阅读说明：本技术 磁传感器 (Magnetic sensor ) 是由 高野研一 斋藤祐太 平林启 于 2020-02-14 设计创作，主要内容包括：磁传感器(1)具有相互连接的多个MR元件(11A～14A)。多个MR元件(11A～14A)属于在各自由层(26)的磁化方向沿同一方向旋转规定角度时电阻增加的组(G1)和电阻减少的组(G2)中的任一组。一组的电阻元件的电阻的增加所引起的磁传感器(1)的输出的变动和另一组的电阻元件的电阻的减少所引起的磁传感器(1)的输出的变动相抵消。(A magnetic sensor (1) has a plurality of MR elements (11A-14A) connected to each other. The plurality of MR elements (11A-14A) belong to either a group (G1) in which the resistance increases and a group (G2) in which the resistance decreases when the elements are rotated in the same direction by a predetermined angle from the magnetization direction of the layer (26). The fluctuation of the output of the magnetic sensor (1) caused by the increase of the resistance element of one group and the fluctuation of the output of the magnetic sensor (1) caused by the decrease of the resistance element of the other group are offset.)

1. A magnetic sensor, wherein,

the magnetic recording medium includes a plurality of mutually connected resistance elements, each resistance element including at least one MR element, each MR element having a free layer magnetized in an initial magnetization direction when an external magnetic field is not applied and having a magnetization direction changed from the initial magnetization direction when the external magnetic field is applied, the plurality of resistance elements belonging to any one of a group in which resistance increases and a group in which resistance decreases when the layers are rotated by a predetermined angle in the same direction from the magnetization direction of the layers,

the two groups are configured such that a variation in output of the magnetic sensor caused by an increase in resistance of the resistance elements of one group and a variation in output of the magnetic sensor caused by a decrease in resistance of the resistance elements of the other group cancel out each other.

2. A magnetic sensor according to claim 1,

the plurality of resistance elements have first and second resistance elements connected in series and third and fourth resistance elements connected in series, a power supply voltage is applied to the first and fourth resistance elements, the second and third resistance elements are grounded, and output voltages are taken out from between the first resistance element and the second resistance element and between the third resistance element and the fourth resistance element,

the first and fourth resistance elements belong to the same group, and the second and third resistance elements belong to other groups.

3. A magnetic sensor according to claim 2,

each MR element has a reference layer having a magnetization direction fixed with respect to an external magnetic field, the initial magnetization direction of the free layer of the MR elements of the one group is rotated by a first angle theta 1 in a first rotation direction with respect to the magnetization direction of the reference layer, and the initial magnetization direction of the free layer of the MR elements of the other group is rotated by a second angle theta 2 in a second rotation direction opposite to the first rotation direction with respect to the magnetization direction of the reference layer, wherein 0 DEG < theta 1 < 180 DEG, and 0 DEG < theta 2 < 180 deg.

4. A magnetic sensor according to any one of claims 1 to 3,

the free layer of one of the MR elements and the free layer of the other of the MR elements are magnetized in substantially anti-parallel orientations with respect to each other.

5. A magnetic sensor according to claim 4,

each MR element has a pair of bias magnets for applying a bias magnetic field to the free layer,

the pair of bias magnets are a pair of end bias magnets facing both side ends of the free layer in the initial magnetization direction and having a central axis substantially orthogonal to the central axis of the free layer, or a pair of side bias magnets facing both side portions of the free layer in the initial magnetization direction and having a central axis substantially parallel to the central axis of the free layer.

6. A magnetic sensor according to claim 5,

the pair of bias magnets are the pair of end bias magnets, and the size of the end bias magnets is larger than the size of the free layer in a direction orthogonal to the initial magnetization direction.

7. A magnetic sensor according to claim 5,

the pair of bias magnets are the pair of side bias magnets, and the size of the side bias magnets is larger than the size of the free layer in a direction parallel to the initial magnetization direction.

8. A magnetic sensor according to claim 5,

the pair of bias magnets of the one part of the MR elements and the pair of bias magnets of the other MR elements are formed of materials having coercive forces different from each other.

9. A magnetic sensor according to claim 8,

the pair of bias magnets of the MR elements of the one part are made of CoPt or a material in which at least one of Cr, B, and Ta is added to CoPt, and the pair of bias magnets of the other MR elements are made of FePt or a material in which at least one of Ni, Nb, Cu, Ag, Mo, and Ti is added to FePt.

10. A magnetic sensor according to claim 5,

the pair of bias magnets of the one MR element is the end bias magnet, the pair of bias magnets of the other MR element is the side bias magnet, and the end bias magnet and the side bias magnet are magnetized in the same direction.

11. A magnetic sensor according to any one of claims 1 to 3,

the MR element has a pair of bias magnets for applying bias magnetic fields to the free layer, the pair of bias magnets of at least one of the MR elements are opposed to both side ends of the free layer in the initial magnetization direction, and the central axes of the bias magnets are inclined in a range of 25 DEG to 65 DEG with respect to the central axis of the free layer.

12. The magnetic sensor of claim 11,

the free layer and the bias magnet are each substantially parallelogram-shaped with two sides adjacent to each other at an angle other than 90 ° as viewed from the lamination direction of the MR element.

13. The magnetic sensor of claim 11,

the at least one MR element includes at least two MR elements, central axes of the free layers of the at least two MR elements are parallel to each other, and central axes of the bias magnets of some of the MR elements are inclined in opposite directions with respect to central axes of the bias magnets of other MR elements.

