Magnetic random access memory designs with controlled magnetic switching mechanism by magnetostatic coupling

• US 20050237793A1
• Filed: 06/27/2005
• Published: 10/27/2005
• Est. Priority Date: 08/28/2003
• Status: Active Grant

• Current Assignee: Headway Technologies Incorporated (TDK Corporation)
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Min, Tai, Wang, Po Kang
• Granted Patent: US 7,242,046 B2
• Time in Patent Office: Days
• US Class Current: 365/158
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• 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
• CPC Class Codes: H01F 41/308 lift-off processes, e.g. ion milling, for trimming or patterning
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

A magnetic tunneling junction (MTJ) memory cell for a magnetic random access memory (MRAM) array is formed as a chain of magnetostatically coupled segments. The segments can be circular, elliptical, lozenge shaped or shaped in other geometrical forms. Unlike the isolated cells of typical MTJ designs which exhibit curling of the magnetization at the cell ends and uncompensated pole structures, the present multi-segmented design, with the segments being magnetostatically coupled, undergoes magnetization switching at controlled nucleation sites by the fanning mode. As a result, the multi-segmented cells of the present invention are not subject to variations in switching fields due to irregularities an structural defects.

Claims

1. A magnetostatically coupled multi-segmented magnetic tunnel junction (MTJ) cell, said cell having artificial nucleation sites for magnetization switching and a reduced sensitivity to defects and shape irregularities comprising:

at least two discrete, separated MTJ cell segments, the centers of said segments being distributed along a common line and forming, thereby, a linear chain of cell segments; and

the segments having a crystalline anisotropy; and

the segments having certain geometrical shapes; and

the segments being magnetized along said common linear direction; and

the magnetization of said segments being maintained by magnetostatic coupling between said segments; and

the magnetization of said segments being capable of a substantially simultaneous change in direction by the application of an external switching field to a location among said segments which provides a nucleation site for said direction change.

2. The multi-segmented MTJ cell of claim 1 wherein each segment further comprises:

a ferromagnetic free layer;

an insulating tunneling layer formed on said free layer;

a multi-layered magnetically pinned layer formed on said tunneling layer, said pinned layer further comprising;

a first ferromagnetic layer adjacent to said tunneling layer;

a non-magnetic coupling layer formed on said first ferromagnetic layer;

a second ferromagnetic layer formed on said coupling layer;

an antiferromagnetic pinning layer formed on said second ferromagnetic layer; and

said multi-layered magnetically pinned layer has a net magnetic moment which is substantially zero as a result of the magnetic moments of said first and second ferromagnetic layers being substantially equal and strongly magnetically coupled in an anti-parallel configuration.

3. The multi-segmented MTJ cell of claim 2 wherein said free magnetic layer is a multilayer comprising a third and fourth ferromagnetic layer separated by a non magnetic spacer layer and wherein the magnetizations of said ferromagnetic layers are substantially equal and may be weakly or strongly coupled in antiparallel directions to produce a substantially zero net magnetic moment.

4. The multi-segmented MTJ cell of claim 2 wherein the tunneling layer is a layer of insulating material chosen from the group of insulating materials consisting of as Al₂O₃, ZrO₂ or HfO₂ and combinations thereof.

5. The multi-segmented MTJ cell of claim 4 wherein the tunneling layer is a layer of Al₂O₃ formed to a thickness of between approximately 5 and 50 angstroms.

6. The multi-segmented MTJ cell of claim 2 wherein the coupling layer is a layer chosen from the group of non-magnetic coupling materials consisting of Rh, Ru, Cr and Cu.

7. The multi-segmented MTJ cell of claim 6 wherein the coupling layer is a layer of Ru formed to a thickness of between approximately 5 and 50 angstroms.

8. The multi-segmented MTJ cell of claim 2 wherein the antiferromagnetic pinning layer is a layer chosen from the group of antiferromagnetic materials consisting of PtMn, NiMn, OsMn, IrMn, NiO, FeMn and CoNiO.

