Mg-Zn oxide tunnel barriers and method of formation

• US 7,252,852 B1
• Filed: 11/05/2004
• Issued: 08/07/2007
• Est. Priority Date: 12/12/2003
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Parkin, Stuart Stephen Papworth
• Primary Examiner(s): Bashore; Alain L.
• Application Number:
  US10/982,075
• Time in Patent Office: 1,005 Days
• Field of Search: 427/131, 427/163.2, 428/811.1, 438/3, 438/257, 360/324.2, 360/324.12
• US Class Current: 427/131
• 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: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• 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 10/3268 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 10/3281 only by use of asymmetry of the magnetic film pair itself, i.e. so-called pseudospin valve [PSV] structure, e.g. NiFe/Cu/Co
• CPC Class Codes: H01F 10/329 Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect
• CPC Class Codes: H01F 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H01F 41/307 insulating or semiconductive spacer
• CPC Class Codes: H10N 50/01 Manufacture or treatment
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: Y10T 428/1114 having tunnel junction effect
• CPC Class Codes: Y10T 428/1143 with defined structural feature
• CPC Class Codes: Y10T 428/115 Magnetic layer composition
• CPC Class Codes: Y10T 428/1157 Substrate composition

Abstract

ZnMg oxide tunnel barriers are grown which, when sandwiched between ferri- or ferromagnetic layers, form magnetic tunnel junctions exhibiting high tunneling magnetoresistance (TMR). The TMR may be increased by annealing the magnetic tunnel junctions. The zinc-magnesium oxide tunnel barriers may be incorporated into a variety of other devices, such as magnetic tunneling transistors and spin injector devices. The ZnMg oxide tunnel barriers are grown by first depositing a zinc and/or magnesium layer onto an underlying substrate in oxygen-poor (or oxygen-free) conditions, and subsequently depositing zinc and/or magnesium onto this layer in the presence of reactive oxygen.

Claims

1. A method, comprising:

depositing a metal layer onto a surface of an underlayer, wherein the surface is selected to be substantially free of oxide; and

directing additional metal towards the metal layer, in the presence of oxygen, to form a magnesium-zinc oxide tunnel barrier in contact with the underlayer, the oxygen reacting with the additional metal and the metal layer, wherein;

at least one of the metal layer and the additional metal includes Zn, and

at least one of the metal layer and the additional metal includes Mg.

2. The method of claim 1, wherein the metal layer includes Mg but substantially no Zn.

3. The method of claim 1, wherein the metal layer includes Zn but substantially no Mg.

4. The method of claim 1, wherein the metal layer includes both Mg and Zn.

5. The method of claim 1, wherein the additional metal includes Mg but substantially no Zn.

6. The method of claim 1, wherein the additional metal includes Zn but substantially no Mg.

7. The method of claim 1, wherein the additional metal includes both Mg and Zn.

8. The method of claim 1, wherein the metal layer includes Mg but substantially no Zn, and the additional metal includes Zn but substantially no Mg.

9. The method of claim 1, wherein the metal layer includes Zn but substantially no Mg, and the additional metal includes Mg but substantially no Zn.

10. The method of claim 1, wherein the tunnel barrier is a [Zn_1-xMg_x]O tunnel barrier, in which x represents an atomic percentage in the range of 1 to 99.

11. The method of claim 1, wherein the tunnel barrier includes a layer of [Zn_1-yMg_y]O and a layer of [Zn_1-xMg_x]O, wherein x and y represent respective atomic percentages in the ranges of 1 to 99 and 1 to 100, respectively.

12. The method of claim 1, wherein the thickness of the metal layer is selected to be large enough to prevent oxidation of the underlayer but small enough that, upon reaction of the oxygen with the metal layer, substantially all the metal in the metal layer is oxidized.

13. The method of claim 1, further comprising annealing the tunnel barrier to improve its performance.

14. The method of claim 1, wherein the metal layer is deposited in the absence of reactive oxygen, the metal layer being oxidized as the tunnel barrier is formed.

15. The method of claim 1, wherein the tunnel barrier has a thickness of between 3 and 50 angstroms.

16. The method of claim 1, wherein the metal layer has a thickness of between 3 and 50 angstroms.

17. The method of claim 1, wherein the metal layer has a thickness of between 3 and 20 angstroms.

18. The method of claim 1, wherein the underlayer includes a semiconductor adjacent to the tunnel barrier.

19. The method of claim 1, wherein the underlayer includes a layer of at least one magnetic material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials.

20. The method of claim 19, wherein the magnetic layer is adjacent to the tunnel barrier.

21. The method of claim 20, wherein the magnetic layer is ferromagnetic, bcc and substantially (100) oriented.

22. The method of claim 19, wherein the magnetic layer includes an alloy of Fe and Co, and the Fe content of the alloy is between 1 and 99 atomic percent.

