Nonvolatile memory system and operating method of memory controller

• US 9,355,738 B2
• Filed: 06/02/2015
• Issued: 05/31/2016
• Est. Priority Date: 06/09/2014
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Im, Jung Been
• Primary Examiner(s): NGUYEN, HIEN N
• Application Number:
  US14/728,345
• Publication Number:
  US 20150357043A1
• Time in Patent Office: 364 Days
• US Class Current: 1/1
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/28 using differential sensing or reference cells, e.g. dummy cells
• CPC Class Codes: G11C 16/32 Timing circuits
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data
• CPC Class Codes: G11C 16/3431 Circuits or methods to detect disturbed nonvolatile memory cells, e.g. which still read as programmed but with threshold less than the program verify threshold or read as erased but with threshold greater than the erase verify threshold, and to reverse the disturbance via a refreshing programming or erasing step
• CPC Class Codes: G11C 16/3459 Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 2211/5621 Multilevel programming verification

Abstract

An operating method of a memory controller configured to control a nonvolatile memory device including a plurality of memory cells is provided. The operating method includes: programming evaluation data into desired memory cells among the plurality of memory cells; performing initial verify shift (IVS) charge loss evaluation on the desired memory cells after a time elapses from a time point when the evaluation data is programmed, the IVScharge loss evaluation including an operation of detecting threshold voltage variation of the desired memory cells over a period based on the time elapsed from the time point when the evaluation data is programmed; and storing a result of the IVScharge loss evaluation; and adjusting levels of a plurality of read voltages used in the nonvolatile memory device based on the stored result of the charge loss evaluation.

Claims

1. An operating method of a memory controller configured to control a nonvolatile memory device including a plurality of memory cells, the operating method comprising:

programming evaluation data into desired memory cells among the plurality of memory cells;

performing charge loss evaluation on the desired memory cells after a time elapses from a time point when the evaluation data is programmed, the charge loss evaluation including an operation of detecting threshold voltage variation of the desired memory cells over a period based on the time elapsed from the time point when the evaluation data is programmed;

storing a result of the charge loss evaluation; and

adjusting levels of a plurality of read voltages used in the nonvolatile memory device based on the stored result of the charge loss evaluation.

2. The operating method as set forth in claim 1, wherein the charge loss evaluation is periodically performed.

3. The operating method as set forth in claim 1, wherein the storing the result of the charge loss evaluation includes:

storing a physical address of the desired memory cells, the time elapsed from the time point when the evaluation data is programmed, and the detected threshold voltage variation.

4. The operating method as set forth in claim 1, wherein the evaluation data is set data such that the desired memory cells are programmed to have an uppermost program state among a plurality of program states of the plurality of memory cells.

5. The operating method as set forth in claim 1, wherein the storing the result of the charge loss evaluation includes:

storing a physical address of the desired memory cells and the time point when the evaluation data is programmed.

6. The operating method as set forth in claim 1, wherein performing the charge loss evaluation on the desired memory cells comprises:

reading the desired memory cells using a reference voltage,

detecting a number of on-cells of the desired memory cells based on a result of the reading the desired memory cells, and

detecting the threshold voltage variation based on the detected number of the on-cells.

7. The operating method as set forth in claim 1, wherein the performing the charge loss evaluation on the desired memory cells includes:

detecting the threshold voltage variation based on a change amount of a lower limit of threshold voltage distribution of the desired memory cells.

8. The operating method as set forth in claim 1, wherein the adjusting the levels of the read voltages includes:

selecting one of a plurality of sub-lookup tables based on the stored result of the charge loss evaluation, and

adjusting the levels of the read voltages based on the selected sub-lookup table, and

each of the sub-lookup tables includes information on the threshold voltage variation to program elapsed time and the levels of the read voltage.

9. The operating method as set forth in claim 1, further comprising:

detecting power-off elapsed time based on the stored result of the charge loss evaluation and the desired memory cells when power is on after off; and

restoring current time based on the detected power-off elapsed time.

