Read operation for non-volatile storage that includes compensation for coupling

• US 20060221714A1
• Filed: 04/05/2005
• Published: 10/05/2006
• Est. Priority Date: 04/05/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Chen, Jian, Li, Yan
• Granted Patent: US 7,187,585 B2
• Time in Patent Office: Days
• US Class Current: 365/185.200
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• 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 16/3422 Circuits or methods to evaluate read or write disturbance in nonvolatile memory, without steps to mitigate the problem

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 compensate for this coupling, the read process for a given memory cell will take into account the programmed state of an adjacent memory cell.

Claims

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

receiving a request to read data from a first non-volatile storage element;

performing a read operation on a second non-volatile storage element in response to said request, said second non-volatile storage element adjacent said first non-volatile storage element, said second non-volatile storage element capable of storing data for multiple groupings of data;

determining a reference value for reading said first non-volatile storage element based on a subset of said groupings of data capable of being stored in said second non-volatile storage element; and

reading data stored in said first non-volatile storage element in response to said request using said reference value.

2. A method according to claim 1, wherein:

said multiple groupings of data include a lower page and an upper page.

3. A method according to claim 2, wherein:

determining a reference value includes reading upper page data for said second non-volatile storage element, said reference value is based on said upper page data and not on lower page data for said second non-volatile storage element.

4. A method according to claim 2, wherein determining a reference value and read data stored in said first non-volatile storage element include:

determining whether upper page data is programmed for said second non-volatile storage element;

reading data in said first non-volatile storage element with a first reference value that does not compensate for a floating gate coupling effect from said second non-volatile storage element if said upper page data is not programmed for said second non-volatile storage element;

determining whether upper page data for said second non-volatile storage element is programmed to a first subset of data states;

reading data in said first non-volatile storage element with said first reference if said upper page data for said second non-volatile storage element is not programmed to said first subset of data states; and

reading data in said first non-volatile storage element with said first reference plus an offset if said upper page data for said second non-volatile storage element is programmed to said first subset of data states.

5. A method according to claim 4, wherein:

said first non-volatile storage element is capable of storing data in four data states including a first data state, a second data state, a third data state and a fourth data state;

said first reference indicates a threshold voltage between said second data state and said third data state; and

said reading data in said first non-volatile storage element with said first reference plus an offset comprises;

applying a voltage corresponding to said first reference to a control gate for said first non-volatile storage element,

sensing conduction by said first non-volatile storage element,

applying a voltage corresponding to said first reference plus said offset to said control gate for said first non-volatile storage element,

sensing conduction by said first non-volatile storage element, and

storing an appropriate result.

6. A method according to claim 4, wherein:

said first non-volatile storage element is capable of storing data in four data states including a first data state, a second data state, a third data state and a fourth data state; and

said step of reading data stored in said first non-volatile storage element further includes performing read operations using a second reference value, said second reference value plus offset, a third reference value, and said third reference value plus offset.

7. A method according to claim 1, wherein:

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

8. A method according to claim 1, wherein:

said first non-volatile storage element is a multi-state NAND flash memory device.

9. A method according to claim 1, wherein:

said first non-volatile storage element includes a floating gate.

10. A method according to claim 1, wherein:

said first non-volatile storage element includes a dielectric region for storing charge.

11. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements including a first set of non-volatile storage elements and a second set of non-volatile storage elements adjacent to said first set of set of non-volatile storage elements, said first set of non-volatile storage elements and said second set of non-volatile storage elements store multiple groupings of data; and

one or more managing circuits in communication with said plurality of non-volatile storage elements, said one or more managing circuits read from said first set of non-volatile storage elements after first reading from said second set of non-volatile storage elements, said one or more managing circuits determine a reference value for reading said first non-volatile storage element based on a subset of said groupings of data capable of being stored in said second non-volatile storage element and subsequently read data stored in said first non-volatile storage element using said reference value.

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

said one or more managing circuits include a state machine, decoders and sense amplifiers.

13. A non-volatile storage system according to claim 12, wherein each of said sense amplifiers comprise:

a sense node in communication with a non-volatile storage element being read, said sensing amplifier measures current conduction at said sense node to sense data stored in said non-volatile storage element being read,

a first capacitive device connected to said sense node,

a second capacitive device selectively connected to said sense node, and

a selection circuit connected to said second capacitive device, said selection circuit receives an indication from an adjacent non-volatile storage element and selectively connects said second capacitive device to said sense node based on said indication from said adjacent non-volatile storage element.