14. A magnetic sensor according to claim 13,

all of the bias magnets are magnetized in the same direction.

15. A magnetic sensor according to claim 1,

the plurality of resistance elements are each formed of one of a single MR element, a plurality of MR elements connected in series, or a plurality of MR element groups in which MR element groups formed of a plurality of MR elements connected in series are connected in parallel.

16. A magnetic sensor according to claim 1,

and detecting magnetic fields in two directions in the plane of the free layer.

Technical Field

The present application is based on japanese application filed on 19/3/2019, i.e. japanese patent application 2019-. These applications are incorporated by reference in their entirety.

The present invention relates to a magnetic sensor, and more particularly, to a magnetic sensor using a magnetoresistance effect element.

Background

A magnetic sensor including a magnetoresistance effect element detects an external magnetic field based on a resistance change caused by the magnetoresistance effect. A magnetic sensor using a magnetoresistance effect element has high output and sensitivity to a magnetic field and is easy to be miniaturized, compared with other magnetic sensors. The magnetic sensor disclosed in japanese patent laid-open No. 2009-162499 includes a free magnetic layer (hereinafter, referred to as a free layer) whose magnetization direction changes according to an external magnetic field, a nonmagnetic layer (hereinafter, referred to as a spacer layer) that exhibits a magnetoresistance effect, and a fixed magnetic layer (hereinafter, referred to as a reference layer) whose magnetization direction is fixed with respect to the external magnetic field. In order to stabilize the magnetization direction of the free layer when no external magnetic field is applied, a permanent magnet layer (hereinafter, referred to as a bias magnet) to which a bias magnetic field is applied is provided on the side of the free layer.

Disclosure of Invention

Magnetic sensors are subjected to various stresses during and after manufacture. When an external magnetic field is not applied, the magnetization direction of the free layer is fixed in a certain direction by the bias magnet, but if stress is applied, the magnetization direction changes according to the inverse magnetostrictive effect. The change in the magnetization direction may affect the resistance of the magnetoresistance effect element, or even the output of the magnetic sensor when no external magnetic field is applied. However, the stress applied to the magnetic sensor cannot be predicted in many cases, and even if the stress can be predicted, it is difficult to control the stress. Therefore, in order to ensure the accuracy of the magnetic sensor, it is desirable that the output of the magnetic sensor when the external magnetic field is not applied is not easily affected by stress.

The invention provides a magnetic sensor, which is not easily affected by stress when an external magnetic field is not applied.

A magnetic sensor of the present invention has a plurality of resistance elements connected to each other. Each of the resistance elements has at least one MR element, and each of the MR elements has a free layer which is magnetized in an initial magnetization direction when an external magnetic field is not applied and which has a magnetization direction which changes from the initial magnetization direction when an external magnetic field is applied. The plurality of resistance elements belong to either a group in which resistance increases or a group in which resistance decreases when the layers are rotated by a predetermined angle in the same direction from the magnetization direction. The variation in the output of the magnetic sensor caused by the increase in the resistance of the resistive elements of one of the two groups and the variation in the output of the magnetic sensor caused by the decrease in the resistance of the resistive elements of the other group cancel each other out.

According to the present invention, it is possible to provide a magnetic sensor whose output is less susceptible to stress when an external magnetic field is not applied.

The above and other objects, features and advantages of the present application will become apparent from the following detailed description with reference to the accompanying drawings illustrating the present application.

Drawings

Fig. 1A to 1D are schematic configuration diagrams of a magnetic sensor according to a first embodiment of the present invention.

Fig. 2A and 2B are schematic configuration diagrams of MR elements of the magnetic sensor shown in fig. 1A to 1D.

Fig. 3A to 3C are plan views conceptually showing magnetizations of the free layer, the reference layer, and the pinned layer in a state where an external magnetic field is not present, respectively.

Fig. 4A to 4D are schematic configuration diagrams of magnetic sensors of comparative examples.

Fig. 5A to 5C are conceptual diagrams illustrating increase and decrease in resistance when stress is applied to each MR sensor.

Fig. 6A and 6B are diagrams showing the bias magnetic field applied to the free layer and the magnetization of the free layer in the magnetic sensor according to the first embodiment.

Fig. 7A and 7B are schematic configuration diagrams of a magnetic sensor according to a second embodiment of the present invention.

Fig. 8A and 8B are schematic configuration diagrams of the MR element of the magnetic sensor shown in fig. 7A and 7B.

Fig. 9A to 9C are diagrams showing the bias magnetic field applied to the free layer and the magnetization of the free layer in the magnetic sensor according to the second embodiment.

Fig. 10A and 10B are schematic configuration diagrams of a magnetic sensor according to a third embodiment of the present invention.

Fig. 11A to 11D are schematic configuration diagrams of a magnetic sensor according to a fourth embodiment of the present invention.

Fig. 12A to 12C are diagrams for explaining a method of applying a load to the magnetic sensor in the examples and the comparative examples.

Fig. 13A and 13B are graphs showing the relationship between the displacement and the voltage offset in the comparative example and the example, respectively.

Fig. 14A to 14D are schematic configuration diagrams of magnetic sensors according to modified examples of the present invention.

Fig. 15A and 15B are schematic configuration diagrams of the orientation detector.

