Magnetic sensor and magnetic measurement method

Abstract

A magnetic sensor (1) according to one embodiment of the present invention is provided with: a magnetic detection unit (2) provided with a magnetoresistive effect element (10) having a fixed magnetic layer (11), a free magnetic layer (13), and an intermediate layer (12) formed between the fixed magnetic layer (11) and the free magnetic layer (13); a magnetic field calculation unit (4) that calculates a measured magnetic field on the basis of the output of the magnetic detection unit (2); and a saturation magnetic field application unit (3) that applies a magnetic field to the free magnetic layer (13) in the direction of the measurement magnetic field to magnetically saturate the free magnetic layer (13), and the magnetic field calculation unit (4) calculates the measurement magnetic field for the free magnetic layer (13) on the basis of a first output of the magnetic detection unit (2) when the measurement magnetic field is applied and a second output of the magnetic detection unit (2) when the free magnetic layer (13) is magnetically saturated. A small magnetic field can be measured with high precision by removing 1 / f noise.

Description

Technical Field

[0001] The present invention relates to a magnetic sensor including a magnetoresistive element and a magnetism measuring method. Background Art

[0002] As magnetic sensors for detecting and measuring magnetic fields, there are magnetic sensors with magnetoresistance effect elements that utilize the GMR (giant magnetoresistance) effect and the TMR (tunneling magnetoresistance) effect. The magnetoresistance effect elements in these magnetic sensors have a structure in which a fixed magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer are stacked in this order. In the magnetoresistance effect element, if an external magnetic field of the object to be measured is applied, the magnetization direction of the free magnetic layer changes, causing a resistance change corresponding to the angle between the magnetization direction of the free magnetic layer and the magnetization direction of the fixed magnetic layer. A magnetic sensor with a magnetoresistance effect element can detect a magnetic field using the resistance change of the magnetoresistance effect element.

[0003] Magnetic sensors with magnetoresistive elements have 1 / f noise that cannot be removed by filters. 1 / f noise is inversely proportional to frequency, and increases with lower frequencies, which may hinder high-precision measurements. Therefore, various methods are used to remove 1 / f noise.

[0004] Patent document 1 discloses a magnetic sensor in which, in an even-function type magnetic sensor, 1 / f noise is removed by taking the difference between the output when a bias magnetic field is applied in a certain direction (+X direction) and the output when a bias magnetic field is applied in the opposite direction (-X direction).

[0005] Patent document 2 discloses a measuring device which is designed to measure the Hall electromotive force of a semiconductor sample. In order to remove the noise caused by the Schottky barrier generated between the electrode and the sample, the frequency band of the voltage difference Vm is shifted to the low-frequency side to remove the frequency band of the voltage difference Vm which is greatly affected by the 1 / f noise.

[0006] Patent Document 3 discloses a magnetic field sensing device that samples a bridge signal with a first current and a second current by switching two sample-and-hold functions, and determines the value of a magnetic field based on the difference between the sampled first and second bridge signals.

[0007] Patent Document 4 discloses a sensor device that takes the difference of a signal modulated by switching the positive and negative sides of a sensor signal in a modulator in order to remove 1 / f noise of an output signal.

[0008] Prior Art Literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2018-115972

[0011] Patent Document 2: Japanese Patent Application Publication No. 2020-148727

[0012] Patent Document 3: Japanese Patent Publication No. 2012-518788

[0013] Patent Document 4: JP 2009-544004 Summary of the invention

[0014] Problems to be solved by the invention

[0015] In a magnetic sensor having a magnetoresistive effect element, there is a problem that 1 / f noise in a low frequency region reduces the detection accuracy of the magnetic sensor. In order to solve this problem, various devices and methods have been proposed in the past. The present invention aims to provide a magnetic sensor having a magnetoresistive effect element and a magnetic measurement method, wherein the magnetoresistive effect element removes 1 / f noise by a structure different from the conventional one, thereby being able to measure a small magnetic field with high accuracy.