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

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

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

said multiple groupings of data include lower pages and upper pages; and

said one or more managing circuits determine a reference value by reading upper page data of said second non-volatile storage element, said reference value is based on said upper page data and not on lower page data for said second non-volatile storage element.

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

said first set of non-volatile storage elements include a second grouping of data programmed subsequent to writing to adjacent non-volatile storage elements for a first grouping of data.

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

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

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

said plurality of non-volatile storage elements include dielectric regions for storing charge.

19. A method for reading data from a first set of non-volatile storage elements, comprising:

reading a flag associated with a second set of non-volatile storage elements, said second set of non-volatile storage elements are adjacent to said first set of non-volatile storage elements, said second set of non-volatile storage elements store multiple groupings of data, said flag indicates whether said one of said groupings has been programmed;

reading said data from said first set of non-volatile storage elements without compensating for a coupling between said first set of non-volatile storage elements and said second set of non-volatile storage elements if said flag indicates that said one of said groupings has not been programmed for said second set of non-volatile storage elements; and

reading said data from said first set of non-volatile storage elements with compensation for coupling between said first set of non-volatile storage elements and said second set of non-volatile storage elements if said flag indicates that said one of said groupings has been programmed.

20. A method according to claim 19, wherein:

said reading a flag includes reading a group of non-volatile storage elements and determining whether any of said group of non-volatile storage elements has data in a most programmed data state.

21. A method according to claim 19, further comprising:

communicating said data for said first set of non-volatile storage elements while reading additional data for additional non-volatile storage elements.

22. A method according to claim 19, wherein:

said multiple groupings of data include a first page and a second page; and

said flag indicates whether said second page has been programmed for said second set of non-volatile storage elements.

23. A method according to claim 22, wherein said reading said data from said first set of non-volatile storage elements with compensation comprises:

applying a first voltage to control gates for said first set of non-volatile storage elements;

sensing conduction of said first set of non-volatile storage elements;

applying said first voltage plus an offset to said control gates for said first non-volatile storage elements;

sensing conduction of said first set of non-volatile storage elements; and

storing an appropriate result of said two sensing steps.

24. A method according to claim 22, wherein

said first set of non-volatile storage elements are capable of storing data in four data states including a first data state, a second data state, a third data state and a fourth data state;

and

said reading said data from said first set of non-volatile storage elements with compensation comprises using a first reference, a first reference plus offset, a second reference, a second reference plus offset, a third reference, and a third reference plus offset.

25. A method according to claim 19, wherein:

said first set of non-volatile storage elements include a second grouping of data programmed subsequent to writing to adjacent non-volatile storage elements for a first grouping of data.

26. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements including a first set of non-volatile storage elements and a second set of non-volatile storage elements adjacent to said first set of set 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 a flag associated with said second set of non-volatile storage elements, said second set of non-volatile storage elements store multiple groupings of data, said flag indicates whether one of said groupings have been programmed for said second set of non-volatile storage elements, said one or more managing circuits read data from said first set of non-volatile storage elements using a first reference compare value if said flag indicates that said one of said groupings has not been programmed and reads said data from said first set of non-volatile storage elements using an offset to said first reference compare value if said flag indicates that said one of said groupings has been programmed.

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

said one or more managing circuits include a state machine, decoders and sense amplifiers.

28. A non-volatile storage system according to claim 26, wherein said one or more managing circuits includes sense amplifiers, each of said sense amplifiers comprise:

a sense node in communication with a non-volatile storage element being read, said sensing amplifier measures current conduction at said sense node to sense data stored in said non-volatile storage element being read,

a first capacitive device connected to said sense node,

a second capacitive device selectively connected to said sense node, and

a selection circuit connected to said second capacitive device, said selection circuit receives an indication from an adjacent non-volatile storage element and selectively connects said second capacitive device to said sense node based on said indication from said adjacent non-volatile storage element.

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

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

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

said multiple groupings of data includes a lower page and an upper page; and

said flag indicates whether said upper page for said second set of non-volatile storage elements has been programmed.

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

said plurality of non-volatile storage elements store data programmed with respect to a second grouping of data subsequent to writing to adjacent non-volatile storage elements for a first grouping of data.

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

programming a first non-volatile storage elements and a second set of non-volatile storage elements, said first set of non-volatile storage elements and said second set of non-volatile storage elements each store first and second groupings of data, said programming includes writing to a particular non-volatile storage element with respect to said second grouping of data subsequent to writing to adjacent non-volatile storage elements for said first grouping of data;

reading charge information from said second set of non-volatile storage elements; and

performing a read operation on said first set of non-volatile storage elements, said read operation uses a first compensation for non-volatile storage elements of said first set of non-volatile storage elements adjacent to non-volatile storage elements of said second set of non-volatile storage elements that have charge information read which provide a first indication and said read operation does not use said first compensation for non-volatile storage elements of said first set of non-volatile storage elements adjacent to non-volatile storage elements of said second set of non-volatile storage elements that have charge information read which does not provide said first indication.