Fig. 16A and 16B are schematic configuration diagrams of other orientation detectors.

Description of the symbols

27C tilt the bias magnet.

Detailed Description

Magnetic sensors according to several embodiments of the present invention will be described below with reference to the drawings. In the following description and the drawings, the X direction coincides with the magnetization directions of the pinned layer and the reference layer and the short axis direction of the free layer. The Y direction is a direction orthogonal to the X direction and coincides with the long axis direction of the free layer. The Z direction is a direction orthogonal to the X direction and the Y direction, and coincides with the lamination direction of the multilayer film of the MR element (magnetoresistance effect element). In the drawings, the directions of arrows indicating the X, Y, Z direction are sometimes referred to as the + X direction, + Y direction, + Z direction, and the directions opposite to the directions of the arrows are sometimes referred to as the-X direction, -Y direction, -Z direction.

(first embodiment)

Fig. 1A shows a schematic configuration of a magnetic sensor 1 according to a first embodiment. The magnetic sensor 1 includes four resistance elements (hereinafter, referred to as a first resistance element 11, a second resistance element 12, a third resistance element 13, and a fourth resistance element 14), and these resistance elements 11 to 14 are connected to each other by a bridge circuit (wheatstone bridge). The four resistance elements 11 to 14 are divided into two groups 11, 12 and 13, 14, and the resistance elements 11, 12 and the resistance elements 13, 14 of each group are connected in series. The first resistance element 11 and the fourth resistance element 14 are connected to the power supply voltage Vcc, and the second resistance element 12 and the third resistance element 13 are Grounded (GND). The output voltage between the first resistance element 11 and the second resistance element 12 is taken out as a midpoint voltage V1, and the output voltage between the third resistance element 13 and the fourth resistance element 14 is taken out as a midpoint voltage V2. Therefore, if the resistances of the first to fourth resistance elements 11 to 14 are R1 to R4, the midpoint voltages V1 and V2 are determined as follows.

(number 1)

(number 2)

The first to fourth resistance elements 11 to 14 each include at least one MR element. In the present embodiment, the first to fourth resistance elements 11 to 14 are each composed of a single MR element (hereinafter referred to as first to fourth MR elements 11A to 14A). Although not shown, each of the first to fourth resistance elements 11 to 14 may be formed of any one of a plurality of MR elements connected in series or a plurality of MR element groups formed of a plurality of MR elements connected in series and connected in parallel. The first to fourth MR elements 11A to 14A have the same configuration, and therefore the first MR element 11 will be described here. Fig. 2A shows a schematic perspective view of the first MR element 11A. The first MR element 11A has a multilayer film 20 and a pair of bias magnets 27 sandwiching the multilayer film 20 in the Y direction. The multilayer film 20 has a general spin valve type film structure. The multilayer film 20 has a substantially rectangular planar shape with the X direction being a short side and the Y direction being a long side, as viewed from the Z direction. The multilayer film 20 includes an antiferromagnetic layer 21, a pinned layer 22, a nonmagnetic intermediate layer 23, a reference layer 24, a spacer layer 25, and a free layer 26, which are laminated in this order. The multilayer film 20 is sandwiched between a pair of electrode layers (not shown) in the Z direction, and a sense current is caused to flow from the electrode layers to the multilayer film 20 in the Z direction.

The free layer 26 is a magnetic layer that is magnetized in the initial magnetization direction D1 (see fig. 2B) when no external magnetic field is applied and that changes (rotates) in magnetization direction from the initial magnetization direction D1 when an external magnetic field is applied, and may be formed of NiFe, for example. The pinned layer 22 is a ferromagnetic layer whose magnetization direction is fixed with respect to an external magnetic field by exchange coupling with the antiferromagnetic layer 21. The antiferromagnetic layer 21 may be formed of PtMn, IrMn, NiMn, or the like. The reference layer 24 is a ferromagnetic layer sandwiched between the pinned layer 22 and the spacer layer 25, and is magnetically coupled with the pinned layer 22 via a nonmagnetic intermediate layer 23 of Ru, Rh, or the like, more specifically, antiferromagnetically coupled with the pinned layer 22. Therefore, the magnetization directions of the reference layer 24 and the pinned layer 22 are both fixed with respect to the external magnetic field, and the magnetization directions thereof are set to be the phasesIn anti-parallel directions. This stabilizes the magnetization direction of the reference layer 24, and suppresses a leakage magnetic field to the outside by canceling out the magnetic field emitted from the reference layer 24 by the magnetic field emitted from the pinned layer 22. The spacer layer 25 is a nonmagnetic layer that is located between the free layer 26 and the reference layer 24 and exerts a magnetoresistance effect. The spacer layer 25 is a nonmagnetic conductive layer made of a nonmagnetic metal such as Cu or is made of Al₂O₃Or the like, a tunnel barrier layer formed of a nonmagnetic insulator. When the spacer layer 25 is a nonmagnetic conductive layer, the first MR element 11A functions as a giant magnetoresistance effect (GMR) element, and when the spacer layer 25 is a tunnel barrier layer, the first MR element 11A functions as a tunnel magnetoresistance effect (TMR) element. The first MR element 11A is more preferably a TMR element in that the MR change rate is large and the output voltage of the bridge circuit can be increased.

