Tunnel junction sensor with a multilayer free-layer structure

• US 6,674,617 B2
• Filed: 03/07/2002
• Issued: 01/06/2004
• Est. Priority Date: 03/07/2002
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gill, Hardayal Singh
• Primary Examiner(s): EVANS, JEFFERSON A
• Application Number:
  US10/094,243
• Publication Number:
  US 20030169542A1
• Time in Patent Office: 670 Days
• Field of Search: 360/324.1, 360/324.11, 360/324.12, 360/324.2
• US Class Current: 360/324.12
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/06 using galvano-magnetic devices
• CPC Class Codes: G11B 5/02 Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: G11B 5/3909 Arrangements using a magnetic tunnel junction

Abstract

A tunnel junction sensor according to the invention replaces the prior art free layer with a free layer structure which allows a wider range of magnetoresistive materials to be used. The preferred free layer structure of the invention includes a negative magnetostriction layer which allows use of magnetoresistive materials which otherwise have unacceptably high magnetostriction values. The materials and thicknesses of the layers are selected to result in a total magnetostriction near zero even though magnetoresistive material with high magnetostriction is included. The preferred embodiment includes a softening layer of material such as selected compositions of nickel-iron which maintain the desired magnetic softness of the free layer structure and have a magnetostriction constant near zero.

Claims

1. A thin film tunnel junction sensor for sensing an external magnetic field comprising:

an antiferromagnetic layer;

a pinned ferromagnetic layer;

a barrier layer in contact with the pinned ferromagnetic layer; and

a free layer structure including;

a first layer of ferromagnetic material disposed adjacent to the barrier layer and having a first magnetostriction value which is positive and a first coercivity;

a second layer of ferromagnetic material having a second magnetostriction value which is negative and a second coercivity; and

a third layer of ferromagnetic material having a third magnetostriction value and a third coercivity, the third coercivity being lower than the second coercivity and the first, second and third magnetostriction values summing to approximately zero.

2. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is iron.

3. The thin film tunnel junction sensor of claim 2 wherein the barrier layer is MgO.

4. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is Co₅₀Fe₅₀.

5. The thin film tunnel junction sensor of claim 4 wherein the barrier layer is MgO.

6. The thin film tunnel junction sensor of claim 1 wherein the second layer of ferromagnetic material is nickel.

7. The thin film tunnel junction sensor of claim 1 wherein the second layer of ferromagnetic material is an amorphous alloy of cobalt.

8. The thin film tunnel junction sensor of claim 1 wherein the second layer of ferromagnetic material is Co₉₀Nb₁₀.

9. The thin film tunnel junction sensor of claim 1 wherein the third layer of ferromagnetic material is Ni₈₀Fe₂₀.

10. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is Co₅₀Fe₅₀ and the second layer of ferromagnetic material is nickel.

11. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is Co₅₀Fe₅₀ and has a first thickness and the second layer of ferromagnetic material is nickel and has a second thickness which is approximately two times the first thickness.

12. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is Co₅₀Fe₅₀, the second layer of ferromagnetic material is nickel or an amorphous alloy of cobalt and the third layer of ferromagnetic material is an alloy of nickel and iron.

13. The thin film tunnel junction sensor of claim 1 wherein the first layer of ferromagnetic material is iron, the second layer of ferromagnetic material is nickel or an amorphous alloy of cobalt and the third layer of ferromagnetic material is an alloy of nickel and iron.

14. A method for fabricating a thin film tunnel junction sensor for sensing an external magnetic field comprising the steps of:

depositing an antiferromagnetic layer;

depositing a pinned ferromagnetic layer;

depositing a barrier layer in contact with the pinned ferromagnetic layer; and

depositing a free layer structure including;

a first layer of ferromagnetic material disposed adjacent to the barrier layer and having a first magnetostriction value which is positive and a first coercivity;

a second layer of ferromagnetic material having a second magnetostriction value which is negative and a second coercivity; and

a third layer of ferromagnetic material having a third magnetostriction value and a third coercivity, the third coercivity being lower than the second coercivity and the first, second and third magnetostriction values summing to approximately zero.

15. The method of claim 14 wherein the first layer of ferromagnetic material is iron or Co₅₀Fe₅₀.

16. The method of claim 15 wherein the barrier layer is MgO.

17. The method of claim 14 wherein the second layer of ferromagnetic material is nickel or an amorphous alloy of cobalt.

18. The method of claim 14 wherein the second layer of ferromagnetic material is Co₉₀Nb₁₀.

19. The method of claim 14 wherein the third layer of ferromagnetic material is Ni₈₀Fe₂₀.

20. The method of claim 14 wherein the first layer of ferromagnetic material is Co₅₀Fe₅₀ and has a first thickness and the second layer of ferromagnetic material is nickel and has a second thickness which is approximately two times the first thickness.

21. A disk drive comprising:

a thin film disk including a thin film of ferromagnetic material on a planar surface of the disk;

a spindle rotatably supporting the disk; and

a tunnel junction magnetic sensor having an air bearing surface supported over the planar surface of the disk, the magnetic sensor including;

a antiferromagnetic layer;

a pinned layer;

a barrier layer adjacent to the pinned layer;

a magnetoresistive layer disposed adjacent to the barrier layer and having a first magnetostriction which is positive;

a negative magnetostriction layer disposed adjacent to the magnetoresistive layer and having a second magnetostriction which is negative; and

a softening ferromagnetic layer disposed adjacent to the negative magnetostriction layer, having a coercivity lower than a coercivity of the negative magnetostriction layer and having a third magnetostriction which results in approximately zero total magnetostriction when summed with the first and second magnetostriction.

22. The disk drive of claim 21 wherein the magnetoresistive layer is iron or Co₅₀Fe₅₀.

23. The disk drive of claim 22 wherein the barrier layer is MgO.

24. The disk drive of claim 21 wherein the negative magnetostriction layer is nickel or an amorphous alloy of cobalt.

25. The disk drive of claim 21 wherein the negative magnetostriction layer is Co₉₀Nb₁₀.

26. The disk drive of claim 21 wherein the softening ferromagnetic layer is Ni₈₀Fe₂₀.