Magnetoresistance effect element and magnetic sensor

Abstract

In a magnetoresistance effect element 11 comprising an intermediate layer 14 between a free layer 12 and a fixed layer 13, magnetization directions of the free layer 12 and the fixed layer 13 are orthogonal to each other when an external magnetic field is not applied. The free layer 12 includes a ferromagnetic layer 21, an anti-parallel coupling layer 23, and a ferromagnetic layer 22. The fixed layer 13 includes a ferromagnetic layer 31, an anti-parallel coupling layer 33, and a ferromagnetic layer 32. The ferromagnetic layer 21 and the ferromagnetic layer 22 are stacked with the anti-parallel coupling layer 23 therebetween, and are antiferromagnetically coupled by RKKY interaction. The ferromagnetic layer 31 and the ferromagnetic layer 32 are stacked with the anti-parallel coupling layer 33 therebetween, and are antiferromagnetically coupled by RKKY interaction. The ferromagnetic layers 31, 32 in the fixed layer 13 each have a higher anisotropic magnetic field Hk than the ferromagnetic layers 21, 22 in the free layer 12. Thus, the present invention can provide a magnetoresistance effect element and a magnetic sensor having a wide dynamic range.

Description

Magnetoresistance effect element and magnetic sensor

[0001] The present invention relates to a magnetoresistance effect element having a wide dynamic range and a magnetic sensor using the same.

[0002] In magnetic sensors used for non-contact current sensors and the like, there is a demand for a linear output type magnetoresistance effect element having a wide dynamic range (detection magnetic field range). Accordingly, various means have been proposed to widen the dynamic range of magnetoresistance effect elements used in magnetic sensors. For example, Patent Document 1 describes a magnetic balance type current sensor in which a magnetic shield is provided on a lower layer or an upper layer of a magnetoresistance effect element, and the apparent dynamic range is widened by attenuating an induced magnetic field from a current to be measured. Patent Document 2 discloses that a first magnetic detection module in which a plurality of first magnetic detection elements are connected in series and a second magnetic detection module in which a plurality of second magnetic detection elements are connected in series are connected in series, and describes a magnetic detection device in which detection sensitivity to a magnetic field from a magnetic field generation source is different between the first magnetic detection element and the second magnetic detection element.

[0003] International Publication No. 2010 / 143718 International Publication No. 2017 / 212694

[0004] The magnetic balance type current sensor using a magnetic shield described in Patent Document 1 has problems that an additional shield forming step increases production cost, and the influence of hysteresis of the magnetic shield tends to be large. There is also a problem that it is difficult to obtain a linear output up to a high magnetic field region (for example, 50 mT or more). The magnetic detection device described in Patent Document 2 requires a configuration in which the magnetic field intensity or sensitivity is changed among a plurality of magnetic detection elements forming a bridge circuit, and thus has a problem of lacking versatility. An object of the present invention is to provide a magnetoresistance effect element and a magnetic sensor having a wide dynamic range.

[0005] As a means to solve the above-mentioned problems, the present invention has the following configuration. A magnetoresistive element having an intermediate layer between a free layer and a fixed layer, wherein, when no external magnetic field is applied, the magnetization directions of the free layer and the fixed layer are orthogonal, the free layer and the fixed layer each have a first ferromagnetic layer, an antiparallel coupling layer and a second ferromagnetic layer, the first ferromagnetic layer and the second ferromagnetic layer are stacked via the antiparallel coupling layer and are antiferromagnetically coupled by RKKY interaction, and the anisotropic magnetic field Hk of the ferromagnetic layer in the fixed layer is greater than the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer.

[0006] In a magnetoresistive element with a spin valve structure in which a free layer and a fixed layer are formed via an intermediate layer, the anisotropic magnetic field Hk of the ferromagnetic layers in the free layer and the fixed layer is increased by making the free layer and the fixed layer, respectively, structured such that a first ferromagnetic layer and a second ferromagnetic layer are antiferromagnetically coupled via an antiparallel coupling layer through an RKKY interaction. By increasing the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer, the dynamic range of a magnetoresistive element arranged so that the magnetization directions of the fixed layer and the free layer are orthogonal when viewed from the stacking direction can be widened.

[0007] The crystalline magnetic anisotropy constant K of the ferromagnetic layer in the fixed layer may be greater than the crystalline magnetic anisotropy constant K of the ferromagnetic layer in the free layer. By configuring each layer such that the crystalline magnetic anisotropy constant K of the ferromagnetic layer in the fixed layer is greater than that of the ferromagnetic layer in the free layer, the anisotropic magnetic field Hk of the ferromagnetic layer in the fixed layer can be made greater than the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer.

[0008] The product Ms·t between the magnetization Ms of the ferromagnetic layer and the film thickness t in the fixed layer is smaller than the product Ms·t between the magnetization Ms of the ferromagnetic layer and the film thickness t in the free layer. Since the magnetostatic energy increases in proportion to the product Ms·t between the magnetization Ms and the film thickness t, the smaller Ms·t becomes, the less likely the ferromagnetic layer is to be magnetized in the direction of the magnetic field. For this reason, a layer with a ferromagnetic layer with a small Ms·t becomes a fixed layer with a large anisotropic magnetic field Hk, and a layer with a ferromagnetic layer with a large Ms·t becomes a free layer with a small anisotropic magnetic field Hk.

[0009] The product Ms1・t1 of the magnetization Ms1 of the first ferromagnetic layer and the film thickness t1 may be approximately equal to the product Ms2・t2 of the magnetization Ms2 of the second ferromagnetic layer and the film thickness t2. By making the Ms1・t1 of the first ferromagnetic layer and the Ms2・t2 of the second ferromagnetic layer approximately equal and balancing them, the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer becomes larger, thereby widening the dynamic range of the magnetoresistive element.

[0010] The first ferromagnetic layer and the second ferromagnetic layer in the free layer may be made of the same material. The first ferromagnetic layer and the second ferromagnetic layer in the free layer may each be made of multiple layers, and the layer adjacent to the antiparallel coupling layer in the first ferromagnetic layer and the layer adjacent to the antiparallel coupling layer in the second ferromagnetic layer may be made of the same material. By making the layer adjacent to the antiparallel coupling layer of the same material, the antiferromagnetic coupling between the first ferromagnetic layer and the second ferromagnetic layer becomes stronger, and the anisotropic magnetic field Hk of the free layer becomes larger. In addition, the antiferromagnetic coupling between the first ferromagnetic layer and the second ferromagnetic layer becomes stronger. By constructing the first and second ferromagnetic layers from the same material, the TCR (Temperature Coefficient of Resistance) of the first ferromagnetic layer and the TCR of the second ferromagnetic layer become equivalent, allowing the balance of Ms·t to be maintained over a wide temperature range. Therefore, the anisotropic magnetic field Hk of the free layer can be maintained at a high level over a wide temperature range.

[0011] The main component of the material constituting the first ferromagnetic layer and the second ferromagnetic layer may be a NiFe alloy. By using a NiFe alloy as the main component of the material constituting the first ferromagnetic layer and the second ferromagnetic layer, the hysteresis (hysteresis effect) of the free layer can be reduced.

[0012] The first ferromagnetic layer and the second ferromagnetic layer in the free layer may each consist of multiple layers, and the first ferromagnetic layer and the second ferromagnetic layer in the free layer may be stacked symmetrically with respect to the antiparallel coupling layer. By stacking each layer constituting the first ferromagnetic layer and the second ferromagnetic layer with the same material and film thickness so as to be symmetrical with respect to the antiparallel coupling layer, it becomes easier to achieve both high ΔMR and low hysteresis. Furthermore, the anisotropic magnetic field Hk of the free layer can be increased by strengthening the antiferromagnetic coupling.

[0013] The first ferromagnetic layer and the second ferromagnetic layer in the free layer may be alloy layers selected from a CoFeB alloy layer, a NiFe alloy layer, and a CoFe alloy layer, or a stack of two or more alloy layers from among these alloy layers. By forming the first ferromagnetic layer and the second ferromagnetic layer in the free layer as a single layer or multiple layers of each of the above alloy layers, the anisotropic magnetic field Hk of the free layer is increased.

[0014] The intermediate layer may be an MgO layer, and the CoFeB alloy layer may be adjacent to the intermediate layer. By providing the CoFeB alloy layer adjacent to the MgO layer of the intermediate layer, the atoms constituting the CoFeB alloy layer can be rearranged by annealing, making the crystal structure of the CoFeB alloy layer harmonize with the crystal structure of the MgO layer. As a result, △MR increases, the structure due to antiferromagnetic bonding in the free layer becomes stronger, and the anisotropic magnetic field Hk of the free layer increases.

[0015] The fixed layer and the free layer each have an antiferromagnetic layer laminated adjacent to one of the ferromagnetic layers, and the ferromagnetic layer and the antiferromagnetic layer may be exchange-coupled. The antiferromagnetic coupling between the ferromagnetic layer and the antiferromagnetic layer provided adjacent to the ferromagnetic layer can increase the anisotropic magnetic field Hk of the ferromagnetic layer.

[0016] At least one of the fixed layer and the free layer may have a plurality of first structures, each consisting of a first ferromagnetic layer, an antiparallel coupling layer, and a second ferromagnetic layer stacked in that order, with two adjacent first structures connected via the antiparallel coupling layer.