Fig. 2B is a schematic plan view of the first MR element 11A as viewed from the direction a of fig. 2A. Fig. 3A to 3C conceptually show the magnetizations of the free layer 26, the reference layer 24, and the pinned layer 22 in a state where an external magnetic field is not present. The arrows in fig. 3A to 3C schematically indicate the magnetization directions. The free layer 26 is magnetized in an initial magnetization direction D1 substantially parallel to the longitudinal direction (Y direction) by the bias magnetic field of the bias magnet 27. The initial magnetization direction D1 of the free layer 26 is substantially parallel to the magnetization direction D2 of the bias magnet 27. The long axis of the free layer 26 in the Y direction is referred to as a central axis C1. The reference layer 24 is magnetized in a magnetization direction D3 substantially parallel to the short axis direction (X direction). If an external magnetic field is applied in the magnetically sensitive direction of the free layer 26, i.e., the X direction, the magnetization direction of the free layer 26 rotates clockwise or counterclockwise in fig. 2B depending on the direction and strength of the external magnetic field. Thus, the relative angle between the magnetization direction D3 of the reference layer 24 and the magnetization direction of the free layer 26 changes, and the resistance to the sense current changes.

Fig. 4A is a view similar to fig. 1A showing the configuration of the magnetic sensor 101 of the comparative example. The initial magnetization directions of the free layers 26 of the first to fourth MR elements 11A to 14A are oriented in the same direction. The magnetization direction of the reference layer 24 of the first to fourth MR elements 11A to 14A is directed in the direction of the arrow in the figure. Therefore, if an external magnetic field is applied in the + X direction, the resistances of the first and third MR elements 11A, 13A decrease and the resistances of the second and fourth MR elements 12A, 14A increase. Thereby, as shown in fig. 4B, the midpoint voltage V1 increases and the midpoint voltage V2 decreases. In the case where an external magnetic field is applied in the-X direction, in contrast, the midpoint voltage V1 decreases and the midpoint voltage V2 increases. By detecting the difference V1-V2 between the midpoint voltages V1 and V2, a sensitivity doubled as compared with the case of detecting the midpoint voltages V1 and V2 can be obtained. Even if the midpoint voltages V1 and V2 are shifted in the same direction in fig. 4B (for example, even if they are shifted upward), the influence can be eliminated by detecting the difference.

If the first to fourth MR elements 11A to 14A are subjected to stress in the same direction, the initial magnetization direction D1 of the free layer 26 rotates according to the inverse magnetostrictive effect. Fig. 4C shows a state where the tensile stress S is applied to the first to fourth MR elements 11A to 14A at an angle of 45 ° to the X axis and the Y axis. The inverse magnetostrictive effect acts in different directions depending on the positive and negative magnetostriction constants and whether the stress is tensile stress S or compressive stress. When a tensile stress is applied and the magnetostriction constant of the free layer 26 is positive, and when a compressive stress is applied and the magnetostriction constant of the free layer 26 is negative, the initial magnetization direction D1 of the free layer 26 rotates in a direction parallel to the stress. When a tensile stress is applied and the magnetostriction constant of the free layer 26 is negative, and when a compressive stress is applied and the magnetostriction constant of the free layer 26 is positive, the initial magnetization direction D1 of the free layer 26 rotates in a direction perpendicular to the stress. If a tensile stress S is applied at an angle of 45 ° in fig. 4C, the initial magnetization direction D1 of the free layer 26 of the first and third MR elements 11A, 13A rotates toward the magnetization direction D3 of the reference layer 24, and therefore the resistance of the first and third MR elements 11A, 13A decreases. Since the initial magnetization direction D1 of the free layer 26 of the second and fourth MR elements 12A, 14A rotates in the direction opposite to the magnetization direction of the reference layer 24, the resistance of the second and fourth MR elements 12A, 14A increases. Thus, as shown in fig. 4D, the midpoint voltage V1 increases, the midpoint voltage V2 decreases, and V1-V2 increase. That is, the outputs V1-V2 of the magnetic sensor 101 when no external magnetic field is applied are shifted from zero by the external stress. The deviation of the outputs V1-V2 affects the accuracy of measurement of the external magnetic field.

The external stress is generated by a force received from a sealing resin or the like, for example, when the magnetic sensor is sealed in a package. Stress is also generated when the magnetic sensor sealed in the package is mounted on a substrate or the like and modularized (for example, in a soldering step). Stress may be generated in a process (for example, screw fastening) when the module is assembled to a product, and thermal stress due to, for example, a temperature change may be generated even when the module is used as a product. These stresses are difficult to predict and measure, and difficult to control. Therefore, it is substantially desirable that the outputs V1-V2 be less susceptible to external stresses.

