

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

the group of read operations includes testing for a first condition of the neighbor non-volatile storage element, testing for a second condition of the neighbor non-volatile storage element and testing for a third condition of the neighbor non-volatile storage element;

the set of read operations includes a first subset of read operations, a second subset of read operations, a third subset of read operations and a fourth subset of read operations;

the first subset of read operations includes multiple read operations that apply a first voltage to the neighbor non-volatile storage element, the first voltage is associated with the first condition;

the second subset of read operations includes multiple read operations that apply a second voltage to the neighbor non-volatile storage element, the second voltage is associated with the second condition but not the first condition;

the third subset of read operations includes multiple read operations that apply a third voltage to the neighbor non-volatile storage element, the third voltage is associated with the third condition;

the fourth subset of read operations includes multiple read operations that apply a fourth voltage to the neighbor non-volatile storage element;

the one or more managing circuits perform the first subset of read operations after the testing for the first condition and prior to the testing for the second condition;

the one or more managing circuits perform the second subset of read operations after the testing for the second condition and prior to the testing for the third condition; and

the one or more managing circuits perform the third subset of read operations after the testing for the third condition.

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

a set of latches including a first one bit latch, a second one bit latch and a third one bit latch;

wherein the one or more managing circuits store results of the group of read operations in the first one bit latch, the one or more managing circuits store results of the set of the read operations in the first one bit latch and a second one bit latch, the one or more managing circuits use the third one bit latch to indicate whether the first one bit latch and a second one bit latch have valid data from the set of the read operations.

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

the group of read operations includes testing for a first condition of the neighbor non-volatile storage element, testing for a second condition of the neighbor non-volatile storage element, testing for a third condition of the neighbor non-volatile storage element and testing for a fourth condition of the neighbor non-volatile storage element;

the first set of read operations includes a first subset of read operations, a second subset of read operations, and a third subset of read operations;

the first subset of read operations includes multiple read operations that apply a first voltage to the neighbor non-volatile storage element, the first voltage is associated with the first condition;

the second subset of read operations includes multiple read operations that apply a second voltage to the neighbor non-volatile storage element, the second voltage is associated with the second condition and the third condition;

the third subset of read operations includes multiple read operations that apply a third voltage to the neighbor non-volatile storage element, the third voltage is associated with the fourth condition;

the first subset of read operations are performed after the testing for the first condition and prior to the testing for the second condition;

the second subset of read operations are performed after the testing for the second condition and testing for the third condition, the second set of read operations are performed before the testing for the fourth condition; and

the third subset of read operations are performed after the testing for the fourth condition.

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

the group of read operations includes testing for a first condition of the neighbor non-volatile storage element, testing for a second condition of the neighbor non-volatile storage element, and testing for a third condition of the neighbor non-volatile storage element;

the neighbor non-volatile storage element is capable of being in a fourth condition;

the set of read operations includes a first subset of read operations and a second subset of read operations;

the first subset of read operations includes multiple read operations that apply a first voltage to the neighbor non-volatile storage element, the first voltage is associated with the first condition and the fourth condition;

the second subset of read operations includes multiple read operations that apply a second voltage to the neighbor non-volatile storage element, the second voltage is associated with the second condition and the third condition;

the first subset of read operations are performed after the testing for the first condition and prior to the testing for the second condition; and

the second subset of read operations are performed after the testing for the second condition and testing for the third condition.

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

the group of read operations includes testing for a first condition of the neighbor non-volatile storage element, testing for a second condition of the neighbor non-volatile storage element, testing for a third condition of the neighbor non-volatile storage element and testing for a fourth condition of the neighbor non-volatile storage element;

the first set of read operations includes a first read operation, a second read operation and a third read operation;

the first read operation includes applying a first voltage to the neighbor non-volatile storage element, the first voltage is associated with the first condition;

the second read operation includes applying a second voltage to the neighbor non-volatile storage element, the second voltage is associated with the second condition and the third condition;

the third read operation includes applying a third voltage to the neighbor non-volatile storage element, the third voltage is associated with the fourth condition;

the first read operation is performed after the testing for the first condition and prior to the testing for the second condition;

the second read operation is performed after the testing for the second condition and testing for the third condition, the second read operation is performed before the testing for the fourth condition; and

the third read operation is are performed after the testing for the fourth condition.

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

the one or more managing circuits include any one or combination of power control circuitry, address decoder circuits, a state machine circuit, a controller circuit and read/write circuits; and

the group of read operations are started prior to starting the set of read operations.

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

the set of non-volatile storage elements are multi-state flash memory devices.

