Magnetic sensor

Abstract

The magnetic sensor includes a non-magnetic substrate and a sensing element 31. The sensing element 31 has a long-side direction and a short-side direction, has uniaxial magnetic anisotropy in a direction intersecting the long-side direction, and senses a magnetic field through the magneto-impedance effect. The sensing element 31 includes a plurality of soft magnetic layers 105a to 105d, and a plurality of non-magnetic layers 106a to 106c formed of a non-magnetic material and laminated between the plurality of soft magnetic layers 105a to 105d. The soft magnetic layers 105a to 105d facing each other with the respective non-magnetic layers 106a to 106c interposed therebetween are antiferromagnetically coupled.

Description

Technical Field

[0001] The present invention relates to a magnetic sensor. Background Art

[0002] As an existing technology described in a publication, there is a magneto-impedance effect element having: a thin-film magnet formed on a non-magnetic substrate and formed of a hard magnetic film; an insulating layer covering the upper part of the thin-film magnet; and a magneto-sensitive part formed on the insulating layer, given uniaxial anisotropy, and formed of one or more rectangular soft magnetic films (see Patent Document 1).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-249406 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] In a magnetic sensor using an induction element having a soft magnetic layer as a magneto-impedance effect element, depending on the stacking structure of the induction element, the signal-to-noise ratio (SN ratio) in the output from the magnetic sensor sometimes decreases.

[0008] An object of the present invention is to suppress a decrease in the SN ratio in the output of a magnetic sensor utilizing the magneto-impedance effect.

[0009] Means for Solving the Problems

[0010] A magnetic sensor to which the present invention is applied includes a non-magnetic substrate and an induction element. The induction element has a long-side direction and a short-side direction, has uniaxial magnetic anisotropy in a direction crossing the long-side direction, and senses a magnetic field by the magneto-impedance effect. The induction element has a plurality of soft magnetic layers and a plurality of non-magnetic layers formed of a non-magnetic material and stacked between the plurality of soft magnetic layers. The soft magnetic layers sandwiching each non-magnetic layer are antiferromagnetically coupled.

[0011] Here, each of the non-magnetic layers may be formed of Ru or a Ru alloy.

[0012] In addition, the thickness of each of the non-magnetic layers may be in the range of 0.6 nm or more and 1.4 nm or less.

[0013] In addition, it may be that when the soft magnetic layer is observed in the stacking direction of the soft magnetic layer, the induction element does not form a closed magnetic domain.

[0014] Effects of the Invention

[0015] According to the present invention, it is possible to suppress a decrease in the signal-to-noise ratio in the output of a magnetic sensor utilizing the magneto-impedance effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 (a) to (b) are diagrams for explaining an example of a magnetic sensor to which the present embodiment is applied.

[0017] Figure 2 is a diagram for explaining the configuration of an induction element to which the present embodiment is applied.

[0018] Figure 3 is a diagram for explaining the relationship between the magnetic field applied in the longitudinal direction of the induction element in the induction unit of the magnetic sensor and the impedance of the induction unit.

[0019] Figure 4 (a) to (d) are diagrams for explaining the relationship between the intensity of the magnetic field H applied to the induction element in a conventional magnetic sensor and the change in magnetic domains in the induction element.

[0020] Figure 5 is a diagram for explaining the relationship between the intensity of the magnetic field applied to the induction element and the intensity of magnetization in the induction element.

[0021] Figure 6 is for Figure 2 a photograph taken of the state of magnetic domains of an induction element to which the present embodiment is applied and having the laminated structure shown.

[0022] Figure 7 (a) to (b) are photographs taken of the state of magnetic domains of a conventional induction element. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0024] Figure 1 (a) to (b) are diagrams for explaining an example of a magnetic sensor 1 to which the present embodiment is applied. Figure 1 (a) is a top view of the magnetic sensor 1, Figure 1 (b) is a cross-sectional view taken along the Figure 1 IB-IB line in (a).

[0025] As Figure 1 (b) shows, the magnetic sensor 1 to which the present embodiment is applied includes: a thin-film magnet 20 provided on a non-magnetic substrate 10 and composed of a hard magnet (hard magnet layer 103); and an induction unit 30 laminated opposite to the thin-film magnet 20 and including a soft magnet (soft magnet layer 105) and a non-magnet (non-magnet layer 106, see the following​​​​​​​Figure 2 ) and is configured to sense a magnetic field.

[0026] The cross-sectional structure of the magnetic sensor 1 will be described in detail later.

[0027] Here, the hard magnet is a material with a so-called large coercive force, that is, if it is magnetized by an external magnetic field, it remains magnetized even when the external magnetic field is removed. On the other hand, the soft magnet is a material with a so-called small coercive force, that is, it is easily magnetized by an external magnetic field, but if the external magnetic field is removed, it quickly returns to a state of no magnetization or small magnetization.

[0028] It should be noted that in this specification, the elements (such as the thin-film magnet 20) constituting the magnetic sensor 1 are represented by two digits, and the layers (such as the hard-magnet layer 103) processed into the elements are represented by numbers in the 100 series. Moreover, for the numbers of the elements, the numbers of the layers processed into the elements are sometimes recorded in parentheses. For example, in the case of the thin-film magnet 20, it is recorded as the thin-film magnet 20 (hard-magnet layer 103). In the figure, it is recorded as 20 (103). The same applies to other cases.

[0029] Using Figure 1 (a) The planar structure of the magnetic sensor 1 will be described. As an example, the magnetic sensor 1 has a quadrilateral planar shape. Here, the induction portion 30 and the yoke 40 formed on the uppermost part of the magnetic sensor 1 will be described.