In the present embodiment, the first to fourth resistance elements 11 to 14 (first to fourth MR elements 11A to 14A) belong to any one of the first group G1 in which the resistance increases or decreases when the initial magnetization direction D1 of all the free layers 26 is rotated in the same direction by a predetermined angle (45 ° in the illustrated example) by an external stress, and the second group G2 in which the resistance decreases when the resistance of the resistance element of the first group G1 increases and the resistance increases when the resistance of the resistance element of the first group G1 decreases. The MR elements belonging to the first group G1 are referred to as a first group of MR elements, and the MR elements belonging to the second group G2 are referred to as a second group of MR elements. For convenience of explanation, the resistance of the MR element belonging to the first group G1 is increased, and the resistance of the MR element belonging to the second group G2 is decreased. The second and third MR elements 12A, 13A belong to a first group G1, and the first and fourth MR elements 11A, 14A belong to a second group G2. As shown in fig. 1A, the initial magnetization direction D1 of the free layer 26 of the first group of MR elements (the second and third MR elements 12A, 13A) is rotated by a first angle θ 1(0 ° < θ 1 < 180 °, about 90 ° in the present embodiment) in the clockwise direction (first rotation direction) with respect to the magnetization direction D3 of the reference layer 24. The initial magnetization direction D1 of the free layer 26 of the second group of MR elements (the first and fourth MR elements 11A, 14A) is rotated by a second angle θ 2(0 ° < θ 2 < 180 °, about 90 ° in the present embodiment) in the counterclockwise direction (the second rotation direction opposite to the first rotation direction) with respect to the magnetization direction of the reference layer 24. In other words, in the first and second groups of MR elements, when a vector representing the initial magnetization direction D1 of the free layer 26 is F and a vector representing the magnetization direction D3 of the reference layer 24 is R, the orientations of the vector products F × R are opposite to each other.

If a tensile stress S is applied at an angle of 45 ° in fig. 1C, the initial magnetization direction D1 of the free layer 26 of the first and fourth MR elements 11A, 14A rotates in the direction of the magnetization direction D3 of the reference layer 24, and the electric resistance of the first and fourth MR elements 11A, 14A decreases. The initial magnetization direction D1 of the free layer 26 of the second and third MR elements 12A, 13A rotates in the direction opposite to the magnetization direction D3 of the reference layer 24, and the resistances of the second and third MR elements 12A, 13A increase. As shown in FIG. 1D, both midpoint voltage V1 and midpoint voltage V2 increase, inhibiting the variation of V1-V2. That is, in the state where the external stress is applied, the deviation of the outputs V1-V2 of the magnetic sensor can be reduced as compared with the comparative example.

There is a possibility that external stress is applied from all directions. As described above, the external stress may be a tensile stress, and the external stress may be a compressive stress. In the case where the magnetostriction constant of the free layer 26 is positive and the tensile stress S is applied in the direction of fig. 1C, as described above, the second and third MR elements 12A, 13A belong to the first group of MR elements, and the first and fourth MR elements 11A, 14A belong to the second group of MR elements. However, for example, when the free layer 26 has a positive magnetostriction constant and a tensile stress is applied in a direction orthogonal to the direction shown in fig. 1C, the first and fourth MR elements 11A and 14A belong to the first group of MR elements, and the second and third MR elements 12A and 13A belong to the second group of MR elements. Thus, it is not uniquely determined which MR element belongs to which group. However, it should be noted that the first and fourth MR elements 11A, 14A always belong to the same group, and the second and third MR elements 12A, 13A always belong to other groups.

Fig. 5A to 5C schematically show increases and decreases in the resistances of the first to fourth MR elements 11A to 14A, and fig. 5A corresponds to fig. 1C. Referring to fig. 5A, the resistances of the second and third MR elements 12A, 13A (first group G1) increase, the resistances of the first and fourth MR elements 11A, 14A (second group G2) decrease, and the midpoint voltages V1, V2 both increase. Referring to fig. 5B, the resistances of the second and third MR elements 12A and 13A (the second group G2) decrease, the resistances of the first and fourth MR elements 11A and 14A (the first group G1) increase, and the midpoint voltages V1 and V2 both decrease. Whether the magnetic sensor is in the state of fig. 5A or in the state of fig. 5B depends on the external stress or the magnetostriction constant of the free layer 26, but the magnetic sensor 1 of the present embodiment is always in either of the states of fig. 5A and 5B. Thus, even in either case, the offset of the outputs V1-V2 of the magnetic sensor decreases. This is because the first group G1 and the second group G2 are arranged such that a variation in the output of the magnetic sensor due to an increase or decrease in the resistance of the resistive element of the first group G1 and a variation in the output of the magnetic sensor due to an increase or decrease in the resistance of the resistive element of the second group G2 cancel each other out. In contrast, if fig. 5C corresponding to the comparative example shown in fig. 4C is referred to, the resistance elements of the first group G1 (the second and fourth MR elements 12A, 14A) and the resistance elements of the second group G2 (the first and third MR elements 11A, 13A) are not arranged as described above. Therefore, the output V1-V2 of the magnetic sensor tends to be shifted more.

In the present embodiment, the pair of bias magnets 27 face the both side ends 26A and 26B (see fig. 2B) in the initial magnetization direction D1 of the free layer 26, and the central axis C2 of the bias magnet 27 is substantially orthogonal to the central axis C1 of the free layer 26. In the present specification, such a bias magnet 27 is referred to as an end bias magnet 27A. The free layer 26 of some of the MR elements (first and second MR elements 11A, 12A) and the free layer 26 of the other MR element (third and fourth MR elements 13A, 14A) are magnetized in directions substantially antiparallel to each other. That is, the end bias magnets 27A of some of the MR elements (the first and second MR elements 11A, 12A) and the end bias magnets 27A of the other MR elements (the third and fourth MR elements 13A, 14A) are magnetized in directions substantially antiparallel to each other. Antiparallel means that the directions are different in the range of 160 ° to 200 °.

