MEMORY, MEMORY CONTROLLER, MEMORY SYSTEM, METHOD OF MEMORY, MEMORY CONTROLLER AND MEMORY SYSTEM

• US 20140223246A1
• Filed: 01/03/2014
• Published: 08/07/2014
• Est. Priority Date: 02/06/2013
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Kyungryun Kim, Sangyong Yoon
• Inventors: YOON, Sangyong, KIM, Kyungryun
• Granted Patent: US 9,613,687 B2
• Time in Patent Office: Days
• US Class Current: 714/718
• 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;

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 being based on a number of read commands issued by the memory controller to the memory, and the reliability verification read operation for reading data from at least one memory cell associated with at least one unselected word line in the memory, the unselected word line being a word line not selected during the read operation; and

performing the reliability verification read operation for the at least one unselected word line based on the determining.

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 determining determines to perform the reliability verification read operation 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 determining determines to perform the reliability verification read operation.

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

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

9. The method of claim 1, wherein the performing performs the reliability verification read operation for 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 memory cells connected to the open word line are in an erased state.

10. The method of claim 1, further comprising:

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

performing a control operation 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 read verification operation is greater than a threshold.

12. The method of claim 11, wherein the control operation copies data of a block including the selected word line to a new block and closes the block including the selected word line.

13. The method of claim 10, 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 the selected word line.

15. 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, configured to determine whether to perform a reliability verification read operation based on the count value and a reference value, and the reliability verification read operation for reading data from at least one memory cell associated with at least one unselected word line in the memory, the unselected word line being a word line not selected during the read operation; and

the read controller configured to performing the reliability verification read operation for the at least one unselected word line based on the determination.

16. The memory controller of claim 15, further comprising:

a first register configured to store a desired value.

17. The memory controller of claim 16, 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.

18. The memory controller of claim 16, 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.

19. The memory controller of claim 15, wherein the counter is configured to rest the count value if the read controller determines to perform the reliability verification read operation.

20. The memory controller of claim 15, 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.

21. The memory controller of claim 15, wherein the read controller is configured to perform the reliability verification read operation for at least one unselected word line adjacent to the selected word line.

22. The memory controller of claim 15, wherein the unselected word line is an open word line, and each of the memory cells connected to the open word line are in an erased state.

23. The memory controller of claim 15, wherein the read controller is configured to perform the reliability verification read operation for 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 memory cells connected to the open word line are in an erased state.

24. The memory controller of claim 15, wherein the read controller is configured to determine if data read during the reliability verification read operation meets a condition, and to perform a control operation if the condition is met.

25. The memory controller of claim 24, wherein the condition is if a bit error rate of the data read during the read verification operation is greater than a threshold.

26. The memory controller of claim 25, wherein the control operation copies data of a block including the selected word line to a new block and closes the block including the selected word line.

27. The memory controller of claim 24, wherein the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

28. The memory controller of claim 27, wherein the control operation closes the block including the selected word line.

29. A memory system, comprising:

at least one memory; and

a memory controller configured to control the memory, the memory controller configured to determine whether to perform a reliability verification read operation based on 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 the reliability verification read operation for reading data from at least one memory cell associated with at least one unselected word line in the memory, the unselected word line being a word line not selected during a read operation; and

the memory controller configured to perform the reliability verification read operation for the at least one unselected word line based on the determining.

30. The memory system of claim 29, wherein the memory is a non-volatile memory.

31. The memory system of claim 30, 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.

32. The memory system of claim 29, wherein the memory controller is configured to generate a random number as the reference value.

33. The memory system of claim 32, 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.

34. The memory system of claim 32, 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.

35. The memory system of claim 34, wherein the memory controller is configured to reset the count value if the determining determines to perform the reliability verification read operation.

36. The memory system of claim 32, 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.

37. The memory system of claim 29, wherein the memory controller is configured to perform the reliability verification read operation for at least one unselected word line adjacent to the selected word line.

38. The memory system of claim 29, wherein the unselected word line is an open word line, and each of the memory cells connected to the open word line are in an erased state.

39. The memory system of claim 29, wherein the memory controller is configured to perform the reliability verification read operation for 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 memory cells connected to the open word line are in an erased state.

40. The memory system of claim 29, the memory controller is configured to determine if data read during the reliability verification read operation meets a condition, and to perform a control operation if the condition is met.

41. The memory system of claim 40, wherein the condition is if a bit error rate of the data read during the read verification operation is greater than a threshold.

42. The memory system of claim 41, wherein the control operation copies data of a block including the selected word line to a new block and closes the block including the selected word line.

43. The memory system of claim 40, wherein the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

44. The memory system of claim 43, wherein the control operation closes the block including the selected word line.

45. 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;

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 being based on a number of read commands issued by the memory controller to the nonvolatile memory, and the reliability verification read operation for reading threshold voltage distributions from at least one of the nonvolatile memory cells associated with at least one unselected wordline in the selected block, the unselected wordline being a wordline not selected during the read operation and not programmed after an erase operation; and

performing the reliability verification read operation for the at least one unselected wordline based on the determining.

46. The method of claim 45, further comprising:

generating a random number as the reference value.

47. The method of claim 46, wherein the generating generates the random number such that an average of random numbers generated over time approaches a desired value.

48. The method of claim 46, wherein the determining determines to perform the reliability verification read operation if the count value is greater than or equal to the random number.

49. The method of claim 48, further comprising:

resetting the count value if the determining determines to perform the reliability verification read operation.

50. The method of claim 45, further comprising:

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

wherein

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

51. The method of claim 45, wherein the performing performs the reliability verification read operation for at least one unselected word line adjacent to the selected word line.

52. The method of claim 45, 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.

53. The method of claim 45, wherein the performing performs the reliability verification read operation for 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.

54. The method of claim 45, further comprising:

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

performing a control operation if the condition is met.

55. The method of claim 54, wherein the condition is if a bit error rate of the data read during the read verification operation is greater than a threshold.

56. The method of claim 55, wherein the control operation copies data of a block including the selected word line to a new block and closes the block including the selected word line.

57. The method of claim 54, wherein the condition is if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

58. The method of claim 57, wherein the control operation closes the block including the selected word line.

59. 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, the reliability verification read 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

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

60. The method of claim 59, wherein the performing a reliability verification read operation performs the reliability verification read operation for at least one unselected word line adjacent to the selected word line.

61. The method of claim 59, 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.

62. The method of claim 59, wherein the performing performs the reliability verification read operation for 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.

63. The method of claim 59, wherein the determining determines to perform the post-process if a bit error rate of the data read during the read verification operation is greater than a threshold.

64. The method of claim 63, 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.

65. The method of claim 59, wherein the determining determines to perform the post-process if a number of off memory cells read during the reliability verification read operation is greater than a threshold.

66. The method of claim 65, wherein the post-process closes the block including the selected word line.