JP7404964B2 - magnetic sensor - Google Patents

Description

The present invention relates to a magnetic sensor and a method of manufacturing the same, and particularly to a magnetic sensor for detecting extremely weak magnetic fields and a method of manufacturing the same.

As a magnetic sensor, a type of magnetic sensor that detects the direction and strength of a magnetic field based on a change in the resistance value of a magnetoresistive element is known, as described in Patent Document 1. The magnetic sensor described in Patent Document 1 secures a sufficient resistance value by bending the magnetoresistive element in a meandering shape, and also arranges a plurality of hard magnetic bodies (magnets) that divide the magnetoresistive element. A magnetic bias is applied to the magnetoresistive element. By applying a magnetic bias to the magnetoresistive element, the magnetoresistive element is ideally made into a single magnetic domain, which makes it possible to reduce irregular noise superimposed on the detection signal.

Patent No. 5066579

However, in the magnetic sensor described in Patent Document 1, since the magnetoresistive element is divided in the longitudinal direction by a plurality of hard magnetic bodies, the length of the magnetoresistive element is correspondingly shortened. There is a problem in that when the length of the magnetoresistive element becomes shorter, the noise density increases in proportion to the square root of the area of the magnetoresistive element.

Therefore, an object of the present invention is to provide a magnetic sensor that can apply a magnetic bias to a magnetoresistive element without dividing the magnetoresistive element, and a method for manufacturing the same.

A magnetic sensor according to the present invention includes a magnetoresistive element that extends in a first direction and has a fixed magnetization direction in a second direction that intersects the first direction, and a magnetoresistive element that is stacked on the magnetoresistive element. The device is characterized by comprising a magnetization direction control layer that applies a magnetic bias in the first direction to the device.

According to the present invention, since the magnetization direction control layer that applies a magnetic bias to the magnetoresistive element is laminated on the magnetoresistive element, there is no need to divide the magnetoresistive element by a plurality of hard magnetic bodies. This makes it possible to reduce irregular noise superimposed on the detection signal while suppressing an increase in noise density.

In the present invention, the magnetoresistive element includes an antiferromagnetic layer, a magnetization fixed layer laminated on the antiferromagnetic layer, and a magnetically sensitive layer laminated on the magnetization fixed layer via a nonmagnetic layer. The direction control layer may be laminated on the magnetically sensitive layer. According to this, it becomes possible to apply a sufficient magnetic bias to the magnetically sensitive layer. In this case, the magnetization direction control layer may be made of the same magnetic material as the antiferromagnetic layer, and may have a different thickness from the antiferromagnetic layer. According to this, it becomes possible to magnetize the fixed magnetization directions of the antiferromagnetic layer and the magnetization direction control layer in mutually different directions while reducing manufacturing costs. Furthermore, in this case, the magnetization direction control layer may be thinner than the antiferromagnetic layer. According to this, it becomes possible to magnetize the antiferromagnetic layer more strongly than the magnetization direction control layer.

The magnetic sensor according to the present invention may further include a nonmagnetic bias adjustment layer provided between the magnetoresistive element and the magnetization direction control layer. According to this, it becomes possible to adjust the magnetic bias by adjusting the thickness of the bias adjustment layer. In this case, the bias adjustment layer incompletely covers the magnetoresistive element, so that the magnetization direction control layer has a first region that covers the magnetoresistive element through the bias adjustment layer, and a first region that covers the magnetoresistive element through the bias adjustment layer. It is also possible to include a second region that covers the magnetoresistive element. According to this, it becomes possible to finely adjust the magnetic bias depending on the area ratio of the first region and the second region.

A magnetic sensor according to the present invention includes an insulating layer that covers a magnetoresistive element and a magnetization direction control layer, and a magnetic field that is provided on the insulating layer and arranged in a second direction through a magnetic gap that overlaps with the magnetoresistive element. It is also possible to further include a first ferromagnetic layer and a second ferromagnetic layer. According to this, it becomes possible to effectively apply the detection magnetic field in the second direction to the magnetoresistive element. In this case, at least one of the first and second ferromagnetic layers may overlap the magnetoresistive element via the insulating layer. According to this, it becomes possible to more effectively apply the detection magnetic field to the magnetoresistive element.

