Memory, memory controller, memory system, method of memory, memory controller and memory system

• US 9,613,687 B2
• Filed: 01/03/2014
• Issued: 04/04/2017
• Est. Priority Date: 02/06/2013
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Kyungryun, Yoon, Sangyong
• Primary Examiner(s): Tabone, Jr., John J
• Application Number:
  US14/147,063
• Publication Number:
  US 20140223246A1
• Time in Patent Office: 1,187 Days
• Field of Search: 714718, 714768, 36518511, 36518517, 36518524, 365222, 36518505, 36518533, 36523001, 36523317, 365236, 711E12008, 711103, 711105, 711166, 711167
• CPC Class Codes: G06F 11/1012 using codes or arrangements adapted for a specific type of error G06F11/1048 takes precedence
• CPC Class Codes: G06F 11/1048 using arrangements adapted for a specific error detection or correction feature
• 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 16/3427 Circuits or methods to prevent or reduce disturbance of the state of a memory cell when neighbouring cells are read or written
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 2211/5644 Multilevel memory comprising counting devices
• CPC Class Codes: G11C 29/028 with adaption or trimming of parameters
• CPC Class Codes: H03M 13/373 with erasure correction and erasure determination, e.g. for packet loss recovery or setting of erasures for the decoding of Reed-Solomon codes
• CPC Class Codes: H10B 43/20 characterised by three-dimensional arrangements, e.g. with cells on different height levels

Abstract

In one embodiment, the method includes performing a read operation on a memory, and determining, by a memory controller, whether to perform a reliability verification read operation based on a count value and a reference value. The count value is based on a number of read commands issued by the memory controller to the memory, and the reliability verification read operation is for reading data from at least one memory cell associated with at least one unselected word line in the memory. An unselected word line is a word line not selected during the read operation. The method further includes performing the reliability verification read operation for the at least one unselected word line based on the determining.

Claims

1. A method of operating a memory controller, comprising:

performing a read operation on a memory;

comparing, by the memory controller, a count value with a reference value, the count value being based on a number of read commands issued by the memory controller to the memory;

performing a reliability verification read operation for at least one unselected word line of the memory to verify reliability of the memory when the count value reaches the reference value, the unselected word line being a word line not selected during the read operation; and

performing a read reclaim according to a result of the reliability verification read operation.

2. The method of claim 1, further comprising:

generating a random number as the reference value.

3. The method of claim 2, wherein the generating generates the random number such that an average of random numbers generated over time approaches a desired value.

4. The method of claim 2, wherein the reliability verification read operation is performed if the count value is greater than or equal to the random number.

5. The method of claim 4, further comprising:

resetting the count value if the reliability verification read operation is performed.

6. The method of claim 2, further comprising:

maintaining count values and random numbers for each of a plurality of blocks in the memory; and

wherein

the comparing uses the count value and the random number associated with the block to which the read operation is directed.

7. The method of claim 1, wherein the performing the reliability verification read operation performs the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation.

8. The method of claim 1, wherein the unselected word line is an open word line, and each of the at least one memory cell connected to the open word line is in an erased state.

9. The method of claim 1, wherein the performing the reliability verification read operation,

performs the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation, and

perform the reliability verification read operation for at least one open word line if any open word lines exist, and the at least one memory cell connected to the open word line is in an erased state.

10. The method of claim 1, wherein the performing the read reclaim comprises:

determining if the data read during the reliability verification read operation meets a condition; and

performing the read reclaim if the condition is met.

11. The method of claim 10, wherein the condition is if a bit error rate of the data read during the reliability verification read operation is greater than a threshold.

12. The method of claim 1, wherein the read reclaim copies data of a block including the selected word line to a new block and closes the block including a selected word line selected during the read operation.

13. The method of claim 1, further comprises:

performing a control operation if the result of the reliability verification read operation meets a condition,

wherein the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

14. The method of claim 13, wherein the control operation closes the block including a selected word line selected during the read operation.

15. The method of claim 1,

wherein the read reclaim is performed when the result of the reliability verification read operation indicates a low reliability.

