Variable current sinking for coarse/fine programming of non-volatile memory

• US 7,002,843 B2
• Filed: 01/27/2004
• Issued: 02/21/2006
• Est. Priority Date: 01/27/2004
• Status: Expired due to Fees

• Current Assignee: SanDisk Technologies LLC (Western Digital Corporation)
• Original Assignee: SanDisk Corporation (Western Digital Corporation)
• Inventors: Mokhlesi, Nima, Guterman, Daniel C., Fong, Yupin
• Primary Examiner(s): TRAN, MICHAEL THANH
• Application Number:
  US10/766,786
• Publication Number:
  US 20050162924A1
• Time in Patent Office: 756 Days
• Field of Search: 365/185.03, 365/185.28
• US Class Current: 365/185.03
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• 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 16/3481 Circuits or methods to verify correct programming of nonvolatile memory cells whilst programming is in progress, e.g. by detecting onset or cessation of current flow in cells and using the detector output to terminate programming
• CPC Class Codes: G11C 27/005 with non-volatile charge storage, e.g. on floating gate or MNOS

Abstract

A non-volatile memory device is programmed by first performing a coarse programming process and subsequently performing a fine programming process. The coarse/fine programming methodology is enhanced by using an efficient verification scheme that allows some non-volatile memory cells to be verified for the coarse programming process while other non-volatile memory cells are verified for the fine programming process. The fine programming process can be accomplished using current sinking, charge packet metering or other suitable means.

Claims

1. An apparatus for programming, comprising:

a non-volatile storage element having a gate and two control terminals; and

a switchable current sinking device in communication with one of said control terminals, said switchable current sinking device provides a coarse current sink to said one of said control terminals if said non-volatile storage element is in a coarse programming mode and provides a fine current sink to said one of said control terminals if said non-volatile storage element is in a fine programming mode, said switchable current sinking device includes a first current sink unit that provides said coarse current sink, a second current sink unit that provides said fine current sink, and a switch for selecting either said first current sink unit or said second current sink unit.

2. An apparatus according to claim 1, further comprising:

a sense circuit in communication with said non-volatile storage element; and

a programming mode indication circuit providing an output indicating whether said non-volatile storage element is in said coarse programming mode or said fine programming mode based on said sense circuit, said switch is in communication with said programming mode indication circuit and switches between said first current sink unit or said second current sink unit based on information from said programming mode indication circuit.

3. An apparatus according to claim 1, wherein:

said two control terminals are bit lines.

4. An apparatus according to claim 1, wherein:

said one of said control terminals is a source terminal.

5. An apparatus according to claim 1, wherein:

said non-volatile storage element is a flash memory element.

6. An apparatus according to claim 1, wherein:

said non-volatile storage element is a multi-state flash memory element.

7. An apparatus for programming a non-volatile storage element, comprising:

a sense circuit in communication with said non-volatile storage element;

a programming mode indication circuit providing an output indicating whether said non-volatile storage element is in a coarse programming mode or a fine programming mode based on said sense circuit; and

a switchable current sinking device in communication with said programming mode indication circuit and said non-volatile storage element, said switchable current sinking device provides a coarse current sink to said non-volatile storage element if said non-volatile storage element is in said coarse programming mode and provides a fine current sink to said non-volatile storage element if said non-volatile storage element is in said fine programming mode.

8. An apparatus according to claim 7, further comprising:

a selection circuit in communication with said programming mode indication circuit and said sense circuit, said selection circuit provides a coarse reference signal to said sense circuit if said non-volatile storage element is in said coarse programming mode and provides a fine verification signal to said sense circuit if said non-volatile storage element is in said fine programming mode.

9. An apparatus according to claim 8, wherein:

said sense circuit compares either said coarse reference signal or said fine reference signal to data for said non-volatile storage element based on output from said program mode indication circuit to determine if said non-volatile storage element has reached a particular verification level.

10. An apparatus according to claim 9, wherein:

said programming mode indication circuit includes a storage unit, said storage unit stores data indicating whether said non-volatile storage element is in said coarse programming mode or said fine programming mode.

11. An apparatus according to claim 8, wherein:

said sense circuit includes electronic circuitry to perform a bit line discharge analysis to determine whether or not said non-volatile storage element meets a verification requirement.

12. An apparatus according to claim 7, wherein:

said coarse current sink is a greater current sink than said fine current sink.

13. An apparatus according to claim 7, wherein:

said switchable current sinking device includes a single current sink that can operate in two current sink modes.