In the present invention, the magnetoresistive element includes first and second magnetoresistive elements, and the magnetization direction control layer includes first and second magnetization layers laminated on the first and second magnetoresistive elements, respectively. The magnetoresistive element includes a direction control layer, the first magnetoresistive element and the second magnetoresistive element are bridge-connected, and the directions of the magnetic biases applied to the first and second magnetoresistive elements are the same. However, the directions of the currents flowing through the first and second magnetoresistive elements may be the same. According to this, the relationship between the direction of magnetic bias and the direction of current flow is constant. This greatly reduces irregular noise, making it possible to detect extremely weak magnetic fields.

The method for manufacturing a magnetic sensor according to the present invention includes a film forming step of laminating a magnetoresistive element and a magnetization direction control film made of an antiferromagnetic material, and annealing at a first temperature while applying a magnetic field in a second direction. By this, the first annealing step for orienting the fixed magnetization direction of the magnetoresistive element in the second direction is different from the first temperature while applying a magnetic field in the first direction intersecting the second direction. The method is characterized by comprising a second annealing step in which the magnetization direction control film is magnetized in the first direction by annealing at a second temperature.

According to the present invention, it is possible to magnetize the magnetoresistive element and the magnetization direction control film in different directions.

In the film forming process, after forming a magnetoresistive element by forming an antiferromagnetic layer, a magnetization fixed layer, a nonmagnetic film, and a magnetization fixed layer in this order, a layer made of the same magnetic material as the antiferromagnetic layer, In addition, the magnetization direction control film may be formed to be thinner than the antiferromagnetic layer, and the second annealing temperature may be lower than the first annealing temperature. According to this, it becomes possible to magnetize the antiferromagnetic layer more strongly than the magnetization direction control film.

As described above, according to the present invention, it is possible to apply a magnetic bias to the magnetoresistive element without dividing the magnetoresistive element. This makes it possible to reduce irregular noise superimposed on the detection signal while suppressing an increase in noise density.

FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 10 according to a preferred embodiment of the present invention. FIG. 2 is a schematic plan view for explaining the structure on the element forming surface 21 of the sensor chip 20. As shown in FIG. FIG. 3 is a schematic cross-sectional view taken along line AA shown in FIG. FIG. 4 is a circuit diagram for explaining the connection relationship of the magnetoresistive elements R1 to R4. FIG. 5 is a schematic cross-sectional view for explaining a first example of the layer structure of the magnetoresistive elements R1 to R4. FIG. 6 is a schematic cross-sectional view for explaining a second example of the layer structure of the magnetoresistive elements R1 to R4. FIG. 7 is a graph showing the relationship between the thickness of the bias adjustment film 57 and the anisotropic magnetic field (Hk) of the magnetically sensitive layer 54. FIG. 8 is a schematic plan view showing a state in which the bias adjustment film 57 is an incomplete film.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 10 according to a preferred embodiment of the present invention.

As shown in FIG. 1, the magnetic sensor 10 according to the present embodiment includes a substrate 2 whose surface forms an xz plane, a sensor chip 20 placed on the surface of the substrate 2, and magnetic collectors 30 to 32. . The sensor chip 20 has an element formation surface 21 forming an xy plane, and the element formation surface 21 faces one end of the magnetic flux collector 30 in the z direction. The magnetic flux collectors 31 and 32 are provided on the back side of the sensor chip 20. The magnetic collectors 30 to 32 are blocks made of a soft magnetic material with high magnetic permeability, such as ferrite.

As shown in FIG. 1, in this embodiment, the sensor chip 20 is mounted so that the element forming surface 21 of the sensor chip 20 is perpendicular to the surface of the substrate 2. In other words, the sensor chip 20 is mounted with the sensor chip 20 lying at 90 degrees with respect to the substrate 2. Therefore, even if the magnetic flux collector 30 has a long length in the z direction, the magnetic flux collector 30 can be stably fixed to the substrate 2.

FIG. 2 is a schematic plan view for explaining the structure on the element forming surface 21 of the sensor chip 20. As shown in FIG. Further, FIG. 3 is a schematic cross-sectional view taken along the line AA shown in FIG.