[0030] The induction portion 30 includes a plurality of induction elements 31, a connection portion 32 that serially connects adjacent induction elements 31 in a meandering shape, and a terminal portion 33 to which a wire for supplying current is connected. In Figure 1 (a) In the induction portion 30 of the magnetic sensor 1 shown, four induction elements 31 are arranged side by side in the long side direction. The induction element 31 is a magneto-impedance effect element.

[0031] For the induction element 31, for example, the length in the long side direction is 1 mm to 2 mm, and the width in the short side direction is 50 μm to 150 μm. In addition, the interval between adjacent induction elements 31 is 50 μm to 150 μm.

[0032] The connection portion 32 is provided between the ends of adjacent induction elements 31 and serially connects adjacent induction elements 31 in a meandering shape. Figure 1In the magnetic sensor 1 shown in (a), four sensing elements 31 are arranged in parallel, so there are three connecting parts 32. The number of connecting parts 32 varies according to the number of sensing elements 31. For example, when there are three sensing elements 31, there are two connecting parts 32. In addition, when there is one sensing element 31, there is no connecting part 32. It should be noted that the width of the connecting part 32 can be set according to the magnitude of the pulse voltage applied to the sensing part 30 by the voltage application part 3, etc. For example, the width of the connecting part 32 can be the same as that of the sensing element 31.

[0033] Terminal parts 33 are respectively provided at the ends (two) of the sensing elements 31 not connected by the connecting part 32. The terminal parts 33 only need to be of a size capable of connecting wires. It should be noted that in the sensing part 30 of the present embodiment, since there are four sensing elements 31, two terminal parts 33 are provided on the left side in Figure 1 (a). When the number of sensing elements 31 is odd, the two terminal parts 33 can be arranged separately on the left and right.

[0034] In addition, the magnetic sensor 1 includes a magnetic yoke 40 provided opposite to the ends in the long side direction of the sensing element 31. Here, two magnetic yokes 40a and 40b are respectively provided opposite to the two ends in the long side direction of the sensing element 31. It should be noted that when the magnetic yokes 40a and 40b are not distinguished from each other, they are referred to as the magnetic yoke 40. The magnetic yoke 40 guides the magnetic force lines to the ends in the long side direction of the sensing element 31. Therefore, the magnetic yoke 40 is made of a soft magnetic material (soft magnetic layer 105) through which magnetic force lines easily pass. It should be noted that when the magnetic force lines sufficiently pass through in the long side direction of the sensing element 31, the magnetic yoke 40 may not be provided.

[0035] Based on the above, the size of the magnetic sensor 1 is several millimeters square in planar shape. It should be noted that the size of the magnetic sensor 1 can also be other values.

[0036] Next, Figure 1 (b) is used to explain the cross-sectional structure of the magnetic sensor 1. The magnetic sensor 1 is composed of a non-magnetic substrate 10, on which a bonding layer 101, a control layer 102, a hard magnetic layer 103 (thin film magnet 20), a dielectric layer 104, a sensing part 30 formed by a soft magnetic layer 105 and a non-magnetic layer 106, and a magnetic yoke 40 formed by the soft magnetic layer 105 are sequentially arranged (stacked) and bonded.

[0037] The substrate 10 is a substrate made of a non-magnetic material, and examples thereof include oxide substrates such as glass and sapphire, semiconductor substrates such as silicon, or metal substrates such as aluminum, stainless steel, and metals plated with nickel-phosphorus.

[0038] The adhesion layer 101 is a layer for improving the adhesion between the control layer 102 and the substrate 10. As the adhesion layer 101, an alloy containing Cr or Ni is preferably used. Examples of the alloy containing Cr or Ni include CrTi, CrTa, NiTa, etc. The thickness of the adhesion layer 101 is, for example, 5 nm to 50 nm. It should be noted that if the adhesion between the control layer 102 and the substrate 10 is not a problem, the adhesion layer 101 does not have to be provided. It should be noted that in this specification, the composition ratio of the alloy containing Cr or Ni is not shown. The same applies hereinafter.

[0039] The control layer 102 is a layer for controlling the magnetic anisotropy of the thin film magnet 20 composed of the hard magnetic layer 103 to be easily presented in the in-plane direction of the film. As the control layer 102, Cr, Mo, or W or an alloy containing them (hereinafter, referred to as the alloy containing Cr, etc. constituting the control layer 102) is preferably used. Examples of the alloy containing Cr, etc. constituting the control layer 102 include CrTi, CrMo, CrV, CrW, etc. The thickness of the control layer 102 is, for example, 10 nm to 300 nm.

[0040] The hard magnetic layer 103 constituting the thin film magnet 20 preferably uses an alloy having Co as the main component and containing either or both of Cr and Pt (hereinafter, referred to as the Co alloy constituting the thin film magnet 20). Examples of the Co alloy constituting the thin film magnet 20 include CoCrPt, CoCrTa, CoNiCr, CoCrPtB, etc. It should be noted that Fe may also be included. The thickness of the hard magnetic layer 103 is, for example, 1 μm to 3 μm.

[0041] The alloy containing Cr, etc. constituting the control layer 102 has a bcc (body-centered cubic) structure. Therefore, the hard magnet (hard magnetic layer 103) constituting the thin film magnet 20 is preferably an hcp (hexagonal close-packed) structure that is easy to grow crystals on the control layer 102 composed of the alloy containing Cr, etc. having a bcc structure. If the hcp-structured hard magnetic layer 103 grows crystals on the bcc structure, it is easy to orient the c-axis of the hcp structure in the in-plane direction. Therefore, the thin film magnet 20 composed of the hard magnetic layer 103 is likely to have magnetic anisotropy in the in-plane direction. It should be noted that the hard magnetic layer 103 is a polycrystal formed by a collection of different crystal orientations, and each crystal has magnetic anisotropy in the in-plane direction. This magnetic anisotropy comes from crystal magnetic anisotropy.