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

the set of non-volatile storage elements are multi-state NAND flash memory devices.

15. A non-volatile storage system, comprising:

a set of non-volatile storage elements including a first non-volatile storage element and a second non-volatile storage element; and

means for reading data from the first non-volatile storage element in response to a particular request to read the data, comprising;

means for performing a first set of read operations on the first non-volatile storage element, at least a subset of the first set of read operations apply different voltages to a second non-volatile storage element,

means for performing a second set of read operations on the second non-volatile storage element, the second set of read operations are at least partially temporally intermixed with the first set of read operations,

means for choosing information from a subset of the first set of read operations based on the second set of read operations, and

means for reporting data in the first non-volatile storage element based on the chosen information.

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

each of the different voltages is associated with a different condition of the second non-volatile storage element.

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

at least one of the second set of read operations is performed prior to the first set of read operations.

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

the first non-volatile storage element and the second non-volatile storage element are part of a NAND string that includes other non-volatile storage elements;

at least one read operation of the first set of read operations applies a read compare voltage to the first non-volatile storage element, a first overdrive voltage to the second non-volatile storage element and a second overdrive voltage to the other non-volatile storage elements;

at least another read operation of the first set of read operations applies the read compare voltage to the first non-volatile storage element, a third overdrive voltage to the second non-volatile storage element and the second overdrive voltage to the other non-volatile storage elements; and

the first overdrive voltage is different than the second overdrive voltage.

19. A non-volatile storage system, comprising:

a group of non-volatile storage elements including a first set of non-volatile storage elements and a second set of non-volatile storage elements; and

one or more managing circuits in communication with the group of non-volatile storage elements, the one or more managing circuits test the second set of non-volatile storage elements for a first condition and test the second set of non-volatile storage elements for a second condition, the one or more managing circuits perform a first set of one or more read operations for the first set of non-volatile storage elements while applying a first voltage to the second set of non-volatile storage elements, the first voltage is associated with the first condition, the one or more managing circuits perform a second set of one or more read operation for the first set of non-volatile storage elements while applying a second voltage to the second set of non-volatile storage elements, the second voltage is associated with the second condition, the first set of one or more read operations is performed after the one or more managing circuits test for the first condition and before the one or more managing circuits test for the second condition, the second set of one or more read operations is performed after the one or more managing circuits test for the second condition, the one or more managing circuits identify data based on the first set of one or more read operations for non-volatile storage elements of the first set of non-volatile storage elements that are next to non-volatile storage elements of the second set of non-volatile storage elements having the first condition, the one or more managing circuits identify data based on the second set of one or more read operations for non-volatile storage elements of the first set of non-volatile storage elements that are next to non-volatile storage elements of the second set of non-volatile storage elements having the second condition.

20. A non-volatile storage system according to claim 19, further comprising:

a first word line in communication with the one or more managing circuits and the first set of non-volatile storage elements;

a second word line in communication with the one or more managing circuits and the second set of non-volatile storage elements, the first set of non-volatile storage elements and the second set of non-volatile storage elements are in a block with other non-volatile storage elements;

other word lines in communication with the one or more managing circuits and the other non-volatile storage elements;

the one or more managing circuits assert a first set of read compare voltages on the first word line during the first set of read operations and during the second set of read operations;

the one or more managing circuits assert the first voltage on the second word line during the first set of read operations;

the one or more managing circuits assert the second voltage on the second word line during the second set of read operations; and

the one or more managing circuits assert a read overdrive voltage on the other word lines during the first set of read operations and during the second set of read operations.

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

the one or more managing circuits test the second set of non-volatile storage elements for a third condition after the second set of one or more read operations, the one or more managing circuits perform a third set of one or more read operation for the first set of non-volatile storage elements while applying a third voltage to the second set of non-volatile storage elements, the third voltage is associated with the second condition, the one or more managing circuits identify data based on the third set of one or more read operations for non-volatile storage elements of the first set of non-volatile storage elements that are next to non-volatile storage elements of the second set of non-volatile storage elements having the third condition.

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

the one or more managing circuits perform a fourth set of one or more read operation for the first set of non-volatile storage elements while applying a fourth voltage to the second set of non-volatile storage elements, the third voltage is associated with a fourth condition, the one or more managing circuits identify data based on the fourth set of one or more read operations for non-volatile storage elements of the first set of non-volatile storage elements that are next to non-volatile storage elements of the second set of non-volatile storage elements having the fourth condition.

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

the third condition corresponds to a single data state.

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

the third condition corresponds to two data states.

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

the group of non-volatile storage elements are multi-state NAND flash memory devices.