9. The multi-segmented MTJ cell of claim 8 wherein said pinning layer is a layer of PtMn formed to a thickness between approximately 30 and 300 angstroms.

10. The multi-segmented MTJ cell of claim 2 wherein the ferromagnetic free layer and the first and second ferromagnetic layers of the pinned layer are formed of ferromagnetic materials chosen from the group of ferromagnetic materials consisting of CoFe, NiFe, CoNiFe, CoZrTa, CoFeB and CoHfTa and are formed to a thickness between approximately 20 and 200 angstroms.

11. The multi-segmented MTJ cell of claim 3 wherein said first, second, third and fourth ferromagnetic layers of the pinned layer are formed of ferromagnetic materials chosen from the group of ferromagnetic materials consisting of CoFe, NiFe, CoNiFe, CoZrTa, CoFeB, CoZrTa, CoNbTa and CoHfTa and are formed to a thickness between approximately 20 and 200 angstroms.

12. The multi-segmented MTJ cell of claim 1, wherein each segment of said cell is shaped by a process comprising photolithography and ion-milling.

13. The multi-segmented MTJ cell of claim 1, wherein the shape of each segment of said cell is chosen from the group of segment shapes consisting of segments which are all circles of equal area, segments which are all circles of unequal area, segments which are all ellipses of equal aspect ratio, segments which are all ellipses of aspect ratio between 1 and 10, segments which are all ellipses of equal aspect ratio and equal area, segments which are all ellipses, segments which are all lozenge shaped and segments which are all complex geometrical shapes.

14. The multi-segmented MTJ cell of claim 13 wherein the centers of each cell segment lie on a common line.

15. The multi-segmented MTJ cell of claim 14 wherein each segment is circular.

16. The multi-segmented MTJ cell of claim 15 wherein each circular segment has the same radius.

17. The multi-segmented MTJ cell of claim 16 wherein there are two circular segments.

18. The multi-segmented MTJ cell of claim 14 wherein the cell forms a chain of between 2 and 10 circular segments.

19. The multi-segmented MTJ cell of claim 14 wherein the crystalline anisotropy of each segment is perpendicular to said common line.

20. The multi-segmented MTJ cell of claim 14 wherein each segment is elliptical and has a major axis perpendicular to the common line joining their centers.

21. The multi-segmented MTJ cell of claim 14 wherein each segment is elliptical with its minor axis being perpendicular to the common line joining their centers.

22. The multi-segmented cell of claim 21 wherein the cell forms a chain of between 2 and 10 elliptical elements and has a crystalline anisotropy that is perpendicular to the common line joining its centers.

23. The multi-segmented MTJ cell of claim 14 wherein each segment is lozenge shaped.

24. The multi-segmented MTJ cell of claim 22 wherein the cell forms a chain of between 2 and 10 lozenge shaped elements.

25. The multi-segmented MTJ cell of claim 24 wherein the crystalline anisotropy of each segment is perpendicular to the line joining its centers.

29. The MTJ cell of claim 3 wherein the tunneling layer is a layer of insulating material chosen from the group of insulating materials consisting of as Al₂O₃, ZrO₂ or HfO₂ and combinations thereof.

30. The multi-segmented MTJ cell of claim 29 wherein the coupling layer is a layer of Ru formed to a thickness of between approximately 5 and 50 angstroms.

31. The multi-segmented MTJ cell of claim 3 wherein the coupling layer is a layer chosen from the group of non-magnetic coupling materials consisting of Rh, Ru, Cr and Cu.

32. The multi-segmented MTJ cell of claim 3 wherein the antiferromagnetic pinning layer is a layer chosen from the group of antiferromagnetic materials consisting of PtMn, NiMn, OsMn, IrMn, NiO, FeMn and CoNiO.

33. The multi-segmented MTJ cell of claim 32 wherein said pinning layer is a layer of PtMn formed to a thickness between approximately 30 and 300 angstroms.

34. The multi-segmented MTJ cell of claim 2 wherein each segment of said cell is shaped by a process comprising photolithography and ion-milling.