10. A nonvolatile memory system comprising:

a nonvolatile memory device including a plurality of memory cells; and

a memory controller configured to program evaluation data into desired memory cells among the plurality of memory cells, perform charge loss evaluation on the desired memory cells in which the evaluation data is stored after a threshold time elapses from a time point when the evaluation data is programmed, and store a result of the charge loss evaluation in an charge loss evaluation table, the charge loss evaluation including an operation of detecting threshold voltage variation of the desired memory cells over a period based on the time elapsed from the time point when the evaluation data is programmed.

11. The nonvolatile memory system as set forth in claim 10, wherein the memory controller includes a memory, and the memory controller is configured to store the charge loss evaluation table in the memory.

12. The nonvolatile memory system as set forth in claim 11, wherein the result of the charge loss evaluation includes a physical address of the desired memory cells, a time elapsed from the time point when the evaluation data is programmed, and the detected threshold voltage variation.

13. The nonvolatile memory system as set forth in claim 11, wherein the charge loss evaluation table includes a physical address of the desired memory cells and the time point when the evaluation data is programmed.

14. The nonvolatile memory system as set forth in claim 11, wherein the memory includes a plurality of sub-lookup tables, the memory controller is configured to select one of the sub-lookup tables based on the stored result of the charge loss evaluation and adjust levels of a plurality of read voltages of the nonvolatile memory device based on the selected sub-lookup table, and each of the sub-lookup tables includes information on the threshold voltage variation to program elapsed time and the levels of the read voltages.

15. The nonvolatile memory system as set forth in claim 11, wherein the nonvolatile memory device comprises at least one three dimensional memory block,

wherein the at least one three dimensional memory block includes a plurality of strings connected between a bit line and a common source line, each of the plurality of strings including a plurality of memory cells connected in a series, each of the plurality of memory cells being connected to word lines stacked in a direction perpendicular to a substrate.

16. An method of operating a memory system including a controller configured to control a nonvolatile memory device, the nonvolatile memory device including a plurality of memory cells, the operating method comprising:

performing charge loss evaluation on first memory cells among the plurality of memory cells, the first memory cells being programmed with evaluation data, after a time elapses from a time point when the first memory cells were programmed with evaluation data;

storing a result of the performing the charge loss evaluation on the first memory cells; and

controlling a read operation of the first memory cells based on the result of the performing the charge loss evaluation on the first memory cells.

17. The method of claim 16, wherein

the charge loss evaluation includes detecting threshold voltage changes of the first memory cells over a time period, and

the controlling the read operation of the first memory cells includes adjusting read voltage levels applied to the first memory cells during the read operation based on the result of the performing the charge loss evaluation on the first memory cells.

18. The method of claim 16, further comprising:

performing at least one subsequent charge loss evaluation on the first memory cells after the performing charge loss evaluation, the charge loss evaluation and the at least one subsequent charge loss evaluation including detecting threshold variation changes in the first memory cells over time periods determined based on the time point when the evaluation data is programmed in the first memory cells and when the charge loss evaluation and the at least one subsequent charge loss evaluation are performed;

storing a result of the performing at least one subsequent charge loss evaluation on the first memory cells; and

adjusting read voltage levels applied to the first memory cells during the read operation after the at least one subsequent charge loss evaluation based on the result of the performing at least one subsequent charge loss evaluation.

19. The method of claim 16, further comprising:

selecting one of a plurality of sub-lookup tables based on the stored result of the performing the charge loss evaluation on the first memory cells,

wherein each of the sub-lookup tables includes information on the threshold voltage variation to program elapsed time and the levels of the read voltage, and

the controlling the read operation of the first memory cells includes adjusting the levels of the read voltages applied to the first memory cells based on the information in the selected sub-lookup table.

20. The method of claim 16, further comprising:

programming evaluation data into second memory cells among the plurality of memory cells during the performing charge loss evaluation on the first memory cells;

performing charge loss evaluation on the first memory cells and the second memory cells after the time elapses from a time point when the evaluation data is programmed into the second memory cells;

storing a result of the performing charge loss evaluation on the first memory cells and the second memory cells;

controlling the read operation of the first memory cells and a read operation of the second memory cells based on the result of the performing charge loss evaluation on the first memory cells and the second memory cells.