[0042] Note that, in order to promote the crystal growth of the alloy containing Cr, etc. that constitutes the control layer 102 and the Co alloy that constitutes the thin film magnet 20, it is appropriate to heat the substrate 10 to 100°C to 600°C. By this heating, the alloy containing Cr, etc. that constitutes the control layer 102 is prone to crystal growth, and it is easy to perform crystal orientation in such a manner that the hard magnetic layer 103 having an hcp structure has an easy magnetization axis in the plane. That is, it is easy to impart magnetic anisotropy to the plane of the hard magnetic layer 103.

[0043] The dielectric layer 104 is composed of a non-magnetic dielectric, and electrically insulates the thin film magnet 20 from the induction portion 30. Examples of the dielectric that constitutes the dielectric layer 104 include oxides such as SiO2, Al2O3, and TiO2, or nitrides such as Si3N4 and AlN. In addition, the thickness of the dielectric layer 104 is, for example, 0.1 μm to 30 μm.

[0044] Each induction element 31 of the induction portion 30 is formed by alternately laminating three or more soft magnetic layers 105 and two or more (i.e., a plurality of) non-magnetic layers 106. Figure 2 FIG. is for explaining the configuration of the induction element 31 to which the present embodiment is applied, and is Figure 1 an enlarged cross-sectional view of the induction element 31 in the magnetic sensor 1 shown in (b).

[0045] In Figure 2 the example shown, in the induction element 31, four soft magnetic layers 105a, 105b, 105c, 105d, and three non-magnetic layers 106a, 106b, 106c are alternately laminated. Note that, in the description of the present embodiment, without distinguishing the four soft magnetic layers 105a to 105d and the three non-magnetic layers 106a to 106c from each other, they are respectively described as the soft magnetic layer 105 and the non-magnetic layer 106.

[0046] In addition, as Figure 2 shown, the lowermost layer and the uppermost layer of the induction element 31 are composed of the soft magnetic layer 105. In other words, in the induction element 31, the non-magnetic layer 106 is laminated between a plurality of soft magnetic layers 105.

[0047] In the magnetic sensor 1 of the present embodiment, in order to achieve the effect, the number of the soft magnetic layers 105 must be three or more. In addition, from the viewpoints of the thickness and manufacturing cost of the induction element 31, the number of the soft magnetic layers 105 is preferably 20 or less.

[0048] In the sensing element 31, the soft magnetic layers 105 facing each other with the non-magnetic layer 106 interposed therebetween are antiferromagnetically coupled (AFC: Anti-Ferro-Coupling) through the action of the non-magnetic layer 106. More specifically, in the sensing element 31, the soft magnetic layer 105a and the soft magnetic layer 105b facing each other with the non-magnetic layer 106a interposed therebetween are antiferromagnetically coupled, the soft magnetic layer 105b and the soft magnetic layer 105c facing each other with the non-magnetic layer 106b interposed therebetween are antiferromagnetically coupled, and the soft magnetic layer 105c and the soft magnetic layer 105d facing each other with the non-magnetic layer 106c interposed therebetween are antiferromagnetically coupled.

[0049] As the soft magnetic layer 105, it is preferable to use an amorphous alloy obtained by adding high melting point metals such as Nb, Ta, and W to an alloy mainly composed of Co (hereinafter, referred to as the Co alloy constituting the soft magnetic layer 105). Examples of the Co alloy constituting the soft magnetic layer 105 include CoNbZr, CoFeTa, and CoWZr.

[0050] In addition, the thickness of each soft magnetic layer 105 can be in the range of 1 nm or more and 250 nm or less, and preferably in the range of 10 nm or more and 125 nm or less.

[0051] As the non-magnetic layer 106, a non-magnetic transition metal having the function of antiferromagnetically coupling the soft magnetic layers 105 facing each other with the non-magnetic layer 106 interposed therebetween can be used. Specifically, metals such as Ru, Re, Cr, and Cu, and alloys containing them can be cited, and Ru or an Ru alloy is preferably used.

[0052] In addition, the thickness of each non-magnetic layer 106 also varies depending on the material constituting the non-magnetic layer 106. In the case of using Ru, it can be in the range of 0.6 nm or more and 1.4 nm or less, and preferably in the range of 0.8 nm or more and 1.2 nm or less. When the thickness of the non-magnetic layer 106 is outside this range, the antiferromagnetic coupling energy between the soft magnetic layers 105 facing each other with the non-magnetic layer 106 interposed therebetween may become weak. In this case, the closed magnetic domains described later are likely to be formed in the sensing element 31.

[0053] Moreover, for the sensing element 31, uniaxial magnetic anisotropy is imparted in a direction crossing the long side direction, for example, in the short side direction orthogonal to the long side direction (i.e., the width direction of the sensing element 31). It should be noted that the direction crossing the long side direction only needs to have an angle of more than 45° with respect to the long side direction.

[0054] Back to Figure 1(a) and (b), the conductive layer 107 forming the connection part 32 and the terminal part 33 only needs to be a conductor with excellent conductivity. For example, Ag, Cu, Au, Al, etc. can be used, and there is no particular limitation. In addition, the connection part 32 and the terminal part 33 may be constituted by a soft magnetic layer 105 and a non-magnetic layer 106 formed integrally with the sensing element 31.