[0017] The fixed layer has a configuration in which multiple first structures are provided, each consisting of two adjacent first structures connected by an antiparallel coupling layer, thereby improving the strong magnetic field resistance of the magnetoresistive element. Furthermore, the dynamic range of the magnetoresistive element is increased when the free layer also has this configuration.

[0018] The first ferromagnetic layer of one of the adjacent first structures is laminated on one side of the antiparallel coupling layer via two adjacent first structures, and the second ferromagnetic layer of the other of the adjacent first structures is laminated on the other side of the antiparallel coupling layer via two adjacent first structures, and the first ferromagnetic layer of one of the first structures and the second ferromagnetic layer of the other first structure may be antiferromagnetically coupled by RKKY interaction.

[0019] The addition of RKKY interactions in adjacent first structures to the RKKY interactions within the same first structure stabilizes the antiferromagnetic coupling between the first and second ferromagnetic layers. Consequently, the high-field resistance of the magnetoresistive element is improved.

[0020] The number of the first structures may be five or less. With the above configuration, it is possible to improve resistance to strong magnetic fields while suppressing an increase in the overall thickness of the magnetoresistive element.

[0021] The magnetic sensor of the present invention is equipped with the magnetoresistive element described above and is characterized by linearity between the detected magnetism and the output within a predetermined measurement range. By increasing the anisotropic magnetic field Hk of the free layer, the range in which linearity between the detected magnetism and the output is present and measurement with high accuracy can be extended. "Linearity within a predetermined measurement range" means that, if ΔV is the difference between the actual output and the straight line representing the relationship between the ideal magnetism and the output within a predetermined measurement range (dynamic range) of the magnetic sensor, and FS is the range of the ideal output corresponding to the measurement range, then the ratio of ΔV to FS (%) (ΔV / FS) × 100 is 3 (%) or less.

[0022] By increasing the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer, the dynamic range of a magnetoresistive element arranged so that the magnetization directions of the fixed layer and the free layer are orthogonal can be widened. Therefore, it becomes possible to provide a magnetoresistive element with a wide dynamic range and a magnetic sensor with linear output using the same.

[0023] This is a schematic plan view showing the structure of a magnetoresistive (GMR) element. This is a schematic plan view showing the structure of a magnetoresistive (TMR) element. This is a schematic diagram showing the stacked structure of a magnetoresistive element in the cross-section along line A-A in Figures 1 and 2. This is a circuit block diagram of a magnetic detection device. This is a schematic diagram showing the process of forming the fixed layer in the manufacturing method of a magnetic detection device. This is a schematic diagram showing the process of forming the free layer in the manufacturing method of a magnetic detection device. This is a schematic diagram showing the process of forming the fixed layer in the manufacturing method of a magnetic detection device. This is a schematic diagram showing the process of forming the free layer in the manufacturing method of a magnetic detection device. This is a diagram showing the configuration of a bottom-pin type magnetoresistive element (TMR) of Example 1. This is a diagram showing the configuration of a bottom-pin type magnetoresistive element (TMR) of Comparative Example 1. This is a graph showing the MH curve of the fixed layer of the magnetoresistive elements of Example 1 and Comparative Example 1. This is a graph showing the MH curve of the free layer of the magnetoresistive elements of Example 1 and Comparative Example 1. This is a graph showing the MH curve of the free layer of the magnetoresistive element of Comparative Example 1. This is a diagram showing the configuration of a top-pin type magnetoresistive magnetometer (TMR) in Example 2. This is a diagram showing the configuration of a top-pin type magnetoresistive magnetometer (TMR) in Comparative Example 2. This is a graph showing the MH curve of the fixed layer of the magnetoresistive magnetometers in Example 2 and Comparative Example 2. This is a graph showing the MH curve of the free in Comparative Example 2. This is a diagram showing the configuration of a bottom-pin type magnetoresistive magnetometer (TMR) in Example 3. This is a diagram showing the configuration of a bottom-pin type magnetoresistive magnetometer (TMR) in Example 4. This is a graph showing the MH curve of the fixed layer of the magnetoresistive magnetometers in Example 3 and Example 4. This is a graph showing the MH curve of the free layer of the magnetoresistive magnetometers in Example 3 and Example 4. This is a diagram showing the configuration of a top-pin type magnetoresistive magnetometer (TMR) in Example 5. This is a diagram showing the configuration of a top-pin type magnetoresistive magnetometer (TMR) in Example 6. This is a graph showing the MH curve of the fixed layer of the magnetoresistive magnetometers in Example 5 and Example 6. This graph shows the MH curve of the free layer of the magnetoresistive elements in Examples 5 and 6. This diagram shows the configuration of the magnetoresistive element (TMR) in the magnetic sensors of Examples 7-1 to 7-6.This graph shows a method for evaluating the linearity between the measured magnetic field and output of a magnetic sensor. This graph shows the output of magnetic sensors in Examples 7-1 to 7-3, which use magnetoresistive elements with an SFF structure in the free layer. This graph shows the output of magnetic sensors in Examples 7-4 to 7-6, which use magnetoresistive elements with an SAF structure in the free layer. This schematic diagram shows the change in magnetization direction due to a magnetic field in a free layer with an SFF structure. This schematic diagram shows the change in magnetization direction due to a magnetic field in a free layer with an SAF structure. This schematic diagram shows a magnetoresistive element with a free layer having a multiple SAF structure. This schematic diagram shows a magnetoresistive element with a fixed layer having a multiple SAF structure. This schematic diagram shows a magnetoresistive element with a free layer and a fixed layer having a multiple SAF structure. This schematic diagram shows free layers with a different number of first structures in bottom-pin type magnetoresistive elements (TMRs) of Examples 8-1 to 8-6. This schematic diagram shows the configuration of the free layer in the magnetoresistive elements of Examples 8-1 to 8-6. This is an MH curve (vertical axis = M・t) comparing the number of first structures in the free layer. This is a graph showing the dependence of the number of first structures on the saturation magnetization of the entire free layer. This is an MH curve (vertical axis = saturation rate) comparing the number of first structures in the free layer. This is a graph showing the relationship between the saturation rate, the linear region magnetic field, and the number of first structures. This is a graph showing the number of first structures and the proportion of ferromagnetic layers where RKKY occurs on both the upper and lower surfaces. This is a graph showing the definition of the linear region magnetic field. This is a schematic diagram showing the configuration of a bottom-pin type magnetoresistive element (TMR) of this embodiment, which has fixed layers with different numbers of first structures. This is a schematic diagram showing the film configuration of the fixed layer in the magnetoresistive elements of Examples 9-1 to 9-6. This is an MH curve (vertical axis = M・t) comparing the number of first structures in the fixed layer. This is a graph showing the dependence of the number of first structures on the saturation magnetization of the entire fixed layer. This is an MH curve (vertical axis = saturation rate) comparing the number of first structures in the fixed layer. This graph shows the relationship between the saturation rate and the number of first structures.

[0024] Embodiments of the present invention will be described below with reference to the accompanying drawings. In each drawing, the same component is given the same number, and descriptions will be omitted as appropriate. Reference coordinates will be shown in each drawing as appropriate to indicate the positional relationship of each component. In the reference coordinates, the stacking direction of the magnetoresistive element is the Z direction, the magnetization direction of the free layer of the magnetoresistive element at zero magnetic field is the X direction, and the magnetization direction of the fixed layer is the Y direction. Note that the X, Y, and Z directions in the reference coordinates are mutually orthogonal.

[0025] Figure 1 is a schematic plan view showing the structure of a GMR (Giant Magneto Resistance) element 1, which is an example of a magnetoresistive element. The GMR element 1 has a meander shape in which a plurality of elongated patterns 2, arranged so that their longitudinal directions are parallel to each other, are connected by folded portions 3. By connecting the elongated patterns 2 at the folded portions 3, the plurality of elongated patterns 2 are electrically connected in series, and electrodes 4 are provided at both ends of the elongated patterns 2 connected in series.

[0026] The film of the elongated pattern 2, which has a meander shape, comprises a free layer 12 and a fixed layer 13 (see Figure 3) stacked in the Z direction. At zero magnetic field, the magnetization direction of the free layer 12 is in the X direction, and the magnetization direction of the fixed layer 13 is in the Y direction. The sensitivity direction of the GMR element 1 is in the width direction (Y direction) perpendicular to the longitudinal direction of the elongated pattern 2, and the external magnetic field can be measured based on the change in resistance between the electrodes 4 due to the change in the magnetization state that occurs in the free layer 12 in response to the magnitude of the external magnetic field.

[0027] Figure 2 is a schematic plan view showing the structure of a TMR (Tunnel Magnetoresistance) element 5, another example of a magnetoresistive element. The TMR element 5 comprises an upper electrode 6, a lower electrode 7, and a film 8 provided between the upper electrode 6 and the lower electrode 7. The film 8 has a free layer 12 and a fixed layer 13 (see Figure 3) stacked in the Z direction. Similar to the GMR element 1, in the TMR element 5, the magnetization direction of the free layer 12 is in the X direction and the magnetization direction of the fixed layer 13 is in the Y direction at zero magnetic field, and the magnetization directions of the free layer 12 and the fixed layer 13 are orthogonal.

