Current switched magnetoresistive memory cell

• US 6,744,086 B2
• Filed: 05/15/2002
• Issued: 06/01/2004
• Est. Priority Date: 05/15/2001
• Status: Expired

• Current Assignee: NVE Corporation
• Original Assignee: NVE Corporation
• Inventors: Daughton, James M., Tondra, Mark C., Pohm, Arthur V.
• Primary Examiner(s): Elms, Richard
• Assistant Examiner(s): Menz, Doug
• Application Number:
  US10/147,367
• Publication Number:
  US 20030007398A1
• Time in Patent Office: 748 Days
• Field of Search: 257/295, 257/421, 257/422, 257/424, 257/108, 365/158, 365/171, 365/173
• US Class Current: 257/295
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: H01F 1/408 half-metallic, i.e. having only one electronic spin direction at the Fermi level, e.g. CrO2, Heusler alloys H01F10/1936 takes precedence
• CPC Class Codes: H01F 10/1936 Half-metallic, e.g. epitaxial CrO2 or NiMnSb films
• CPC Class Codes: H01F 10/3268 the exchange coupling being asymmetric, e.g. by use of additional pinning, by using antiferromagnetic or ferromagnetic coupling interface, i.e. so-called spin-valve [SV] structure, e.g. NiFe/Cu/NiFe/FeMn
• CPC Class Codes: H01F 10/3272 by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets

Abstract

A ferromagnetic thin-film based digital memory cell with a memory film of an anisotropic ferromagnetic material and with a source layer positioned on one side thereof so that a majority of conduction electrons passing therefrom have a selected spin orientation to be capable of reorienting the magnetization of the film. A disruption layer is positioned on the other side of the memory film so that conduction electrons spins passing therefrom are substantially random in orientation. The magnitude of currents needed to operate the cell can be reduced using coincident thermal pulses to raise the cell temperature.

Claims

1. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:

a substrate; and

a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising;

a memory film of an anisotropic ferromagnetic material capable of conducting an electrical current therethrough;

a source layer positioned on one side of said memory film capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation; and

a disruption layer positioned on another side of said memory film capable of conducting an electrical current therethrough so that conduction electrons spins passing therefrom are substantially random in orientation.

2. The device of claim 1 further comprising an electrically insulative intermediate layer provided between said source layer and said memory film.

3. The device of claim 1 wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said disruption layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said disruption layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation.

4. The device of claim 1 wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof.

5. The device of claim 1 wherein said source layer is of a ferromagnetic material and further comprising a magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction.

6. The device of claim 3 further comprising a first electrically insulative intermediate layer provided between said first source layer and said first memory film, and a second electrically insulative intermediate layer provided between said second source layer and said second memory film.

7. The device of claim 3 further comprising a first electrically insulative intermediate layer provided between said first source layer and said first memory film, and a conductive intermediate layer provided between said second source layer and said second memory film.

8. The device of claim 3 wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction.

9. The apparatus of claim 5 wherein said magnetization reference layer comprises an antiferromagnetic layer.

10. The apparatus of claim 8 wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer.

11. The apparatus of claim 9 wherein said magnetization reference layer further comprises a reference ferromagnetic thin-film layer provide between said antiferromagnetic layer and said source layer but separated from said source layer by an antiparallel magnetization directing layer forcing those magnetizations of said reference ferromagnetic thin-film layer and said source layer to be oppositely directed.

12. The apparatus of claim 10 wherein said first magnetization reference layer farther comprises a first reference ferromagnetic thin-film layer provide between said first antiferromagnetic layer and said first source layer but separated from said first source layer by a first antiparallel magnetization directing layer forcing those magnetizations of said first reference ferromagnetic thin-film layer and said first source layer to be oppositely directed, and a second reference ferromagnetic thin-film layer provide between said second antiferromagnetic layer and said second source layer but separated from said second source layer by a second antiparallel magnetization directing layer forcing those magnetizations of said second reference ferromagnetic thin-film layer and said second source layer to be oppositely directed.

13. The device of claim 1 wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes.

14. The device of claim 2 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

15. The device of claim 2 wherein said source layer is of a ferromagnetic material and further comprising a magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction.

16. The device of claim 6 wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction.

17. The device of claim 6 wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω

-μ

m².

18. The device of claim 9 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

19. The device of claim 10 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

20. The device of claim 11 wherein said source layer and said reference ferromagnetic thin-film layer are of unequal thicknesses.

21. The device of claim 12 wherein said first source layer and said first reference ferromagnetic thin-film layer are of unequal thicknesses, and said second source layer and said second reference ferromagnetic thin-film layer are of unequal thicknesses.

22. The device of claim 15 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

23. The device of claim 16 wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω

-μ

m².

24. The device of claim 18 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.

25. The device of claim 19 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.

26. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:

a substrate; and

a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising;

an electrically insulative intermediate layer;

a source layer on one side of said insulative, intermediate layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation;

a memory film of an anisotropic ferromagnetic material on another side of said insulative intermediate layer capable of conducting an electrical current therethrough; and

an antiparallel maintenance layer adjacent to a ferromagnetic material layer together on a side of at least one of said source layer and said memory film across from said intermediate layer.