As shown in FIGS. 2 and 3, four magnetoresistive elements R1 to R4 extending in the y direction and three ferromagnetic films M1 to M3 are provided on the element forming surface 21 of the sensor chip 20. ing. The fixed magnetization directions of the magnetoresistive elements R1 to R4 are all aligned in the x direction (+x direction or -x direction). Further, as will be described later, a magnetic bias in the y direction (+y direction or −y direction) is applied to each of the magnetoresistive elements R1 to R4.

The magnetoresistive elements R1 to R4 are formed on the surface of the sensor substrate 22 that constitutes the element forming surface 21. As a material for the sensor substrate 22, silicon or alumina titanium carbide (ALTIC) can be used. The magnetoresistive elements R1 to R4 are covered with an insulating film 23 made of Al ₂ O ₃ or the like, and the ferromagnetic films M1 to M3 are formed on the insulating film 23. The ferromagnetic films M1 to M3 are made of a soft magnetic film with high magnetic permeability, such as permalloy. The ferromagnetic films M1 to M3 may be ferromagnetic layers formed by laminating a plurality of films. The ferromagnetic films M1 to M3 are covered with an insulating film 24 made of Al ₂ O ₃ or the like, and a magnetic flux collector 30 is arranged on the insulating film 24 . The insulating film 24 may be an insulating layer formed by laminating a plurality of films. FIG. 2 also shows the planar position of the magnetic flux collector 30 on the element forming surface 21.

The ferromagnetic films M1 to M3 form magnetic gaps G1 to G4 extending in the y direction, and the magnetoresistive elements R1 to R4 overlap with the magnetic gaps G1 to G4, respectively, in plan view from the z direction. will be placed in Although not particularly limited, in this embodiment, the width Gx of the magnetic gaps G1 to G4 in the x direction is narrower than the width Rx of the magnetoresistive elements R1 to R4 in the x direction. When viewed from above, the ferromagnetic film M1 overlaps with the magnetoresistive elements R1 to R4, the ferromagnetic film M2 overlaps with the magnetoresistive elements R1 and R3, and the ferromagnetic film M3 overlaps with the magnetoresistive elements R2. , R4. As a result, the detected magnetic field directed from the ferromagnetic film M1 toward the ferromagnetic films M2 and M3, or the detected magnetic field directed from the ferromagnetic films M2 and M3 toward the ferromagnetic film M1, is directed in the x direction with respect to the magnetoresistive elements R1 to R4. is applied to

FIG. 4 is a circuit diagram for explaining the connection relationship of the magnetoresistive elements R1 to R4.

As shown in FIG. 4, magnetoresistive element R1 is connected between terminal electrodes 41 and 42, magnetoresistive element R2 is connected between terminal electrodes 41 and 43, and magnetoresistive element R3 is connected between terminal electrodes 43 and 44. The magnetoresistive element R4 is connected between the terminal electrodes 42 and 44. A power supply potential Vcc is applied to the terminal electrode 41, and a ground potential GND is applied to the terminal electrode 44. Therefore, current flows through the magnetoresistive elements R1 to R4 in the directions indicated by arrows I11 to I14, respectively. That is, current flows in the same direction in the magnetoresistive elements R1 to R4.

As described above, the magnetoresistive elements R1 to R4 all have the same magnetization fixed direction. Therefore, when the magnetic flux collected by the magnetic flux collector 30 is applied to the magnetoresistive elements R1 to R4, the magnetoresistive elements R1 and R3 located on one side (-x direction side) when viewed from the magnetic flux collector 30 A difference occurs between the amount of resistance change and the amount of resistance change of the magnetoresistive elements R2 and R4 located on the other side (+x direction side) when viewed from the magnetic collector 30. Since the magnetoresistive elements R1 to R4 constitute a differential bridge circuit, a change in the electrical resistance of the magnetoresistive elements R1 to R4 according to the magnetic flux density appears on the terminal electrodes 42 and 44. .

