Alternate row-based reading and writing for non-volatile memory

• US 7,573,747 B2
• Filed: 10/31/2007
• Issued: 08/11/2009
• Est. Priority Date: 12/29/2005
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Guterman, Daniel C
• Primary Examiner(s): Dinh; Son
• Assistant Examiner(s): NGUYEN, NAM THANH
• Application Number:
  US11/933,348
• Publication Number:
  US 20080049506A1
• Time in Patent Office: 650 Days
• Field of Search: 365/185.18, 365/185.01, 365/189.01
• US Class Current: 365/185.18
• 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

Abstract

A set of storage elements is programmed beginning with a word line WLn adjacent a select gate line for the set. After programming the first word line, the next word line WLn+1 adjacent to the first word line is skipped and the next word line WLn+2 adjacent to WLn+1 is programmed. WLn+1 is then programmed. Programming continues according to the sequence {WLn+4, WLn+3, WLn+6, WLn+5, . . . } until all but the last word line for the set have been programmed. The last word line is then programmed. By programming in this manner, some of the word lines of the set (WLn+1, WLn+3, etc.) have no subsequently programmed neighboring word lines. The memory cells of these word lines will not experience any floating gate to floating gate coupling threshold voltage shift impact due to subsequently programmed neighboring memory cells. The word lines having no subsequently programmed neighbors are read without using offsets or compensations based on neighboring memory cells. The other word lines are read using compensations based on data states within both subsequently programmed neighboring word lines.

Claims

1. A method of reading non-volatile storage, comprising:

receiving a request for one or more pages of data stored in a block of non-volatile storage elements, the block includes a plurality of word lines, the one or more pages of data are stored in non-volatile storage elements in communication with a first subset of the plurality of word lines, the first subset includes a first word line and less than all of the word lines of the plurality;

reading one or more additional pages of data stored in the block in response to the request, wherein the one or more additional pages of data are stored in non-volatile storage elements in communication with a second subset of the plurality of word lines, the second subset includes a second word line adjacent to the first word line; and

reading the one or more requested pages of data stored in the block including reading storage elements of the first word line using offsets from a predetermined set of offsets based on charge levels of adjacent storage elements of the second word line and charge levels of adjacent storage elements of a third word line.

2. The method of claim 1, wherein reading the storage elements of the first word line includes:

for each storage element of the first word line, determining an offset from the predetermined set of offsets based on a charge level stored in a first adjacent non-volatile storage element of the second word line and a charge level stored in a second adjacent non-volatile storage element of the third word line; and

performing a set of read processes for the storage elements of the first word line, each read process of the set uses a different one of the offsets from the predetermined set of offsets and is performed on all of the storage elements of the first word line, each storage element of the first word line provides final data from an appropriate one of the read processes associated with the offset determined for the each storage element.

3. The method of claim 1, wherein one offset in the predetermined set of offsets is a zero offset corresponding to a first adjacent non-volatile storage element in an erased state and a second adjacent non-volatile storage element in the erased state.

4. The method of claim 1, wherein:

the third word line is part of the first subset of word lines;

reading the one or more requested pages of data includes reading the storage elements of the third word line and reading the storage elements of the first word line subsequent to reading the storage elements of the third word line; and

reading the one or more additional pages of data includes reading the storage elements of the second word line subsequent to reading the storage elements of the third word line and prior to reading the storage elements of the first word line.

5. The method of claim 1, wherein:

the third word line is part of the second subset of word lines;

reading the one or more additional pages of data includes reading the storage elements of the third word line prior to reading the storage elements of the first word line and prior to reading the storage elements of the second word line; and

reading the one or more requested pages of data includes reading the storage elements of the first word line after reading the storage elements of the second word line and after reading the storage elements of the third word line.

6. The method of claim 1, wherein:

the first subset includes an additional word line;

reading the one or more requested pages of data includes reading the storage elements of the additional word line without using offsets based on a charge level of adjacent storage elements.

7. The method of claim 1, further comprising:

providing the one or more requested pages of data; and

maintaining the one or more additional pages of data.

8. The method of claim 7, further comprising:

receiving a different request including the one or more additional pages of data;

providing the one or more additional pages of data in response to the different request using the maintained pages of data.

9. The method of claim 1, wherein a word line adjacent to a first select line for the block is WLn and a word line adjacent to word line WLn is word line WLn+1, the method further comprising, in response to a request for any data in the block:

reading data from the storage elements of word line WLn+1;

reading data from the storage elements of word line WLn after reading data from the storage elements of word line WLn+1;

reading data from the storage elements of each remaining word line of the block except for a last word adjacent to a second select line for the block after reading data from the storage elements of WLn+1, wherein reading data from the storage elements of each remaining word line is performed according to a word line sequence {WLn+3, WLn+2, WLn+5, WLn+4 . . . }.

