System for performing read operation on non-volatile storage with compensation for coupling

• US 20070206426A1
• Filed: 03/17/2006
• Published: 09/06/2007
• Est. Priority Date: 03/03/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima
• Granted Patent: US 7,436,733 B2
• Time in Patent Office: Days
• US Class Current: 365/189.70
• 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 16/26 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 2211/5621 Multilevel programming verification
• CPC Class Codes: G11C 7/02 with means for avoiding parasitic signals
• CPC Class Codes: H10B 69/00 Erasable-and-programmable ROM [EPROM] devices not provided for in groups H10B41/00 - H10B63/00, e.g. ultraviolet erasable-and-programmable ROM [UVEPROM] devices

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 adjacent floating gates (or other adjacent charge storing elements). The problem occurs most pronouncedly between sets of adjacent memory cells that have been programmed at different times. To account for this coupling, 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.

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 plurality of non-volatile storage elements, said one or more managing circuits read data from a selected non-volatile storage element connected to a selected word line by applying a read compare voltage to said selected word line, said one or more managing circuits apply a first pass voltage to a first set of unselected word lines while applying a second pass voltage to a neighbor unselected word line, said one or more managing circuits sense a condition of said selected non-volatile storage element in conjunction with said read compare voltage, said first pass voltage and said second pass voltage.

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

said one or more managing circuits sense information about non-volatile storage elements connected to said neighbor unselected word line and choose whether to use said second pass voltage based on said information about said neighbor non-volatile storage element

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

said one or more managing circuits sense information about a non-volatile storage element connected to said neighbor unselected word line and that is a neighbor to said selected non-volatile storage element;

said one or more managing circuits perform additional iterations of said applying said read compare voltage, applying said first pass voltage, applying said second pass voltage and sensing said condition, with varying said second pass voltage during different iterations; and

said one or more managing circuits determine data stored in said non-volatile storage element being read based on one of said iterations associated with said sensed information about said neighbor non-volatile storage element.

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

said one or more managing circuits sense said condition of said selected non-volatile storage element as part of a verify operation during a programming process for said selected non-volatile storage element.

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

said one or more managing circuits sense said condition of said selected non-volatile storage element as part of a read process.

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

said one or more managing circuits determine that a neighbor of said selected non-volatile storage element is programmed, said applying said second pass voltage is performed in response to said determining that said neighbor is programmed.

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

said selected non-volatile storage element includes data programmed with respect to a second grouping of data subsequent to writing to neighboring non-volatile storage elements for a first grouping of data.

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

said one or more managing circuits receive a request to read data, said sensing of said condition of said selected non-volatile storage element is performed as part of a read process in response to said request to read data; and

said one or more managing circuits report said data based on said sensing.

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

said one or more managing circuits receive a request to read data;

said one or more managing circuits read said data using a first read operation in response to said request;

said one or more managing circuits determine existence of an error associated with said data; and

said applying said read compare, applying said first pass, applying said second pass voltage to neighbor unselected word line and sensing said condition are performed to recover said data from said error in response to said determining existence of said error; and

said one or more managing circuits report said recovered data.

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

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

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

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

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 one or more managing circuits include any one or a combination of a state machine, decoders and sense amplifiers.

14. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements; and

one or more managing circuits in communication with said plurality of non-volatile storage elements, said one or more managing circuits apply a read voltage to a selected non-volatile storage element, said one or more managing circuits use a particular voltage for a neighbor of said selected non-volatile storage element based on a current state of said neighbor, said read voltage is applied to said selected non-volatile storage element and said particular voltage is applied to said neighbor during a read process, said one or more managing circuits sense a condition of said selected non-volatile storage element during said read process.

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

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

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

said using said particular voltage for a neighbor comprises applying multiple voltages to said neighbor, one of said multiple voltages is said particular voltage, said one or more non-volatile storage elements sense and store said condition of said selected non-volatile storage in response to said particular voltage.