The differential signals output from the terminal electrodes 42 and 43 are input to a differential amplifier 47 provided on or outside the substrate 2. The output signal of the differential amplifier 47 is fed back to the terminal electrode 45. As shown in FIG. 4, a compensation coil C is connected between the terminal electrode 45 and the terminal electrode 46, so that the compensation coil C generates a canceling magnetic field according to the output signal of the differential amplifier 47. . The compensation coil C can be integrated into the sensor chip 20.

The compensation coil C has a section C1 extending in the y direction along the magnetoresistive element R1, a section C2 extending in the y direction along the magnetoresistive element R2, and a section C2 extending in the y direction along the magnetoresistive element R3. It includes a section C3 extending in the direction, and a section C4 extending in the y direction along the magnetoresistive element R4. Then, when a current flows from the terminal electrode 45 toward the terminal electrode 46, the current flows in the directions shown by arrows I21 to I24 in the sections C1 to C4, respectively. That is, current flows in the sections C1, C3 and the sections C2, C4 in opposite directions. This allows the compensation coil C to cancel the detection magnetic fields applied to the magnetoresistive elements R1, R3 and the magnetoresistive elements R2, R4 in opposite directions. Then, by converting the current output from the differential amplifier 47 into a current voltage by the detection circuit 48, it becomes possible to detect the strength of the external magnetic flux.

FIG. 5 is a schematic cross-sectional view for explaining the layer structure of the magnetoresistive elements R1 to R4.

In the first example shown in FIG. 5, on the surface of the sensor substrate 22 constituting the element formation surface 21, a buffer layer 50, an antiferromagnetic layer 51, a fixed magnetization layer 52, a nonmagnetic layer 53, a magnetically sensitive layer 54, A magnetization direction control film 55 and a protective layer 56 are laminated in this order. Of these, the antiferromagnetic layer 51, the magnetization fixed layer 52, the nonmagnetic layer 53, and the magnetically sensitive layer constitute magnetoresistive elements R1 to R4.

The buffer layer 50 is made of a NiCr film with a thickness of about 50 angstroms, for example. The antiferromagnetic layer 51 is made of, for example, an IrMn film with a thickness of about 70 angstroms. The magnetization fixed layer 52 has a structure in which, for example, CoFe films 52A and 52C with a thickness of about 15 angstroms are sandwiched between Ru films 52B with a thickness of about 8 angstroms. The nonmagnetic layer 53 is made of, for example, a Cu film with a thickness of about 20 angstroms. The magnetically sensitive layer 54 is made of a laminated film of, for example, a CoFe film 54A of about 10 angstroms and a NiFe film 54B of about 70 angstroms. The magnetization direction control film 55 is made of, for example, an IrMn film with a thickness of about 50 angstroms. The protective layer 56 is made of, for example, Ru, Ta, or a laminated film of these.

In this specification, the term "layer" refers to a film made of a single material or a laminate of a plurality of films made of different materials, which together realize one function. Therefore, the magnetization direction control film 55 may be a magnetization direction control layer formed by laminating a plurality of films.

Here, the antiferromagnetic layer 51 is magnetized in the x direction, so that the fixed magnetization direction of the magnetization fixed layer 52 is in the x direction. On the other hand, the magnetization direction control film 55 is magnetized in the y direction, so that a magnetic bias in the y direction is applied to the magnetosensitive layer 54. Here, as a method of magnetizing the antiferromagnetic layer 51 and the magnetization direction control film 55 in different directions, after forming the buffer layer 50 to the protective layer 56 using a sputtering method or the like, the antiferromagnetic layer 51 and the magnetization direction control film 55 are One method is to separately perform an annealing process for magnetizing the magnetization direction control film 51 in the x direction and an annealing process for magnetizing the magnetization direction control film 55 in the y direction. Here, even if the antiferromagnetic layer 51 and the magnetization direction control film 55 are made of the same antiferromagnetic material, if their film thicknesses are different from each other, the orientation of the adjacent soft magnetic material films will be disrupted. Since the temperatures (blocking temperatures: T _B ) are different from each other, the antiferromagnetic layer 51 and the magnetization direction control film 55 can be magnetized in different directions by performing the annealing process twice.

