CPP GMR and magnetostriction improvement by laminating Co90Fe10free layer with thin Fe50Co50layers

• US 7,141,314 B2
• Filed: 02/25/2004
• Issued: 11/28/2006
• Est. Priority Date: 02/25/2004
• Status: Expired due to Fees

• Current Assignee: Headway Technologies Incorporated (TDK Corporation)
• Original Assignee: Headway Technologies Incorporated (TDK Corporation)
• Inventors: Liu, Yue, Zhang, Kunliang, Li, Min, Sbiaa, Rachid, Liao, Simon
• Primary Examiner(s): Bernatz, Kevin M.
• Application Number:
  US10/786,806
• Publication Number:
  US 20050186452A1
• Time in Patent Office: 1,007 Days
• Field of Search: None
• US Class Current: 428/811.2
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: Y10T 428/1121 Multilayer
• CPC Class Codes: Y10T 428/1143 with defined structural feature
• CPC Class Codes: Y10T 428/115 Magnetic layer composition

Abstract

A current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) sensor of the synthetic spin valve type and its method of formation are disclosed, the sensor including a novel laminated free layer having ultra-thin (less than 3 angstroms thickness) laminas of Fe₅₀ Co₅₀ (or any iron rich alloy of the form Co_xFe_1−x with x between 0.25 and 0.75) interspersed with thicker layers of Co₉₀Fe₁₀ and Cu spacer layers to produce a free layer with good coercivity, a coefficient of magnetostriction that can be varied between positive and negative values and a high GMR ratio, due to enhancement of the bulk scattering coefficient by the laminas. The configuration of the lamina and layers in periodic groupings allow the coefficient of magnetostriction to be finely adjusted and the coercivity and GMR ratio to be optimized. The sensor performance can be further improved by including layers of Cu and Fe₅₀Co₅₀ in the synthetic antiferromagnetic pinned layer.

Claims

1. A current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) magnetic field sensor of the synthetic spin valve type comprising:

a substrate;

a seed layer formed on the substrate;

an antiferromagnetic pinning layer formed on the seed layer;

a synthetic antiferromagnetic pinned layer formed on the pinning layer, said pinned layer further comprising ferromagnetic layer AP2, formed on said pinning layer, a non-magnetic coupling layer formed on AP2 and ferromagnetic layer AP1 formed on said coupling layer;

a spacer layer formed on said AP1 layer;

a laminated free layer formed on said spacer layer, the free layer including a plurality of layers of a second ferromagnetic material, each said layer being formed to a thickness between approximately 2.5 and 15 angstroms and each said layer being separated from an adjacent said layer by a lamina of a first ferromagnetic material formed to a thickness less than approximately 3 angstroms or by a Cu spacer layer formed to a thickness between approximately 1 and 4 angstroms; and

wherein each said lamina of said first ferromagnetic material has a positive coefficient of magnetostriction and each said layer of said second ferromagnetic material has a negative coefficient of magnetostriction, whereby the coefficient of magnetostriction of said free layer can be made positive or negative, wherein said laminated free layer includes at least one lamina of said first ferromagnetic material; and

a capping layer formed on said free layer.

2. The sensor of claim 1, wherein said first ferromagnetic material is any of the ferromagnetic alloys of the form Co_xFe₁₀₀₋

x with x between 25 and 75 and said second ferromagnetic material is Co₉₀Fe₁₀.

3. The sensor of claim 2 wherein said AP1 layer includes at least one layer of said first ferromagnetic material formed to a thickness between approximately 2.5 and 15 angstroms and at least one layer of said second ferromagnetic material of thickness between approximately 2.5 and 15 angstroms.

4. The sensor of claim 1 wherein said free layer comprises:

a first layer of Co₉₀Fe₁₀;

a first lamina of Fe₅₀Co₅₀ formed on said first layer;

a second layer of Co₉₀Fe₁₀ formed on said first lamina;

a first spacer layer of Cu formed on said first lamina;

a third layer of Co₉₀Fe₁₀ formed on said first spacer layer;

a second lamina of Fe₅₀Co₅₀ formed on said second layer;

a fourth layer of Co₉₀Fe₁₀ formed on said second lamina;

a second spacer layer of Cu formed on said third layer;

a fifth layer of Co₉₀Fe₁₀ formed on said second spacer layer.

