Read disturbance management in a non-volatile memory system

• US 7,937,521 B2
• Filed: 01/29/2008
• Issued: 05/03/2011
• Est. Priority Date: 01/29/2008
• Status: Active Grant

• Current Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Original Assignee: Cadence Design Systems Incorporated (Cadence Group)
• Inventors: Reid, Robert Alan
• Primary Examiner(s): SONG, HUA JASMINE
• Application Number:
  US12/022,146
• Publication Number:
  US 20090193174A1
• Time in Patent Office: 1,190 Days
• Field of Search: 711/100, 711/103, 711/165, 711/170, 711/E12.001, 711/12.008, 365/185.11
• US Class Current: 711/100
• CPC Class Codes: G06F 12/0246 in block erasable memory, e.g. flash memory
• CPC Class Codes: G06F 2212/7211 Wear leveling

Abstract

An invention is provided for read disturbance management in a non-volatile memory. The invention includes storing a read count data for a memory location in non-volatile memory. The read count data indicating an amount of read operations accessing the memory location since data was last written to the memory location. Then, when data is read from the memory location while the value of the read count data is less than a predetermined threshold value, the value of the read count data is incremented. However, when the value of the read count data equals the predetermined threshold value, the data is moved to a new memory location, thereby avoiding read disturbance effects.

Claims

1. A method for read disturbance management in a non-volatile memory which includes a plurality of memory blocks, comprising the operations of:

loading a block table from a single memory block of the non-volatile memory into system memory, the block table including a plurality of entries mapping a physical block address of the non-volatile memory to a logical block address of the non-volatile memory;

maintaining read count data in the block table for a non-volatile memory location, wherein the read count data indicates an amount of read operations accessing the memory location since data was last written to the memory location;

modifying a value of the read count data when data is read from the memory location while the amount of said read operations is less than a predetermined threshold value; and

moving the data to a new memory location when the value of the amount of said read operations is equal to the predetermined threshold value.

2. A method as recited in claim 1, wherein the memory location is a memory block that includes a plurality of pages, wherein the value of the read count data is modified when data is read from any page of the plurality of pages while the amount of said read operations is less than the predetermined threshold value.

3. A method as recited in claim 2, wherein the data stored in the entire memory block is moved to a new memory block when the amount of said read operations is equal to the predetermined threshold value.

4. A method as recited in claim 1, further comprising the operation of setting a value of the read count data associated with the memory location from which the data is moved and setting a value of the read count data associated with the new memory location.

5. A method as recited in claim 4, further comprising the operation of storing the block table in a single memory block of the non-volatile memory.

6. A method as recited in claim 1, wherein the read count data is stored in a counter.

7. A method as recited in claim 1, wherein the predetermined threshold value is less than a number of reads that can occur to a memory location of the non-volatile memory before read disturbance causes data changes in adjacent memory cells.

8. A method for read disturbance management in a non-volatile memory which includes a plurality of memory blocks, comprising the operations of:

loading a block table from a single memory block of the non-volatile memory into system memory, the block table including a plurality of entries mapping a physical block address of the non-volatile memory to a logical block address of the non-volatile memory and read count data associated with each memory block of the non-volatile memory, wherein the read count data indicates an amount of read operations accessing the associated memory block since data was last written to the memory block;

modifying a value of the read count data associated with a memory block when data is read from the associated memory block while the amount of said read operations is less than a predetermined threshold value; and

moving the data from the associated memory block to a new memory block when the amount of said read operations is equal to the predetermined threshold value.

9. A method as recited in claim 8, wherein each memory block includes a plurality of pages, and wherein the value of the read count data is modified when data is read from any page of the plurality of pages of the associated memory block while the amount of said read operations is less than the predetermined threshold value.

10. A method as recited in claim 9, wherein data stored in the entire memory block is moved to a new memory block when the amount of said read operations is equal to the predetermined threshold value.

11. A method as recited in claim 8, further comprising the operation of storing the block table in a single memory block of the non-volatile memory.

12. A method as recited in claim 11, further comprising the operation of loading the block table into system memory during power up.

13. A method as recited in claim 8, wherein the predetermined threshold value is less than a number of reads that can occur to a memory location of the non-volatile memory before read disturbance causes data changes in adjacent memory cells.

14. A block table for use with a non-volatile memory, comprising:

a plurality of entries corresponding to logical memory block addresses in a non-volatile memory; and

a plurality of read count data entries, each associated with a logical memory block address, each read count data entry indicating an amount of read operations accessing the associated logical memory block address since data was last written to the associated logical memory block address,

wherein a value of a read count data entry is modified when data is read from the associated logical memory block address while the amount of said read operations is less than a predetermined threshold value, and wherein data stored in the associated logical memory block address is moved to a new memory block when the amount of said read operations is equal to the predetermined threshold value.

15. A block table as recited in claim 14, further comprising a plurality of physical memory block addresses, wherein each physical memory block address is mapped to a particular logical memory block address.

16. A block table as recited in claim 14, further comprising a plurality of memory block status flags, wherein each memory block status flag indicates a status of an associated memory block.

17. A block table as recited in claim 14, further comprising a plurality of wear level indicators, each wear level indicator indicating a relative wear level of an associated memory block relative to other memory blocks of the non-volatile memory.

18. A block table as recited in claim 14, wherein the block table is stored in a single memory block of the non-volatile memory, and wherein the block table is loaded into system memory during power up.