Since the magnetization direction of the end bias magnet 27A is changed for each MR element, a part of the end bias magnets 27A and the other end bias magnets 27A are formed of materials having different coercive forces. For example, the end bias magnets 27A of the first and second MR elements 11A, 12A are formed of CoPt or a material in which at least one of Cr, B, and Ta is added to CoPt, and the end bias magnets 27A of the third and fourth MR elements 13A, 14A are formed of FePt or a material in which at least one of Ni, Nb, Cu, Ag, Mo, and Ti is added to FePt. The former has a coercive force of 1500 to 5000Oe, and the latter has a coercive force of 5000 to 13000 Oe. First, all the end bias magnets 27A are magnetized in a magnetic field (for example, a magnetic field of 15000Oe or more) exceeding the coercive force of all the end bias magnets 27A. Thereby, all the end bias magnets 27A are magnetized in the same direction. Next, an intermediate magnetic field (for example, a magnetic field of about 7500 Oe) of the former coercive force and the latter coercive force is applied in opposite directions. The end bias magnets 27A of the first and second MR elements 11A, 12A are magnetized in opposite directions by a newly applied magnetic field, but the magnetization directions of the end bias magnets 27A of the third and fourth MR elements 13A, 14A are not changed. This makes it possible to change the magnetization direction of the end bias magnet 27A for each MR element.

Fig. 6A shows the distribution of the bias magnetic field in the longitudinal direction Y of the free layer 26 by normalization. Fig. 6B shows the distribution of the initial magnetization of the free layer 26, and the arrows indicate the initial magnetization directions of the free layer 26 at the respective positions. In general, the magnetization direction tends to be oriented in a direction other than the longitudinal direction Y at the longitudinal end of the free layer 26, but in the present embodiment, the magnetization direction of the free layer 26 coincides with the longitudinal direction Y over the entire length in the longitudinal direction Y. This is because the bias magnets 27 are positioned at both ends of the free layer 26 in the longitudinal direction Y, and hence a particularly strong bias magnetic field is applied to both ends of the free layer 26 in the longitudinal direction Y. As shown in fig. 2B, in the present embodiment, the dimension L1 of the end bias magnet 27A is larger than the dimension L2 of the free layer 26 in the direction X orthogonal to the initial magnetization direction D1. Thus, a strong bias magnetic field is applied to both ends of the free layer 26 in the longitudinal direction Y, and the magnetization direction of the free layer 26 is easily oriented in the longitudinal direction Y at both ends of the free layer 26 in the longitudinal direction Y.

(second embodiment)

Next, a second embodiment of the present invention will be explained. This embodiment is the same as the first embodiment except for the configuration of the bias magnet 27. Fig. 7A shows a schematic configuration of a magnetic sensor 1A according to a second embodiment. Fig. 8A and 8B are views similar to fig. 2A and 2B showing the configuration of the first MR element 11A. In the present embodiment, the pair of bias magnets 27 are opposed to the both side portions 26C and 26D in the initial magnetization direction D1 of the free layer 26, and the central axis C2 thereof is substantially parallel to the central axis C1 of the free layer 26. In the present specification, such a bias magnet 27 is referred to as a side bias magnet 27B. In the direction (Y direction) parallel to the initial magnetization direction D1, the dimension L3 of the side bias magnet 27 is larger than the dimension L4 of the free layer 26. Since the bias magnetic field of the side bias magnet 27B is wound to the side of the side bias magnet 27B as shown in fig. 8B, the magnetization direction D2 of the side bias magnet 27B and the initial magnetization direction D1 of the free layer 26 are in a substantially antiparallel relationship in the present embodiment. On the other hand, the relationship between the initial magnetization direction D1 of the free layer 26 and the magnetization direction D3 of the reference layer 24 is the same as that of the first embodiment. Therefore, as shown in fig. 7B, the magnetic sensor 1A of the present embodiment operates on the same principle as the magnetic sensor 1 of the first embodiment.

Fig. 9A shows the distribution of the bias magnetic field in the longitudinal direction of the free layer 26 in the present embodiment by normalization. As described above, in the present embodiment, the magnetization direction D2 of the side bias magnet 27B and the direction of the bias magnetic field applied to the free layer 26 are antiparallel, and therefore the bias magnetic field is negative. Note that the vertical axis of fig. 6A and the vertical axis of fig. 9A are labeled with the same reference value. In example 1, the size of the side bias magnet 27B coincides with the size of the free layer 26 in the direction (Y direction) parallel to the initial magnetization direction D1. In example 2, the size of the side bias magnet 27B is larger than the size of the free layer 26 in the direction (Y direction) parallel to the initial magnetization direction D1. Fig. 9B shows the distribution of the initial magnetization of the free layer 26 of embodiment 1, and fig. 9C shows the distribution of the initial magnetization of the free layer 26 of embodiment 2. The arrows indicate the initial magnetization direction at each location of the free layer 26. Even in any of the embodiments, the initial magnetization direction is oriented toward the long-side direction Y of the free layer 26 in almost all regions of the free layer 26. In example 1, since the bias magnetic field is slightly weak at the end (portion a) in the longitudinal direction of the free layer 26, the magnetization direction tends to be slightly oriented in a direction other than the longitudinal direction. In example 2, since a large bias magnetic field is applied to the free layer 26 also at the end in the longitudinal direction, the magnetization direction further coincides with the longitudinal direction over the entire length in the longitudinal direction.