[0016] Means for solving problems

[0017] The present invention, in one aspect, is a magnetic sensor, characterized in that it comprises: a magnetic detection unit, which comprises a magnetoresistance effect element having a fixed magnetic layer, a free magnetic layer, and an intermediate layer formed between the fixed magnetic layer and the free magnetic layer; a magnetic field calculation unit, which calculates a measured magnetic field based on the output of the magnetic detection unit; and a saturation magnetic field application unit, which applies a magnetic field to the free magnetic layer along the direction of the measured magnetic field to magnetically saturate the free magnetic layer, the magnetic field calculation unit calculates the measured magnetic field based on a first output of the magnetic detection unit when the measured magnetic field is applied to the free magnetic layer, and a second output of the magnetic detection unit when the free magnetic layer is magnetically saturated.

[0018] The magnetic field calculation unit may calculate the measurement magnetic field based on a difference between the first output and the second output.

[0019] The first output includes the output of the measured magnetic field and 1 / f noise, and the second output includes the output of the state of magnetic saturation of the free magnetic layer and 1 / f noise. Therefore, the 1 / f noise can be removed from the first output based on the first output and the second output. For example, by using the difference between the first output and the second output, the 1 / f noise can be removed from the first output. In addition, since the output of the state of magnetic saturation of the free magnetic layer is known, the measured magnetic field with the influence of 1 / f noise removed from the first output can be obtained based on the first output, the second output, and the known output.

[0020] Alternatively, the fixed magnetic layer fixes the magnetization direction in a first direction, the free magnetic layer has a magnetization direction orthogonal to the first direction when the magnetic field is not applied, and the direction of the measured magnetic field is parallel or antiparallel to the first direction.

[0021] According to this structure, the relationship between the magnetization direction of the free magnetic layer and the magnetization direction of the fixed magnetic layer is different depending on the direction of the measurement magnetic field. Therefore, the resistance value of the magnetoresistance effect element changes inversely depending on whether the direction of the measurement magnetic field is parallel or antiparallel to the first direction. Therefore, the relationship between the measurement magnetic field and the resistance of the magnetoresistance effect element becomes an odd function, and the magnitude and direction of the measurement magnetic field can be measured.

[0022] Alternatively, the magnetoresistance effect element may be provided, and a plurality of the magnetoresistance effect elements may constitute a bridge circuit. By using a bridge circuit composed of a plurality of magnetoresistance effect elements, the output corresponding to the measured magnetic field becomes larger than when a single magnetoresistance effect element is used, thereby improving the measurement accuracy of the magnetic sensor.

[0023] Alternatively, the fixed magnetic layer fixes the magnetization direction in a first direction, and in the free magnetic layer, the magnetization direction when the magnetic field is not applied is a direction orthogonal to the first direction, the direction of the measured magnetic field is the first direction, and in each of the plurality of magnetoresistance effect elements, the direction of the magnetic field applied to the free magnetic layer by the saturation magnetic field application unit is parallel or antiparallel to the first direction.

[0024] According to this structure, when the free magnetic layer of the magnetoresistive effect element is saturated, the plurality of magnetoresistive effect elements constituting the bridge circuit have the same resistance value. Therefore, as the second output from the bridge circuit, an output containing only 1 / f noise can be obtained, which is a known output in a state where the saturation magnetic field is removed. In addition, since the voltage value obtained as the second output from the bridge circuit becomes smaller, the calculation for obtaining the measured magnetic field becomes simple.

[0025] The saturation magnetic field applying unit may be a coil, a current line, or a magnet. By applying a magnetic field using the coil, the current line, or the magnet, the free magnetic layer can be magnetically saturated.

[0026] The present invention, in one aspect, is a magnetic measurement method, which measures a magnetic field based on the output of a magnetic detection unit, wherein the magnetic detection unit has a magnetoresistance effect element having a fixed magnetic layer, a free magnetic layer, and an intermediate layer formed between the fixed magnetic layer and the free magnetic layer. The magnetic measurement method is characterized in that it comprises: a magnetic field measurement step, in which a first output of the magnetic detection unit is obtained when the measuring magnetic field is applied; a saturation magnetic field measurement step, in which a magnetic field is applied along the direction of the measuring magnetic field to obtain a second output of the magnetic detection unit in a state in which the free magnetic layer is saturated; and a magnetic field calculation step, in which the measuring magnetic field is calculated based on the first output and the second output.