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

said one or more managing circuits read said current condition of said neighbor prior to using said particular voltage for said neighbor.

said neighbor and said selected non-volatile storage element are multi-state flash memory devices;

said reading said current condition of said neighbor includes determining which state said neighbor is programmed to;

said using a particular voltage for said neighbor comprises applying multiple voltages to said neighbor including applying one voltage for each state said neighbor can be programmed to, one of said multiple voltages is said particular voltage, said particular voltage is associated with said state said neighbor is programmed to;

data sensed by said one or more managing circuits in response to voltages of said multiple voltages that are not associated with said state said neighbor is programmed to are discarded; and

said sensing said condition is performed by said one or more managing circuits in response to said particular voltage.

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

said selected non-volatile storage element is a multi-state flash memory device that stores at least two bits of data programmed into said selected non-volatile storage element using full sequence programming.

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

said selected non-volatile storage element is a multi-state flash memory device that stores at least two bits of data programmed into a first page and a second page;

said one or more managing circuits can program said selected non-volatile storage element to a first state, a second state, a third state or a fourth state;

a first compare level exists between said first state and said second state;

a second compare level exists between said second state and said third state;

a third compare level exists between said third state and said fourth state;

said of applying said read voltage, using said particular voltage and sensing are part of a process of reading said first page using said third compare point; and

said one or more managing circuits sense a condition of said selected non-volatile storage element in response to said first compare level without regard to said current condition of said neighbor.

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

said one or more managing circuits determine that said neighbor is programmed, said using said particular voltage for said neighbor is performed in response to said determining that said neighbor is programmed.

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

said selected non-volatile storage element is a multi-state flash memory device that stores at least two bits of data programmed into a first page and a second page;

said selected non-volatile storage element capable of being in a first state, a second state, a third state or a fourth state;

a first compare level exists between said first state and said second state;

a second compare level exists between said second state and said third state;

a third compare level exists between said third state and said fourth state;

said one or more managing circuits determine that data is to be read from said first page;

said using said particular voltage for said neighbor comprises applying two different voltages to said neighbor, one of said two different voltages is said particular voltage, said particular voltage is associated with said state said neighbor is programmed to and data sensed in response to voltages of said multiple voltages that are not associated with said state said neighbor is programmed to are discarded;

said read voltage corresponds to said second compare level; and

said sensing said condition is performed in response to said particular voltage and said second compare level.

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

said selected non-volatile storage element is a multi-state flash memory device that stores at least two bits of data programmed into a first page and a second page;

said selected non-volatile storage element capable of being in a first state, a second state, a third state or a fourth state;

three compare levels exist for reading including a first compare level, a second compare level and a third compare level;

said first compare level exists between said first state and said second state;

said read voltage corresponds to said first compare level said second compare level exists between said second state and said third state;

said third compare level exists between said third state and said fourth state;

said method further comprises determining that data is to be read from said second page;

said using said particular voltage for said neighbor comprises applying two different voltages to said neighbor for said three compare levels, one of said two different voltages is said particular voltage, said particular voltage is associated with said state said neighbor is programmed to;

said sensing a condition is performed in response to said first compare level and said particular voltage;

said one or more managing circuits sense said selected non-volatile storage element in response to said second compare level and said particular voltage, sense selected non-volatile storage element in response to said third compare level and said particular voltage, and determine data stored in said selected non-volatile storage element.

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

said one or more managing circuits program said selected non-volatile storage element with respect to a second grouping of data subsequent to programming neighbor non-volatile storage elements for a first grouping of data.

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

said one or more managing circuits perform said sensing of said condition of said selected non-volatile storage element in response to a request to read.

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

said one or more managing circuits perform said sensing of said condition of said selected non-volatile storage element as part of a process to recover data.

26. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements, a first subset of said non-volatile storage elements connected to a first word line, a second subset of said non-volatile storage elements connected to a second word line, additional subsets of said non-volatile storage elements connected to additional word lines, said first word line is capable of being selected for reading, said second word line neighbors said first word line; and

one or more managing circuits are in communication with said plurality of non-volatile storage elements, said one or more managing circuits read data from said first subset of non-volatile storage elements by reading condition information from said second set of non-volatile storage elements and performing at least two read processes for said first subset of said non-volatile storage elements, each of said at least two read processes includes applying a different voltage to said second word line, for each of said first subset of said non-volatile storage elements said one or more managing circuits select respective data from a subset of said read processes based on said condition information for a respective neighbor in said second set of non-volatile storage elements, at least one of said at least two read processes includes applying a voltage to said second word line that is different than a voltage concurrently applied to said additional word lines.

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

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

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

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

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

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

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

said at least two read processes includes four read processes including a first read process, a second read process, a third read process and a fourth read process;

said first read process includes applying a read compare voltage to said first word line, applying a first pass voltage to said second word line, and applying said first pass voltage to said additional word lines;

said second read process includes applying said read compare voltage to said first word line, applying a second pass voltage to said second word line, and applying said first pass voltage to said additional word lines;

said third read process includes applying said read compare voltage to said first word line, applying a third pass voltage to said second word line, and applying said first pass voltage to said additional word lines; and

said fourth read process includes applying said read compare voltage to said first word line, applying a fourth pass voltage to said second word line, and applying said first pass voltage to said additional word lines.

31. A method for reading data from non-volatile storage, comprising:

a plurality of non-volatile storage elements, a first subset of said non-volatile storage elements connected to a first word line, a second subset of said non-volatile storage elements connected to a second word line, additional subsets of said non-volatile storage elements connected to additional word lines, said first word line is capable of being selected for reading, each of said first subset of non-volatile storage elements has a corresponding neighbor in said second subset of non-volatile storage elements; and

one or more managing circuits are in communication with said plurality of non-volatile storage elements, said one or more managing circuits read data from said first subset of non-volatile storage elements by reading condition information from said second set of non-volatile storage elements and performing at least a first read process and a second read process for said first subset of said non-volatile storage elements,

said condition information indicates at least a first condition or a second condition,

said first read process includes applying a first voltage to said first word line, applying a second voltage to said second word line and applying a third voltage to said additional word lines,

said second read process includes applying said first voltage to said first word line, applying a fourth voltage to said second word line and applying said third voltage to said additional word lines,

for each of said first subset of non-volatile storage elements, data is reported from said first read process if its corresponding neighbor was in said first condition and data is reported from said second read process if its corresponding neighbor was in said second condition.

32. A non-volatile storage system according to claim 31, wherein:

said one or more managing circuits perform a third read process and a fourth read process for said first subset of said non-volatile storage elements;

said third read process includes applying said first voltage to said first word line, applying a fifth voltage to said second word line and applying said third voltage to said additional word lines;

said fourth read process includes applying said first voltage to said first word line, applying a sixth voltage to said second word line and applying said third voltage to said additional word lines;

said condition information is capable of indicating a third condition or a fourth condition; and

for each of said first subset of non-volatile storage elements, data is reported from said third read process if its corresponding neighbor was in said third condition and data is reported from said fourth read process if its corresponding neighbor was in said fourth condition.

33. A non-volatile storage system according to claim 32, wherein:

said fourth condition corresponds to an erased state; and

said first condition, said second condition and said third condition correspond to programmed states.

34. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements; and

one or more managing circuits in communication with said plurality of non-volatile storage elements, said one or more managing circuits provide a compare voltage to a selected non-volatile storage element, sense a condition of a non-volatile storage element neighboring said selected non-volatile storage element, provide compensation to said non-volatile storage element neighboring said selected non-volatile storage element based on said condition, and sense data for said a selected non-volatile storage element in response to said compare voltage and said compensation.