NON-VOLATILE STORAGE WITH BIAS BASED ON SELECTED WORD LINE

• US 20080159007A1
• 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 7,554,853 B2
• Time in Patent Office: Days
• US Class Current: 365/185.27
• CPC Class Codes: G11C 16/3418 Disturbance prevention or evaluation; Refreshing of disturbed memory data

Abstract

A non-volatile storage system in which a body bias is applied 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 non-volatile storage system, comprising:

a set of non-volatile storage elements formed, at least in part, on a substrate;

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

one or more control circuits in communication with the set of non-volatile storage elements, the one or more control circuits perform an operation on the at least one non-volatile storage element while biasing the substrate, a level of the biasing varies based on a position of the selected word line in the set of word lines.

2. The non-volatile storage system 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 non-volatile storage system 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 non-volatile storage system of claim 1, wherein:

the operation comprises a verify or read operation.

5. The non-volatile storage system 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 non-volatile storage system of claim 1, wherein:

the one or more control circuits bias the substrate by 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 non-volatile storage system 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 non-volatile storage system of claim 7, wherein:

the one or more control circuits bias the substrate by 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 non-volatile storage system of claim 7, wherein:

the one or more control circuits bias the substrate by 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 non-volatile storage system of claim 1, wherein:

the one or more control circuits bias the substrate by 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 non-volatile storage system 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 non-volatile storage system of claim 10, wherein:

the one or more control circuits apply 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 non-volatile storage system 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 non-volatile storage system of claim 13, wherein:

the one or more control circuits ground 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 non-volatile storage system of claim 1, wherein:

the one or more control circuits bias 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 bias 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 non-volatile storage system, comprising:

a set of non-volatile storage elements;

a set of word lines in communication with set of non-volatile storage elements;

one or more control circuits in communication with the set of non-volatile storage elements, the one or more control circuits perform operations on non-volatile storage elements of the set of non-volatile storage elements, 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 non-volatile storage system of claim 16, wherein:

the set of non-volatile storage elements are formed, at least in part, on a substrate; and

the one or more control circuits bias the set of non-volatile storage elements by biasing the substrate.

18. The non-volatile storage system 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 non-volatile storage system 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 non-volatile storage system of claim 16, wherein:

the operations comprises at least one of programming, verify and read operations.

21. The non-volatile storage system 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 non-volatile storage system, comprising:

a set of non-volatile storage elements formed, at least in part, on a substrate;

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

one or more control circuits in communication with the set of non-volatile storage elements, the one or more control circuits determine a programming condition of the at least one non-volatile storage element by applying a voltage to the selected word line and biasing the substrate at a level which is set based on a position of the selected word line in the set of word lines.

23. The non-volatile storage system of claim 22, wherein:

the one or more control circuits determining the programming condition via at least one of a read and a verify operation.

24. The non-volatile storage system 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 non-volatile storage system 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 non-volatile storage system 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.