[0027] The magnetic field calculation step may calculate the measurement magnetic field based on a difference between the first output and the second output.

[0028] By calculating the measured magnetic field based on the first output obtained in the magnetic field measuring step and the second output obtained in the saturation magnetic field measuring step, a measured magnetic field from which 1 / f noise of the magnetoresistive element is removed can be obtained. For example, by using the difference between the first output and the second output, 1 / f noise can be removed from the first output.

[0029] Effects of the Invention

[0030] According to the present invention, a magnetic sensor and a magnetic measurement method can be provided, which can remove 1 / f noise from the measured magnetic field, thereby being able to measure a small magnetic field with high accuracy and having high magnetic resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a block diagram of a magnetic sensor according to an embodiment.

[0032] Figure 2 It is a perspective view schematically showing the stacked structure of the magnetoresistive effect element.

[0033] Figure 3 It is a perspective view schematically showing a stacked structure of a magnetoresistive effect element according to a modification.

[0034] Figure 4 This is a graph showing the relationship between the 1 / f noise generated in the magnetoresistive element and the output of the magnetic detection unit.

[0035] Figure 5A This is a flowchart of the magnetic measurement method involved in the embodiment.

[0036] Figure 5B This is a flow chart of a magnetic measurement method according to a specific example.

[0037] Figure 6The diagram is a schematic diagram showing the magnetic state of the magnetoresistive element and the output of the magnetic detection unit in each step of the magnetism measuring method according to the embodiment.

[0038] Figure 7 This is a graph showing the relationship between the magnetic field applied to the free magnetic layer and the output of the magnetic detection unit.

[0039] Figure 8 This is a diagram for explaining an example of the operation sequence of the magnetic sensor.

[0040] Fig. 9 It is a diagram for explaining another example of the operation sequence of the magnetic sensor.

[0041] Fig.10 Yes Description Fig. 9 A diagram showing the saturation magnetic field measurement step in the operational sequence shown.

[0042] Fig.11 : is a block diagram of a magnetic sensor according to a modification.

[0043] Fig.12 This is a block diagram of a full-bridge circuit used as the magnetic detection portion of a magnetic sensor.

[0044] Fig.13 Yes Fig.12 Block diagram of the full bridge circuit in the state where a magnetic field is applied and the free magnetic layer is saturated.

[0045] Fig.14A This is a graph showing the first output in the simulation.

[0046] Fig. 14B This is a graph showing the relationship between the frequency and noise of the first output in the simulation.

[0047] Fig.15A This is a graph showing the second output in the simulation.

[0048] Fig. 15B This is a graph showing the relationship between the frequency and noise of the second output in the simulation.

[0049] Fig.16A This is a graph showing the output of the measured magnetic field in the simulation.

[0050] Fig. 16B This is a graph showing the relationship between the frequency of the output of the measurement magnetic field in the simulation and the noise.

[0051] Fig.17 This is a block diagram showing a modified example of the full-bridge circuit.

[0052] Fig.18 This is a block diagram showing a modified example of the full-bridge circuit.

[0053] Fig.19This is a block diagram showing a modified example of the full-bridge circuit. DETAILED DESCRIPTION

[0054] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, the same components are denoted by the same reference numerals and description thereof is omitted. In order to show the positional relationship of each component, reference coordinates are preferably shown in each of the drawings.

[0055] Figure 1 As shown in the figure, the magnetic sensor 1 of the present embodiment includes a magnetic detection unit 2, a saturation magnetic field application unit 3, a magnetic field calculation unit 4, an amplifier 5, an analog-digital conversion circuit 6, and a control unit 7.

[0056] The magnetic detection unit 2 detects the external magnetic field to be measured. Figure 2 ), a full-bridge circuit 15 composed of a plurality of magnetoresistance effect elements 10, and half-bridge circuits 21a and 21b (reference Fig.12 ) etc. to constitute the magnetic detection unit 2.