[0055] In the magnetic sensor 1 of the present embodiment, the bonding layer 101, the control layer 102, the hard magnetic layer 103, and the dielectric layer 104 are processed in a planar shape to be quadrilateral (see Figure 1 ). Thus, in two opposite sides of the exposed side surfaces, the thin film magnet 20 becomes the N pole ( Figure 1 (N) in (b)) and the S pole ( Figure 1 (S) in (b)). It should be noted that the line connecting the N pole and the S pole of the thin film magnet 20 is oriented in the long side direction of the sensing element 31 of the sensing part 30. Here, the long side direction means that the angle formed by the line connecting the N pole and the S pole and the long side direction is less than 45°. It should be noted that the smaller the angle formed by the line connecting the N pole and the S pole and the long side direction, the better.

[0056] In the magnetic sensor 1, the magnetic force lines emitted from the N pole of the thin film magnet 20 are first emitted to the outside of the magnetic sensor 1. Then, a part of the magnetic force lines pass through the sensing element 31 through the magnetic yoke 40a and are emitted to the outside again through the magnetic yoke 40b. Then, the magnetic force lines that have passed through the sensing element 31 and the magnetic force lines that have not passed through the sensing element 31 return to the S pole of the thin film magnet 20 together. That is, the thin film magnet 20 applies a magnetic field (the bias magnetic field Hb described later) in the long side direction of the sensing element 31.

[0057] It should be noted that the N pole and the S pole of the thin film magnet 20 are collectively referred to as two magnetic poles, and when the N pole and the S pole are not distinguished, they are referred to as magnetic poles.

[0058] It should be noted that as shown in Figure 1 (a), the magnetic yoke 40 (magnetic yokes 40a, 40b) is configured such that the shape observed from the surface side of the substrate 10 becomes narrower as it approaches the sensing part 30. This is to concentrate the magnetic field (converge the magnetic induction lines) on the sensing part 30. That is, the magnetic field in the sensing part 30 is enhanced to further improve the sensitivity. It should be noted that the width of the part of the magnetic yoke 40 (magnetic yokes 40a, 40b) opposite to the sensing part 30 may not be reduced.

[0059] Here, the interval between the magnetic yoke 40 (magnetic yokes 40a, 40b) and the sensing part 30 may be, for example, 1 μm to 100 μm.

[0060] (Function of the magnetic sensor 1)

[0061] Next, the operation of the magnetic sensor 1 will be described. Figure 3 FIG. for explaining the relationship between the magnetic field applied in the long side direction of the sensing element 31 in the sensing section 30 of the magnetic sensor 1 and the impedance of the sensing section 30. Figure 3 In, the horizontal axis is the magnetic field H and the vertical axis is the impedance Z. For the impedance Z of the sensing section 30, a high-frequency current is passed between the two terminal sections 33 for measurement.

[0062] As Figure 3 shown, the impedance Z of the sensing section 30 increases as the magnetic field H applied in the long side direction of the sensing element 31 increases. In the range where the applied magnetic field H is less than the anisotropic magnetic field Hk of the sensing element 31, when using the portion where the change amount ΔZ of the impedance Z with respect to the change amount ΔH of the magnetic field H is steep (ΔZ / ΔH is large), the weak change of the magnetic field H can be extracted in the form of the change amount ΔZ of the impedance Z. Figure 3 In, the center of the magnetic field H where ΔZ / ΔH is large is denoted as the magnetic field Hb. That is, the change amount (ΔH) of the magnetic field H in the vicinity of the magnetic field Hb ( Figure 3 the range indicated by the arrow in ) can be measured with high precision. The magnetic field Hb is sometimes referred to as the bias magnetic field.

[0063] (Problems that occur in conventional magnetic sensors)

[0064] However, in a conventional magnetic sensor having the sensing element 31 as a magneto-impedance effect element, depending on the stacking structure of the sensing element 31, the signal-to-noise ratio (SN ratio) of the output from the magnetic sensor sometimes decreases. For example, when the sensing element 31 is composed of a single layer of soft magnetic layer or when a single layer of non-magnetic layer is stacked between two layers of soft magnetic layers, the SN ratio sometimes decreases. It is speculated that this is because a closed magnetic domain with a circular magnetization direction is formed in the sensing element 31 (details will be described later), and near the magnetic field Hb, the magnetic wall constituting the closed magnetic domain moves as the magnetic field H changes.

[0065] Hereinafter, the phenomenon of the decrease in the SN ratio of the magnetic sensor due to the closed magnetic domain formed in the sensing element 31 will be specifically described.

[0066] Figure 4 (a) to (d) are FIGS. for explaining the relationship between the intensity of the magnetic field H applied to the sensing element 31 in a conventional magnetic sensor and the change of the magnetic domain in the sensing element 31. It should be noted that here, in the initial state where the magnetic field H is 0, uniaxial magnetic anisotropy has been imparted in the short side direction of the sensing element 31.

[0067] Figure 4(a) shows an example of the magnetic domain structure of the induction element 31 in a very weak state where the magnetic field H is close to 0 (referred to as the "initial permeability range", details will be described later). Figure 4 (b) shows the state where the magnetic field H is stronger than the state shown in Figure 4 (a) (referred to as the "irreversible magnetic wall movement range", details will be described later), and shows an example of the magnetic domain structure of the induction element 31. Figure 4 (c) shows the state where the magnetic field H is stronger than the state shown in Figure 4 (b) (referred to as the "rotational magnetization range", details will be described later), and shows an example of the magnetic domain structure of the induction element 31. Figure 4 (d) shows the state where the magnetic field H is stronger than the state shown in Figure 4 (c) (referred to as "saturation", details will be described later), and shows an example of the magnetic domain structure of the induction element 31.