27. The device of claim 26 wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes.

28. The device of claim 26 wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said antiparallel maintenance layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said antiparallel maintenance layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation.

29. The device of claim 26 wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof.

30. The device of claim 26 wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction.

31. The device of claim 26 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

32. The device of claim 28 wherein said electrically insulative intermediate layer is a first electrically insulative intermediate layer, and further comprising a second electrically insulative intermediate layer provided between said second source layer and said second memory film.

33. The device of claim 28 wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction.

34. The apparatus of claim 30 wherein said magnetization reference layer comprises an antiferromagnetic layer.

35. The device of claim 30 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

36. The device of claim 32 wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω

-μ

m².

37. The device of claim 32 wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction.

38. The apparatus of claim 33 wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer.

39. The device of claim 34 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

40. The device of claim 37 wherein said first and second electrically insulative intermediate layers are sufficiently thin so as to each have a barrier resistance area product that is less than 2 Ω

-μ

m².

41. The device of claim 38 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

42. The device of claim 39 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.

43. The device of claim 41 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.

44. A ferromagnetic thin-film based digital memory cell, said memory cell comprising:

a substrate; and

a bit structure formed of a plurality of layers provided in a selected sequence between a pair of electrodes in electrical contact therewith at opposite ends of said sequence and supported on said substrate comprising;

an electrically conductive intermediate layer;

a source layer on one side of said conductive intermediate layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation;

a memory film of an anisotropic ferromagnetic material on another side of said conductive intermediate layer capable of conducting an electrical current therethrough, and

an antiparallel maintenance layer adjacent to a ferromagnetic material layer together on a side of at least one of said source layer and said memory film across from said intermediate layer.

45. The device of claim 44 wherein said substrate further comprises a monolithic integrated circuit structure containing electronic circuit components of which at least one is electrically connected to one of said electrodes.

46. The device of claim 44 wherein said source layer is a first source layer and said memory film is a first memory film, and further comprises a second memory film of an anisotropic ferromagnetic material positioned on an opposite side of said antiparallel maintenance layer from said first memory film and capable of conducting an electrical current therethrough, and a second source layer positioned on an opposite side of said second memory film from said antiparallel maintenance layer capable of conducting an electrical current therethrough so that a majority of conduction electrons passing therefrom have a selected spin orientation.

47. The device of claim 44 wherein a said memory film and said source layer have a length along a selected direction and a width substantially perpendicular thereto that is smaller in extent than said length and have a shaped end portion extending over a portion of said length in which said width gradually reduces to zero at that corresponding end thereof.

48. The device of claim 44 wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction.

49. The device of claim 46 further comprising an electrically insulative intermediate layer provided between said second source layer and said second memory film.

50. The device of claim 46 wherein said first and second source layers are of ferromagnetic materials and further comprising a first magnetization reference layer positioned at least in part on a side of said first source layer opposite said first memory film and resulting in said first source layer having a relatively fixed magnetization direction, and a second magnetization reference layer positioned at least in part on a side of said second source layer opposite said second memory film and resulting in said second source layer having a relatively fixed magnetization direction.

51. The apparatus of claim 48 wherein said magnetization reference layer comprises an antiferromagnetic layer.

52. The device of claim 49 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

53. The device of claim 49 wherein said source layer is of a ferromagnetic material and further comprising magnetization reference layer positioned at least in part on a side of said source layer opposite said memory film and resulting in said source layer having a relatively fixed magnetization direction.

54. The apparatus of claim 50 wherein said first magnetization reference layer comprises a first antiferromagnetic layer, and said second magnetization reference layer comprises a second antiferromagnetic layer.

55. The device of claim 51 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

56. The device of claim 53 wherein said electrically insulative intermediate layer is sufficiently thin so as to have a barrier resistance area product that is less than 2 Ω

-μ

m².

57. The device of claim 54 further comprising a plurality of memory cells including said memory cell and an electrical current conductor positioned across an insulating layer from said memory cell.

58. The device of claim 55 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.

59. The device of claim 57 wherein said plurality of memory cells are each supported on a substrate and separated from one another by spacer material therebetween, and wherein a magnetic material layer in said first magnetization reference layer has a characteristic magnetic property that is maintained below a critical temperature above which such magnetic property is not maintained, said memory cells each having a first interconnection structure providing electrical contact thereto positioned against at least one side thereof, and said electrical conductor exhibits sufficient electrical resistance where across from a said memory cell for a sufficient electrical current therethrough to cause substantial heating of said memory cell to raise temperatures thereof to have said magnetic material layer therein approach said critical temperature thereof while being substantially above temperatures of at least an adjacent said memory cell because of sufficient extents of, and smallness of thermal conductivities of, said first interconnection structure positioned against said memory cell and of those portions of said substrate and said spacer material positioned thereabout.