BIASING NON-VOLATILE STORAGE TO COMPENSATE FOR TEMPERATURE VARIATIONS

• US 20080158970A1
• 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 7,583,535 B2
• Time in Patent Office: Days
• US Class Current: 365/185.17
• CPC Class Codes: G11C 11/5621 using charge storage in a floating gate
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/3454 Arrangements for verifying correct programming or for detecting overprogrammed cells
• CPC Class Codes: G11C 2211/5644 Multilevel memory comprising counting devices
• CPC Class Codes: G11C 2211/565 Multilevel memory comprising elements in triple well structure
• CPC Class Codes: G11C 29/00 Checking stores for correct operation ; Subsequent repair; Testing stores during standby or offline operation
• CPC Class Codes: G11C 7/04 with means for avoiding disturbances due to temperature effects

Abstract

A body bias is applied to a non-volatile storage system to compensate for temperature-dependent variations in threshold voltage, sub-threshold slope, depletion layer width and/or 1/f noise. A desired bias level is set based on a temperature-dependent reference signal. In one approach, a level of the biasing can decrease as temperature increases. The body bias can be applied by applying a voltage to a p-well and n-well of a substrate, applying a voltage to the p-well while grounding the n-well, or grounding the body and applying a voltage to the source and/or drain of a set of non-volatile storage elements. Further, temperature-independent and/or temperature-dependent voltages can be applied to selected and unselected word lines in the non-volatile storage system during program, read or verify operations. The temperature-dependent voltages can vary based on different temperature coefficients.

Claims

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

biasing a substrate on which a set of non-volatile storage elements are formed, at least in part, the set of non-volatile storage elements are associated with a set of word lines, the biasing is temperature-dependent; and

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

2. The method of claim 1, wherein:

the operation comprises a read or verify operation which involves applying a temperature-independent voltage to the selected word line to determine a condition of the at least one non-volatile storage element.

3. The method of claim 2, wherein:

the operation involves applying temperature-independent voltages to unselected word lines of the set of word lines during the biasing.

4. The method of claim 1, wherein:

a level of the biasing decreases as temperature increases.

5. The method of claim 1, wherein:

the biasing is set to vary with temperature to compensate at least one temperature-varying characteristic of non-volatile storage elements of the set of non-volatile storage elements.

6. The method of claim 5, wherein:

the at least one temperature-varying characteristic comprises threshold voltage.

7. The method of claim 5, wherein:

the at least one temperature-varying characteristic comprises a sub-threshold slope.

8. The method of claim 5, wherein:

the at least one temperature-varying characteristic comprises depletion layer width.

9. The method of claim 5, wherein:

the at least one temperature-varying characteristic comprises 1/f noise.

10. 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.

11. The method of claim 1, wherein:

the biasing comprises applying a forward body bias.

12. The method of claim 1, wherein:

the biasing comprises applying a reverse body bias.

13. The method of claim 1, further comprising:

during the biasing, applying a temperature-independent voltage to at least one of a source side and a drain side of the set of non-volatile storage elements.

14. The method of claim 13, further comprising:

during the biasing, applying a temperature-dependent read or verify voltage to a selected word line of one or more non-volatile storage elements undergoing read or verify operations.

15. The method of claim 14, wherein:

the temperature-dependent read or verify voltage varies with temperature according to a first temperature coefficient; and

the temperature-dependent biasing varies with temperature according to a second temperature coefficient which differs from the first temperature coefficient.

16. The method of claim 13, further comprising:

during the biasing, applying temperature-dependent voltages to unselected word lines of the set of word lines.

17. The method of claim 16, wherein:

the temperature-dependent voltages applied to the unselected word lines vary with temperature according to a first temperature coefficient; and

the temperature-dependent biasing varies with temperature according to a second temperature coefficient which differs from the first temperature coefficient.

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

biasing a substrate on which a set of non-volatile storage elements are formed, at least in part, the set of non-volatile storage elements are associated with a set of word lines, the biasing comprises applying a temperature-dependent voltage 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, and a level of the temperature-dependent voltage is based on a desired bias level; and

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

19. The method of claim 18, further comprising:

grounding an n-well region of the substrate while applying the temperature-dependent voltage to the p-well region, the p-well region is provided in the n-well region.

20. The method of claim 18, wherein:

the temperature-dependent voltage is applied to an n-well region of the substrate while being applied to 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.

21. The method of claim 18, wherein:

the operation comprises a read or verify operation which involves applying a temperature-independent voltage to the selected word line to determine a condition of the at least one non-volatile storage element.

22. The method of claim 18, wherein:

the desired bias level decreases as temperature increases.

23. The method of claim 18, 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.

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

biasing a substrate on which a set of non-volatile storage elements are formed, at least in part, the set of non-volatile storage elements are associated with a set of word lines, the biasing comprises applying a temperature-independent voltage to the substrate, and applying a temperature-dependent voltage to at least one of a source side and a drain side of the set of non-volatile storage elements, a difference between the temperature-independent voltage and the temperature-dependent voltage is based on a desired bias level; and

during the biasing, performing an operation on at least one non-volatile storage element of the set of non-volatile storage elements.

25. The method of claim 24, wherein:

the biasing comprises applying the temperature-dependent voltage 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.

26. The method of claim 24, wherein:

the temperature-independent voltage comprises a ground voltage.

27. The method of claim 24, wherein:

the biasing comprises applying the temperature-independent voltage 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.

28. The method of claim 24, further comprising:

grounding an n-well region of the substrate while the temperature-independent 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, the p-well region is provided in the n-well region, and the n-well region is provided in a p-type substrate region.

29. The method of claim 24, wherein:

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

the operation comprises a read or verify operation which involves applying a temperature-independent voltage to the selected word line to determine a condition of the at least one non-volatile storage element.

30. The method of claim 24, wherein:

the desired bias level decreases as temperature increases.

31. The method of claim 24, 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.

32. The method of claim 24, further comprising:

during the biasing, applying a temperature-dependent read or verify voltage to a selected word line of one or more non-volatile storage elements undergoing read or verify operations.

33. The method of claim 32, wherein:

the temperature-dependent read or verify voltage varies with temperature according to a first temperature coefficient; and

the temperature-dependent voltage applied to the at least one of the source side and the drain side of the set of non-volatile storage elements varies with temperature according to a second temperature coefficient which differs from the first temperature coefficient.

34. The method of claim 24, further comprising:

during the biasing, applying temperature-dependent voltages to unselected word lines of the set of word lines.

35. The method of claim 34, wherein:

the temperature-dependent voltages applied to the unselected word lines vary with temperature according to a first temperature coefficient; and

the temperature-dependent voltage applied to the at least one of the source side and the drain side of the set of non-volatile storage elements varies with temperature according to a second temperature coefficient which differs from the first temperature coefficient.