5. The sensor of claim 4 wherein the thickness said first layer is between approximately 5 and 15 angstroms, the thickness of said second, third, fourth and fifth layers is between approximately 2.5 and 7.5 angstroms, the thickness of each lamina is less than approximately 3 angstroms and the thickness of each spacer layer is between approximately 1 and 4 angstroms.

6. The sensor of claim 5 wherein the laminated configuration of the free layer produces a positive coefficient of magnetostriction.

7. The sensor of claim 1 wherein said AP1 layer includes a lamination of bilayers, wherein each bilayer is a layer of Fe₅₀Co₅₀, of thickness between approximately 7.5 and 15 angstroms, formed on a layer of Cu of thickness between approximately 1 and 4 angstroms.

8. A method of forming a current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) magnetic field sensor of the synthetic spin valve type having a coefficient of magnetostriction that can be varied from positive to negative by changing a laminated configuration of its free layer comprising:

providing a substrate;

forming a seed layer on the substrate;

forming an antiferromagnetic pinning layer on the seed layer;

forming a synthetic antiferromagnetic pinned layer on the pinning layer, said formation further comprising forming ferromagnetic layer AP2 on said pinning layer, forming a non-magnetic coupling layer on AP2 and forming ferromagnetic layer AP1 on said coupling layer;

forming a spacer layer on said AP1 layer;

forming a laminated free layer on the spacer layer, said laminated free layer including a plurality of layers of a second ferromagnetic material, each said layer being formed to a thickness between approximately 2.5 and 15 angstroms and each said layer being separated from an adjacent said layer by a lamina of a first ferromagnetic material formed to a thickness less than approximately 3 angstroms or by a Cu spacer layer formed to a thickness between approximately 1 and 4 angstroms; and

wherein each lamina of said first ferromagnetic material has a positive coefficient of magnetostriction and each layer of said second ferromagnetic material has a negative coefficient of magnetostriction, whereby the number and arrangement of laminas of said first ferromagnetic material and the number and arrangement of layers of said second ferromagnetic material determine a coefficient of magnetostriction of the free layer having a value within a range from positive to negative, wherein said laminated free layer includes at least one lamina of said first ferromagnetic material;

then

forming a capping layer on said free layer.

9. The method of claim 8, wherein said first ferromagnetic material is the ferromagnetic alloy of the form Co_xFe₁₀₀₋

x with x between 25 and 75 and said second ferromagnetic material is Co₉₀Fe₁₀.

10. The method of claim 8 wherein formation of said free layer comprises:

forming a first layer of Co₉₀Fe₁₀;

forming a first lamina of Fe₅₀Co₅₀ on said first layer;

forming a second layer of Co₉₀Fe₁₀ on said first lamina;

forming a first spacer layer of Cu on said first lamina;

forming a third layer of Co₉₀Fe₁₀ on said first spacer layer;

forming a second lamina of Fe₅₀Co₅₀ on said second layer;

forming a fourth layer of Co₉₀Fe₁₀ on said second lamina;

forming a second spacer layer of Cu on said third layer;

forming a fifth layer of Co₉₀Fe₁₀ on said second spacer layer.

11. The method of claim 10 wherein the thickness said first layer is between approximately 5 and 15 angstroms, the thickness of said second, third, fourth and fifth layers is between approximately 2.5 and 7.5 angstroms, the thickness of each lamina is less than approximately 3 angstroms and the thickness of each spacer layer is between approximately 1 and 4 angstroms.

12. The method of claim 8 wherein the laminated configuration of the free layer produces a positive coefficient of magnetostriction.

13. The method of claim 8 wherein said AP1 layer includes a lamination of bilayers, wherein each bilayer is a layer of Fe₅₀Co₅₀, of thickness between approximately 7.5 and 15 angstroms, formed on a layer of Cu of thickness between approximately 1 and 4 angstroms.