Magnetic thin film, magnetic sensor provided with same, and method for manufacturing magnetic sensor

Abstract

[Problem] To enhance the flatness of a hard magnetic film without using a plurality of targets in forming a base film. [Solution] A magnetic sensor 100 comprises a base film 30 provided on a substrate 10, a hard magnetic film 40 provided on a surface 34 of the base film 30 so as to be in contact with the base film 30, and a magnetoresistance effect element 60 provided on the hard magnetic film 40. The base film 30 includes a first base film 31 positioned on the substrate 10 side, and a second base film 32 that is made of the same material as the first base film 31 and is in contact with the hard magnetic film 40. In the base film 30, dislocation is present at an interface 33 between the first base film 31 and the second base film 32.

Description

Magnetic thin film, magnetic sensor including the same, and method for manufacturing the magnetic sensor

[0001] The present disclosure relates to a magnetic thin film, particularly to a magnetic thin film having a structure in which a hard magnetic film is laminated on the surface of an underlayer, and also to a magnetic sensor having a structure in which a magnetoresistive effect element is laminated on the magnetic thin film, and a method for manufacturing the same.

[0002] Non-Patent Document 1 proposes a method for improving the perpendicular orientation of a Co alloy magnetic film by using a laminated film consisting of a first underlayer made of TiCr and a second underlayer made of CoCr as the underlayer of the Co alloy magnetic film.

[0003] High-density magnetic recording using MR heads and single-layer perpendicular media (Journal of the Magnetic Society of Japan, Vol. 21, No. 6, 1997)

[0004] However, in the method proposed in Non-Patent Document 1, two targets made of different materials are required to form the first and second undercoating films by sputtering.

[0005] This disclosure describes a technique for improving the flatness of a hard magnetic film without using multiple targets to form an underlayer.

[0006] A magnetic sensor according to one aspect of the present disclosure comprises an underlayer film provided on a substrate, a hard magnetic film provided on the surface of the underlayer film so as to be in contact with the underlayer film, and a magnetoresistive effect element provided on the hard magnetic film, wherein the underlayer film includes a first underlayer film located on the substrate side and a second underlayer film made of the same material as the first underlayer film and in contact with the hard magnetic film, and dislocations occur in the underlayer film at the interface between the first underlayer film and the second underlayer film.

[0007] A method for manufacturing a magnetic sensor according to one aspect of the present disclosure includes a first step of forming a first underlayer film on a substrate using a vacuum chamber, a second step of forming a second underlayer film made of the same material as the first underlayer film on the surface of the first underlayer film using a vacuum chamber, a third step of forming a hard magnetic film in contact with the second underlayer film, and a fourth step of forming a magnetoresistive effect element on the hard magnetic film, and after performing the first step and before performing the second step, the surface of the first underlayer film is exposed to an atmosphere with a lower degree of vacuum than the degree of vacuum in the vacuum chamber in the first and second steps.

[0008] A magnetic thin film according to one aspect of the present disclosure comprises an underlayer film provided on a substrate, the underlayer film including a first underlayer film located on the substrate side and a second underlayer film made of the same material as the first underlayer film and having dislocations at the interface with the first underlayer film, and a hard magnetic film provided on the surface of the underlayer film so as to be in contact with the underlayer film.

[0009] According to the present disclosure, a technique for improving the flatness of a hard magnetic film is provided without using multiple targets to form an underlayer.

[0010] Fig. 1 is a schematic cross-sectional view illustrating a configuration of a magnetic sensor 100 according to a first embodiment of the technology disclosed herein. Fig. 2 is a schematic cross-sectional view illustrating a configuration of a magnetic sensor 200 according to a second embodiment of the technology disclosed herein.

[0011] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0012] FIG. 1 is a schematic cross-sectional view illustrating the configuration of a magnetic sensor 100 according to a first embodiment of the technique disclosed herein.

