Non-volatile memory with dynamic multi-mode operation

• US 8,045,377 B2
• Filed: 12/10/2009
• Issued: 10/25/2011
• Est. Priority Date: 02/16/2007
• Status: Active Grant

• Current Assignee: Mosaid Technologies Incorporated (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Original Assignee: Mosaid Technologies Incorporated (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Inventors: Kim, Jin-Ki
• Primary Examiner(s): AUDUONG, GENE NGHIA
• Application Number:
  US12/635,280
• Publication Number:
  US 20100174854A1
• Time in Patent Office: 684 Days
• Field of Search: 365/185.01, 365/185.03, 365/185.11, 365/185.12, 365/185.17, 365/185.33
• US Class Current: 365/185.03
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7204 Capacity control, e.g. partitioning, end-of-life degradation
• CPC Class Codes: G06F 2212/7206 Reconfiguration of flash memory system
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/06 Auxiliary circuits, e.g. for writing into memory
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/349 Arrangements for evaluating degradation, retention or wearout, e.g. by counting erase cycles
• CPC Class Codes: G11C 16/3495 Circuits or methods to detect or delay wearout of nonvolatile EPROM or EEPROM memory devices, e.g. by counting numbers of erase or reprogram cycles, by using multiple memory areas serially or cyclically
• CPC Class Codes: G11C 2211/5641 Multilevel memory having cells with different number of storage levels
• CPC Class Codes: G11C 2211/5646 Multilevel memory with flag bits, e.g. for showing that a "first page" of a word line is programmed but not a "second page"

Abstract

A method and system for extending the life span of a flash memory device. The flash memory device is dynamically configurable to store data in the single bit per cell (SBC) storage mode or the multiple bit per cell (MBC) mode, such that both SBC data and MBC data co-exist within the same memory array. One or more tag bits stored in each page of the memory is used to indicate the type of storage mode used for storing the data in the corresponding subdivision, where a subdivision can be a bank, block or page. A controller monitors the number of program-erase cycles corresponding to each page for selectively changing the storage mode in order to maximize lifespan of any subdivision of the multi-mode flash memory device.

Claims

1. A method for extending life span of a NAND flash memory device, comprising:

receiving a programming instruction to program data in a subdivision configured in a first storage mode;

programming the data to a new subdivision if program/erase cycles corresponding to the subdivision is reached; and

,

converting the subdivision to a second storage mode.

2. The method of claim 1, wherein programming the data to the new subdivision is carried out before converting.

3. The method of claim 1, wherein programming includes comparing the program/erase cycles corresponding to the subdivision to a predetermined limit.

4. The method of claim 3, wherein programming includes programming the data to the subdivision if the program/erase cycles corresponding to the subdivision is less than the predetermined limit.

5. The method of claim 1, wherein converting includes changing storage mode data corresponding to the subdivision from the first storage mode to the second storage mode.

6. The method of claim 5, wherein the storage mode data includes a mode tag bit for identifying one of the first storage mode and the second storage mode of the subdivision.

7. The method of claim 6, wherein the mode tag bit is stored in an address mapping table.

8. The method of claim 6, wherein the mode tag bit is stored in the subdivision.

9. The method of claim 1, wherein the first storage mode is a multiple bit per cell (MBC) storage mode and the second storage mode is a single bit per cell (SBC) storage mode.

10. The method of claim 9, wherein converting includes resetting a counter for tracking SBC program/erase cycles of the subdivision.

11. The method of claim 9, further including reclaiming the subdivision configured for SBC storage for MBC storage.

12. The method of claim 11, wherein reclaiming includes determining if the subdivision can be reclaimed.

13. The method of claim 12, wherein determining includes comparing SBC program/erase cycles corresponding to the subdivision to a reclaim limit, and ending reclaiming if the SBC program/erase cycles reaches the reclaim limit.

14. The method of claim 13, further including determining a status of a lock bit corresponding to the subdivision if the SBC program/erase cycles corresponding to the subdivision is less than the reclaim limit.

15. The method of claim 14, further including changing storage mode data corresponding to the subdivision from the SBC storage mode to the MBC storage mode if the lock bit is not set.

16. The method of claim 15, further including setting the lock bit corresponding to the subdivision.

17. The method of claim 1, wherein the first storage mode is a single bit per cell (SBC) storage mode and the second storage mode is a multiple bit per cell (MBC) storage mode.

18. The method of claim 17, wherein converting the subdivision from the MBC storage mode to the SBC storage mode is prevented if a lock bit corresponding to the subdivision is set.

19. A method for storing data in a NAND flash memory device in either a first storage mode or a second storage mode, comprising:

a) receiving a command for programming the data in the second storage mode;

b) converting at least one subdivision of the NAND flash memory device from the first storage mode to the second storage mode when there are no available subdivisions configured to store the data in the second storage mode; and

c) programming the data to the at least one subdivision configured in the second storage mode.

20. The method of claim 19, wherein the NAND flash memory device is powered up to include the at least one subdivision configured in the first storage mode, and internal flash operations are executed in response to the command after the NAND flash memory device is powered up.

21. The method of claim 19, wherein the first storage mode is a multiple bit per cell (MBC) storage mode and the second storage mode is a single bit per cell (SBC) storage mode.

22. The method of claim 19, wherein programming further includes setting a mode tag corresponding to the at least one subdivision to a state indicative of the second storage mode.

23. The method of claim 19, wherein converting includes resetting a program/erase counter corresponding to the at least one subdivision.

24. The method of claim 19, wherein the command for programming the data in the second storage mode is provided in response to a predetermined criteria, the predetermined criteria being a specific profile of the data that includes a set of data file types.

25. The method of claim 19, wherein the at least one subdivision includes a block, the block having a predetermined number of pages.

26. The method of claim 19, wherein the at least one subdivision includes a page, and a predetermined number of the pages are included in a block.

27. The method of claim 19, wherein the first storage mode is a single bit per cell (SBC) storage mode and the second storage mode is a multiple bit per cell (MBC) storage mode.

28. The method of claim 27, wherein converting includes comparing an SBC program/erase counter corresponding to the at least one subdivision to a reclaim limit, and determining that the program/erase counter is less than the reclaim limit.

29. The method of claim 28, wherein converting further includes checking a state of a lock bit corresponding to the at least one subdivision if the SBC program/erase counter is less than the reclaim limit where the state of the lock bit indicates if the at least one subdivision has been previously converted from the MBC storage mode to the SBC storage mode, the at least one subdivision being converted from the MBC storage mode to the SBC storage mode if the state of the lock bit is false.

30. The method of claim 29, wherein the at least one subdivision is converted from the MBC storage mode to the SBC storage mode by changing a state of a mode tag corresponding to the at least one subdivision if the state of the lock bit is false, and setting the lock bit to true after the state of the mode tag is changed.