16. A memory controller, comprising:

a counter configured to generate a count value based on a number of read commands issued by the memory controller to a memory;

a read controller configured to,

perform a read operation, and

perform a reliability verification read operation for at least one memory cells associated with at least one unselected word line in the memory to verify reliability of the memory when the count value reaches the reference value, wherein

the memory controller is configured to perform a read reclaim according to a result of the reliability verification read operation.

17. The memory controller of claim 16, further comprising:

a first register configured to store a desired value.

18. The memory controller of claim 17, further comprising:

a random number generator configured to generate a random number based on the desired value; and

wherein

the read controller is configured to determine whether to perform the reliability verification read operation using the random number as the reference value.

19. The memory controller of claim 17, further comprising:

a second register storing information about program/erase cycles of the memory; and

wherein

the memory controller is configured to change the desired value based on the information.

20. The memory controller of claim 16, wherein the counter is configured to rest the count value if the read controller determines to perform the reliability verification read operation.

21. The memory controller of claim 16, wherein

the counter is configured to maintain a respective count value for each of a plurality of blocks in the memory;

a random number generator is configured to maintain a respective random number for each of the plurality of blocks;

the read controller is configured to determine whether to perform the reliability verification read operation based on the respective count value and the respective random number associated with the block to which the read operation is directed, the respective random number serving as the reference value.

22. The memory controller of claim 16, wherein the read controller is configured to perform the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation.

23. The memory controller of claim 16, wherein the unselected word line is an open word line, and each of the at least one memory cell connected to the open word line are in an erased state.

24. The memory controller of claim 16, wherein the read controller is configured to,

perform the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation, and

perform the reliability verification read operation for at least one open word line if any open word lines exist, and the at least one memory cell connected to the open word line is in an erased state.

25. The memory controller of claim 16, wherein the read controller is configured to,

determine if the data read during the reliability verification read operation meets a condition, and

perform the read reclaim if the condition is met.

26. The memory controller of claim 25, wherein the condition is if a bit error rate of the data read during the read verification operation is greater than a threshold.

27. The memory controller of claim 16, wherein the read reclaim copies data of a block including a selected word line selected during the read operation to a new block and closes the block including the selected word line.

28. The memory controller of claim 16, wherein

the read controller is configured to perform a control operation if the result of the reliability verification read operation meets a condition, and

the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

29. The memory controller of claim 28, wherein the control operation closes the block including a selected word line selected during the read operation.

30. A memory system, comprising:

at least one memory; and

a memory controller configured to,

control the memory,

compare a count value and a reference value, the count value being based on a number of read operations performed by the memory controller on the memory, and

perform a reliability verification read operation for at least one memory cells associated with at least one unselected word line in the memory to verify reliability of the memory when the count value reaches the reference value, wherein

the memory controller is configured to perform a read reclaim according to a result of the reliability verification read operation.

31. The memory system of claim 30, wherein the memory is a non-volatile memory.

32. The memory system of claim 31, wherein the memory includes strings of memory cells, each string including a plurality of memory cells connected in series, and the plurality of memory cells in a string associated with different word lines.

33. The memory system of claim 30, wherein the memory controller is configured to generate a random number as the reference value.

34. The memory system of claim 33, wherein the memory controller is configured to generate the random number such that an average of random numbers generated over time approaches a desired value.

35. The memory system of claim 33, wherein the memory controller is configured to determine to perform the reliability verification read operation if the count value is greater than or equal to the random number.

36. The memory system of claim 35, wherein the memory controller is configured to reset the count value if the the reliability verification read operation is performed.

37. The memory system of claim 33, wherein

the memory controller is configured to maintain count values and random numbers for each of a plurality of blocks in the memory;

and

the memory controller is configured to use the count value and the random number associated with the block to which the read operation is directed.

38. The memory system of claim 30, wherein the memory controller is configured to perform the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation.

39. The memory system of claim 30, wherein the unselected word line is an open word line, and each of the at least one memory cell connected to the open word line are in an erased state.

40. The memory system of claim 30, wherein the memory controller is configured to,

perform the reliability verification read operation for the at least one unselected word line adjacent to a selected word line selected during the read operation, and

perform the reliability verification read operation for at least one open word line if any open word lines exist, and the at least one memory cell connected to the open word line are in an erased state.

41. The memory system of claim 30, the memory controller is configured to,

determine if the data read during the reliability verification read operation meets a condition, and

perform the read reclaim if the condition is met.

