JP2014016320A - Magnetic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor in which deterioration of detection accuracy is suppressed.SOLUTION: There is provided a magnetic sensor which detects an external magnetic field on the basis of a resistance value change in a magneto resistance effect element (10). The magnetic sensor includes: first magneto resistance effect elements (11a, 11b) having pin layers (17, 18) in which the magnetization direction is fixed, a free layer (15) in which the magnetization direction is changed according to an applied magnetic field, and a non-magnetic intermediate layer (16) which is provided between the free layer and the pin layers; and second magneto resistance effect elements (12a, 12b) having a free layer. A first bridge circuit is configured by a plurality of first magneto resistance effect elements connected in series from a power source to the ground. A second bridge circuit is configured by a plurality of second magneto resistance effect elements connected in series from the power source to the ground. The magnetic sensor further includes a selection part (30) which, on the basis of the midpoint potential of the first bridge circuit and the midpoint potential of the second bridge circuit, outputs one of the two midpoint potentials to the outside.

Description

  The present invention relates to a magnetic sensor that detects an external magnetic field based on changes in resistance values of a plurality of magnetoresistive elements.

  Conventionally, for example, as disclosed in Patent Document 1, a thin film magnetoresistive element constituted by a soft magnetic thin film and a giant magnetoresistive thin film has been proposed.

JP 11-274599 A

  In general, the giant magnetoresistive thin film has a multilayer structure. Therefore, there is a risk that thermal stress due to the difference in linear expansion coefficient is generated between the layers due to fluctuations in the external temperature, thereby damaging the giant magnetoresistive thin film. The giant magnetoresistive thin film is applied to a magnetic sensor or the like that detects an external magnetic field. However, if the above-described damage occurs in the giant magnetoresistive thin film, the detection accuracy of the magnetic sensor may be reduced.

  In view of the above problems, an object of the present invention is to provide a magnetic sensor in which a decrease in detection accuracy is suppressed.

  In order to achieve the above object, the present invention provides a magnetic sensor for detecting an external magnetic field based on a change in resistance value of a plurality of magnetoresistive elements (10), wherein the plurality of magnetoresistive elements (10). A pinned layer (17) whose magnetization direction is fixed, a free layer (15) whose magnetization direction changes according to the applied magnetic field, and a nonmagnetic intermediate layer provided between the free layer and the pinned layer (16) and a first magnetoresistive element (11a, 11b) having a free layer and a second magnetoresistive element (12a, 12b) having a free layer. The first bridge circuit is configured by connecting the magnetoresistive effect elements in series, and the second bridge circuit is configured by connecting the plurality of second magnetoresistive effect elements in series from the power source to the ground. Of the first bridge circuit Based on the midpoint potential of the point potential and the second bridge circuit, characterized by having a selection section for outputting either one to the outside of the two midpoint potential (30).

  As described above, according to the present invention, the first magnetoresistance effect elements (11a, 11b) have a multilayer structure, and the second magnetoresistance effect elements (12a, 12b) have a single layer structure. Therefore, the sum total of the thermal stress generated between the layers due to the difference in linear expansion coefficient is smaller in the second magnetoresistive element (12a, 12b) than in the first magnetoresistive element (11a, 11b). Therefore, the second magnetoresistance effect elements (12a, 12b) are less likely to be damaged by thermal stress than the first magnetoresistance effect elements (11a, 11b).

  As described above, the first bridge circuit is configured by the first magnetoresistance effect elements (11a, 11b), and the second bridge circuit is configured by the second magnetoresistance effect elements (12a, 12b). Then, the selection unit (30) outputs either one of the two midpoint potentials to the outside based on the midpoint potential of the first bridge circuit and the midpoint potential of the second bridge circuit. According to this, it is assumed that the first magnetoresistive effect element (11a, 11b) having a multilayer structure is damaged by the above-described thermal stress, and the midpoint potential of the first bridge circuit no longer becomes a signal corresponding to the external magnetic field. In addition, the midpoint potential of the second bridge circuit configured by the second magnetoresistive effect element (12a, 12b) having a single layer structure can be output to the outside. Therefore, a decrease in detection accuracy of the magnetic sensor (100) is suppressed.

It is a block diagram showing a schematic structure of a magnetic sensor concerning a 1st embodiment. It is sectional drawing which shows schematic structure of a 1st magnetoresistive effect element. It is sectional drawing which shows schematic structure of a 2nd magnetoresistive effect element. It is a top view which shows the planar shape of a magnetoresistive effect element.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
The magnetic sensor according to the present embodiment will be described with reference to FIGS. In FIGS. 2 and 3, magnetoresistive elements 11 a to 12 b to be described later are described in a simplified manner, and current paths are indicated by broken lines.

