Operating non-volatile memory with boost structures

• US 7,508,710 B2
• Filed: 11/13/2006
• Issued: 03/24/2009
• Est. Priority Date: 11/13/2006
• Status: Active Grant

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima
• Primary Examiner(s): Ho; Hoai V
• Application Number:
  US11/558,980
• Publication Number:
  US 20080112230A1
• Time in Patent Office: 862 Days
• Field of Search: 365/185.02, 365/185.05, 365/185.17, 365/185.18, 365/185.28, 365/185.31
• US Class Current: 365/185.17
• CPC Class Codes: G11C 16/10 Programming or data input circuits

Abstract

A method for operating non-volatile memory having boost structures. The boost structures are provided for individual NAND strings and can be individually controlled to assist in programming, verifying and reading processes. The boost structures can be commonly boosted and individually discharged, in part, based on a target programming state or verify level. The boost structures assists in programming so that the programming and pass voltage on a word line can be reduced, thereby reducing side effects such as program disturb. During verifying, all storage elements on a word line can be verified concurrently. The boost structure can also assist during reading. In one approach, the NAND string has dual source-side select gates between which the boost structure contacts the substrate at a source/drain region, and a boost voltage is provided to the boost structure via a source-side of the NAND string.

Claims

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

configuring a NAND string to receive a boost voltage, the NAND string comprising a plurality of storage elements, the NAND string formed, at least in part, on a substrate, a boost structure extending along the NAND string; and

applying the boost voltage to a first end of the NAND string, the boost voltage reaches the boost structure via a location along the NAND string at which the boost structure contacts the substrate.

2. The method of claim 1, wherein:

the boost voltage is applied to the first end of the NAND string via a source side select gate of the NAND string.

3. The method of claim 1, wherein:

the boost structure contacts the substrate at a source/drain region along the NAND string.

4. The method of claim 1, wherein:

the plurality of storage elements are arranged between;

(a) inner and outer select gates at the first end of the NAND string and (b) a second end of the NAND string, and the boost structure contacts the substrate at a source/drain region along the NAND string which is between the inner and outer select gates.

5. The method of claim 4, wherein:

the configuring comprises turning on the outer select gate and turning off the inner select gate.

6. The method of claim 1, wherein a voltage of the boost structure is boosted responsive to said applying step, the method further comprising:

applying an elevated voltage to word lines associated with the NAND string while the voltage of the boost structure is boosted.

7. The method of claim 6, wherein the plurality of storage elements are arranged between:

(a) inner and outer select gates at the first end of the NAND string and (b) a second end of the NAND string, the method further comprising;

turning off the inner and outer select gates while applying the elevated voltage.

8. The method of claim 6, further comprising:

discharging the boost structure, at least in part, during the applying of the elevated voltage.

9. The method of claim 8, wherein the plurality of storage elements are arranged between:

(a) the first end of the NAND string and (b) a select gate at a second end of the NAND string, and the discharging of the boost structure comprises turning on the select gate.

10. The method of claim 8, wherein:

the boost structure is discharged to a level which is based on a programming state to which at least one of the storage elements is to be programmed.

11. The method of claim 8, further comprising:

controlling a level to which the boost structure is discharged by controlling a level and/or duration of a voltage applied to a drain side of the NAND string.

12. The method of claim 8, wherein the boost structure is only partly discharged in the discharging step, the method further comprising:

applying a programming voltage to at least one of the storage elements while the boost structure is only partly discharged.

13. The method of claim 8, further comprising:

controlling a level to which the boost structure is discharged by controlling a level and/or duration of a voltage applied to a bit line at a drain side of the NAND string.