[0028] In the TMR element 5, an upper electrode 6 connecting the upper (Z2) side and a lower electrode 7 connecting the lower (Z1) side of adjacent films 8 when viewed in the Z direction are alternately provided along the films 8 to be connected, thereby connecting multiple films 8 in series in the stacking direction of the free layer 12 and the fixed layer 13. Electrodes 9 are provided at each end of the multiple films 8 connected in series. The TMR element 5 measures the external magnetic field in the Y direction, which is the sensitivity direction, based on the change in resistance between the two electrodes 9 caused by the change in the resistance value in the stacking direction (Z direction) of the fixed layer 13, which is caused by the change in the magnetization state of the free layer 12 in response to the magnitude of the external magnetic field.

[0029] Figure 3 is a schematic diagram showing the stacked structure of the GMR element 1 and TMR element 5 in the cross-section along line A-A in Figures 1 and 2. In the following, common features of the GMR element 1 and TMR element 5 will be described together as the magnetoresistive element 11.

[0030] The magnetoresistive element 11 is a magnetoresistive film with a spin valve structure, comprising an intermediate layer 14 between a free layer 12 and a fixed layer 13. When no external magnetic field is applied, the magnetization directions of the free layer 12 and the fixed layer 13 are orthogonal. The magnetization directions of the ferromagnetic layers constituting the free layer 12 and the fixed layer 13, which are arranged with the intermediate layer 14 in between, are determined by the magnetic field applied during the deposition of each ferromagnetic layer.

[0031] Figure 3 shows a so-called bottom-pin type magnetoresistive element 11, in which a fixed layer 13 is provided on the substrate 17 side with respect to the intermediate layer 14, and a free layer 12 is provided on the side opposite to the substrate 17. However, a so-called top-pin type may also be used, in which the free layer 12 is provided on the substrate 17 side and the fixed layer 13 is provided on the side opposite to the substrate 17.

[0032] Examples of materials for the ferromagnetic layers (first ferromagnetic layer) 21 and (second ferromagnetic layer) 22 constituting the free layer 12, and the ferromagnetic layers (first ferromagnetic layer) 31 and (second ferromagnetic layer) 32 constituting the fixed layer 13 include CoFe alloy (cobalt-iron alloy), NiFe alloy (nickel-iron alloy), and CoFeB alloy (cobalt-iron-boron alloy). Each of the ferromagnetic layers 21, 22, 31, and 32 can be a single-layer structure of these alloys or a laminated structure in which two or more layers of different types of alloys are stacked.

[0033] From the viewpoint of increasing the anisotropic magnetic field Hk of the free layer 12, it is preferable that the ferromagnetic layers 21 and 22 are formed from a CoFeB alloy layer, a NiFe alloy layer, and a CoFe alloy layer.

[0034] Examples of materials for the intermediate layer 14 include Al2O3, TiOx, MgO, and Cu. Examples of materials for the base layer 15 include Ta, Ru, and NiFeCr alloys, which are used in a single-layer or multilayer structure. Examples of materials for the insulating layer 16 include Al2O3. Examples of materials for the substrate 17 include Si. As mentioned above, Figure 3 shows a multilayer structure common to both the GMR element 1 and the TMR element 5, so it is omitted from the description in Figure 3, but when the magnetoresistive element 11 is a TMR element 5, a lower electrode 7 (see Figure 2) is formed between the base layer 15 and the insulating layer 16. Examples of materials for the lower electrode 7 include Cu and Al.

[0035] The antiferromagnetic layer (Ex Bias layer) 24 aligns the magnetization direction of the ferromagnetic layer 21 of the free layer 12 in a specific direction through exchange coupling. The antiferromagnetic layer (Ex Bias layer) 34 fixes the magnetization direction of the ferromagnetic layer 32 of the fixed layer 13 through exchange coupling. The materials of these antiferromagnetic layers 24 and 34 are not particularly limited, but antiferromagnetic materials containing element X (where X is one or more elements from Pt, Pd, Ir, Rh, Ru, Os) and one or both of Mn and Cr are used. The material of the protective layer 19 is not limited, but Ru and Ta are used.

[0036] The magnetoresistive element 11 is designed with materials and film thickness such that the anisotropic magnetic field Hk of the ferromagnetic layers 31 and 32 in the fixed layer 13 is greater than the anisotropic magnetic field Hk of the ferromagnetic layers 21 and 22 in the free layer 12.

[0037] Ru is an example of a material that constitutes the antiparallel coupling layer 23 of the free layer 12 and the antiparallel coupling layer 33 of the fixed layer 13. The film thickness t23 and t33 of the antiparallel coupling layers 23 and 33 are, for example, in the range of 0.3 to 0.45 nm or 0.75 to 0.95 nm. This allows the ferromagnetic layers on both sides of the Ru layer in the stacking direction to be antiferromagnetically coupled (also referred to as antiferromagnetic coupling, as appropriate).

[0038] When the magnetoresistive element 11 is a TMR element 5, the ferromagnetic layers 21 and 22 of the free layer 12 contain a CoFeB alloy as an essential material. The composition of the CoFeB alloy is not particularly limited, but in (Co100-xFex)100-yBy, x is preferably 25 to 100 and y is preferably 10 to 30. 100-x and x represent the composition ratio of Co to Fe in CoFe, and 100-y and y represent the composition ratio of CoFe to B in (CoFe)B. Hereinafter, one of 100-x and x, and one of 100-y and y will be omitted, and (Co100-xFex)100-yBy will be written as ((100-x)CoFex)By. For example, when x = 50 and y = 20, it will be written as (50CoFe)B20.

[0039] When the intermediate layer 14 is MgO, it is preferable that the CoFeB alloy layer is in contact with the intermediate layer 14. By providing the CoFeB alloy layer in contact with the MgO of the intermediate layer 14, the atoms constituting the CoFeB alloy layer can be rearranged by annealing, making the crystal structure of the CoFeB alloy layer harmonize with the crystal structure of the MgO layer. As a result, ΔMR increases, and the structure due to the antiferromagnetic coupling between the ferromagnetic layer 21 and the ferromagnetic layer 22 in the free layer 12 becomes stronger, and the anisotropic magnetic field Hk of the free layer 12 increases.

[0040] In the magnetoresistance effect element 11, an antiferromagnetic layer 24 is provided on the Z2 side of the free layer 12, and an antiferromagnetic layer 34 is provided on the Z1 side of the pinned layer 13, respectively. Exchange coupling between the antiferromagnetic layer 24 and the ferromagnetic layer 21, and between the antiferromagnetic layer 34 and the ferromagnetic layer 32, respectively, improves the high magnetic field resistance of the free layer 12 and the pinned layer 13. However, if high magnetic field resistance can be ensured by the free layer 12 and the pinned layer 13 themselves, one or both of the antiferromagnetic layers 24 and 34 may not be provided.

[0041] The free layer 12 includes a ferromagnetic layer 21, an antiparallel coupling layer 23, and a ferromagnetic layer 22. The ferromagnetic layer 21 and the ferromagnetic layer 22 are stacked with the antiparallel coupling layer 23 interposed therebetween, and are antiferromagnetically coupled by RKKY interaction. By adopting a structure including the ferromagnetic layer 21 and the ferromagnetic layer 22 that are antiferromagnetically coupled via RKKY interaction across the antiparallel coupling layer 23, the anisotropic magnetic field Hk of the free layer 12 can be increased.

[0042] By increasing the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer 12, the dynamic range of the magnetoresistance effect element 11 in which the magnetization directions of the free layer 12 and the pinned layer 13 are arranged orthogonal to each other can be widened.

[0043] The pinned layer 13 includes a ferromagnetic layer 31, an antiparallel coupling layer 33, and a ferromagnetic layer 32. The ferromagnetic layer 31 and the ferromagnetic layer 32 are in contact with the antiparallel coupling layer 33 on the Z1 side and the Z2 side, respectively, and are antiferromagnetically coupled by RKKY interaction. By adopting a structure in which the ferromagnetic layer 31 and the ferromagnetic layer 32 of the pinned layer 13 are antiferromagnetically coupled via RKKY interaction, the anisotropic magnetic field Hk can be increased.

[0044] The overall anisotropic magnetic field Hk of the ferromagnetic layer 31 and the ferromagnetic layer 32 in the pinned layer 13 is larger than the overall anisotropic magnetic field Hk of the ferromagnetic layer 21 and the ferromagnetic layer 22 in the free layer 12. Therefore, when an external magnetic field is applied, the magnetization state of the free layer 12 changes while the pinned layer 13 maintains its magnetization state.

[0045] Preferably, the crystalline magnetic anisotropy constant K of the ferromagnetic layers 31 and 32 in the fixed layer 13 is greater than the crystalline magnetic anisotropy constant K of the ferromagnetic layers 21 and 22 in the free layer 12. This makes it possible to make the anisotropic magnetic field Hk of the ferromagnetic layers 31 and 32 greater than the anisotropic magnetic field Hk of the ferromagnetic layers 21 and 22. For example, by making the main components of the ferromagnetic layers 31 and 32 Co, Fe, or alloy films thereof, which have a relatively large crystalline magnetic anisotropy constant K, and making the alloy film of Ni and Fe, which has a relatively small crystalline magnetic anisotropy constant K, the main component of the free layer 12, the anisotropic magnetic field Hk between the fixed layer 13 and the free layer 12 can be adjusted. Alternatively, by making the ferromagnetic layers 31 and 32 and the ferromagnetic layers 21 and 22 from the same material and making the film thickness of the ferromagnetic layers 31 and 32 smaller than the film thickness of the ferromagnetic layers 21 and 22, the anisotropic magnetic field Hk can be adjusted.