As an example, as described above, when the antiferromagnetic layer 51 is made of an IrMn film with a thickness of about 70 angstroms, and the magnetization direction control film 55 is made of an IrMn film with a thickness of about 50 angstroms, while applying a magnetic field in the x direction, The antiferromagnetic layer 51 and the magnetization direction control film 55 are magnetized in the x direction by annealing at about 280°C, and then the magnetization direction control film is magnetized by annealing at about 240°C while applying a magnetic field in the y direction. 55 is changed in the y direction. In the second annealing step, the magnetization direction of the thick antiferromagnetic layer 51 does not change and is maintained in the x direction. In this way, if the antiferromagnetic layer 51 and the magnetization direction control film 55 are made of the same antiferromagnetic material, manufacturing costs can be reduced. Furthermore, by making the film thickness of the magnetization direction control film 55 thinner than the film thickness of the antiferromagnetic layer 51, the magnetic bias in the y direction becomes weaker than the fixed magnetization component in the x direction applied to the magnetosensitive layer 54. Therefore, it is possible to prevent a decrease in detection sensitivity due to excessive magnetic bias.

Alternatively, the antiferromagnetic layer 51 and the magnetization direction control film 55 may be made of antiferromagnetic materials having different directions. According to this, even if both film thicknesses are the same, they can be magnetized in different directions due to the difference in blocking temperature. Antiferromagnetic materials that can be used for the antiferromagnetic layer 51 and the magnetization direction control film 55 include IrMn (T _B =280°C), NiMn (T _B =375°C), and PtMn (T _B =340°C). , α-Fe ₂ O ₃ (T _B =320°C), PtPdMn (T _B =300°C), CrMnPt (T _B =280°C), RuRhMn (T _B =225°C), NiO (T _B =210°C) , FeMn (T _B =180°C), and the like. The above blocking temperature _TB changes depending on the film thickness.

The strength of the magnetic bias applied to the magnetically sensitive layer 54 by the magnetization direction control film 55 can be adjusted by the type and film thickness of the antiferromagnetic material that constitutes the magnetization direction control film 55. Further, as shown in FIG. 6, the magnetic bias applied to the magnetically sensitive layer 54 may be adjusted by providing a nonmagnetic bias adjusting film 57 between the magnetically sensitive layer 54 and the magnetization direction control film 55. do not have. As the material of the bias adjustment film 57, for example, Ru can be used. The bias adjustment film 57 may be a bias adjustment layer formed by laminating a plurality of films.

FIG. 7 is a graph showing the relationship between the thickness of the bias adjustment film 57 and the anisotropic magnetic field (Hk) of the magnetically sensitive layer 54. The anisotropic magnetic field is the strength of the magnetic field required to align the magnetization direction in a certain direction. Therefore, the larger the anisotropic magnetic field, the stronger the magnetic bias by the magnetization direction control film 55, and the lower the magnetic field sensitivity of the magnetosensitive layer 54.

As shown in FIG. 7, the anisotropic magnetic field of the magnetosensitive layer 54 in the absence of the magnetization direction control film 55 is about 4 Oe. On the other hand, by providing the magnetization direction control film 55 made of IrMn with a thickness of 50 angstroms, the anisotropic magnetic field of the magnetosensitive layer 54 increases to about 67 Oe. When the bias adjustment film 57 is provided between the magnetosensitive layer 54 and the magnetization direction control film 55, the anisotropic magnetic field of the magnetosensitive layer 54 decreases as the thickness of the bias adjustment film 57 increases. When the thickness is 5 angstroms, the anisotropic magnetic field of the magnetosensitive layer 54 decreases to about 7 Oe. In this way, the magnetic field sensitivity of the magnetically sensitive layer 54 can be adjusted by adjusting the thickness of the bias adjustment film 57.

The bias adjustment film 57 does not need to be a complete film that covers the entire surface of the magnetically sensitive layer 54, but may be a partial film that partially covers the magnetically sensitive layer 54, as shown in FIG. 8, which is a schematic plan view. It doesn't matter. If the bias adjustment film 57 is an incomplete film, the magnetization direction control film 55 has a region that covers the magnetosensitive layer 54 via the bias adjustment film 57 and a region that covers the magnetosensitive layer 54 without the bias adjustment film 57. There will be an area to cover. Therefore, it is possible to adjust the magnetic bias applied to the magnetically sensitive layer 54 depending on the ratio of these regions. The incomplete bias adjustment film 57 can be formed by adjusting film forming conditions such as sputtering conditions.