[0057] Figure 2 1 is a perspective view schematically showing the structure of the magnetoresistive effect element 10 provided in the magnetic detection unit 2. As the magnetoresistive effect element 10, for example, a GMR element (giant magnetoresistive effect element) or a TMR element (tunneling magnetoresistive effect element) is used, and it has a structure in which a fixed magnetic layer 11, an intermediate layer 12, and a free magnetic layer 13 are stacked in this order. The resistance value of the magnetoresistive effect element 10 changes according to the relative relationship between the fixed magnetic layer 11 whose magnetization direction is fixed and the magnetization direction of the free magnetic layer 13 whose magnetization direction is changed by the external magnetic field. The magnetic sensor 1 can measure the direction and strength of the measured external magnetic field based on the change in the resistance value of the magnetoresistive effect element 10. Hereinafter, the magnetization direction of the fixed magnetic layer 11 is also appropriately referred to as the Pin direction.

[0058] When the magnetoresistive element 10 is a GMR element, the fixed magnetic layer 11 is formed by using a ferromagnetic layer such as a CoFe alloy (cobalt-iron alloy). The intermediate layer 12 is formed by using a non-magnetic intermediate layer such as Cu. The free magnetic layer 13 is formed by using a soft magnetic material such as a CoFe alloy or a NiFe alloy (nickel-iron alloy), and is formed into a single-layer structure, a stacked structure, a laminated iron structure, etc.

[0059] In order to stabilize the output of the magnetic sensor 1, the free magnetic layer 13 is directed in the direction ( Figure 2 The bias magnetic field is applied in a direction perpendicular to the Y-axis direction (indicated by arrows on both sides). Thus, the magnetization direction of the soft magnetic material forming the free magnetic layer 13 can be made consistent when no magnetic field is applied.

[0060] The fixed magnetic layer 11 of the magnetoresistive element 10 fixes the magnetization direction in the first direction ( Figure 2 The free magnetic layer 13 has a magnetization direction that is orthogonal to the first direction when no magnetic field is applied ( Figure 2 The X2 direction of the X axis is indicated by the black arrow).

[0061] Therefore, the resistance value of the magnetoresistive effect element 10 changes in the opposite direction depending on whether the direction of the measured magnetic field indicated by the arrows on both sides in the figure is the Y1 direction or the Y2 direction in the Y-axis direction. The resistance value has opposite signs in the first direction, i.e., the Y-axis, depending on whether the direction of the measured magnetic field is the Y1 direction or the Y2 direction. That is, since the resistance value becomes an odd function with respect to the measured magnetic field, the direction and magnitude of the measured magnetic field can be continuously measured.

[0062] Instead of the above-mentioned GMR element, a TMR element may be used as the magnetoresistive element 10. In this case, the intermediate layer 12 is an insulating barrier layer containing MgO, Al2O3, titanium oxide, or the like.

[0063] Figure 1 The saturation magnetic field applying unit 3 shown applies a magnetic field to the magnetoresistance effect element 10 provided in the magnetic detection unit 2 to magnetically saturate the free magnetic layer 13, and is composed of, for example, a coil, a current line, or a magnet. When a TMR element is used as the magnetoresistance effect element 10, STT (Spin Transfer Torque) can also be used as a means for saturating the free magnetic layer 13 instead of a coil, a current line, or a magnet.

[0064] The magnetic field calculation unit 4 calculates the measured magnetic field based on the output of the magnetic detection unit 2, and is composed of, for example, a CDS (Correlated Double Sampling) circuit. The magnetic field calculation unit 4 calculates the measured magnetic field based on the first output when the measured magnetic field is applied to the free magnetic layer 13 and the second output when the free magnetic layer 13 is magnetically saturated. For example, by taking the difference between the first output and the second output, 1 / f noise can be removed from the first output.

[0065] In the magnetic sensor 1 , after the magnetic field calculation unit 4 calculates the measurement magnetic field, a signal corresponding to the calculated measurement magnetic field is amplified by the amplifier 5 and then converted into digital data by the analog-to-digital conversion circuit 6 .