[0046] In the fixed layer 13, the product Ms·t between the magnetization Ms of the ferromagnetic layers 31 and 32 and the film thickness t is smaller than the Ms·t of the ferromagnetic layers 21 and 22 in the free layer 12. The magnetostatic energy increases proportionally to Ms·t, making the ferromagnetic layers more easily magnetized in the direction of the magnetic field. Therefore, by making the Ms·t of the fixed layer 13 smaller than the Ms·t of the free layer 12, the magnetostatic energy is reduced, making the fixed layer 13 less easily magnetized by a magnetic field than the free layer 12. As a result, the anisotropic magnetic field Hk of the ferromagnetic layers 31 and 32 in the fixed layer 13 can be made larger than the anisotropic magnetic field Hk of the ferromagnetic layers 21 and 22 in the free layer 12.

[0047] The magnetization and film thickness of the ferromagnetic layers 21 and 22 of the free layer 12 are set to Ms21 (Ms1), Ms22 (Ms2), and t21 (t1), t22 (t2), and the magnetization and film thickness of the ferromagnetic layers 31 and 32 of the fixed layer 13 are set to Ms31, Ms32, and t31, t32. In this case, by setting Ms21・t21 + Ms22・t22 > Ms31・t31 + Ms32・t32, the magnetostatic energy of the fixed layer 13 can be made smaller than that of the free layer 12, and the anisotropic magnetic field Hk of the fixed layer 13 can be made larger than that of the free layer 12.

[0048] As shown in FIG. 3, when an antiferromagnetic layer 24 is provided on the side of the free layer 12 opposite to the intermediate layer 14, an increase in Ms·t reduces the exchange coupling magnetic field Hex generated at the interface between the free layer 12 and the antiferromagnetic layer 24. Therefore, an increase in Ms·t becomes a factor that reduces the anisotropy magnetic field Hk of the ferromagnetic layers 21 and 22 in the free layer 12.

[0049] From the viewpoint of increasing the anisotropy magnetic field Hk of the entire ferromagnetic layer in the free layer 12, it is preferable to substantially equalize the product of the magnetization Ms and the film thickness t of the two ferromagnetic layers 21 and 22 to balance the two. That is, it is preferable to substantially equalize the product Ms21·t21 of the magnetization Ms (Ms1) of the ferromagnetic layer 21 and the film thickness t21, and the product Ms22·t22 of the magnetization Ms22 (Ms2) of the ferromagnetic layer 22 and the film thickness t22. In the present embodiment, the phrase Ms21·t21 and Ms22·t22 being "substantially equal" means that 0.85 ≤ (Ms21·t21) / (Ms22·t22) ≤ 1.15 holds true. It is more preferable that 0.9 ≤ (Ms21·t21) / (Ms22·t22) ≤ 1.1 holds true, and it is further preferable that 0.95 ≤ (Ms21·t21) / (Ms22·t22) ≤ 1.05 holds true. From the viewpoint of increasing the anisotropy magnetic field Hk, similarly for the pinned layer 13, the product of the magnetization Ms and the film thickness t of the two ferromagnetic layers 31 and 32 may be substantially equalized to balance the two.

[0050] By adopting a structure in which Ms1·t1 and Ms2·t2, which are the products of magnetization and film thickness of the two ferromagnetic layers 21 and 22 in the free layer 12, are approximately the same, that is, a SAF (Synthetic Anti Ferro) structure, the effective magnetic anisotropy of the free layer 12 can be increased. When the magnetocrystalline anisotropy constants of the two ferromagnetic layers 21 and 22 are K1 and K2, respectively, the effective anisotropy magnetic field eff Hk of SAF is represented by the following formula. eff Hk=2(K1·t1+K2·t2) / (Ms1·t1−Ms2·t2) From the above formula, it can be seen that balancing Ms1·t1 and Ms2·t2, which are the products Ms·t of magnetization and film thickness of the two ferromagnetic layers 21 and 22, that is, making them substantially equal, increases the effective anisotropy magnetic field eff Hk.

[0051] It is preferable that the ferromagnetic layer 21 and the ferromagnetic layer 22 in the free layer 12 are made of the same material. By using the same material, the antiferromagnetic coupling between the ferromagnetic layer 21 and the ferromagnetic layer 22 becomes stronger, and the anisotropic magnetic field Hk of the free layer 12 increases.

[0052] Furthermore, by using the same material, the TCR (temperature coefficient of resistance) of the ferromagnetic layer 21 and the ferromagnetic layer 22 become equivalent, allowing a balanced state between Ms21・t21 and Ms22・t22 (a balanced state between Ms1・t1 and Ms2・t2) to be maintained over a wide temperature range. Therefore, it becomes possible to increase the anisotropic magnetic field Hk of the free layer 12 over a wide temperature range.

[0053] The ferromagnetic layers 21 and 22 in the free layer 12 may be a single layer or multiple layers. If there are multiple layers, it is preferable that the layers in contact with the antiparallel coupling layer 23 in the ferromagnetic layers 21 and 22 are made of the same material, from the viewpoint of increasing the anisotropic magnetic field Hk of the free layer 12.

[0054] From the viewpoint of reducing the hysteresis of the free layer 12, it is preferable that the main component of the ferromagnetic layers 21 and 22 in the free layer 12 is a NiFe alloy. In the present invention, "main component" refers to the material constituting the layer with the greatest thickness when the ferromagnetic layers 21 and 22 are composed of multiple layers, and the material constituting that layer when they are composed of a single layer.

[0055] When the ferromagnetic layers 21 and 22 in the free layer 12 are each composed of multiple layers, it is preferable that the ferromagnetic layers 21 and 22 in the free layer 12 are stacked symmetrically with respect to the antiparallel coupling layer 23. By stacking each layer constituting the ferromagnetic layers 21 and 22 with the same material and film thickness t21 and t22 so as to be symmetrical with respect to the antiparallel coupling layer 23, it becomes easier to achieve both high ΔMR and low hysteresis in the magnetoresistive element 11. Furthermore, the antiferromagnetic coupling between the ferromagnetic layer 21 and the ferromagnetic layer 22 can be strengthened to increase the anisotropic magnetic field Hk of the free layer 12.

[0056] (Magnetic Detection Device) Figure 4 is a circuit block diagram of the magnetic detection device (magnetic sensor) 50 of this embodiment. The magnetic detection device 50 is composed of a full-bridge circuit 40. In the figure, the magnetization direction of the ferromagnetic layer 22 on the Z1 side in the free layer 12 (see Figure 3) is indicated by a dashed arrow, and the magnetization direction of the ferromagnetic layer 31 on the Z2 side in the fixed layer 13 is indicated by a solid arrow. The full-bridge circuit 40 is configured such that two series circuits 42a and 42b, in which the order of magnetoresistive elements 11 with opposite fixed magnetization directions in the Y direction is reversed, are connected in parallel between the power supply voltage 41 and the ground potential 44.

[0057] The differential output between the output potential of the midpoint terminal 43a of the series circuit 42a and the output potential of the midpoint terminal 43b of the series circuit 42b, which constitute the full-bridge circuit 40, is obtained as the output voltage for detecting the external magnetic field.

[0058] In the magnetic detection device 50, the direction of magnetism of the ferromagnetic layers 21 and 22 in the free layer 12 of the magnetoresistive element 11 changes to follow the direction of the external magnetic field. At this time, the resistance value of the magnetoresistive element 11 changes according to the relative angle between the magnetization direction of the ferromagnetic layers 31 and 32 of the fixed layer 13 and the magnetization direction of the ferromagnetic layers 21 and 22 of the free layer 12. That is, the resistance value of the magnetoresistive element 11 changes according to the relative angle between the magnetization direction of the ferromagnetic layer 31 of the fixed layer 13 that is in contact with the intermediate layer 14 and the magnetization direction of the ferromagnetic layer 22 of the free layer 12.

[0059] When the direction and strength of the external magnetic field change, the detection output voltage of the full-bridge circuit 40 also changes accordingly. Therefore, the external magnetic field can be detected based on the detection output voltage obtained from the full-bridge circuit 40. Figure 4 shows a magnetic detection device 50 with sensitivity in the Y direction, configured to detect external magnetic fields in the vertical (Y) direction relative to the plane of the paper. By combining this with a magnetic detection device with sensitivity in the X direction, configured to detect magnetic fields in the horizontal (X) direction relative to the plane of the paper in Figure 4, it is possible to simultaneously detect magnetic fields in both the vertical and horizontal directions.

[0060] (Manufacturing Method for Magnetic Detection Device) Figures 5a to 5d schematically show the manufacturing method of the magnetic detection device 50 of Figure 4, and illustrate the relationship between the substrate 17 and the direction of magnetic field application in the film formation process. In the process shown in Figure 5a, two fixed layers 13 are formed on the substrate 17. In the process of forming the ferromagnetic layer 32 (see Figure 3) of the fixed layer 13, the ferromagnetic layer 32 is formed while applying a magnetic field to the substrate 17 in the direction indicated by the white arrow in the 270° (Y1) direction. Subsequently, due to the RKKY interaction that occurs between the ferromagnetic layer 32 and the ferromagnetic layer 31 via the antiparallel coupling layer 33, it is possible to form a fixed layer 13 in the 90° (Y2) direction indicated by the solid black arrow, where the magnetization direction of the ferromagnetic layer 31 is.

