Article comprising anisotropic Co-Fe-Cr-N soft magnetic thin films

• US 5,998,048 A
• Filed: 03/02/1998
• Issued: 12/07/1999
• Est. Priority Date: 03/02/1998
• Status: Expired due to Fees

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Jin, Sungho, Zhu, Wei, Klemmer, Timothy J., Van Dover, Robert Bruce, Tiefel, deceased, Thomas Henry
• Primary Examiner(s): KILIMAN, LESZEK B
• Application Number:
  US09/033,204
• Time in Patent Office: 645 Days
• Field of Search: 478/694 T, 478/694 TS, 478/694 TM, 478/900, 427/128-131, 204/192.2
• US Class Current: 428/836.3
• CPC Class Codes: G11B 5/3109 Details G11B5/3103 takes precedence
• CPC Class Codes: G11B 5/39 using magneto-resistive devices or effects
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: H01F 10/132 containing cobalt
• CPC Class Codes: H01F 10/138 containing nanocrystallites, e.g. obtained by annealing
• CPC Class Codes: H01F 10/265 Magnetic multilayers non exchange-coupled H01F10/32 takes precedence
• CPC Class Codes: Y10S 428/90 Magnetic feature

Abstract

The invention is embodied in an anisotropic, soft magnetic thin film article comprising a cobalt-iron-chromium-nitrogen (Co--Fe--Cr--N) alloy. The thin film is formed such that the alloy has a relatively high saturation magnetization (4πM_s), e.g., greater than approximately 8 kilogauss (kG), a relatively low coercivity (H_c), e.g., less than approximately 2.0 oersteds (Oe), a relatively high squareness ratio (M_r /M_s), e.g., greater than approximately 0.90, and a relatively high anisotropy field (H_k), e.g., greater than approximately 20 Oe, in an as-deposited condition or, alternatively, with a relatively low temperature treatment, e.g., below approximately 300° Celsius. The inventive films are suitable for use in electromagnetic devices, e.g., in microtransformer cores, inductor cores and in magnetic read-write heads.

Claims

1. An article, comprising:

a non-magnetic substrate; and

an anisotropic, magnetically soft film supported by said substrate, said film including an alloy of cobalt-iron-chromium-nitrogen (Co--Fe--Cr--N) and having a saturation magnetization (4π

M_s) of at least approximately 8 kilogauss (kG), an anisotropy field (H_k) within the range from approximately 15 to 300 oersteds (Oe) and a magnetic hysteresis (M-H) loop squareness ratio (remanent magnetization, M_r, to saturation magnetization, M_s) of at least approximately 0.90, wherein said alloy contains, by atomic percentage, at least approximately 15% cobalt (Co), and wherein said article has been heat treated at a temperature of no more than approximately 150°

Celsius.

2. The article as recited in claim 1, wherein said film has an anisotropy field (H_k) greater than approximately 50 Oe, and has a ferromagnetic resonance (FMR) frequency greater than approximately 1 gigahertz (GHz).

3. The article as recited in claim 1, wherein said Co--Fe--Cr--N alloy includes chromium (Cr) within the range from approximately 0 to 15 weight %.

4. The article as recited in claim 1, wherein said Co--Fe--Cr--N alloy contains cobalt (Co) within the range from approximately 20 to 80 weight %, iron (Fe) within the range from approximately 20 to 80 weight %, chromium (Cr) within the range from approximately 1 to 12 weight %, and nitrogen (N) within the range from approximately 0.2 to 8.0 weight %.

5. The article as recited in claim 1, wherein said film further comprises a plurality of thin film layers and wherein said article further comprises a corresponding plurality of dielectric spacer layers formed between said thin film layers in such a way that a multilayer structure is formed.

6. The article as recited in claim 5, wherein said plurality of dielectric spacer layers further comprises polyimide or ceramic insulators.

7. The article as recited in claim 1, wherein said film is formed on said substrate in such a way that the average grain structure size of said film is less than approximately 500 angstroms (Å

).

8. The article as recited in claim 1, further comprising one or more exchange bias films formed on said film, said exchange bias films selected from a group consisting of antiferromagnetic, ferromagnetic and ferrimagnetic material.

9. The article as recited in claim 1, wherein said article is part of an electromagnetic device selected from a group consisting of a microtransformer, an inductor and a magnetic read-write head.

10. The article as recited in claim 1, wherein said article is for use at an operating frequency of at least approximately 10 megahertz (MHz), and wherein said film is saturated along an easy-axis of magnetization into a single domain state and then operated in an alternating current (AC) field along a hard-axis of magnetization.

11. The article as recited in claim 1, wherein said film has an easy-axis coercive force of at least approximately 30 oersteds (Oe).

12. A method for making a magnetically soft thin film article, said method comprising the steps of:

providing a non-magnetic substrate; and

depositing at least one anisotropic, magnetically soft thin film in such a way that said non-magnetic substrate supports said film, said film including an alloy of cobalt-iron-chromium-nitrogen (Co--Fe--Cr--N) and having a saturation magnetization (4π

M_s) of at least approximately 8 kilogauss (kG), an anisotropy field (H_k) within the range from approximately 15 to 300 oersteds (Oe) and a magnetic hysteresis (M-H) loop squareness ratio (remanent magnetization, M_r, to saturation magnetization, M_s) of at least approximately 0.90, wherein said alloy contains, by atomic percentage, at least approximately 15% cobalt (Co), and wherein said article has been heat treated at a temperature of no more than approximately 150°

Celsius.

13. The method as recited in claim 12, wherein said Co--Fe--Cr--N alloy includes chromium (Cr) within the range from approximately 0 to 15 weight %.

14. The method as recited in claim 12, wherein the Co--Fe--Cr--N alloy contains cobalt (Co) within the range from approximately 30 to 60 weight %, iron (Fe) within the range from approximately 30 to 60 weight %, chromium (Cr) within the range from approximately 1 to 12 weight %, and nitrogen (N) within the range from approximately 0.7 to 5.0 weight %.

15. The method as recited in claim 12, wherein said depositing step is selected from the group consisting of sputtering, evaporation, molecular beam epitaxial growth, ion beam deposition and laser ablation.

16. The method as recited in claim 12, wherein said forming step further comprises depositing the elements of said alloy without nitrogen on said substrate, and then adding nitrogen to said alloy by ion implantation.

17. The method as recited in claim 12, wherein said forming step further comprises sputter-depositing said magnetically soft thin film on said substrate with a deposition angle of at least approximately 10 degrees.

18. The method as recited in claim 12, wherein said forming step further comprises sputter-depositing said magnetically soft thin film on said substrate at ambient temperature and in the presence of an applied magnetic field having a strength greater than approximately 2.0 oersteds (Oe).

19. The method as recited in claim 12, further comprising, after said depositing step, the step of heat treating said magnetically soft thin film below a temperature of approximately 150°

Celsius.

20. The method as recited in claim 12, wherein said depositing step further comprises depositing a plurality of magnetically soft thin film layers interleaved with corresponding plurality of dielectric spacer layers.

21. The method as recited in claim 12, further comprising the step of incorporating said magnetically soft thin film into an electromagnetic device selected from the group consisting of a microtransformer core, an inductor core, and a magnetic read-write head.