[0013] 1, the magnetic sensor 100 according to this embodiment includes a substrate 10, an insulating film 20 provided on a surface 11 of the substrate 10, an underlayer film 30 provided on a surface 21 of the insulating film 20, a hard magnetic film 40 provided on a surface 34 of the underlayer film 30, a protective film 50 provided on a surface 41 of the hard magnetic film 40, and a magnetoresistive element 60 provided on a surface 51 of the protective film 50. The laminate of the underlayer film 30 and the hard magnetic film 40 constitutes the magnetic thin film according to this embodiment.

[0014] The insulating film 20 is made of SiO ２ and Al ２ O ３ The insulating film 30 is an amorphous thin film made of an insulating material such as silicon dioxide, and serves to separate the substrate 10 and the base film 30 by being interposed between them.

[0015] The underlayer 30 is a crystalline thin film made of an alloy containing CrTi, and is used to enhance the orientation of the hard magnetic film 40. If the proportion of Cr in the underlayer 30 is set to 16 to 25 at %, the orientation of the hard magnetic film 40 can be further enhanced.

[0016] The hard magnetic film 40 is a crystalline thin film made of an alloy containing CoPt, and is used to apply a magnetic bias to the magnetoresistive element 60. If the proportion of C0 in the hard magnetic film 40 is set to 66 to 73 at %, the coercive force can be further increased.

[0017] The protective film 50 protects the surface 41 of the hard magnetic film 40 and can be made of the same material as the underlayer 30, for example.

[0018] The magnetoresistive element 60 is an element whose electrical resistance value changes depending on the direction and strength of a magnetic field, and may have a structure in which multiple functional films are stacked. Since a magnetic bias is applied to the magnetoresistive element 60 by the hard magnetic film 40, the magnetoresistive element 60 is ideally made into a single magnetic domain, thereby reducing random noise.

[0019] The underlayer 30 includes a first underlayer 31 located on the substrate 10 and insulating film 20 side and in contact with the surface 21 of the insulating film 20, and a second underlayer 32 located on the hard magnetic film 40 side and in contact with the hard magnetic film 40. Although the first underlayer 31 and the second underlayer 32 are made of the same material, dislocations occur at an interface 33 between them, and the interface 33 can be confirmed by observing a TEM image or the like. The interface 33 where dislocations occur plays a role in alleviating stress in the underlayer 30.

[0020] Here, if the stress of the underlayer 30 is large, it will have an adverse effect on the characteristics of the hard magnetic film 40 formed on its surface 34. Specifically, if the stress of the underlayer 30 is large and the hard magnetic film 40 is formed under conditions that increase the crystal grain size in order to increase the coercivity, the surface roughness of the surface 41 of the hard magnetic film 40 will increase, deteriorating the characteristics of the magnetoresistive element 60 formed thereon. In order to reduce the surface roughness of the surface 41 of the hard magnetic film 40, the hard magnetic film 40 can be formed under conditions that decrease the crystal grain size, but in this case the coercivity of the hard magnetic film 40 will decrease.

[0021] In contrast, when the stress of the underlayer 30 is relaxed, even if the hard magnetic film 40 is formed under conditions that result in a small crystal grain size, the crystal orientation is more aligned than when the stress of the underlayer 30 is large, making it possible to maintain the coercive force of the hard magnetic film 40. This increases the coercive force of the hard magnetic film 40, allowing a stronger magnetic bias to be applied to the magnetoresistive element 60. Furthermore, because the crystal grain size of the hard magnetic film 40 is small, the surface roughness of the surface 41 of the hard magnetic film 40 is reduced, thereby improving the characteristics of the magnetoresistive element 60 itself.