42. The memory system of claim 41, wherein the condition is if a bit error rate of the data read during the read verification operation is greater than a threshold.

43. The memory system of claim 30, wherein the read reclaim copies data of a block including the selected word line to a new block and closes the block including a selected word line selected during the read operation.

44. The memory system of claim 30, wherein

the memory controller is configured to perform a control operation if the result of the reliability verification read operation meets a condition, and

the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

45. The memory system of claim 44, wherein the control operation closes the block including the selected word line.

46. A method of operating a nonvolatile memory system, comprising:

performing a read operation on nonvolatile memory cells connected to a selected wordline in a selected block in a nonvolatile memory device;

comparing, by a memory controller, a count value with a reference value, the count value being based on a number of read commands issued by the memory controller to the nonvolatile memory;

performing a reliability verification read operation for the at least one unselected wordline of the nonvolatile memory device when the count value reaches the reference value to verify threshold voltage distributions of the selected block, the unselected wordline being a wordline not selected during the read operation and not programmed after an erase operation; and

closing the selected block according to a result of the reliability verification operation.

47. The method of claim 46, further comprising:

generating a random number as the reference value.

48. The method of claim 47, wherein the generating generates the random number such that an average of random numbers generated over time approaches a desired value.

49. The method of claim 47, wherein the reliability verification read operation is performed if the count value is greater than or equal to the random number.

50. The method of claim 49, further comprising:

resetting the count value if the reliability verification read operation is performed.

51. The method of claim 46, further comprising:

maintaining count values and random numbers for each of a plurality of blocks in the nonvolatile memory device; and

wherein

the comparing uses the count value and the random number associated with the selected block.

52. The method of claim 46, wherein the performing the reliability verification read operation performs the reliability verification read operation for the at least one unselected word line adjacent to the selected word line.

53. The method of claim 46, wherein the unselected word line is an open word line, and each of the nonvolatile memory cells connected to the open word line are in an erased state.

54. The method of claim 46, wherein the performing the reliability verification read operation,

performs the reliability verification read operation for the at least one unselected word line adjacent to the selected word line, and

performs the reliability verification read operation for at least one open word line if any open word lines exist, and nonvolatile memory cells connected to the open word line are in an erased state.

55. The method of claim 46, wherein the closing the selected block comprises:

determining if the threshold voltage distribution read during the reliability verification read operation meets a condition; and

closing the selected block if the condition is met.

56. The method of claim 55, wherein the condition is if a bit error rate of the threshold voltage distribution read during the read verification operation is greater than a threshold.

57. The method of claim 46, wherein the closing comprises preventing further program of the at least a portion of the nonvolatile memory device.

58. The method of claim 55, wherein the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

59. The method of claim 46, wherein the selected block is closed when the result of the reliability verification read operation indicates a low reliability.

60. A method of operating a nonvolatile memory system, comprising:

performing a read operation on nonvolatile memory cells connected to a selected wordline in a selected block in a nonvolatile memory device;

performing a reliability verification read operation to verify reliability of the selected block, the reliability verification read operation being an operation for reading data from at least one of the nonvolatile memory cells with at least one unselected wordline in the selected block, the unselected wordline being a wordline not selected during the read operation; and

performing a post-process for the selected block based on a result of the reliability verification read operation.

61. The method of claim 60, wherein the performing a reliability verification read operation performs the reliability verification read operation for the at least one unselected word line adjacent to the selected word line.

62. The method of claim 60, wherein the unselected word line is an open word line, and each of the nonvolatile memory cells connected to the open word line are in an erased state.

63. The method of claim 60, wherein the performing,

performs the reliability verification read operation for the at least one unselected word line adjacent to the selected word line, and

performs the reliability verification read operation for at least one open word line if any open word lines exist, and the nonvolatile memory cells connected to the open word line are in an erased state.

64. The method of claim 60, wherein the post-process is performed if a bit error rate of the data read during the read verification operation is greater than a threshold.

65. The method of claim 64, wherein the post-process copies data of a block including the selected word line to a new block and closes the block including the selected word line.

66. The method of claim 60, wherein the post-process is performed if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

67. The method of claim 66, wherein the post-process closes the selected block including the selected word line.