33. A method according to claim 32, wherein:

said first grouping of data is a lower page and said second grouping of data is an upper page;

said first set of non-volatile storage elements stores lower page 0 and upper page 2; and

said second set of non-volatile storage elements stores lower page 1 and upper page 3.

34. A method according to claim 32, wherein:

said first grouping of data is a first page and said second grouping of data is a second page; and

said first indication indicates that a particular non-volatile storage element of said second set of non-volatile storage elements has its second page programmed.

35. A method according to claim 32, wherein:

said first compensation includes using an offset voltage to a normal read compare voltage applied to a word line connected to said first set of non-volatile storage elements.

36. A method according to claim 32, wherein:

said first compensation includes connecting a capacitor to a sense amplifier.

37. A method according to claim 32, wherein:

said first compensation includes reducing a source line bias.

38. A method according to claim 32, wherein:

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

39. A method for reading data from a first set of non-volatile storage elements, comprising:

performing a read operation on a second set of non-volatile storage elements, said second set of non-volatile storage elements are adjacent said first non-volatile storage element;

providing a predetermined demarcation current to discriminate between data stored in said first set of non-volatile storage elements;

sensing said first set of non-volatile storage elements in parallel during a first pass;

identifying those non-volatile storage elements having conduction currents higher than said predetermined demarcation current;

inhibiting conduction currents for those non-volatile storage elements having conduction currents higher than said predetermined demarcation current;

sensing said first set of non-volatile storage elements in parallel during a second pass;

storing and reporting data indicating a programmed value based on said sensing during said first pass for non-volatile storage elements of said first set of non-volatile storage elements adjacent to non-volatile storage elements of said second set of non-volatile storage elements that store information which does not provide a first indication; and

storing and reporting data indicating a programmed value based on said sensing during said second pass for non-volatile storage elements of said first set of non-volatile storage elements adjacent to non-volatile storage elements of said second set of non-volatile storage elements that store information which provide said first indication.

40. A method according to claim 39, wherein:

said second set of non-volatile storage elements store data for a first grouping and a second grouping;

said performing a read operation includes reading data for said second grouping; and

said first indication indicates that data for said second grouping is programmed.

41. A method according to claim 39, wherein:

said first set of non-volatile storage elements and said second set of non-volatile storage elements store data programmed with respect to a second grouping of data subsequent to programming adjacent non-volatile storage elements for a first grouping of data.

42. A method according to claim 39, wherein:

said second set of non-volatile storage elements store data for a first grouping and a second grouping;

said performing a read operation includes reading a flag indicating whether data for said second grouping has been programmed;

said performing a read operation is aborted if said flag is not in a first state; and

said second set of non-volatile storage elements do not store information which provide said first indication if said flag is not in said first state.

43. A method according to claim 39, wherein:

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

44. A non-volatile storage system, comprising:

a plurality of non-volatile storage elements;

one or more managing circuits in communication with said plurality of non-volatile storage elements; and

a set of sensing circuits in communication with said one or more managing circuits and said plurality of non-volatile storage elements, said sensing circuits sense data stored in said non-volatile storage elements, each of said sensing circuits comprise;

a sense node in communication with a non-volatile storage element being read, said sensing circuit measures current conduction at said sense node to sense data stored in said non-volatile storage element being read,

a first capacitive device selectively connected to said sense node, and

a selection circuit connected to said first capacitive device, said selection circuit receives an indication from an adjacent non-volatile storage element and selectively connects said first capacitive device to said sense node based on said indication from said adjacent non-volatile storage element.

45. A non-volatile storage system according to claim 44, wherein said sensing circuits further comprise a second capacitive device connected to said sense node.

46. A non-volatile storage system according to claim 44, wherein:

said adjacent non-volatile storage element stores data for a first grouping and a second grouping;

said one or more managing circuits cause a reading of said second grouping for said adjacent non-volatile storage element;

if said second grouping for said adjacent non-volatile storage element stores a first value then said first capacitive device is connected to said sense node; and

if said second grouping for said adjacent non-volatile storage element stores a second value then said first capacitive device is not connected to said sense node.

47. A non-volatile storage system according to claim 44, wherein:

said one or more managing circuits include a state machine.

48. A non-volatile storage system according to claim 44, wherein:

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