As described above, the magnetic sensor 10 according to the present embodiment includes the magnetization direction control film 55 that applies a magnetic bias in the y direction to the magnetoresistive elements R1 to R4 whose magnetization is fixed in the x direction. It becomes possible to reduce irregular noise superimposed on the detection signal. Moreover, since the magnetization direction control film 55 is formed on both sides of the magnetoresistive elements R1 to R4 without dividing them, the noise density increases in proportion to the square root of the area of the magnetoresistive elements R1 to R4. It is also possible to prevent this. Furthermore, in the magnetic sensor 10 according to the present embodiment, since the relationship between the direction of current and the direction of magnetic bias is constant in all magnetoresistive elements R1 to R4, the effect of reducing irregular noise is very large. This makes it possible to detect extremely weak magnetic fields.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. Needless to say, it is included within the scope.

2 Substrate 10 Magnetic sensor 20 Sensor chip 21 Element formation surface 22 Sensor substrate 23, 24 Insulating films 30 to 32 Magnetic collectors 31, 32 Magnetic collectors 41 to 63 Terminal electrode 47 Differential amplifier 48 Detection circuit 50 Buffer layer 51 Antiferromagnetic layer 52 Magnetization fixed layer 52A, 52C CoFe film 52B Ru film 53 Non-magnetic layer 54 Magnetism sensitive layer 54A CoFe film 54B NiFe film 55 Magnetization direction control film 56 Protective layer 57 Bias adjustment film C Compensation coil C1 to C4 Section G1 to G4 Magnetic gap I11 to I14, I21 to I24 Current direction M1 to M3 Ferromagnetic film R1 to R4 Magnetoresistive element

Claims (7)

a magnetoresistive element that extends in a first direction and has a fixed magnetization direction in a second direction that intersects the first direction;
a magnetization direction control layer that is laminated on the magnetoresistive element and applies a magnetic bias in the first direction to the magnetoresistive element;
a nonmagnetic bias adjustment layer provided between the magnetoresistive element and the magnetization direction control layer,
The bias adjustment layer incompletely covers the magnetoresistive element, so that the magnetization direction control layer includes a first region that covers the magnetoresistive element via the bias adjustment layer, and a first region that covers the magnetoresistive element through the bias adjustment layer. A magnetic sensor comprising a second region that covers the magnetoresistive element without a layer, and a magnetic bias is adjusted by an area ratio of the first region and the second region . The magnetoresistive element includes an antiferromagnetic layer, a magnetization fixed layer laminated on the antiferromagnetic layer, and a magnetically sensitive layer laminated on the magnetization fixed layer via a nonmagnetic layer,
The magnetic sensor according to claim 1, wherein the magnetization direction control layer is laminated on the magnetically sensitive layer via the bias adjustment layer . 3. The magnetic sensor according to claim 2, wherein the magnetization direction control layer is made of the same magnetic material as the antiferromagnetic layer, and has a different thickness from the antiferromagnetic layer. The magnetic sensor according to claim 3, wherein the magnetization direction control layer is thinner than the antiferromagnetic layer. an insulating layer covering the magnetoresistive element and the magnetization direction control layer;
A claim further comprising: first and second ferromagnetic layers provided on the insulating layer and arranged in the second direction via a magnetic gap that overlaps with the magnetoresistive element. The magnetic sensor according to any one of Items 1 to 4 . 6. The magnetic sensor according to claim 5 , wherein at least one of the first and second ferromagnetic layers overlaps the magnetoresistive element via the insulating layer. The magnetoresistive element includes first and second magnetoresistive elements,
The magnetization direction control layer includes first and second magnetization direction control layers laminated on the first and second magnetoresistive elements, respectively,
The first magnetoresistive element and the second magnetoresistive element are bridge-connected,
The directions of the magnetic biases applied to the first and second magnetoresistive elements are the same,
7. The magnetic sensor according to claim 1, wherein the directions of currents flowing through the first and second magnetoresistive elements are the same.

Images