[0022] The position of the interface 33 formed in the underlayer 30 may be at the midpoint in the thickness direction, or may be offset toward the substrate 10. In other words, the thickness of the second underlayer 32 may be greater than the thickness of the first underlayer 31. By offsetting the position of the interface 33 toward the substrate 10, stress is released at an earlier stage during film formation, thereby improving the surface properties of the surface 34 of the underlayer 30. As a result, the surface roughness of the surface 41 of the hard magnetic film 40 can be reduced. Furthermore, the underlayer 30 may have two or more interfaces 33 at different positions in the thickness direction. In this case, the underlayer 30 has a three-layer or more structure. Providing two or more interfaces 33 in the underlayer 30 further reduces stress in the underlayer 30.

[0023] Next, a method for manufacturing the magnetic sensor 100 according to this embodiment will be described.

[0024] First, the substrate 10 is placed in a vacuum chamber, and the insulating film 20, the underlayer 30, the hard magnetic film 40, the protective film 50, and the magnetoresistive element 60 are formed in this order using a sputtering method or the like. Here, the process of forming the underlayer 30 is divided into a first process of forming a first underlayer 31 on the surface 21 of the insulating film 20, and a second process of forming a second underlayer 32 on the surface of the first underlayer 31. The first underlayer 31 and the second underlayer 32 are made of the same material, and therefore can be formed using the same target in the same vacuum chamber.

[0025] After the first step of forming the first base film 31 and before the second step of forming the second base film 32, an intermediate step is performed in which the surface of the first base film 31 is exposed to an atmosphere with a lower degree of vacuum (higher pressure) than the degree of vacuum in the vacuum chamber in the first and second steps. This breaks the continuity of the crystals in the base film 30, and therefore, when the second base film 32 is subsequently formed, an interface 33 is formed between the first base film 31 and the second base film 32.

[0026] The intermediate step may be performed by temporarily removing the substrate 10 from the vacuum chamber and then transferring the substrate 10 to another chamber with a lower degree of vacuum. In the former case, the other chamber with a lower degree of vacuum may be an air atmosphere or an inert gas atmosphere.

[0027] Furthermore, the hard magnetic film 40 may be deposited so as to have a larger crystal grain size by setting the input power of the sputtering device higher. Even when the hard magnetic film 40 is formed under such conditions, the stress in the underlayer 30 is relaxed, and therefore the flatness of the surface 41 of the hard magnetic film 40 is improved.

[0028] As described above, in the method for manufacturing the magnetic sensor 100 according to this embodiment, the above-described intermediate step is performed after the first step and before the second step, thereby alleviating stress in the underlayer 30. This makes it possible to improve the characteristics of the hard magnetic film 40 formed on the surface 34 of the underlayer 30. Moreover, since the first underlayer 31 and the second underlayer 32 are made of the same material, there is no need to use multiple targets to form the underlayer 30.

[0029] FIG. 2 is a schematic cross-sectional view for explaining the configuration of a magnetic sensor 200 according to a second embodiment of the technique disclosed herein.

[0030] 2, the magnetic sensor 200 according to this embodiment has a structure in which a recess R is provided in the above-described magnetic sensor 100. The recess R is provided so as to divide the underlayer 30, the hard magnetic film 40, and the protective film 50 into two, and a portion of the magnetoresistive element 60 is provided on the inner wall of the recess R. The above-described magnetic sensor 100 has a hard magnetic film 40 with a high magnetic flux density and a small crystal grain size, and therefore, as shown in FIG. 2, high detection sensitivity can be obtained even when the magnetoresistive element 60 is provided on the inner wall of the recess R.

[0031] The above describes embodiments of the technology according to the present disclosure, but the technology according to the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the gist of the technology, and it goes without saying that these modifications are also included within the scope of the technology according to the present disclosure.

[0032] The technology according to the present disclosure includes, but is not limited to, the following configuration examples.

[0033] A magnetic sensor according to one aspect of the present disclosure includes an underlayer film provided on a substrate, a hard magnetic film provided on the surface of the underlayer film so as to be in contact with the underlayer film, and a magnetoresistive element provided on the hard magnetic film, the underlayer film including a first underlayer film located on the substrate side and a second underlayer film made of the same material as the first underlayer film and in contact with the hard magnetic film, the underlayer film having dislocations at the interface between the first underlayer film and the second underlayer film, whereby stress in the underlayer film is alleviated, thereby improving the characteristics of the hard magnetic film.