[0061] In the process shown in Figure 5b, two free layers 12 are formed following the process of forming the two fixed layers 13 shown in Figure 5a. In the process of forming the ferromagnetic layer 22 (see Figure 3) of the free layer 12, the ferromagnetic layer 22 is formed while applying a magnetic field to the substrate 17 in the direction indicated by the white arrow in the 0° (X2) direction. Subsequently, due to the RKKY interaction that occurs between the ferromagnetic layer 22 and the ferromagnetic layer 21 via the antiparallel coupling layer 23, a free layer 12 can be formed with the magnetization direction of the ferromagnetic layer 21 in the 180° (X1) direction indicated by the dashed black arrow. In this way, the fixed layer 13 and the free layer 12 are formed continuously.

[0062] In the process shown in Figure 5c, the direction of the magnetic field, indicated by the white arrow, is changed to the 90° (Y2) direction, and a magnetoresistive element 11 is formed on the same substrate 17, in which the magnetization direction of the ferromagnetic layers 31 and 32 in the fixed layer 13 is different from that of the fixed layer 13 formed in the process shown in Figure 5a. In the magnetoresistive element 11 formed in this process, the magnetization direction of the ferromagnetic layer 31 of the fixed layer 13 is 270° (Y1) direction, indicated by the solid black arrow.

[0063] In the process shown in Figure 5d, following the process of forming the two fixed layers 13 shown in Figure 5c, the direction of the magnetic field, indicated by the white arrow, is changed to the 180° (X1) direction, and a free layer 12 is formed on the same substrate 17, in which the magnetization directions of the ferromagnetic layers 21 and 22 are different from the free layer 12 formed in the process shown in Figure 5b. The magnetization direction of the ferromagnetic layer 21 of the free layer 12 formed in this process is the 0° (X2) direction, indicated by the dashed black arrow. The direction in which the magnetic field is applied is determined by the relative relationship between the substrate 17 and the magnetic field, so when changing the direction of the applied magnetic field, either the substrate 17 or the magnetic field application means may be moved.

[0064] In this way, by repeating the process of forming the fixed layer 13 and the free layer 12 by continuous film deposition twice while changing the direction in which the magnetic field is applied, magnetoresistive elements 11 with different magnetization directions for the fixed layer 13 and the free layer 12 can be formed on the same substrate 17.

[0065] After the deposition of multiple magnetoresistive elements 11, each having a fixed layer 13 and a free layer 12 with different magnetization directions, is completed on the substrate 17, annealing is performed in a zero magnetic field (no magnetic field) to generate an exchange-coupled magnetic field Hex between the ferromagnetic layer 32 and the antiferromagnetic layer 34 of the fixed layer 13, and between the ferromagnetic layer 21 and the antiferromagnetic layer 24 of the free layer 12. This ages the magnetoresistive elements 11, resulting in a stable magnetic detection device 50.

[0066] Subsequently, the multiple magnetoresistive elements 11 formed on a single substrate 17 are connected to form the full-bridge circuit 40 shown in Figure 4, thereby completing the manufacturing of the magnetic detection device 50.

[0067] In the magnetic detection device 50 manufactured as described above, the magnetization directions of the free layer 12 and the fixed layer 13 of the magnetoresistive element 11 are orthogonal. Therefore, it can be used as a linear output magnetic sensor in which there is linearity between the detected magnetism and the output within a predetermined measurement range. Furthermore, by increasing the anisotropic magnetic field Hk of the free layer 12 in the magnetoresistive element 11, the range in which linearity is maintained between the detected magnetism and the output and high-precision measurement is extended can be widened, thereby increasing the dynamic range.

[0068] Furthermore, when using a common manufacturing method that involves controlling magnetization through heat treatment in a magnetic field, it is not possible to make the magnetization directions of the fixed layer 13 and the free layer 12 perpendicular. This is because if heat treatment is performed in a magnetic field to control the magnetization direction of the fixed layer 13, the magnetization direction of the free layer 12 will be aligned in the same direction as that of the fixed layer 13.

[0069] The magnetic detection device 50 includes a ferromagnetic layer in which both the free layer 12 and the fixed layer 13 of the magnetoresistive element 11 are antiferromagnetically coupled by RKKY interaction. A magnetoresistive element 11 with such a configuration can be manufactured by the above-described manufacturing method, which defines the magnetization direction by forming a ferromagnetic layer in a magnetic field.

[0070] The magnetoresistive element 11 employs a configuration in which the ferromagnetic layer 21 and the ferromagnetic layer 22 are antiferromagnetically coupled via an antiparallel coupling layer 23 through an RKKY interaction, as a means of increasing the anisotropy Hk of the free layer 12. Other means of increasing the anisotropy Hk of the free layer 12 include, for example, making the element dimensions in the sensitivity direction (detection magnetic field direction) as narrow as possible with respect to the sensitivity orthogonal direction to increase the shape anisotropy of the free layer 12; placing a bias film made of a permanent magnet film in close proximity to the magnetoresistive element 11 and applying a bias magnetic field in the sensitivity orthogonal direction to increase the magnetic anisotropy of the free layer 12; and stacking an antiferromagnetic layer adjacent to the free layer 12 and applying an exchange coupling magnetic field Hex in the sensitivity orthogonal direction to increase the magnetic anisotropy of the free layer 12.

[0071] Figure 30 is a schematic diagram showing a magnetoresistive element 61 having a different stacked structure from the magnetoresistive element 11 shown in Figure 3. Like Figure 3, Figure 30 schematically shows the stacked structure in the cross-section along line A-A in Figures 1 and 2. Note that since this figure schematically shows the stacked structure, it does not represent the relative thickness of each layer in the Z direction. The same applies to Figures 31 and 32, which schematically show the stacked structure in the cross-section along line A-A in Figures 1 and 2.

[0072] The free layer 12 of the magnetoresistive element 61 has multiple first structures 52, each formed by stacking a ferromagnetic layer 21, an antiparallel coupling layer 23, and a ferromagnetic layer 22 in that order. Adjacent first structures 52a and 52b are connected via an antiparallel coupling layer 23d, and adjacent first structures 52b and 52c are connected via an antiparallel coupling layer 23e. The figure shows a free layer 12 having first structures 52a to 52c as an example, but the number of first structures 52 constituting the free layer 12 is not limited to three.

[0073] Figure 31 is a schematic diagram showing a magnetoresistive element 62 having a different stacked structure from the magnetoresistive element 11 shown in Figure 3. The fixed layer 13 of the magnetoresistive element 62 has a plurality of first structures 53, each consisting of a ferromagnetic layer 31, an antiparallel coupling layer 33, and a ferromagnetic layer 32 stacked in that order. Adjacent first structures 53a and 53b are connected via an antiparallel coupling layer 33d, and adjacent first structures 53b and 53c are connected via an antiparallel coupling layer 33e. The figure shows a fixed layer 13 having first structures 53a to 53c as an example, but the number of first structures 53 constituting the fixed layer 13 is not limited to three.

[0074] Figure 32 is a schematic diagram showing a magnetoresistive element 63 having a different stacked structure from the magnetoresistive element 11 shown in Figure 3. The magnetoresistive element 63 comprises a free layer 12 having multiple first structures 52 and a fixed layer 13 having multiple first structures 53. The first structures 52 and 53 shown in the figure are just examples, and the number of free layers 12 and fixed layers 13 is not limited to three, as with the magnetoresistive elements 61 and 62.

[0075] The magnetoresistive elements 61, 62, and 63 shown in Figures 30 to 32 have at least one of the free layer 12 and the fixed layer 13 having multiple first structures 52 and 53. This configuration allows for an increase in the anisotropic magnetic field Hk of the free layer 12, thereby expanding the dynamic range. Furthermore, an increase in the anisotropic magnetic field Hk of the fixed layer 13 improves resistance to strong magnetic fields.

[0076] In the magnetoresistive elements 61 and 63 shown in Figures 30 and 32, a ferromagnetic layer 21 from one of the adjacent first structures 52 is laminated on one side of the antiparallel coupling layer 23 between two adjacent first structures 52, and a ferromagnetic layer 22 from the other of the adjacent first structures 52 is laminated on the other side of the antiparallel coupling layer 23 between the two adjacent first structures 52.

[0077] Specifically, the ferromagnetic layer 21a of the first structure 52a is laminated on one side (Z1) of the antiparallel coupling layer 23d, which is connected via the first structure 52a and the first structure 52b, and the ferromagnetic layer 22b of the first structure 52b is laminated on the other side (Z2) of the antiparallel coupling layer 23d. Similarly, the ferromagnetic layer 21b is laminated on one side of the antiparallel coupling layer 23e, and the ferromagnetic layer 22c is laminated on the other side.

[0078] With the above configuration, the ferromagnetic layer 21 in one first structure 52 and the ferromagnetic layer 22 in the other first structure 52 are antiferromagnetically coupled via the antiparallel coupling layer 23 through RKKY interaction. Therefore, as the proportion of ferromagnetic layers 21 and 22 that are antiferromagnetically coupled on both sides in the stacking direction to form an SAF structure increases, the free layer 12 is stabilized, the anisotropic magnetic field Hk increases, and magnetoresistive elements 61 and 63 with a large dynamic range can be provided.