35. The multi-segmented MTJ cell of claim 3 wherein each segment of said cell is shaped by a process comprising photolithography and ion-milling.

36. The multi-segmented MTJ cell of claim 2 wherein the shape of each segment of said cell is chosen from the group of segment shapes consisting of segments which are all circles of equal area, segments which are all circles of unequal area, segments which are all ellipses of equal aspect ratio, segments which are all ellipses of aspect ratio between 1 and 10, segments which are all ellipses of equal aspect ratio and equal area, segments which are all ellipses, segments which are all lozenge shaped and segments which are all complex geometrical shapes.

37. The multi-segmented MTJ cell of claim 3 wherein the shape of each segment of said cell is chosen from the group of segment shapes consisting of segments which are all circles of equal area, segments which are all circles of unequal area, segments which are all ellipses of equal aspect ratio, segments which are all ellipses of aspect ratio between 1 and 10, segments which are all ellipses of equal aspect ratio and equal area, segments which are all ellipses, segments which are all lozenge shaped and segments which are all complex geometrical shapes.

38. The multi-segmented MTJ cell of claim 36 wherein the centers of each cell segment lie on a common line.

39. The multi-segmented MTJ cell of claim 37 wherein the centers of each cell segment lie on a common line.

40. The multi-segmented MTJ cell of claim 38 wherein each segment is circular.

41. The multi-segmented MTJ cell of claim 39 wherein each segment is circular.

42. The multi-segmented MTJ cell of claim 40 wherein each circular segment has the same radius.

43. The multi-segmented MTJ cell of claim 41 wherein each circular segment has the same radius.

44. The multi-segmented MTJ cell of claim 42 wherein there are two circular segments.

45. The multi-segmented MTJ cell of claim 43 wherein there are two circular segments.

46. The multi-segmented MTJ cell of claim 38 wherein the cell forms a chain of between 2 and 10 circular segments.

47. The multi-segmented MTJ cell of claim 39 wherein the cell forms a chain of between 2 and 10 circular segments.

48. The multi-segmented MTJ cell of claim 38 wherein the crystalline anisotropy of each segment is perpendicular to said common line.

49. The multi-segmented MTJ cell of claim 39 wherein the crystalline anisotropy of each segment is perpendicular to said common line.

50. The multi-segmented MTJ cell of claim 38 wherein each segment is elliptical and has a major axis perpendicular to the common line joining their centers.

51. The multi-segmented MTJ cell of claim 39 wherein each segment is elliptical and has a major axis perpendicular to the common line joining their centers.

52. The multi-segmented MTJ cell of claim 38 wherein each segment is elliptical with its minor axis being perpendicular to the common line joining their centers.

53. The multi-segmented MTJ cell of claim 39 wherein each segment is elliptical with its minor axis being perpendicular to the common line joining their centers.

54. The multi-segmented cell of claim 52 wherein the cell forms a chain of between 2 and 10 elliptical elements and has a crystalline anisotropy that is perpendicular to the common line joining its centers.

55. The multi-segmented cell of claim 53 wherein the cell forms a chain of between 2 and 10 elliptical elements and has a crystalline anisotropy that is perpendicular to the common line joining its centers.

56. The multi-segmented MTJ cell of claim 38 wherein each segment is lozenge shaped.

57. The multi-segmented MTJ cell of claim 39 wherein each segment is lozenge shaped.

58. The multi-segmented MTJ cell of claim 52 wherein the cell forms a chain of between 2 and 10 lozenge shaped elements.

59. The multi-segmented MTJ cell of claim 53 wherein the cell forms a chain of between 2 and 10 lozenge shaped elements.

60. The multi-segmented MTJ cell of claim 52 wherein the crystalline anisotropy of each segment is perpendicular to the line joining its centers.

61. The multi-segmented MTJ cell of claim 53 wherein the crystalline anisotropy of each segment is perpendicular to the line joining its centers.

26-28. -28. (canceled)