23. The method of claim 19, further comprising forming an overlayer on the tunnel barrier to form a magnetic tunnel junction, wherein the overlayer includes a layer of at least one magnetic material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials.

24. The method of claim 23, further comprising annealing the tunnel junction to increase its tunnel magnetoresistance.

25. The method of claim 24, wherein the tunnel junction is annealed at a temperature selected to yield a tunnel magnetoresistance of greater than 50% at room temperature.

26. The method of claim 24, wherein the tunnel junction is annealed at a temperature selected to yield a tunnel magnetoresistance of greater than 70% at room temperature.

27. The method of claim 23, wherein the overlayer and the underlayer each include ferromagnetic material selected from the group consisting of i) Fe, ii) an alloy of Co and Fe, iii) an alloy of Ni and Fe, and iv) an alloy of Ni and Fe and Co.

28. The method of claim 1, comprising forming an overlayer on the tunnel barrier, wherein one of the overlayer and the underlayer includes a non-ferromagnetic, non-ferrimagnetic metal layer, and the other of the overlayer and the underlayer includes a layer of magnetic material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials, thereby constructing a magnetic tunneling transistor that includes the non-ferromagnetic, non-ferrimagnetic metal layer, the tunnel barrier, and the magnetic layer.

29. The method of claim 1, comprising forming an overlayer on the tunnel barrier, wherein the overlayer and the underlayer comprise respective non-ferromagnetic, non-ferrimagnetic metals.

30. A method, comprising:

providing an underlayer having a surface that is substantially free of oxide;

forming a metal layer on the surface to both protect the underlayer from oxidation and to wet the underlayer, the metal layer including at least one of Mg and Zn; and

simultaneously directing oxygen and additional metal, the additional metal including at least one of Mg and Zn, onto the metal layer to form a magnesium-zinc oxide tunnel barrier that is in contact with the underlayer, wherein;

at least one of the metal layer and the additional metal includes Zn; and

at least one of the metal layer and the additional metal includes Mg.

31. The method of claim 30, further comprising annealing the tunnel barrier to improve its performance.

32. A method, comprising:

forming a metal layer of a preselected thickness on a surface of an underlayer to protect the underlayer from oxidation, wherein the metal layer includes at least one of Mg and Zn; and

simultaneously directing oxygen and additional metal that includes at least one of Mg and Zn towards the metal layer, so that the oxygen reacts with the metal layer and the additional metal to form a magnesium-zinc oxide tunnel barrier on the underlayer,

wherein the thickness of the metal layer is selected to be small enough that substantially all the metal of the metal layer reacts with oxygen to form part of the tunnel barrier, and wherein;

at least one of the metal layer and the additional metal includes Zn, and

at least one of the metal layer and the additional metal includes Mg.

33. The method of claim 32, wherein the surface is selected to be substantially free of oxide.

34. The method of claim 32, further comprising forming an overlayer on the tunnel barrier, wherein the overlayer and the underlayer each include at least one material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials, thereby forming a magnetic tunnel junction.

35. The method of claim 34, further comprising annealing the magnetic tunnel junction to increase its tunnel magnetoresistance.

36. A method, comprising:

depositing a metal layer onto a surface of an underlayer, wherein the surface is selected to be substantially free of oxide; and

directing additional metal towards the metal layer, in the presence of oxygen, to form a magnesium-zinc oxide tunnel barrier in contact with the underlayer, the oxygen reacting with the additional metal and the metal layer, wherein;

at least one of the metal layer and the additional metal includes Zn,

at least one of the metal layer and the additional metal includes Mg,

the underlayer includes a layer of at least one magnetic material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials, and

the magnetic material and the tunnel barrier are in proximity with each other to enable spin-polarized current to pass between them.

37. The method of claim 36, wherein the tunnel barrier has a thickness of between 3 and 50 angstroms.

38. The method of claim 36, comprising forming an overlayer on the tunnel barrier to form a magnetic tunnel junction, wherein the overlayer includes a layer of at least one magnetic material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials.

39. The method of claim 38, comprising annealing the tunnel junction to improve its tunnel magnetoresistance.

40. The method of claim 39, wherein the tunnel junction is annealed at temperature in the range of 180°

C. to 400°

C.

41. The method of claim 39, wherein the tunnel junction is annealed at a temperature of at least 180°

C. to improve its tunnel magnetoresistance.

42. The method of claim 39, wherein the tunnel junction is annealed at a temperature of at least 220°

C. to improve its tunnel magnetoresistance.

43. The method of claim 39, wherein the tunnel junction is annealed at a temperature of at least 360°

C. to improve its tunnel magnetoresistance.