In the present embodiment, the free layer 26 of some of the MR elements (the first and second MR elements 11A, 12A) and the free layer 26 of the other MR element (the third and fourth MR elements 13A, 14A) are magnetized in directions substantially antiparallel to each other. That is, the side bias magnets 27B of the first and second MR elements 11A, 12A and the side bias magnets 27B of the third and fourth MR elements 13A, 14A are magnetized in directions substantially antiparallel to each other. The magnetization direction of the side bias magnet 27B can be changed for each MR element, as in the first embodiment.

(third embodiment)

Next, a third embodiment of the present invention will be explained. The magnetic sensor 1B of the present embodiment is the same as that of the first embodiment except for the configuration of the bias magnet 27. Fig. 10A shows a schematic configuration of a magnetic sensor 1B according to a third embodiment. In the present embodiment, some of the bias magnets 27 (the bias magnets 27 of the first and second MR elements 11A, 12A) are end bias magnets 27A, and the other bias magnets 27 (the bias magnets 27 of the third and fourth MR elements 13A, 14A) are side bias magnets 27B. That is, in the present embodiment, both the end bias magnet 27A and the side bias magnet 27B are provided. The end bias magnet 27A and the side bias magnet 27B are configured as described in the first and second embodiments. In the present embodiment, the end bias magnet 27A and the side bias magnet 27B are magnetized in the same direction. Therefore, the present embodiment can simplify the manufacturing process. In addition, since it is not necessary to magnetize a material having a high coercive force with a high voltage, the facility for magnetization can also be simplified. The initial magnetization direction D1 of the free layer 26 in the first to fourth MR elements 11A to 14A is the same as that in the first embodiment, and the relationship between the initial magnetization direction D1 of the free layer 26 and the magnetization direction D3 of the reference layer 24 is also the same as that in the first embodiment. Therefore, as shown in fig. 10B, the magnetic sensor 1B of the present embodiment operates in the same manner as the magnetic sensor 1 of the first embodiment.

(fourth embodiment)

Next, a fourth embodiment of the present invention will be explained. The magnetic sensor 1C of the present embodiment is the same as that of the first embodiment except for the configuration of the bias magnet 27. Fig. 11A shows a schematic configuration of a magnetic sensor 1C according to a fourth embodiment. In the present embodiment, the pair of bias magnets 27 are end bias magnets facing the both side ends 26A, 26B in the initial magnetization direction D1 of the free layer 26. However, unlike the first embodiment, the free layer 26 of at least one MR element and the pair of bias magnets 27 are each a parallelogram in which two sides adjacent to each other form an angle of 45 ° or 135 ° when viewed in the lamination direction Z of the MR elements. Then, the central axis C2 of the bias magnet 27 is inclined 45 ° with respect to the central axis C1 of the free layer 26. In the present specification, such a bias magnet 27 is referred to as a tilt bias magnet 27C. The shapes of the free layer 26 and the oblique bias magnet 27C are not limited to the above, and may be substantially parallelogram shaped with two adjacent sides forming an angle other than 90 °. As shown in fig. 11C, the central axis C2 of the tilted bias magnet 27C may be tilted at an angle θ in the range of 25 ° to 65 ° with respect to the central axis C1 of the free layer 26. The center axis C2 of the tilt bias magnet 27C of the first and second MR elements 11A, 12A and the center axis C2 of the tilt bias magnet 27C of the third and fourth MR elements 13A, 14A are line-symmetric with respect to a line C4 that is located between the first and second MR elements 11A, 12A and the third and fourth MR elements 13A, 14A and is parallel to the center axis C1 of the free layer 26, that is, are tilted in opposite directions. The central axes C1 of all the free layers 26 are oriented in the same direction, and all the inclined bias magnets 27C are magnetized in the same direction.

Fig. 11C schematically shows magnetization of the tilt bias magnet 27C. In the figure, the tilt bias magnet 27C is magnetized in the magnetization direction D2. Therefore, if the tilt bias magnet 27C is divided into minute magnetic regions, the respective minute magnetic regions are magnetized so that the left side is the S pole and the right side is the N pole. Because the tilted bias magnet 27C is tilted in mirror symmetry with respect to the line C4, the tilted bias magnet 27C on the left side exhibits an S-pole along the slope facing the free layer 26, and the tilted bias magnet 27C on the right side exhibits an N-pole along the slope facing the free layer 26. Therefore, the left oblique bias magnet 27C generates an oblique upward bias magnetic field, and the right oblique bias magnet 27C generates an oblique downward bias magnetic field. Therefore, bias magnetic fields having components (i.e., + -Y direction or-Y direction) antiparallel to each other can be applied to the free layers 26 of the first and second MR elements 11A and 12A and the free layers 26 of the third and fourth MR elements 13A and 14A. In the present embodiment, the initial magnetization direction of the free layer 26 of the first to fourth MR elements 11A to 14A is similar to that of the first embodiment, and the relationship between the initial magnetization direction D1 of the free layer 26 and the magnetization direction D3 of the reference layer 24 is also similar to that of the first embodiment. Therefore, as shown in fig. 11B, the magnetic sensor 1C of the present embodiment operates in the same manner as the magnetic sensor 1 of the first embodiment.