  As shown in FIG. 1, the magnetic sensor 100 includes a magnetoresistive effect element 10 and a selection unit 30 as main parts. Two bridge circuits are formed by the magnetoresistive effect elements 11 a to 12 b, and the midpoint potential of the bridge circuit is output to the outside via the selection unit 30. The selection unit 30 outputs one of the two midpoint potentials to the outside based on the two midpoint potentials.

  The magnetoresistive effect element 10 includes first magnetoresistive effect elements 11a and 11b and second magnetoresistive effect elements 12a and 12b. As shown in FIGS. 2 and 3, the magnetoresistive effect elements 11 a to 12 b are formed of a thin film layer laminated on a semiconductor substrate 13 with an oxide film 14 interposed therebetween. The first magnetoresistance effect elements 11a and 11b are composed of a free layer 15, an intermediate layer 16, a fixed layer 17, and a magnet layer 18 that are sequentially stacked on the oxide film 14, and the second magnetoresistance effect elements 12a and 12b are The free layer 15 is laminated on the oxide film 14. The free layer 15 of the first magnetoresistive effect elements 11a and 11b and the free layer 15 of the second magnetoresistive effect elements 12a and 12b are made of the same material, and are formed on the oxide film 14 of the semiconductor substrate 13 in the same manufacturing process. Formed.

  The free layer 15 is a ferromagnetic material. The magnetization direction of the free layer 15 is not fixed, and has the property that the magnetization direction varies with an external magnetic field. Therefore, the second magnetoresistive effect elements 12 a and 12 b are anisotropic magnetoresistive effect elements whose resistance values vary depending on the current flow direction and the magnetization direction of the free layer 15. The fixed layer 17 and the magnet layer 18 correspond to the pinned layer described in the claims.

  The fixed layer 17 is also a ferromagnetic material. However, the magnetization direction is fixed by the magnet layer 18 and has a property that the magnetization direction does not vary by an external magnetic field. The intermediate layer 16 according to the present embodiment has nonmagnetic properties and conductivity, and when a voltage is applied between the free layer 15 and the fixed layer 17, the free layer 15 and the fixed layer 17 A current flows between them. Thus, the 1st magnetoresistive effect element 11a, 11b which concerns on this embodiment is a giant magnetoresistive effect element.

  The ease of current flow depends on the magnetization directions of the free layer 15 and the fixed layer 17, and flows most easily when the magnetization directions of the free layer 15 and the fixed layer 17 are parallel, and flows most easily when they are antiparallel. hard. That is, the resistance value of the magnetoresistive effect element 10 changes smallest when parallel, and the resistance value changes largest when antiparallel. In the present embodiment, the magnetization direction of the fixed layer 17 of the first magnetoresistive effect element 11a and the magnetization direction of the fixed layer 17 of the first magnetoresistive effect element 11b are antiparallel, and the first magnetoresistive effect element Changes in the resistance values of 11a and 11b are opposite. That is, when the resistance value of one of the two first magnetoresistive elements 11a and 11b decreases, the resistance value of the other increases, and when the resistance value of one increases, the resistance value of the other increases.

  As shown in FIG. 2, the side surfaces of the layers 15 to 18 and a part of the oxide film 14 are covered with the first insulating film 19. As shown in FIG. The second insulating film 20 is covered. Then, the first wiring layer 21 is formed on the surface of the first insulating film 19 and the upper surface of the magnet layer 18 of each of the first magnetoresistance effect elements 11a and 11b so as to electrically connect the two magnet layers 18. The second wiring layer 22 is formed on the surface of the second insulating film 20 and the upper surface of the free layer 15 of each of the second magnetoresistive elements 12a and 12b so as to electrically connect the two free layers 15. Has been. Although not shown, a power source is connected to the free layer 15 of the magnetoresistive effect elements 11a and 12a, and a ground is connected to the free layer 15 of the magnetoresistive effect elements 11b and 12b. As a result, a first half bridge circuit is formed in which two first magnetoresistive elements 11a and 11b are connected in series from the power source to the ground, and the two second magnetoresistive elements 12a and 12b are connected from the power source to the ground. A second half-bridge circuit formed in series is formed. The midpoint potential of the first half bridge circuit is the potential of the first wiring layer 21, and the midpoint potential of the second half bridge circuit is the potential of the second wiring layer 22. Each of the wiring layers 21 and 22 is connected to the selection unit 30.

  As shown in FIG. 4, the planar shape of each of the first magnetoresistive effect elements 11a and 11b and the second magnetoresistive effect elements 12a and 12b on the semiconductor substrate 13 is a shape in which one line is folded and is identical. It has become. The first magnetoresistive effect elements 11a and 11b and the second magnetoresistive effect elements 12a and 12b are adjacent to each other so that a gap does not occur between the two as much as possible (a gap that does not cause a short circuit is formed) The interval is constant over the entire length.