[0068] Figure 5 It is a diagram for explaining the relationship between the intensity of the magnetic field applied to the induction element 31 and the intensity of the magnetization in the induction element 31. Figure 5 In this diagram, the horizontal axis represents the magnetic field H (Oe), and the vertical axis represents the magnetization M (a.u.). It should be noted that Figure 5 the relationship between the above-mentioned magnetic field H and magnetization M, and the above "initial permeability range", "irreversible magnetic wall movement range", "rotational magnetization range", and "saturation" is also shown.

[0069] The range in which the magnetic field H externally applied to the induction element 31 ranges from 0 to the magnetic wall movement magnetic field Hw (details will be described later) is called the "initial permeability range".

[0070] Within the initial permeability range, multiple magnetic domains with different directions of magnetization M are formed in the induction element 31. More specifically, the induction element 31 has a first magnetic domain D1 and a second magnetic domain D2 with the direction of magnetization M facing the easy magnetization axis direction (short side direction), and a third magnetic domain D3 and a fourth magnetic domain D4 with the direction of magnetization M facing the hard magnetization axis direction (long side direction). At this time, the first magnetic domain D1 and the second magnetic domain D2 are opposite to each other, and the third magnetic domain D3 and the fourth magnetic domain D4 are also opposite to each other. Moreover, these four magnetic domains are cyclically arranged in the clockwise direction in the figure to form a "first magnetic domain D1" → "third magnetic domain D3" → "second magnetic domain D2" → "fourth magnetic domain D4" → "first magnetic domain D1" cycle. As a result, when these four magnetic domains are viewed as a whole, a closed magnetic domain with a ring-shaped magnetization M direction is formed.

[0071] In addition, macroscopically, in the induction element 31, a plurality of closed magnetic domains are arranged along the long side direction. Moreover, in each closed magnetic domain, based on the relationship between the above-mentioned easy magnetization axis and hard magnetization axis, the areas of the first magnetic domain D1 and the second magnetic domain D2 along the easy magnetization axis are larger than the areas of the third magnetic domain D3 and the fourth magnetic domain D4 along the hard magnetization axis.

[0072] Moreover, within the initial permeability range, with respect to the change in the magnetic field H, each magnetic domain constituting each closed magnetic domain maintains its original state. In other words, when the magnetic field H is in the range of 0 to the magnetic wall movement magnetic field Hw, even if the magnetic field H increases, Figure 4 the magnetic domain structure shown in (a) remains unchanged.

[0073] The range from the magnetic wall movement magnetic field Hw to the magnetization rotation magnetic field Hr (details will be described later) of the magnetic field H externally applied to the induction element 31 is referred to as the "irreversible magnetic wall movement range".

[0074] If the magnetic field H exceeds the magnetic wall movement magnetic field Hw determined based on the characteristics (material, structure, size, etc.) of the soft magnetic layer 105 constituting the induction element 31, magnetic wall movement occurs in each closed magnetic domain (that is, the position of the magnetic wall existing between adjacent magnetic domains moves with the action of the magnetic field H). At this time, in each closed magnetic domain, the magnetic wall existing between the fourth magnetic domain D4 (the direction of its magnetization M is the same as the magnetic field H) and the first and second magnetic domains D1, D2 (adjacent to the fourth magnetic domain D4) moves to the side that increases the area of the fourth magnetic domain D4. In addition, the magnetic wall existing between the third magnetic domain D3 (the direction of its magnetization M is opposite to the magnetic field H) and the first and second magnetic domains D1, D2 (adjacent to the third magnetic domain D3) moves to the side that reduces the area of the third magnetic domain D3. As a result, the area of the fourth magnetic domain D4 is larger than that in the Figure 4 initial permeability range shown in (a), and the areas of the remaining first magnetic domain D1 to the third magnetic domain D3 are smaller than those in the initial permeability range.

[0075] In addition, the magnetic wall movement within the irreversible magnetic wall movement range occurs discontinuously as the magnetic field H increases. As a result, as shown in the enlarged main part of Figure 5 , the change in the magnetization M of the entire induction element 31 with respect to the change in the magnetic field H is not linear or curved, but stepped (sawtooth-shaped). It should be noted that such a relationship between the magnetic field H and the magnetization M is called the Barkhausen effect.

[0076] Moreover, within the range of irreversible magnetic wall movement, the state where the area ratio of each magnetic domain constituting each closed magnetic domain gradually changes with the change in the magnetic field H continues. More specifically, when the magnetic field H is in the range of the magnetic wall movement magnetic field Hw to the magnetization rotation magnetic field Hr, as the magnetic field H increases, the area of the fourth magnetic domain D4 gradually increases, and the areas of the first to third magnetic domains D1 to D3 gradually decrease.

[0077] The range where the externally applied magnetic field H reaches the anisotropic magnetic field Hk from the magnetization rotation magnetic field Hr is called the "rotation magnetization range".

[0078] When the magnetic field H exceeds the magnetization rotation magnetic field Hr determined based on the characteristics (material, structure, size, etc.) of the soft magnetic layer 105 constituting the induction element 31, in each closed magnetic domain, in a state where the positions of the magnetic walls existing between adjacent magnetic domains are substantially fixed, in the first to third magnetic domains D1 to D3 where the direction of magnetization M is different from the direction of the magnetic field H, magnetization rotation occurs (i.e., gradually rotates so that the direction of magnetization M faces the side where the direction of the magnetic field H is the same). At this time, since the magnetization direction of the fourth magnetic domain D4 itself is already the same as the direction of the magnetic field H, it maintains its original state.