(examples)

The outputs V1, V2, V1 to V2 were measured by applying a simulated stress to the magnetic sensor 1 of the first embodiment. As shown in fig. 12A, the magnetic sensor 1 is fixed to the substrate 31 via a lead wire 32. Next, as shown in fig. 12B, the substrate 31 is pressed in the + Z direction from the back side of the substrate 31 by the plate 33. Since the substrate 31 is bent upward, the lead 32 is deformed so as to spread outward. Thereby, tensile stress can be applied to the magnetic sensor 1 via the lead wires 32. Fig. 12C is a top view seen from the direction a of fig. 12B, and as shown in the figure, the substrate 31 is pressed by the plate 33 in the 45 ° direction in which the influence of the external stress is the largest. Thus, the tensile stress S shown in fig. 1B was simulated. The + Z-direction displacement amount D of the substrate 31 is varied to measure variations in the outputs V1, V2, V1-V2. The same test was also performed on the magnetic sensor 101 of the comparative example shown in fig. 4B.

Fig. 13A shows changes in the outputs V1, V2, V1-V2 of the magnetic sensor 101 of the comparative example with respect to the displacement amount D. The offsets of the outputs V1, V2 increase as the displacement amount D increases, but for the reasons described above, the offset of the output V1 increases in the positive direction and the offset of the output V2 increases in the negative direction. Therefore, V1-V2 increase with increasing displacement D. Fig. 13B shows changes in the outputs V1, V2, V1-V2 with respect to the displacement amount D of the magnetic sensor 1 of the first embodiment. Since the offsets of the outputs V1, V2 both increase in the positive direction, V1-V2 hardly change even if the displacement amount D increases, and the offsets can be almost completely suppressed.

Fig. 14A to 14D show modifications of the magnetic sensors 1, 1A, 1B, and 1C according to the first to fourth embodiments, respectively. Only the first resistance element 11 is shown in these figures. The first resistance element 11 has a plurality of MR sensors 11A connected in series. Specifically, the two MR sensors 11A adjacent to each other are connected to each other via an upper lead 28 connected to an upper electrode layer (not shown) or a lower lead 29 connected to a lower electrode layer (not shown). The two MR sensors 11A connected by the upper lead 28 and the two MR sensors 11A connected by the lower lead 29 are connected in series. The upper lead 28 and the lower lead 29 are spaced from the bias magnet 27. Although not shown, the same applies to the second to fourth resistance elements 12 to 14. In the MR sensor 11A constituting a part of the first resistance element 11, the initial magnetization direction D1 of the free layer 26 is oriented in the + Y direction (or substantially + Y direction), and in the other MR sensor 11A, the initial magnetization direction D1 of the free layer 26 is oriented in the-Y direction (or substantially-Y direction). A plurality of MR elements 11A in which the initial magnetization direction D1 of the free layer 26 is oriented in mutually opposite directions may be mixed in one resistance element as long as the resistance of one resistance element increases or decreases under a certain stress.

The magnetic sensor described above can be used as, for example, an azimuth detector or a compass that detects magnetic fields in two directions (X direction and Y direction) in the plane of the free layer 26. Fig. 15A is a schematic configuration diagram of an orientation detector 2A including the magnetic sensor 1. The magnetic sensor 1 has four resistance elements 11 to 14, and each of the resistance elements 11 to 14 has at least one MR sensor capable of detecting magnetic fields in the X-direction and the Y-direction. The structure of each of the resistance elements 11 to 14 is not limited as long as the magnetic field in the X direction and the Y direction can be detected. For example, an MR sensor having a magnetization axis in the X direction and an MR sensor having a magnetization axis in the Y direction may be arranged in series, or at least one MR sensor having a magnetization axis in a direction inclined with respect to the X direction and the Y direction may be provided. Arrows shown inside the resistance elements 11 to 14 indicate the directions of the magnetic fields detectable by the resistance elements 11 to 14. Fig. 15B shows changes in the angle θ (see fig. 15A) of V2-V1 with respect to the magnetic field. Since V2-V1 changes by rotation of the orientation detector 2A in the X-Y plane, a direction in which θ becomes 90 ° and a direction in which θ becomes-90 ° can be detected based on the maximum and minimum values of V2-V1.

Fig. 16A is a schematic configuration diagram of another orientation detector 2B including a magnetic sensor. In the present embodiment, two magnetic sensors 1D and 1E are combined. The first magnetic sensor 1D has the same characteristics as those of the magnetic sensors shown in fig. 14A to 14D, and the second magnetic sensor 1E is configured such that the first sensor 1D is rotated 90 ° clockwise as a whole. Fig. 16B shows changes in the angle θ (see fig. 16A) of V2 to V1 with respect to the magnetic field. The characteristics of the outputs V3-V4 of the second magnetic sensor 1E are shifted by 90 ° with respect to the first magnetic sensor 1D. Therefore, the magnetic field strength in the X direction and the Y direction and the angle θ of the magnetic field can be known by reading the outputs of the first magnetic sensor 1D and the second magnetic sensor 1E in a switched manner. If the output of the first magnetic sensor 1D is set to (V2-V1)₁And the output of the second magnetic sensor 1E is set to (V2-V1)₂Then, the angle θ of the magnetic field can be regarded as θ ═ arctan ((V2-V1)₁/(V2-V1)₂) And then the result is obtained. The orientation detector of the present embodiment can be realized by combining the magnetic sensors 1, 1A, and 1B of the first to third embodiments, for example.

Although detailed description is omitted, the magnetic sensor of the present invention can be applied not only to the above-described orientation detector but also to a sensor for a magnetic encoder, a position detection sensor, a rotation angle detection sensor, a current sensor, a magnetic switch, and a module or a device in which these are assembled.

Although a few preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the appended claims.