[0079] Furthermore, in the magnetoresistive elements 62 and 63 shown in Figures 31 and 32, a ferromagnetic layer 31 from one of the adjacent first structures 53 is laminated on one side of the antiparallel coupling layer 33 between two adjacent first structures 53, and a ferromagnetic layer 32 from the other of the adjacent first structures 53 is laminated on the other side of the antiparallel coupling layer 33 between the two adjacent first structures 53.

[0080] Specifically, the ferromagnetic layer 31a of the first structure 53a is laminated on one side (Z1) of the antiparallel coupling layer 33d, which is connected via the first structure 53a and the first structure 53b, and the ferromagnetic layer 32b of the first structure 53b is laminated on the other side (Z2) of the antiparallel coupling layer 33d. Similarly, the ferromagnetic layer 31b is laminated on one side of the antiparallel coupling layer 33e, and the ferromagnetic layer 32c is laminated on the other side.

[0081] With the above configuration, the ferromagnetic layer 31 in one first structure 53 and the ferromagnetic layer 32 in the other first structure 53 are antiferromagnetically coupled via the antiparallel coupling layer 33 through RKKY interaction. Therefore, as the proportion of the ferromagnetic layers 31 and 32 that are antiferromagnetically coupled on both sides in the stacking direction to form an SAF structure increases, the fixed layer 13 is stabilized, the anisotropic magnetic field Hk increases, and magnetoresistive elements 62 and 63 with excellent resistance to strong magnetic fields can be provided.

[0082] The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[0083] (Example 1, Comparative Example 1: Bottom-pin type magnetoresistive element (TMR)) Figures 6 and 7 show the configurations of the magnetoresistive elements of Example 1 and Comparative Example 1. Example 1 differs in that two ferromagnetic layers in the free layer are antiferromagnetically coupled via an antiparallel coupling layer through an RKKY interaction, while Comparative Example 1 differs in that the free layer consists of ferromagnetic layers that are not antiferromagnetically coupled. Note that in this example and the examples described later, magnetic characteristic data was obtained with a configuration that does not include a lower electrode 7 (see Figure 2). However, the lower electrode 7 is essential in actual TMR magnetic sensors, and a film of the lower electrode 7 is usually provided between the substrate (underlying layer) and the insulating layer.

[0084] Figure 8 is a graph showing the MH curves of the fixed layer of the magnetoresistive elements of Example 1 and Comparative Example 1. Figure 9 is a graph showing the MH curves of the free layer of the magnetoresistive elements of Example 1 and Comparative Example 1. Figure 10 is the MH curve of Comparative Example 1, with the horizontal axis scale, which represents the applied magnetic field in the sensitivity direction, changed from that of Figure 9.

[0085] (Example 2, Comparative Example 2: Top-pin type magnetoresistive element (TMR)) Figures 11 and 12 show the configurations of the magnetoresistive elements of Example 2 and Comparative Example 2. The difference between the two is that in Example 2, the two ferromagnetic layers of the free layer are antiferromagnetically coupled, while in Comparative Example 2, the free layer consists of a ferromagnetic layer that is not antiferromagnetically coupled.

[0086] Figure 13 is a graph showing the MH curves of the fixed layer of the magnetoresistive elements of Example 2 and Comparative Example 2. Figure 14 is a graph showing the MH curves of the free layer of the magnetoresistive elements of Example 2 and Comparative Example 2. Figure 15 is the MH curve of Comparative Example 2, with the horizontal axis scale, which represents the applied magnetic field in the sensitivity direction, changed from that of Figure 14.

[0087] As shown in Examples 1 and 2, when a free layer having a structure with two ferromagnetic layers antiferromagnetically coupled by RKKY interaction is used, the anisotropic magnetic field Hk becomes larger (the slope of the linear part of the MH curve becomes smaller) than in a free layer with an antiferromagnetic layer applied to a ferromagnetic layer that is not antiferromagnetically coupled, as in Comparative Examples 1 and 2.

[0088] Furthermore, although the fixed layer has the same SAF structure as the free layer, it is formed of CoFe with a large crystal magnetic anisotropy constant K, resulting in a gentler slope of the MH curve and a larger anisotropic magnetic field Hk than that of the free layer. As described above, by controlling the direction of the magnetic field during film deposition to form an SAF structure, we were able to increase the anisotropic magnetic field Hk of the free layer while the fixed layer and free layer were in an orthogonal magnetization arrangement, thereby providing a magnetoresistive film (device) with a large dynamic range.

[0089] (Examples 3 and 4: Bottom-pin type magnetoresistive element (TMR)) Figures 16 and 17 show the configuration of the magnetoresistive elements of Examples 3 and 4. Figures 18 and 19 are graphs showing the MH curves of the fixed layer and free layer of the magnetoresistive elements of Examples 3 and 4.

[0090] (Examples 5 and 6: Top-pin type magnetoresistive element (TMR)) Figures 20 and 21 show the configuration of the magnetoresistive elements of Examples 5 and 6. Figures 22 and 23 are graphs showing the MH curves of the fixed layer and free layer of the magnetoresistive elements of Examples 5 and 6.

[0091] It was found that the free layers of Examples 3 and 5 exhibited a larger anisotropic magnetic field Hk than the free layers of Examples 4 and 6. This increase in anisotropic magnetic field Hk is due to the placement of the CoFeB alloy layer adjacent to the interface between the free layer and the intermediate layer (MgO layer), and the placement of the CoFeB alloy layer on the opposite side, separated by an antiparallel coupling layer (Ru layer), as far away from the Ru interface as possible. This arrangement increased the antiferromagnetic coupling between the ferromagnetic layers in the free layer, resulting in a larger anisotropic magnetic field Hk. Furthermore, it was found that when the free layer contains a CoFe alloy, the antiferromagnetic coupling between the ferromagnetic layers in the free layer can be increased by symmetrically arranging the CoFe alloy layer adjacent to the Ru layer at the interface with the Ru layer.

[0092] When NiFe alloy is included as a material constituting the free layer, it is preferable to laminate the layers so that the NiFe alloy layer is placed between the CoFeB alloy layer and the CoFe alloy layer, as shown in Examples 3 to 6. From the viewpoint of increasing ΔMR, it is preferable to include CoFeB alloy in the material constituting the free layer, and from the viewpoint of reducing hysteresis, it is preferable to include NiFe alloy. Note that CoFe alloy is not essential as a material constituting the free layer.

[0093] The magnetoresistive elements of Examples 3 and 5 include a CoFeB alloy layer and a NiFe alloy layer in the free layer, and are stacked symmetrically with the same film thickness around the Ru layer in the SAF structure. This configuration makes it easier to achieve both high ΔMR and low hysteresis in the magnetoresistive element. Furthermore, it becomes easier to match the Ms·t of the upper and lower layers (ferromagnetic layers on both sides) of the Ru layer, thereby strengthening the antiferromagnetic coupling of the SAF structure in the free layer and making it possible to create a magnetoresistive element with a large anisotropic magnetic field Hk, i.e., a large dynamic range.

[0094] The free layer of the top-pin configuration in Example 6 shown in Figure 23 exhibits a particularly small anisotropic magnetic field Hk compared to Examples 3-5. This is because the layer directly beneath the Ru layer in the free layer is a CoFeB alloy layer. In other words, it is thought that the atomic density of the Ru layer decreases when the Ru layer is formed on top of the amorphous CoFeB alloy layer, which degrades the antiferromagnetic coupling of the SAF structure in the free layer and reduces the anisotropic magnetic field Hk.

[0095] (Examples 7-1 to 7-6 Magnetic Sensors) Figure 24 shows the configuration of the magnetoresistive magnetoresistance (TMR) element in the magnetic sensors of Examples 7-1 to 7-6. As shown in the figure, the two ferromagnetic layers in the free layer are composed of a (50CoFe)B20 layer / 85NiFe layer / 90CoFe layer, with the film thickness of the (50CoFe)B20 layer and the 90CoFe layer set to 1.0 nm. In the figure, magnetoresistive magnetoresistance elements were fabricated by varying the film thickness X of one of the 85NiFe layers marked with a ● and the film thickness Y of the other 85NiFe layer marked with a ○.

[0096] For magnetic sensors equipped with magnetoresistive elements with an SFF (Synthetic Ferrimagnetic) structure (Examples 7-1 to 7-3) where the product Ms·t between the magnetization Ms and film thickness t of two ferromagnetic layers in the free layer is different, and magnetoresistive elements with an SAF structure (Examples 7-4 to 7-6) where Ms·t is the same, the relationship between the measured magnetic field and the output was measured in the measurement range of -60 mT to +60 mT.

[0097] Figure 25 is a graph showing a method for evaluating the linearity (nonlinearity) of a magnetic sensor. Referring to the graph in Figure 25, the method for evaluating linearity is explained below. The relationship between the magnetic field under test and the output of the magnetic sensor is measured, and based on the measurement results, a regression line L is obtained as a straight line representing the ideal relationship between the magnetic field and output of the magnetic sensor in a predetermined measurement range by linear approximation using the least squares method. Using the regression line L, the output Omin at the minimum value Tmin and the output Omax at the maximum value Tmax in the measurement range of the magnetic field under test are obtained. FS, which is the difference between Omax and Omin, is calculated. For each measurement value included in the measurement range (Tmin or greater and Tmax or less), ΔV, which is the difference between the actually measured output and the output obtained from the regression line L, is calculated, and the maximum value of ΔV, ΔVmax, is identified. The linearity of the magnetic sensor is evaluated by the ratio of ΔVmax to FS (%FS) = (ΔVmax / FS) × 100.