[0066] The control unit 7 controls each unit constituting the magnetic sensor 1 , and is constituted by a CPU (Central Processing Unit), a program, and the like.

[0067] Figure 31 is a perspective view schematically showing a stacked structure of a magnetoresistance effect element 20 according to a modified example. In the magnetoresistance effect element 20 shown in this figure, the relative relationship between the magnetization direction of the fixed magnetic layer 11 and the magnetization direction of the free magnetic layer 13 is different from Figure 2 That is, the magnetization direction of the free magnetic layer 13 of the magnetoresistive effect element 20 when no saturation magnetic field is applied is the same as the magnetization direction of the fixed magnetic layer 11, that is, the X2 direction of the X axis.

[0068] In the magnetoresistive effect element 20, the resistance value changes in the same manner when the direction of the measured magnetic field indicated by the arrows on both sides of the figure is in the Y1 direction of the Y-axis direction and in the Y2 direction. That is, the resistance value of the magnetoresistive effect element 20 changes in the same manner regardless of the direction of the measured magnetic field, and becomes an even function of the measured magnetic field. Therefore, in terms of being able to obtain an output with a large signal and excellent linearity, Figure 2 The magnetoresistance effect element is 10 times Figure 3 The magnetoresistance effect element 20 is more preferable.

[0069] Figure 4 This is a graph showing the relationship between the 1 / f noise generated in the magnetoresistive element 10 and the output from the magnetic detection unit 2 having one magnetoresistive element 10. The 1 / f noise contained in the output from the magnetic detection unit 2 increases as the frequency decreases, so the low-frequency signal is submerged in the 1 / f noise. Therefore, it is difficult to use the magnetic sensor 1 having the magnetoresistive element 10 to measure a small magnetic field.

[0070] The 1 / f noise generated in the magnetoresistive element 10 can be reduced to a certain extent by adjusting the physical properties, shape, size, etc. of the materials of each layer. However, it is difficult to reduce the 1 / f noise to a level close to white noise. According to the present invention, by using the second output measured in a state where the free magnetic layer 13 is saturated, the 1 / f noise can be removed from the first output containing the measured magnetic field, thereby measuring a small magnetic field with high accuracy.

[0071] Figure 5A is a flow chart of the magnetic measurement method involved in this embodiment, Figure 5B This is a flow chart of a magnetic measurement method according to a specific example. Figure 6 Schematic diagrams schematically showing the magnetic state of the magnetoresistance effect element 10 and the output of the magnetic detection unit in each step of the magnetic measurement method according to the present embodiment. In this figure, the magnetization state of the fixed magnetic layer 11 and the free magnetic layer 13 of the magnetoresistance effect element 10 in each step is shown on the left side of the figure, and the magnetic detection unit 2 (refer to FIG. 1 ) having one magnetoresistance effect element 10 is shown on the right side. Figure 1 ) output.

[0072] like Figure 5AAs shown in FIG. 1 , the magnetic measurement method includes a magnetic field measurement step S1, a saturation magnetic field measurement step S2, and a magnetic field calculation step S3. By measuring the external magnetic field using these steps, the 1 / f noise can be removed from the first output obtained in the magnetic field measurement step S1 to obtain a measured magnetic field. Since the magnetic measurement method of the present invention can remove the 1 / f noise, it is possible to measure a low-frequency and small magnetic field with high accuracy.

[0073] The magnetic field measuring step S1 and the saturation magnetic field measuring step S2 may be performed first. The magnetic field calculating step S3 uses the first output obtained in the magnetic field measuring step S1 and the second output obtained in the saturation magnetic field measuring step S2 to calculate the measured magnetic field. Therefore, the magnetic field calculating step S3 needs to be performed after the magnetic field measuring step S1 and the saturation magnetic field measuring step S2.