10. The method of claim 9, wherein:

the first select line is a source select line.

11. The method of claim 9, wherein:

the first select line is a drain select line.

12. A method of reading data from a non-volatile memory array, comprising:

receiving a request for one or more pages of data stored in non-volatile storage elements associated with a first subset of word lines for a block of non-volatile storage elements;

reading one or more additional pages of data stored in non-volatile storage elements associated with a second subset of word lines for the block in response to the request;

reading the one or more requested pages, wherein reading non-volatile storage elements associated with a particular word line in the first subset includes using offsets from a predetermined set of offsets based on charge levels of non-volatile storage elements associated with a first adjacent word line and charge levels of non-volatile storage elements associated with a second adjacent word line;

providing the one or more requested pages of data; and

maintaining the one or more additional pages of data.

13. The method of claim 12, wherein reading the storage elements of the particular word line includes:

for each storage element of the particular word line, determining an offset from the predetermined set of offsets based on a charge level stored in a first non-volatile storage element of the first adjacent word line and a charge level stored in a second non-volatile storage element of the second adjacent word line; and

performing a set of read processes for the non-volatile storage elements associated with the first word line, each read process of the set uses a different one of the offsets from the predetermined set of offsets and is performed on all of the non-volatile storage elements of the first word line, each non-volatile storage element of the first word line provides final data from an appropriate one of the read processes associated with the offset determined for the each non-volatile storage element.

14. The method of claim 12, wherein reading the one or more requested pages includes:

reading non-volatile storage elements associated with a different word line in the first subset without using offsets based on a charge levels of storage elements associated with word lines adjacent to the different word line.

15. The method of claim 12, wherein the block of non-volatile storage elements is programmed according to a word line programming order that includes:

completing programming for a first word line WLn adjacent to a first select line for the block of storage elements;

completing programming for each remaining word line of the block except for a last word line of the block according to a word line sequence {WLn+2, WLn+1, WLn+4, WLn+3 . . . }, the last word line is adjacent to a second select line; and

completing programming for the last word line of the block.

16. The method of claim 12, wherein maintaining the one or more additional pages of data includes storing the one or more additional pages of data in a plurality of data latches for the memory array.

17. The method of claim 12, wherein maintaining the one or more additional pages of data includes storing the one or more additional pages of data in a controller in communication with the non-volatile memory array.

18. A method of programming a set of non-volatile storage elements in communication with a plurality of word lines, comprising:

programming non-volatile storage elements in communication with a first subset of word lines using a program voltage signal having a first plurality of program voltage pulses and a first step size; and

programming non-volatile storage elements in communication with a second subset of word lines using a program voltage signal having a second plurality of program voltage pulses and a second step size, wherein each word line of the second subset is adjacent to two word lines of the first subset and is programmed after programming is completed for each of the two word lines in the first subset to which it is adjacent, the second step size is larger than the first step size.

19. The method of claim 18, wherein:

the set of non-volatile storage elements includes a first select line and a second select line;

a first word line WLn of the plurality is adjacent to the first select line;

a last word line of the plurality is adjacent to the second select line; and

programming the set of non-volatile storage elements is performed according to a word line programming order that includes;

completing programming for the first word line WLn,

completing programming for each remaining word line except the last word line after completing programming for the first word line, wherein completing programming for each remaining word line is performed according a sequence {WLn+2, WLn+1, WLn+4, WLn+3, . . . }, and

completing programming for the last word line.

20. The method of claim 18, wherein:

programming the set of non-volatile storage elements is performed in response to a request to store a set of data in the set of non-volatile storage elements; and

completing programming of non-volatile storage elements in communication with a particular word line includes successfully verifying that a subset of the of the set of data to be programmed for the particular word line has been programmed for the particular word line, the subset of the set of data includes all data that is to be programmed for the particular word line in response to the request.

21. A method of programming a set of non-volatile storage elements coupled to a plurality of word lines, comprising:

completing programming of non-volatile storage elements in communication with a first word line that is adjacent to a first select line for the set of non-volatile storage elements;

completing programming of non-volatile storage elements in communication with a third word line that is adjacent to a second word line after completing programming for the first word line, the second word line is adjacent to the first word line, wherein programming the storage elements in communication with the third word line includes using a program voltage signal with a first step size; and

completing programming of non-volatile storage elements in communication with the second word line after completing programming for the third word line, wherein programming the non-volatile storage elements in communication with the second word line includes using a program voltage signal with a second step size.

22. The method of claim 21, wherein the second step size is larger than the first step size.

23. The method of claim 21, wherein:

the set of non-volatile storage elements is part of a NAND flash memory array.

24. The method of claim 23, wherein:

the set of non-volatile storage elements includes multi-state flash memory cells.