Multilevel Variable Resistance Memory Cell Utilizing Crystalline Programming States

• US 20100027328A1
• Filed: 10/14/2009
• Published: 02/04/2010
• Est. Priority Date: 01/10/2005
• Status: Active Grant

• Current Assignee: Ovonyx Memory Technology, LLC (Micron Technology, Inc.)
• Original Assignee: Ovonyx Incorporated (Micron Technology, Inc.)
• Inventors: Czubatyj, Wolodymyr, Lowrey, Tyler, Schell, Carl, Dennison, Charles
• Granted Patent: US 8,363,446 B2
• Time in Patent Office: Days
• US Class Current: 365/163
• CPC Class Codes: G11C 11/56 using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency
• CPC Class Codes: G11C 11/5678 using amorphous/crystalline phase transition storage elements
• CPC Class Codes: G11C 13/0004 comprising amorphous/crystalline phase transition cells
• CPC Class Codes: G11C 13/0069 Writing or programming circuits or methods
• CPC Class Codes: G11C 2013/0092 Write characterized by the shape, e.g. form, length, amplitude of the write pulse

Abstract

A method of programming an electrical variable resistance memory device. When applied to variable resistance memory devices that incorporate a phase-change material as the active material, the method utilizes a plurality of crystalline programming states. The crystalline programming states are distinguishable on the basis of resistance, where the resistance values of the different states are stable with time and exhibit little or no drift. As a result, the programming scheme is particularly suited to multilevel memory applications. The crystalline programming states may be achieved by stabilizing crystalline phases that adopt different crystallographic structures or by stabilizing crystalline phases that include mixtures of two or more distinct crystallographic structures that vary in the relative proportions of the different crystallographic structures. The programming scheme incorporates at least two crystalline programming states and further includes at least a third programming state that may be a crystalline, amorphous or mixed crystalline-amorphous state.

Claims

1. A method of programming a variable resistance material comprising:

providing a variable resistance material;

a first programming step, said first programming step transforming said variable resistance material to a first crystalline programming state, said first crystalline programming state having a first resistance;

a second programming step, said second programming step transforming said variable resistance material to a second crystalline programming state, said second crystalline programming state having a second resistance; and

a third programming step, said third programming step transforming said variable resistance material to a third programming state, said third programming state having a third resistance.

2. The method of claim 1, wherein said variable resistance material is a phase-change material.

3. The method of claim 2, wherein said phase-change material comprises Sb, Te, As, Ga, Ge, or In.

4. The method of claim 1, wherein said variable resistance material is a chalcogenide material.

5. The method of claim 4, wherein said chalcogenide material comprises Te or Se.

6. The method of claim 5, wherein said chalcogenide material further comprises Ge, Sb, In, or As.

7. The method of claim 1, wherein said first crystalline programming state consists essentially of a first crystalline phase.

8. The method of claim 7, wherein said first single crystalline phase is cubic.

9. The method of claim 8, wherein said first single crystalline phase is face-centered cubic.

10. The method of claim 7, wherein said first single crystalline phase is hexagonal.

11. The method of claim 7, wherein said second crystalline programming state consists essentially of a second crystalline phase.

12. The method of claim 11, wherein said first crystalline phase is cubic and said second crystalline phase is hexagonal.

13. The method of claim 11, wherein said third programming state is a crystalline programming state.

14. The method of claim 13, wherein said third crystalline programming state comprises a third crystalline phase and a fourth crystalline phase.

15. The method of claim 14, wherein said third crystalline phase is said first crystalline phase.

16. The method of claim 15, wherein said fourth crystalline phase is said second crystalline phase.

17. The method of claim 13, wherein said third programming state consists essentially of a third crystalline phase.

18. The method of claim 11, wherein said third programming state is an amorphous or mixed crystalline-amorphous programming state.

19. The method of claim 7, wherein said second crystalline programming state comprises a second crystalline phase and a third crystalline phase.

20. The method of claim 19, wherein said second crystalline phase is said first crystalline phase.

21. The method of claim 19, wherein said third programming state is an amorphous or mixed crystalline-amorphous programming state.

22. The method of claim 19, wherein said third programming state comprises a fourth crystalline phase and a fifth crystalline phase.

23. The method of claim 22, wherein said fourth crystalline phase is said second crystalline phase.

24. The method of claim 23, wherein said fifth crystalline phase is said third crystalline phase.

25. The method of claim 7, wherein said third programming state is an amorphous or mixed crystalline-amorphous programming state.

26. The method of claim 7, wherein said third programming state is a crystalline programming state.

27. The method of claim 1, wherein said first crystalline programming state comprises a first crystalline phase and a second crystalline phase.

28. The method of claim 27, wherein said first crystalline phase is cubic.

29. The method of claim 27, wherein said first crystalline phase is hexagonal.

30. The method of claim 27, wherein said second crystalline programming state comprises a third crystalline phase and a fourth crystalline phase.

31. The method of claim 30, wherein said third crystalline phase is said first crystalline phase.

32. The method of claim 31, wherein said fourth crystalline phase is said second crystalline phase.

33. The method of claim 27, wherein said third programming state is an amorphous or mixed crystalline-amorphous programming state.

34. The method of claim 27, wherein said third programming state is a third crystalline programming state.

35. The method of claim 1, wherein said third programming state is a crystalline programming state

36. The method of claim 1, wherein said third programming state is an amorphous programming state.

37. The method of claim 1, wherein said third programming state is a mixed crystalline-amorphous programming state.

38. The method of claim 1, further comprising a fourth programming step, said fourth programming step transforming said variable resistance material to a fourth programming state, said fourth programming state having a fourth resistance.

39. The method of claim 38, wherein said fourth programming state is an amorphous programming state.

40. The method of claim 39, wherein said third programming state is a mixed crystalline-amorphous programming state.

41. The method of claim 1, wherein said first resistance is less than said second resistance and said second resistance is less than said third resistance.

42. The method of claim 41, wherein said first resistance increases to a fourth resistance within a first time period following said first programming step, said fourth resistance being less than said second resistance.

43. The method of claim 42, wherein said first time period is one year.

44. The method of claim 42, wherein said first time period is five years.

45. The method of claim 42, wherein said first time period is ten years.

46. The method of claim 42, wherein said second resistance spontaneously increases to a fifth resistance within said first time period following said second programming step, said fifth resistance being less than said third resistance.

47. The method of claim 46, wherein said first time period is one year.

48. The method of claim 46, wherein said first time period is five years.

49. The method of claim 46, wherein said first time period is ten years.

50. The method of claim 46, wherein said third programming state is a crystalline programming state.

51. A method of programming a variable resistance material comprising:

providing a variable resistance material;

a first programming step, said first programming step transforming said variable resistance material to a first crystalline programming state, said first crystalline programming state including a first crystalline phase and a second crystalline phase, said first crystalline programming state having a first resistance; and

a second programming step, said second programming step transforming said variable resistance material to a second crystalline programming state, said second crystalline programming state including a third crystalline phase and a fourth crystalline phase, said second crystalline programming state having a second resistance.

52. The method of claim 51, wherein said first crystalline phase is cubic.

53. The method of claim 52, wherein said second crystalline phase is hexagonal.

54. The method of claim 52, wherein said third crystalline phase is cubic

55. The method of claim 52, wherein said third crystalline phase is hexagonal.