[0079] Moreover, within the rotation magnetization range, the area ratio of each magnetic domain constituting each closed magnetic domain hardly changes with the change in the magnetic field H. On the other hand, the state where the direction of magnetization M of the first to third magnetic domains D1 to D3 gradually changes continues. More specifically, when the magnetic field H is in the range of the magnetization rotation magnetic field Hr to the anisotropic magnetic field Hk, as the magnetic field H increases, although the direction of magnetization M of the fourth magnetic domain D4 remains unchanged, the directions of magnetization M of the other first to third magnetic domains D1 to D3 gradually rotate toward the side where the direction of the magnetic field H is the same.

[0080] Among them, within the rotation magnetization range, the rotation of the direction of magnetization M in the first to third magnetic domains D1 to D3 occurs continuously. Therefore, within the rotation magnetization range, the change in the magnetization M of the entire induction element 31 with respect to the magnetic field H is as Figure 5 shown in a curved shape. Moreover, within the rotation magnetization range, the increase in the magnetization M of the entire induction element 31 with respect to the increase in the magnetic field H slows down as the magnetic field H increases, and becomes substantially flat near the anisotropic magnetic field Hk where it reaches the maximum value.

[0081] The region where the externally applied magnetic field H exceeds the anisotropic magnetic field Hk is called "saturation".

[0082] If the magnetic field H exceeds the above-described anisotropic magnetic field Hk, the direction of magnetization M in each closed magnetic domain is aligned with the direction of the magnetic field H, i.e., the direction of magnetization M in the fourth magnetic domain D4. As a result, the magnetic walls existing between adjacent magnetic domains disappear, and the induction element 31 is formed of one magnetic domain (single magnetic domain).

[0083] In addition, at saturation, as the magnetic domain structure changes from a structure having multiple closed magnetic domains to a structure having a single magnetic domain, the magnetization M of the entire induction element 31 does not change with respect to the change in the magnetic field H and becomes a substantially constant value.

[0084] Generally, in a magnetic sensor, the magnitude of the bias magnetic field Hb is set to an irreversible magnetic wall movement range where the change in magnetization M with respect to the change in magnetic field H, ΔH, is large (i.e., the change in impedance Z with respect to the change in magnetic field H, ΔZ, is large). Moreover, within the irreversible magnetic wall movement range, when closed magnetic domains are formed in the induction element 31, the Barkhausen effect occurs in which the magnetic walls constituting the closed magnetic domains move discontinuously in a stepped manner with the change in the magnetic field H. It is presumed that the discontinuous movement of the magnetic walls in the induction element 31 becomes noise, and the SN ratio in the output obtained from the magnetic sensor decreases.

[0085] Therefore, in order to reduce the noise associated with the discontinuous movement of the magnetic walls and suppress the decrease in the SN ratio in the output obtained from the magnetic sensor, it is preferable to increase the magnetic domains formed in the induction element 31 so that no closed magnetic domains are formed in the induction element 31.

[0086] (Magnetic domain structure of the induction element 31 of the present embodiment)

[0087] In view of this, in the magnetic sensor 1 of the present embodiment, as described above, the induction element 31 is formed into a structure in which three or more soft magnetic layers 105 and two or more non-magnetic layers 106 are alternately laminated, thereby making it difficult to form closed magnetic domains in the induction element 31.

[0088] Hereinafter, the magnetic domain structure of the induction element 31 to which the present embodiment is applied will be described while comparing it with the conventional induction element 31.

[0089] Figure 6 For Figure 2 a photograph taken to capture the state of the magnetic domains of the induction element 31 of the present embodiment having the laminated structure shown. In addition, Figure 7 (a) to (b) are photographs taken to capture the state of the magnetic domains of the conventional induction element 31. Here, Figure 6 and Figure 7 (a) to (b) show the state of the magnetic domains when a magnetic field H of +0.5 Oe is applied to the induction element 31. In addition, Figure 6 andFigure 7 (a) to (b) were taken using Neomagnesia Lite manufactured by Neo Ark Corporation.

[0090] Figure 6 Among them, the film thickness of each soft magnetic layer 105 constituting the induction element 31 was made 0.25 μm, and the thickness of each non-magnetic layer 106 was made 1.0 nm. Figure 7 In (a), as a conventional induction element 31, the magnetic domain state when the induction element 31 is composed of one soft magnetic layer 105 with a thickness of 1.0 μm is shown. In addition, Figure 7 In (b), as a conventional induction element 31, the magnetic domain state when one non-magnetic layer 106 with a thickness of 1.0 nm is laminated between two soft magnetic layers 105 with a thickness of 0.5 μm is shown. In addition, in Figure 6 and Figure 7 the induction element 31 shown in (a) to (b), Co 85 Nb 12 Zr3 is used as the soft magnetic layer 105, and Ru is used as the non-magnetic layer 106.

[0091] As Figure 7 shown in (a) to (b), it can be seen that in the case where the induction element 31 is composed of one soft magnetic layer 105, and in the case where one non-magnetic layer 106 is laminated between two soft magnetic layers 105, a plurality of magnetic domains (corresponding to the first magnetic domain D1 and the second magnetic domain D2) along the short side direction of the induction element 31 are arranged in the long side direction. In addition, it can also be seen that at both ends in the short side direction of the induction element 31, a plurality of magnetic domains (corresponding to the third magnetic domain D3 and the fourth magnetic domain D4) along the long side direction of the induction element 31 are arranged in the long side direction. It is considered that in this example, in Figure 7 the induction element 31 shown in (a) to (b), as Figure 4 shown in (a), closed magnetic domains are formed.

[0092] Moreover, it is speculated that in a conventional magnetic sensor having such an induction element 31 in which closed magnetic domains are formed, noise associated with the discontinuous movement of the magnetic walls constituting the closed magnetic domains is generated as described above, and the SN ratio in the output obtained from the magnetic sensor is reduced.