14. An apparatus according to claim 7, wherein:

said switchable current sinking device includes a first current sink unit that provides said coarse current sink, a second current sink unit that provides said fine current sink, and a switch for selecting either said first current sink unit or said second current sink unit; and

said switch is in communication with said programming mode indication circuit and switches between said first current sink unit or said second current sink unit based on information from said programming mode indication circuit.

15. An apparatus according to claim 7, wherein:

said switchable current sinking device is in communication with a source terminal of said non-volatile storage element.

16. An apparatus according to claim 7, wherein:

said switchable current sinking device is in communication with a bit line of said non-volatile storage element.

17. An apparatus according to claim 7, wherein:

said switchable current sinking device is in communication with a control line of said non-volatile storage element.

18. An apparatus according to claim 7, wherein:

said non-volatile storage element is a flash memory element.

19. An apparatus according to claim 7, wherein:

said non-volatile storage element is a multi-state flash memory element.

20. An apparatus according to claim 19, wherein:

said switchable current sinking device provides different coarse current sinks for different states and provides different fine current sinks for different states.

21. An apparatus for programming non-volatile storage elements, comprising:

a programming circuit in communication with said non-volatile storage elements; and

one or more switchable current sink circuits in communication with said non-volatile storage elements, said one or more switchable current sink circuits cause a first subset of said non-volatile storage elements in a coarse programming phase to be subjected to a first current sink while concurrently a second subset of said non-volatile storage elements in a fine programming phase are subjected to a second current sink.

22. An apparatus according to claim 21, wherein:

said programming circuit provides a common steering signal to said non-volatile storage elements.

23. An apparatus according to claim 21, wherein for a particular non-volatile storage element, one of said switchable current sink circuits comprise:

a sense circuit in communication with said particular non-volatile storage element;

a programming mode indication circuit providing an output indicating whether said particular non-volatile storage element is in said coarse programming phase or said fine programming phase based on said sense circuit; and

a switchable current sinking device in communication with said programming mode indication circuit and said particular non-volatile storage element, said switchable current sinking device provides said first current sink to said particular non-volatile storage element if said particular non-volatile storage element is in said coarse programming phase and provides said second current sink to said particular non-volatile storage element if said particular non-volatile storage element is in said fine programming phase.

24. An apparatus according to claim 23, wherein:

said first current sink is a greater current sink than said second current sink.

25. An apparatus according to claim 23, wherein:

said switchable current sinking device includes a single current sink that can operate in two current sink modes.

26. An apparatus according to claim 23, wherein:

said non-volatile storage elements are flash memory elements.

27. An apparatus according to claim 23, wherein:

said non-volatile storage elements are multi-state flash memory elements.

28. An apparatus according to claim 21, wherein:

said one or more switchable current sink circuits includes one switchable current sink circuit per non-volatile storage element.

29. A method for programming, comprising:

performing a coarse programming phase for a non-volatile storage element, said coarse programming phase includes sinking a first current; and

switching to a fine programming phase for said non-volatile storage element by switching said sinking to a second current, wherein change in a threshold voltage of said non-volatile storage element is decreased during said fine programming phase in comparison to said coarse programming phase.

30. A method according to claim 29, further comprising:

determining whether a threshold voltage of said non-volatile storage element has reached a first verify level, said step of switching is commenced when said threshold voltage of said non-volatile storage element has reached said first verify level; and

determining whether said threshold voltage of said non-volatile storage element has reached a second verify level, said fine programming phase is completed when said threshold voltage of said non-volatile storage element has reached said second verify level.

31. A method according to claim 29, wherein:

said first current is greater than said second current.

32. A method according to claim 29, wherein:

said non-volatile storage element is a flash memory element.

33. A method according to claim 29, wherein:

said non-volatile storage element is a multi-state flash memory element.

34. A method for programming, comprising:

performing a coarse programming phase for multi-state non-volatile storage elements, said coarse programming phase includes sinking a first set of currents such that non-volatile storage elements being programmed to different states sink different currents of said first set of currents; and

switching to a fine programming phase for said non-volatile storage elements by switching said sinking to a second set of currents such that non-volatile storage elements being programmed to different states sink different currents of said second set of currents.

35. An apparatus for programming, comprising:

a multi-state non-volatile storage element having a gate and two control terminals; and

a switchable current sinking device in communication with one of said control terminals, said switchable current sinking device provides a coarse current sink to said one of said control terminals if said multi-state non-volatile storage element is in a coarse programming mode and provides a fine current sink to said one of said control terminals if said multi-state non-volatile storage element is in a fine programming mode, said switchable current sinking device provides different coarse current sinks to said one of said control terminals for different states and provides different fine current sinks to said one of said control terminals for different states.