BIASING NON-VOLATILE STORAGE BASED ON SELECTED WORD LINE

• US 20080158976A1
• Filed: 12/30/2006
• Published: 07/03/2008
• Est. Priority Date: 12/30/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima, Sekar, Deepak Chandra
• Granted Patent: US 7,468,919 B2
• Time in Patent Office: Days
• US Class Current: 365/185.18
• 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 16/26 Sensing or reading circuits; Data output circuits

Abstract

A body bias is applied to a non-volatile storage system to compensate for performance variations which are based on the position of a selected word line which is associated with non-volatile storage elements undergoing program, read or verify operations. In one approach, the body bias increases when the selected word line is closer to a drain side of a NAND string than a source side. In another approach, the body bias varies when the selected word line is an end word line. In another approach, first or second body bias levels can be used when the selected word line is in a first or second group of word lines, respectively. The body bias reduces variations in threshold voltage levels and threshold voltage distributions which are based on the selected word line position. Gate-induced drain leakage (GIDL) is also reduced.

Claims

1. A method for operating non-volatile storage, comprising:

performing an operation on at least one non-volatile storage element of a set of non-volatile storage elements, the at least one non-volatile storage element is in communication with a selected word line of a set of word lines, the set of non-volatile storage elements is in communication with the set of word lines; and

biasing a substrate while performing the operation, the set of non-volatile storage elements are formed, at least in part, on the substrate, and a level of the biasing varies based on a position of the selected word line in the set of word lines.

2. The method of claim 1, wherein:

the level of the biasing increases when the selected word line is closer to a drain-side of the set of word lines.

3. The method of claim 1, wherein:

the level of the biasing varies based on whether or not the selected word line is an end word line in the set of word lines.

4. The method of claim 1, wherein:

the operation comprises a verify or read operation.

5. The method of claim 1, wherein:

the set of non-volatile storage elements are provided in at least one NAND string which is formed, at least in part, on the substrate.

6. The method of claim 1, wherein:

the biasing comprises applying a voltage to the substrate, a level of the voltage varies based on the position of the selected word line in the set of word lines.

7. The method of claim 6, wherein:

the voltage is applied to a p-well region of the substrate, the set of non-volatile storage elements are formed, at least in part, on the p-well region.

8. The method of claim 7, wherein:

the biasing further comprises grounding an n-well region of the substrate while applying the voltage to the p-well region, the p-well region is provided in the n-well region.

9. The method of claim 7, wherein:

the biasing further comprises applying the voltage to an n-well region of the substrate while applying the voltage to the p-well region, the p-well region is provided in the n-well region.

10. The method of claim 1, wherein:

the biasing comprises applying a voltage which is independent of the position of the selected word line in the set of word lines to the substrate, and applying a voltage which varies based on the position of the selected word line in the set of word lines to at least one of a source side and a drain side of the set of non-volatile storage elements.

11. The method of claim 10, wherein:

the voltage which is independent of the position of the selected word line in the set of word lines comprises a ground voltage.

12. The method of claim 10, further comprising:

applying the voltage which is independent of the position of the selected word line in the set of word lines concurrently to a p-well region of the substrate and to an n-well region of the substrate, the set of non-volatile storage elements are formed, at least in part, on the p-well region, the p-well region is provided in the n-well region, and the n-well region is provided in a p-type substrate region.

13. The method of claim 10, wherein:

the voltage which is independent of the position of the selected word line in the set of word lines is applied to a p-well region of the substrate, the set of non-volatile storage elements are formed, at least in part, on the p-well region.

14. The method of claim 13, further comprising:

grounding an n-well region of the substrate while applying the voltage which is independent of the position of the selected word line in the set of word lines to the p-well region, the p-well region is provided in the n-well region.

15. The method of claim 1, wherein:

the biasing comprises biasing the substrate at a first level when the selected word line is in a first group of multiple word lines of the set of word lines, and biasing the substrate at a second level when the selected word line is in a second group of multiple word lines of the set of word lines.

16. A method for operating non-volatile storage, comprising:

performing operations on non-volatile storage elements of a set of non-volatile storage elements, the non-volatile storage elements are in communication with a set of word lines, the performing operations comprises selecting one word line at a time from the set of word lines;

determining a desired bias level based on a position of a currently selected word line in the set of word lines; and

biasing the set of non-volatile storage elements according to the desired bias level while performing the operations.

17. The method of claim 16, wherein:

the biasing comprises biasing a substrate, the set of non-volatile storage elements are formed, at least in part, on the substrate.

18. The method of claim 16, wherein:

the desired bias level increases when the selected word line is closer to a drain-side of the set of word lines.

19. The method of claim 16, wherein:

the desired bias level varies based on whether or not the selected word line is an end word line in the set of word lines.

20. The method of claim 16, wherein:

the operations comprise at least one of a verify operation and a read operation.

21. The method of claim 16, wherein:

the set of non-volatile storage elements are provided in at least one NAND string which is formed, at least in part, on the substrate.

22. A method for operating non-volatile storage, comprising:

determining a condition of at least one non-volatile storage element in a set of non-volatile storage elements, the set of non-volatile storage elements are in communication with a set of word lines, the determining the condition comprises applying a voltage to a selected word line in the set of word lines, the selected word line is in communication with the at least one non-volatile storage element; and

biasing a substrate during the determining the condition, the set of non-volatile storage elements are formed, at least in part, on the substrate, and a level of the biasing is set based on a position of the selected word line in the set of word lines.

23. The method of claim 22, wherein:

the determining the condition involves at least one of a read and a verify operation.

24. The method of claim 22, wherein:

the level of the biasing increases when the selected word line is closer to a drain-side of the set of word lines.

25. The method of claim 22, wherein:

the desired bias level varies based on whether or not the selected word line is an end word line in the set of word lines.

26. The method of claim 22, wherein:

the set of non-volatile storage elements are provided in at least one NAND string which is formed, at least in part, on the substrate.