[0093] On the other hand, as Figure 6 shown, in the induction element 31 of the present embodiment, although two magnetic domains arranged in the long side direction of the induction element 31 are formed, magnetic domains (corresponding to Figure 4(Magnetic domains corresponding to the third magnetic domain D3 and the fourth magnetic domain D4 in ). Incidentally, in the sensing element 31 of the present embodiment, a closed magnetic domain in which the direction of magnetization M forms a ring is not formed.

[0094] From this, it can be understood that in the magnetic sensor 1 of the present embodiment having such a sensing element 31, the noise associated with the discontinuous movement of the magnetic wall constituting the closed magnetic domain is suppressed, and a decrease in the SN ratio in the output obtained from the magnetic sensor 1 can be suppressed.

[0095] (Regarding the manufacturing method of the magnetic sensor 1)

[0096] Next, an example of the manufacturing method of the magnetic sensor 1 will be described.

[0097] As described above, the substrate 10 is a substrate formed of a non-magnetic material, such as an oxide substrate such as glass or sapphire, a semiconductor substrate such as silicon, or a metal substrate such as aluminum, stainless steel, or a metal such as nickel-phosphorus plated. For example, striped grooves or striped irregularities with a radius of curvature Ra of 0.1 nm to 100 nm can be provided on the substrate 10 using a grinding machine or the like. It should be noted that for the direction of the stripes of the striped grooves or striped irregularities, it is preferably provided along the direction connecting the N pole and the S pole of the thin film magnet 20 formed of the hard magnet layer 103. In this way, crystal growth in the hard magnet layer 103 can be promoted along the direction of the grooves. Therefore, the easy magnetization axis of the thin film magnet 20 formed of the hard magnet layer 103 is more likely to be oriented in the groove direction (the direction connecting the N pole and the S pole of the thin film magnet 20). That is, magnetization of the thin film magnet 20 becomes easier.

[0098] Here, as an example, glass with a diameter of about 95 mm and a thickness of about 0.5 mm is used for the substrate 10. When the planar shape of the magnetic sensor 1 is several millimeters square, a plurality of magnetic sensors 1 are manufactured on the substrate 10 together and then divided (cut) into individual magnetic sensors 1.

[0099] After cleaning the substrate 10, on one surface of the substrate 10 (hereinafter, referred to as the surface.), the bonding layer 101, the control layer 102, the hard magnet layer 103, and the dielectric layer 104 are sequentially formed (stacked) to form a laminate.

[0100] First, a bonding layer 101 made of an alloy containing Cr or Ni, a control layer 102 made of an alloy containing Cr or the like, and a hard magnetic layer 103 made of a Co alloy constituting the thin film magnet 20 are sequentially and continuously formed (deposited). This film formation can be carried out by a sputtering method or the like. The substrate 10 is moved so as to face a plurality of targets formed of respective materials in sequence, whereby the bonding layer 101, the control layer 102, and the hard magnetic layer 103 are sequentially stacked on the substrate 10. As described above, in the formation of the control layer 102 and the hard magnetic layer 103, it is advisable to heat the substrate 10 to, for example, 100°C to 600°C in order to promote crystal growth.

[0101] It should be noted that in the film formation of the bonding layer 101, the substrate 10 may or may not be heated. In order to remove moisture or the like adsorbed on the surface of the substrate 10, the substrate 10 can be heated before the bonding layer 101 is formed.

[0102] Next, a dielectric layer 104 made of an oxide such as SiO2, Al2O3, TiO2, or a nitride such as Si3N4, AlN, etc. is formed (deposited). The film formation of the dielectric layer 104 can be carried out by a plasma CVD method, a reactive sputtering method, or the like.

[0103] Then, a pattern based on a photoresist (resist pattern) is formed by a known photolithography technique, and the pattern has an opening in a portion where the sensing element 31 of the sensing portion 30 is to be formed.

[0104] Next, a Co alloy constituting the soft magnetic layer 105 of the sensing element 31 and a non-magnet constituting the non-magnetic layer 106 are alternately formed (deposited). For example, the soft magnetic layer 105a, the non-magnetic layer 106a, the soft magnetic layer 105b, the non-magnetic layer 106b, the soft magnetic layer 105c, the non-magnetic layer 106c, and the soft magnetic layer 105d are sequentially formed. The film formation of the soft magnetic layer 105 and the non-magnetic layer 106 can be carried out using, for example, a sputtering method.

[0105] Thereafter, while removing the resist pattern, the soft magnetic layer 105 and the non-magnetic layer 106 on the resist pattern are removed (lifted off). Thus, the sensing element 31 based on the soft magnetic layer 105 and the non-magnetic layer 106 is formed.

[0106] Next, a resist pattern based on a photoresist is formed by a known photolithography technique, and the resist pattern has an opening in a portion where the magnetic yoke 40 is to be formed.

[0107] Then, a Co alloy constituting the soft magnetic layer 105 is formed (deposited).

[0108] Thereafter, while removing the resist pattern, the soft magnetic layer 105 on the resist pattern is removed (stripped). Thus, the magnetic yoke 40 based on the soft magnetic layer 105 is formed.

[0109] Next, the connection portion 32 and the terminal portion 33 of the induction portion 30 are formed. The connection portion 32 and the terminal portion 33 are formed, for example, by using a metal mask and depositing the conductor layer 107 by sputtering or vacuum evaporation.