  The selection unit 30 is based on the midpoint potential of the first half-bridge circuit (hereinafter referred to as the first midpoint potential) and the midpoint potential of the second half-bridge circuit (hereinafter referred to as the second midpoint potential). One of the two midpoint potentials is output to the outside. The selection unit 30 includes a comparison unit 31, a control unit 32, and switches 33 and 34.

  The comparison unit 31 compares the above-described two midpoint potentials. As a result of comparing the first midpoint potential and the second midpoint potential, if the difference or ratio falls within a predetermined value range (sensitivity difference range), the first half-bridge circuit is configured. The first magnetoresistive effect elements 11 a and 11 b are determined to be normal, and a first control signal is output to the control unit 32. On the other hand, when the value does not fall within the predetermined value range, the comparison unit 31 determines that the first magnetoresistive effect elements 11a and 11b constituting the first half bridge circuit are damaged, and the second The control signal is output to the control unit 32. When the comparison unit 31 according to the present embodiment determines that the first magnetoresistive effect elements 11a and 11b are damaged, the comparison unit 31 outputs a failure signal that notifies the failure to the outside, and also functions to notify the user of the failure. .

  The control unit 32 controls opening and closing of the switches 33 and 34 based on the output signal of the comparison unit 31. When receiving the first control signal, the control unit 32 closes the first switch 33 and opens the second switch 34. On the contrary, when receiving the second control signal, the control unit 32 opens the first switch 33 and closes the second switch 34.

  As shown in FIG. 1, the first switch 33 is provided between the midpoint (first wiring layer 21) of the first half-bridge circuit and the output terminal 50, and the second switch 34 is provided in the second half-bridge circuit. Is provided between the middle point (second wiring layer 22) and the output terminal 50. Therefore, when the first control signal is input from the comparison unit 31 to the control unit 32 and the first switch 33 is closed and the second switch 34 is opened, only the first midpoint potential is externally output via the output terminal 50. Is output. On the other hand, when the second control signal is input from the comparison unit 31 to the control unit 32 and the first switch 33 is opened and the second switch 34 is closed, only the second midpoint potential is output to the output terminal 50. Is output to the outside.

  Next, the function and effect of the magnetic sensor 100 according to this embodiment will be described. As described above, the first magnetoresistance effect elements 11a and 11b have a multilayer structure, and the second magnetoresistance effect elements 12a and 12b have a single layer structure. Therefore, the total sum of thermal stresses generated between the layers due to the difference in linear expansion coefficient is smaller in the second magnetoresistance effect elements 12a and 12b than in the first magnetoresistance effect elements 11a and 11b. Accordingly, the second magnetoresistance effect elements 12a and 12b are less likely to be damaged by thermal stress than the first magnetoresistance effect elements 11a and 11b.

  As described above, the comparison unit 31 outputs the first control signal to the control unit 32 when it is determined that the first magnetoresistance effect elements 11a and 11b constituting the first half bridge circuit are normal. When receiving the first control signal, the control unit 32 closes the first switch 33 and opens the second switch 34. As a result, only the first midpoint potential is output to the outside via the output terminal 50.

  On the contrary, the comparison unit 31 outputs a second control signal to the control unit 32 when determining that the first magnetoresistive effect elements 11a and 11b constituting the first half bridge circuit are damaged. When receiving the second control signal, the control unit 32 opens the first switch 33 and closes the second switch 34. As a result, only the second midpoint potential is output to the outside via the output terminal 50.

  Thus, even if the first magnetoresistive effect elements 11a and 11b having a multilayer structure are damaged by the above-described thermal stress and the first midpoint potential does not become a signal corresponding to the external magnetic field, it has a single layer structure. The midpoint potential (second midpoint potential) of the second half bridge circuit configured by the second magnetoresistance effect elements 12a and 12b is output to the outside. Therefore, a decrease in detection accuracy of the magnetic sensor 100 is suppressed.