[0098] Figure 26 is a graph showing the output of magnetic sensors in Examples 7-1 to 7-3, which have an SFF structure. Figure 27 is a graph showing the output of magnetic sensors in Examples 7-4 to 7-6, which have an SAF structure. Table 1 shows the configuration of the free layer, the film thickness X and Y of the NiFe alloy layer, the Ms·t of the ferromagnetic layer containing the alloy layers of film thickness X and Y, and the nonlinearity of the magnetic sensor in Examples 7-1 to 7-6.

[0099]

[0100] As shown in Figures 26, 27, and Table 1, magnetic sensors with a free layer of SAF structure (synthetic antiferromagnetic structure) exhibited less nonlinearity between the measured magnetic field and the output, and superior linearity, compared to magnetic sensors with an SFF structure (synthetic ferrimagnetic structure). In other words, from the viewpoint of linearity in detecting an external magnetic field, it was found that using an SFF structure for the free layer of the magnetoresistive element of a magnetic sensor is disadvantageous, while using an SAF structure is advantageous.

[0101] When the free layer has an SFF structure, linearity improved as the ratio of the Ms·t of the ferromagnetic layer containing the NiFe alloy layer with thickness Y to the Ms·t of the ferromagnetic layer containing the NiFe alloy layer with thickness X increased. Furthermore, when the free layer has an SAF structure, linearity improved as the Ms·t of the ferromagnetic layer decreased.

[0102] Figure 28 is a schematic diagram showing the change in magnetization direction due to an external magnetic field for a free layer with an SFF structure. As shown in the upper part of the figure, the two ferromagnetic layers in the free layer with an SFF structure have magnetizations oriented in opposite directions, but their magnetization magnitudes Ms·t are different. Therefore, when an external magnetic field is applied, as shown in the middle part of the figure, the two ferromagnetic layers maintain their antiferromagnetic coupling, and first the layer with the larger Ms·t magnetizes in the direction of the external magnetic field. Subsequently, as the external magnetic field increases, as shown in the lower part of the figure, the layer with the smaller Ms·t magnetizes with a delay. The magnetic field at which the antiparallel magnetization state of the two ferromagnetic layers breaks down and the layer with the smaller Ms·t begins to magnetize in the direction of the external magnetic field is called the spinflop magnetic field Hsf. The reason why the output graph of the magnetic sensor with an SFF structure free layer shown in Figure 26 bends at the spinflop magnetic field is thought to be because the magnetization process proceeds in two stages in a free layer with an SFF structure.

[0103] Figure 29 is a schematic diagram showing the change in magnetization direction due to an external magnetic field for a free layer with an SAF structure. As shown in the upper part of the figure, the two ferromagnetic layers in the free layer with an SAF structure have magnetizations oriented in opposite directions and have equal magnitudes Ms·t. Therefore, when an external magnetic field is applied, the two ferromagnetic layers are magnetized simultaneously, as shown in the lower part of the figure. In other words, the free layer with an SAF structure balances the Ms·t of the two ferromagnetic layers, so that the magnetization of both ferromagnetic layers occurs simultaneously when an external magnetic field is applied. As a result, the spinflop magnetic field Hsf becomes near zero, and the magnetization process proceeds in one step. This is considered to be the reason why the output graph of the magnetic sensor with an SAF structure in the free layer shown in Figure 27 does not curve.

[0104] (Examples 8-1 to 8-6 Free Layers of Multiple SAF Structures) Figure 33 is a schematic diagram showing the configuration of free layers 12 with different numbers of first structures 52 in the bottom-pin type magnetoresistive magnetoresistive element (TMR) of this embodiment. Figure 34 is a schematic diagram showing the configuration of free layers 12 in the magnetoresistive element of this embodiment. Figures 33 and 34 show the material used for each layer, the film thickness (nm) of each layer, and the magnetization direction of each layer. As shown in these figures, in this embodiment, the magnetic properties were evaluated by separating the free layers 12.

[0105] In this embodiment, laminates were fabricated having free layers 12 with a single SAF layer and free layers 12 with multiple layers (2 to 6 layers), each with a different number of first structures 52 in the free layer 12. By continuously depositing the free layers 12 while applying a magnetic field in the same direction to all of them, magnetized free layers 12 are obtained in which the ferromagnetic layers 21 and 22, via the antiparallel coupling layer 23 made of Ru, are alternating.

[0106] Figure 35 is a graph showing superimposed MH curves comparing the differences depending on the number of first structures 52 constituting the free layer 12. Specifically, it shows the MH curves of a free layer 12 having 1 to 6 first structures 52, with the horizontal axis representing the magnetic field in the sensitivity direction and the vertical axis representing magnetization (M・t). The direction of the applied magnetic field, which is the magnetic field in the sensitivity direction, is perpendicular to the magnetization direction of the SAF, that is, perpendicular to the magnetization direction of the free layer 12 shown by the arrows in Figures 33 and 34. As shown in the figure, the magnetization of the free layer 12 increased as the applied magnetic field in the sensitivity direction increased.

[0107] Figure 36 shows the saturation magnetization (Total-Ms·t) of the free layer 12 as a whole. As shown in the figure, the saturation magnetization (Total-Ms·t) of the free layer 12 increases as the number of first structures 52, i.e., the number of stacked SAFs, increases. The saturation magnetization of the free layer 12 is calculated by multiplying the magnetization (Ms·t) per ferromagnetic layer constituting one first structure 52 by the number of first structures 52 that the free layer 12 has.

[0108] Figure 37 is a graph comparing MH curves that vary depending on the number of first structures 52 constituting the free layer 12. Specifically, it shows superimposed MH curves for free layers 12 having 1 to 6 first structures 52, with the horizontal axis representing the sensitivity direction magnetic field and the vertical axis representing the saturation rate. Figure 38 is a graph showing the relationship between the saturation rate of the free layer 12 and the linear region magnetic field at ±10 kOe and the number of first structures 52. From the results shown in these figures, it was found that when the saturation rate, normalized by the saturation magnetization of the free layer 12, is used as the vertical axis, in the region of large applied magnetic fields, the change in the saturation rate of the free layer 12 with increasing number of first structures 52 as the SAF is multiplexed becomes smaller. It was also found that the saturation rate decreases sharply from 1 to 4 SAF stacking counts, and then becomes more gradual when the SAF stacking count reaches 5. As shown in Figure 37, the MH curves for the quintuple SAF and the hexaple SAF are almost identical. In light of these results, it is preferable that the number of first structures 52 in the free layer 12 be between 2 and 5.

[0109] As the number of first structures 52 in the free layer 12 increases, the free layer 12 becomes less magnetized and its saturation rate decreases. In a conventional single SAF (ferromagnetic layer / Ru layer / ferromagnetic layer), i.e., a free layer 12 having one first structure 52, the RKKY interaction occurs on one side of each ferromagnetic layer. However, when multiple first structures 52 are duplicated, the proportion of ferromagnetic layers receiving antiferromagnetic coupling from both the top and bottom sides increases. Therefore, it is thought that the influence of the RKKY interaction increases with the duplication of the first structures 52, and as a result, the saturation rate of the free layer 12 decreases.

[0110] Figure 39 is a graph showing the number of first structures 52 and the proportion of ferromagnetic layers where RKKY interaction occurs on both the upper and lower surfaces. For example, when there is one first structure 52 constituting the free layer 12, the number of ferromagnetic layers where RKKY interaction occurs on both the upper and lower surfaces is 0, and the proportion of ferromagnetic layers where RKKY interaction occurs on both the upper and lower surfaces is 0 / 2. When the number of first structures 52 in the free layer 12 is 2, 3, 4, 5, and 6, respectively, the number of ferromagnetic layers where RKKY interaction occurs on both the upper and lower surfaces is 2, 4, 6, 8, and 10. The proportion of ferromagnetic layers where RKKY interaction occurs on both the upper and lower surfaces is 2 / 4, 4 / 6, 6 / 8, 8 / 10, and 10 / 12. As the number of first structures 52 in the free layer 12 increases, the degree to which RKKY interaction has an effect increases, and it can be said that the free layer 12 becomes more difficult to magnetize.

[0111] Figure 40 is a graph showing the definition of the linear region magnetic field. As shown in the figure, a regression line L is determined based on the measurement results, and the linearity of the magnetic sensor is defined as the magnetic field range in which the ratio of △V to FS (%) (△V / FS) × 100 is 3 (%) or less (see Figure 25). The linear region magnetic field occurs in the positive and negative regions of the magnetic field applied in the sensitivity direction, respectively.

[0112] (Examples 9-1 to 9-6 Fixed layer of multiple SAF structure) Figure 41 is a schematic diagram showing the configuration of fixed layers 13 with different numbers of first structures 53 in the bottom-pin type magnetoresistive magnetoresistive element (TMR) of this embodiment. Figure 42 is a schematic diagram showing the film structure of the fixed layer 13 in the magnetoresistive element of this embodiment. Figures 41 and 42 show the material used for each layer, the film thickness (nm) of each layer, and the magnetization direction (arrow) of each layer. As shown in these figures, in this embodiment, the magnetic properties were evaluated by separating the fixed layers 13.