[0110] Thereafter, with respect to the soft magnetic layer 105 constituting the induction element 31, uniaxial magnetic anisotropy is imparted in the width direction (short side direction) of the induction element 31 of the induction portion 30 (see Figure 1 (a)). The imparting of uniaxial magnetic anisotropy to the soft magnetic layer 105 can be performed, for example, by heat treatment at 400 °C in a rotating magnetic field of 3 kG (0.3 T) (heat treatment in a rotating magnetic field) and subsequent heat treatment at 400 °C in a static magnetic field of 3 kG (0.3 T) (heat treatment in a static magnetic field). At this time, the same uniaxial magnetic anisotropy is also imparted to the soft magnetic layer 105 constituting the magnetic yoke 40. However, as long as the magnetic yoke 40 functions as a magnetic circuit, uniaxial magnetic anisotropy may not be imparted.

[0111] Next, the hard magnetic layer 103 constituting the thin film magnet 20 is magnetized. The magnetization of the hard magnetic layer 103 can be performed by applying a magnetic field larger than the coercive force of the hard magnetic layer 103 until the magnetization of the hard magnetic layer 103 reaches saturation in a static magnetic field or a pulsed magnetic field.

[0112] Thereafter, the plurality of magnetic sensors 1 formed on the substrate 10 are divided (cut) into individual magnetic sensors 1. That is, as shown in the top view of Figure 1 (a), the substrate 10, the adhesion layer 101, the control layer 102, the hard magnetic layer 103, the dielectric layer 104, and the soft magnetic layer 105 are cut so that the planar shape becomes a quadrilateral. Thus, the magnetic poles (N pole and S pole) of the thin film magnet 20 are exposed on the side surfaces of the divided (cut) hard magnetic layer 103. In this way, the magnetized hard magnetic layer 103 becomes the thin film magnet 20. This division (cutting) can be performed by a dicing method, a laser cutting method, or the like.

[0113] It should be noted that, before the step of dividing the plurality of magnetic sensors 1 into individual magnetic sensors 1, the adhesion layer 101, the control layer 102, the hard magnetic layer 103, the dielectric layer 104, and the soft magnetic layer 105 between the adjacent magnetic sensors 1 on the substrate 10 can be etched away so that the planar shape becomes a quadrilateral ( Figure 1 the planar shape of the magnetic sensor 1 shown in (a)). Moreover, the exposed substrate 10 can also be divided (cut).

[0114] In addition, after the step of forming the laminate, the bonding layer 101, the control layer 102, the hard magnetic layer 103, and the dielectric layer 104 may be processed so that the planar shape becomes a quadrilateral ( Figure 1 the planar shape of the magnetic sensor 1 shown in (a)).

[0115] It should be noted that the manufacturing method described here has a simplified process compared with the above manufacturing method.

[0116] Through the above operations, the magnetic sensor 1 can be manufactured. It should be noted that the imparting of uniaxial magnetic anisotropy to the soft magnetic layer 105 and / or the magnetization of the thin film magnet 20 can be performed on each magnetic sensor 1 or a plurality of magnetic sensors 1 after the step of dividing the magnetic sensor 1 into individual magnetic sensors 1.

[0117] It should be noted that in the case where the control layer 102 is not provided, it is necessary to heat the hard magnetic layer 103 to 800 °C or higher after film formation to perform crystal growth, thereby imparting magnetic anisotropy in the plane. However, in the case where the control layer 102 is provided as in the magnetic sensor 1 of the first embodiment, the control layer 102 can be used to promote crystal growth, so crystal growth at a high temperature of 800 °C or higher is not required.

[0118] In addition, regarding the imparting of uniaxial magnetic anisotropy to the induction element 31, it can be performed by using a magnetron sputtering method during the deposition of the soft magnetic layer 105, instead of performing it by the above heat treatment in a rotating magnetic field and heat treatment in a static magnetic field. In the magnetron sputtering method, a magnet (magnetic stone) is used to form a magnetic field, and electrons generated by discharge are confined on the surface of the target. As a result, the probability of collision between electrons and gas is increased to promote gas ionization, and the film deposition rate is increased. The magnetic field formed by the magnet (magnetic stone) used in this magnetron sputtering method imparts uniaxial magnetic anisotropy to the soft magnetic layer 105 while depositing the soft magnetic layer 105. In this way, the step of imparting uniaxial magnetic anisotropy by heat treatment in a rotating magnetic field and heat treatment in a static magnetic field can be omitted.

[0119] The embodiments of the present invention have been described above, but the present invention is not limited to these embodiments. Various modifications and combinations can be made as long as they do not violate the gist of the present invention.

[0120] Description of Reference Numerals

[0121] 1... Magnetic sensor, 10... Substrate, 20... Thin film magnet, 30... Induction portion, 31... Induction element, 32... Connection portion, 33... Terminal portion, 40, 40a, 40b... Magnetic yoke, 101... Bonding layer, 102... Control layer, 103... Hard magnetic layer, 104... Dielectric layer, 105... Soft magnetic layer, 106... Non-magnetic layer, 107... Conductive layer.

Claims

1. A magnetic sensor, comprising: a non-magnetic substrate; and a sensing element having a long side direction and a short side direction, having uniaxial magnetic anisotropy in a direction crossing the long side direction, and sensing a magnetic field by a magneto-impedance effect, the sensing element having three or more soft magnetic layers formed of an amorphous alloy and two or more non-magnetic layers formed of a non-magnetic material and laminated between the soft magnetic layers, the soft magnetic layers facing each other across each non-magnetic layer being antiferromagnetically coupled, when observing the soft magnetic layer in the stacking direction of the soft magnetic layer, the sensing element does not form a closed magnetic domain, a current is passed in the plane direction of the soft magnetic layer to measure the impedance.

2. The magnetic sensor according to claim 1, wherein Each of the non-magnetic layers is made of Ru or a Ru alloy.

3. The magnetic sensor according to claim 2, wherein, The thickness of each of the non-magnetic layers is in the range of 0.6 nm or more and 1.4 nm or less.

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