[0034] The magnetic sensor may further include an amorphous insulating film provided between the substrate and the underlayer, whereby the substrate and the underlayer are separated by the insulating film.

[0035] In the above magnetic sensor, the underlayer may contain CrTi, which improves the orientation of the hard magnetic film.

[0036] In the above magnetic sensor, the hard magnetic film may contain CoPt, which increases the coercive force of the hard magnetic film.

[0037] A method for manufacturing a magnetic sensor according to one aspect of the present disclosure includes a first step of forming a first underlayer on a substrate using a vacuum chamber, a second step of forming a second underlayer made of the same material as the first underlayer on a surface of the first underlayer, using the vacuum chamber, a third step of forming a hard magnetic film in contact with the second underlayer, and a fourth step of forming a magnetoresistive element on the hard magnetic film, wherein after performing the first step and before performing the second step, the surface of the first underlayer is exposed to an atmosphere with a lower vacuum than the vacuum in the vacuum chamber used in the first and second steps. This method improves the flatness of the hard magnetic film without using multiple targets to form the underlayer.

[0038] A magnetic thin film according to one aspect of the present disclosure includes an underlayer film provided on a substrate, the underlayer film including a first underlayer film located on the substrate side and a second underlayer film made of the same material as the first underlayer film and having dislocations at the interface with the first underlayer film, and a hard magnetic film provided on the surface of the underlayer film so as to be in contact with the underlayer film, whereby stress in the underlayer film is alleviated, thereby improving the characteristics of the hard magnetic film.

[0039] This application claims the benefit of Japanese Patent Application No. 2024-035719, filed March 8, 2024, the entire disclosure of which is incorporated herein by reference.

[0040] REFERENCE SIGNS LIST 10 Substrate 11 Surface of substrate 20 Insulating film 21 Surface of insulating film 30 Undercoat film 31 First undercoat film 32 Second undercoat film 33 Interface 34 Surface of undercoat film 40 Hard magnetic film 41 Surface of hard magnetic film 50 Protective film 51 Surface of protective film 60 Magnetoresistance effect element 100, 200 Magnetic sensor R Recess

Claims

1. A magnetic sensor comprising: an underlayer provided on a substrate; a hard magnetic film provided on the surface of the underlayer so as to be in contact with the underlayer; and a magnetoresistive element provided on the hard magnetic film, wherein the underlayer includes a first underlayer located on the substrate side and a second underlayer made of the same material as the first underlayer and in contact with the hard magnetic film, and wherein dislocations occur in the underlayer at the interface between the first underlayer and the second underlayer.

2. The magnetic sensor according to claim 1, further comprising an amorphous insulating film provided between the substrate and the base film.

3. The magnetic sensor according to claim 1, wherein the underlayer includes CrTi.

4. The magnetic sensor according to claim 1, wherein the hard magnetic film includes CoPt.

5. A method for manufacturing a magnetic sensor, comprising: a first step of forming a first underlayer on a substrate using a vacuum chamber; a second step of forming a second underlayer made of the same material as the first underlayer on the surface of the first underlayer using the vacuum chamber; a third step of forming a hard magnetic film in contact with the second underlayer; and a fourth step of forming a magnetoresistive effect element on the hard magnetic film, wherein after performing the first step and before performing the second step, the surface of the first underlayer is exposed to an atmosphere with a lower degree of vacuum than the degree of vacuum in the vacuum chamber in the first and second steps.

6. A magnetic thin film comprising: an underlayer film provided on a substrate, the underlayer film including a first underlayer film located on the substrate side; and a second underlayer film made of the same material as the first underlayer film and having dislocations at the interface with the first underlayer film; and a hard magnetic film provided on the surface of the underlayer film so as to be in contact with the underlayer film.

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