[0113] In this embodiment, laminates were fabricated having a fixed layer 13 with a single SAF layer and a fixed layer 13 with multiple layers (2 to 6 layers), each with a different number of first structures 53 in the fixed layer 13. By continuously depositing the fixed layer 13 while applying a magnetic field in the same direction to all of them, a fixed layer 13 is obtained in which the ferromagnetic layer 31 and ferromagnetic layer 32 are magnetized alternately via an antiparallel coupling layer 33 made of Ru.

[0114] Figure 43 is a graph showing superimposed MH curves comparing the differences depending on the number of first structures 53 constituting the fixed layer 13. Specifically, it shows the MH curves of a fixed layer 13 having 1 to 6 first structures 53, with the horizontal axis representing the magnetic field in the sensitivity direction and the vertical axis representing magnetization (M・t). The applied magnetic field direction is parallel to the magnetization direction of the ferromagnetic layer 31 and ferromagnetic layer 32 in the fixed layer 13, that is, parallel to the magnetization direction of the fixed layer 13 indicated by the arrows in Figures 41 and 42.

[0115] Figure 44 shows the saturation magnetization (Total-Ms·t) of the entire fixed layer 13. As shown in the figure, the saturation magnetization of the fixed layer 13 increases as the number of first structures 53 increases and the number of stacked SAFs increases. The saturation magnetization is calculated by multiplying the magnetization (Ms·t) per ferromagnetic layer constituting one first structure 53 by the number of first structures 53 in the fixed layer 13.

[0116] Figure 45 is a graph showing superimposed MH curves comparing the differences depending on the number of first structures 53 constituting the fixed layer 13, specifically the MH curves of a fixed layer 13 having 1 to 6 first structures 53, with the horizontal axis representing the magnetic field in the sensitivity direction and the vertical axis representing the saturation rate. Figure 46 is a graph showing the relationship between the saturation rate of the fixed layer 13 and the number of first structures 53 at ±10 kOe. As shown in these figures, when the saturation rate normalized by the saturation magnetization of the fixed layer 13 is used as the vertical axis, it was found that in the region of large applied magnetic fields, the change in the saturation rate of the fixed layer 13 with increasing number of first structures 53 as the SAF is multiplexed becomes smaller, and the saturation rate decreases sharply from 1 to 3 SAF stacking numbers, and then becomes more gradual when the SAF stacking number reaches 5. As shown in Figure 45, the MH curves of the quintuple SAF and the hexaple SAF almost overlap.

[0117] From the above results, it is preferable that the number of first structures 53 in the fixed layer 13 be between 2 and 5. By setting the number of first structures 53 within the above range, the overall thickness of the magnetoresistive element increases, which reduces the risk of difficulty in forming the element due to increased sidewall short circuits caused by, for example, a larger amount of etching and greater re-adhesion. Therefore, it is preferable to reduce the number of first structures 53 in the fixed layer 13 within the range in which a fixed layer 13 with high magnetic field resistance can be obtained. The same applies to the free layer 12.

[0118] The reason why the fixed layer 13 becomes less magnetized as the number of first structures 53 increases is thought to be because, similar to the free layer 12, the influence of RKKY increases with redundancy.

[0119] The magnetoresistive element of the present invention can be used as a magnetic sensor with a wide dynamic range.

[0120] 1: GMR element 2: Long pattern 3: Folded section 4: Electrode 5: TMR element 6: Upper electrode 7: Lower electrode 8: Film 9: Electrode 11, 61, 62, 63: Magnetoresistive element 12: Free layer 13: Fixed layer 14: Intermediate layer 15: Underlayment layer 16: Insulating layer 17: Substrate 19: Protective layer 21, 21a-21c: Ferromagnetic layer (first ferromagnetic layer) 22, 22a-22c: Ferromagnetic layer (second ferromagnetic layer) 23, 23a-23e: Antiparallel coupling layer 24: Antiferromagnetic layer 31, 31a-31c: Ferromagnetic layer (first ferromagnetic layer) 32, 32a-32c: Ferromagnetic layer (second ferromagnetic layer) 33, 33a-33e: Antiparallel coupling layer 34: Antiferromagnetic layer 40: Full bridge circuit 41: Power supply voltage 42a: Series circuit 42b: Series circuit 43a: Midpoint terminal 43b: Midpoint terminal 44: Ground potential 50: Magnetic detection device 52, 52a-52c, 53, 53a-53c: First structure FS: Output range Hex: Exchange coupling magnetic field Hk: Anisotropic magnetic field Hsf: Spinflop magnetic field K: Crystal magnetic anisotropy constant L: Regression line Ms: Magnetization Ms21: Magnetization (Magnetization Ms1) Ms22: Magnetization (Magnetization Ms2) Ms31: Magnetization Ms32: Magnetization Omax: Output Omin: Output Tmax : Maximum value of the measurement range Tmin: Minimum value of the measurement range X, Y: Film thickness t: Film thickness t21: Film thickness (film thickness t1) t22: Film thickness (film thickness t2) t23: Film thickness t31, t32, t33: Film thickness

Claims

1. A magnetoresistive element comprising an intermediate layer between a free layer and a fixed layer, wherein, when no external magnetic field is applied, the magnetization directions of the free layer and the fixed layer are orthogonal, the free layer and the fixed layer each have a first ferromagnetic layer, an antiparallel coupling layer and a second ferromagnetic layer, the first ferromagnetic layer and the second ferromagnetic layer are stacked via the antiparallel coupling layer and are antiferromagnetically coupled by RKKY interaction, and the anisotropic magnetic field Hk of the ferromagnetic layer in the fixed layer is greater than the anisotropic magnetic field Hk of the ferromagnetic layer in the free layer.

2. The magnetoresistive element according to claim 1, wherein the crystalline magnetic anisotropy constant K of the ferromagnetic layer in the fixed layer is greater than the crystalline magnetic anisotropy constant K of the ferromagnetic layer in the free layer.

3. The magnetoresistive element according to claim 1, wherein the product Ms·t of the magnetization Ms of the ferromagnetic layer in the fixed layer and the film thickness t is smaller than the product Ms·t of the magnetization Ms of the ferromagnetic layer in the free layer and the film thickness t.

4. The magnetoresistive element according to claim 3, wherein the product Ms1・t1 of the magnetization Ms1 of the first ferromagnetic layer and the film thickness t1 is substantially equal to the product Ms2・t2 of the magnetization Ms2 of the second ferromagnetic layer and the film thickness t2.

5. The magnetoresistive element according to claim 1, wherein the first ferromagnetic layer and the second ferromagnetic layer in the free layer are made of the same material.

6. The magnetoresistive element according to claim 1, wherein the first ferromagnetic layer and the second ferromagnetic layer in the free layer are each composed of multiple layers, and the layer adjacent to the antiparallel coupling layer in the first ferromagnetic layer and the layer adjacent to the antiparallel coupling layer in the second ferromagnetic layer are made of the same material.

7. The magnetoresistive element according to claim 6, wherein the main component of the material constituting the first ferromagnetic layer and the second ferromagnetic layer is a NiFe alloy.

8. The magnetoresistive element according to claim 7, wherein the first ferromagnetic layer and the second ferromagnetic layer in the free layer are each composed of multiple layers, and the first ferromagnetic layer and the second ferromagnetic layer in the free layer are stacked symmetrically with respect to the antiparallel coupling layer.

9. The magnetoresistive element according to claim 1, wherein the first ferromagnetic layer and the second ferromagnetic layer in the free layer are alloy layers selected from a CoFeB alloy layer, a NiFe alloy layer, and a CoFe alloy layer, or a stack of two or more alloy layers from among these alloy layers.

10. The magnetoresistive element according to claim 9, wherein the intermediate layer is an MgO layer and the CoFeB alloy layer is adjacent to the intermediate layer.

11. The magnetoresistive element according to claim 1, wherein the fixed layer and the free layer each have an antiferromagnetic layer laminated adjacent to one of the ferromagnetic layers, and one of the ferromagnetic layers and the antiferromagnetic layer are exchange-coupled.

12. The magnetoresistive element according to claim 1, wherein at least one of the fixed layer and the free layer has a plurality of first structures formed by stacking the first ferromagnetic layer, the antiparallel coupling layer and the second ferromagnetic layer in that order, and two adjacent first structures are provided via the antiparallel coupling layer.

13. The magnetoresistive element according to claim 12, wherein the first ferromagnetic layer of one of the adjacent first structures is laminated on one side of the antiparallel coupling layer via two adjacent first structures, and the second ferromagnetic layer of the other of the adjacent first structures is laminated on the other side of the antiparallel coupling layer via two adjacent first structures, and the first ferromagnetic layer of one of the first structures and the second ferromagnetic layer of the other first structure are antiferromagnetically coupled by RKKY interaction.

14. The magnetoresistive element according to claim 12, wherein the number of the first structures is 5 or less.

15. A magnetic sensor comprising the magnetoresistive element described in claim 1, characterized in that there is linearity between the magnetism detected and the output within a predetermined measurement range.

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