  The planar shapes on the semiconductor substrate 13 of the first magnetoresistive elements 11a and 11b and the second magnetoresistive elements 12a and 12b are the same. The first magnetoresistance effect elements 11a and 11b and the second magnetoresistance effect elements 12a and 12b are adjacent to each other, and the distance between them is constant over the entire length. According to this, compared to the configuration in which the first magnetoresistive effect element and the second magnetoresistive effect element have different planar shapes, and the interval between the first magnetoresistive effect element and the second magnetoresistive effect element is indefinite, An increase in the size of the semiconductor substrate 13 is suppressed. In the present embodiment, the first magnetoresistive effect elements 11a, 11b and the second magnetoresistive effect elements 11a, 11b and the second magnetoresistive effect elements 11a, 11b and the second magnetoresistive effect elements 12a, 12b are formed so as not to have a gap as much as possible. The magnetoresistive effect elements 12a and 12b are adjacent to each other. According to this, since it is hard to produce an extra clearance gap, the increase in the physique of the semiconductor substrate 13 is suppressed more effectively. As a result, an increase in the size of the magnetic sensor 100 is suppressed.

  The free layer 15 of the first magnetoresistance effect elements 11a and 11b and the free layer 15 of the second magnetoresistance effect elements 12a and 12b are formed in the same manufacturing process. According to this, the manufacturing method of the magnetic sensor 100 is simplified compared to the manufacturing method in which the free layer of the first magnetoresistive element and the free layer of the second magnetoresistive element are formed in different manufacturing processes. Is done.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the present embodiment, an example in which the first magnetoresistance effect elements 11a and 11b are giant magnetoresistance effect elements has been described. However, as the first magnetoresistive elements 11a and 11b, tunnel magnetoresistive elements in which the intermediate layer 16 has an insulating property can also be adopted.

  In the present embodiment, the application of the magnetic sensor 100 is not particularly limited. However, the magnetic sensor 100 has a magnet (not shown) that forms an external magnetic field, and detects a change in the external magnetic field due to rotation of the detection target based on a change in the resistance value of the magnetoresistive effect element 10. A rotation sensor that detects the rotation state of the detection target can be employed. Further, as the magnetic sensor 100, a current sensor that detects the detected current by detecting a change in the external magnetic field generated from the detected current based on the resistance value change of the plurality of magnetoresistive elements 10 is adopted. You can also.

DESCRIPTION OF SYMBOLS 10 ... Magnetoresistive effect element 11a, 11b ... 1st magnetoresistive effect element 12a, 12b ... 2nd magnetoresistive effect element 15 ... Free layer 16 ... Intermediate | middle layer 17 ... Fixed layer 18 ... Magnetic layer 30 ... Selection unit 100 ... Magnetic sensor

Claims (8)

A magnetic sensor for detecting an external magnetic field based on a change in resistance value of a plurality of magnetoresistive elements (10),
As the plurality of magnetoresistive elements (10), a pinned layer (17, 18) whose magnetization direction is fixed, a free layer (15) whose magnetization direction changes according to an applied magnetic field, the free layer and the pin A first magnetoresistive element (11a, 11b) having a nonmagnetic intermediate layer (16) provided between the first layer and the second magnetoresistive element (12a, 12b) having the free layer. Have
A plurality of the first magnetoresistive elements are connected in series from the power source to the ground, thereby forming a first bridge circuit.
A plurality of the second magnetoresistive elements are connected in series from the power source to the ground, thereby forming a second bridge circuit.
A selection unit (30) for outputting one of two midpoint potentials to the outside based on the midpoint potential of the first bridge circuit and the midpoint potential of the second bridge circuit. Magnetic sensor. The selection unit includes:
A comparator (31) for comparing the midpoint potential of the first bridge circuit with the midpoint potential of the second bridge circuit;
A first switch (33) provided between a midpoint of the first bridge circuit and an output terminal (50);
A second switch (34) provided between a midpoint of the second bridge circuit and the output terminal;
2. The magnetic sensor according to claim 1, further comprising a control unit that controls opening and closing of the first switch and the second switch based on an output signal of the comparison unit. The first magnetoresistive element and the second magnetoresistive element are formed on the same substrate (13), and the planar shape on the substrate is the same,
The magnetic sensor according to claim 1, wherein an interval between the first magnetoresistive effect element and the second magnetoresistive effect element is constant.   4. The magnetic sensor according to claim 1, wherein the free layers of the first magnetoresistive element and the second magnetoresistive element are formed in the same process. 5.   5. The magnetic sensor according to claim 1, wherein the intermediate layer has conductivity, and the first magnetoresistive element is a giant magnetoresistive element.   5. The magnetic sensor according to claim 1, wherein the intermediate layer has insulating properties, and the first magnetoresistive element is a tunnel magnetoresistive element. A magnet for forming the external magnetic field;
2. The rotation state of the detection target is detected by detecting a change in the external magnetic field due to rotation of the detection target based on resistance value changes of the plurality of magnetoresistive elements. The magnetic sensor of any one of -6. The external magnetic field is generated from the detected current,
The magnetic sensor according to claim 1, wherein the detected current is detected based on a change in resistance value of the plurality of magnetoresistive elements due to a change in the external magnetic field.

Images