[0074] The measurements of the magnetic field measurement step S1 and the saturation magnetic field measurement step S2 may be performed multiple times, respectively, and the first output and the second output may be obtained based on the multiple measurement results. For example, the first output and the second output may be obtained as the average value of the multiple measurement results obtained by the multiple measurements. In addition, the maximum value and the minimum value among the multiple measurement results obtained by the multiple measurements may be excluded, and the remaining measurement results may be averaged to obtain the first output and the second output.

[0075] In the magnetic field measurement step S1, the free magnetic layer 13 (reference Figure 2 ) The first output of the magnetic detection unit 2 when the measurement magnetic field is applied. The first output obtained by the measurement includes the measurement magnetic field and the 1 / f noise signal.

[0076] The measured magnetic field measured in the magnetic field measurement step S1 may be a magnetic field in only one direction or a magnetic field in multiple directions. As a magnetic field in multiple directions, for example, magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction in mutually orthogonal XYZ coordinates can be cited. When measuring magnetic fields in multiple directions, they can be measured simultaneously or sequentially.

[0077] In the saturation magnetic field measurement step S2, the saturation magnetic field application unit 3 applies a magnetic field to the free magnetic layer 13, and the second output of the magnetic detection unit 2 is measured in a state where the free magnetic layer 13 is magnetically saturated. In the state where the free magnetic layer 13 is magnetically saturated, even if the magnetic field becomes larger, the resistance value of the magnetoresistive effect element 10 does not change. The saturation magnetic field Hs applied by the saturation magnetic field application unit 3 is set to a size that saturates the free magnetic layer 13, and is applied in a direction parallel to or antiparallel to the direction of the measured magnetic field.

[0078] Figure 7It is a graph showing the relationship between the magnetic field applied to the free magnetic layer 13 and the output of the magnetic detection unit 2. This figure is used to illustrate the saturation magnetic field Hs that makes the free magnetic layer 13 magnetically saturated. The output of the magnetic detection unit 2 is ideally as shown by the dashed line in the figure, the magnetic field applied to the free magnetic layer 13 changes to become a saturation magnetic field Hs or a saturation magnetic field -Hs, and the external magnetic field is fixed in the range above the saturation magnetic field +Hs and below the saturation magnetic field -Hs. But in fact, as shown by the solid line in the figure, the output of the magnetic detection unit 2 changes smoothly before and after the saturation magnetic field +Hs and the saturation magnetic field -Hs, and the external magnetic field changes slightly after becoming the saturation magnetic field +Hs and the saturation magnetic field -Hs.

[0079] In the present embodiment, the so-called "free magnetic layer magnetic saturation" refers to the state in which a magnetic field greater than a saturation magnetic field +Hs or less than a saturation magnetic field -Hs is applied to the free magnetic layer to magnetically saturate the free magnetic layer 13. Here, the so-called saturation magnetic field Hs refers to the magnetic field at the point where a parallel line +LP from the saturation point +Ps of the output from the magnetic detection unit 2 intersects with a tangent line L0 near the zero point where no magnetic field is applied to the free magnetic layer 13, and the so-called saturation magnetic field -Hs refers to the magnetic field at the point where a parallel line -LP from the saturation point -Ps of the output from the magnetic detection unit 2 intersects with the tangent line L0.

[0080] In fact, when the free magnetic layer 13 is magnetically saturated, the magnetic detection unit 2 also has some sensitivity. Therefore, the sensitivity of the magnetic detection unit 2 is corrected (the offset correction in the saturation magnetic field measurement step S2 described below) so that the output above the saturation magnetic field +Hs and below the saturation magnetic field -Hs becomes constant. Figure 7 As shown, the parallel line +LP from the saturation point +Ps and the parallel line -LP from the saturation point -Ps are both parallel to the horizontal axis indicating the magnitude of the magnetic field.

[0081] The second output obtained in the saturation magnetic field measurement step S2 includes a signal of the state of magnetic saturation of the free magnetic layer 13 (hereinafter also appropriately referred to as a saturation magnetic field signal) and a signal of 1 / f noise. The saturation magnetic field signal is a known signal determined by whether the direction of magnetic saturation of the free magnetic layer 13 is the same direction (parallel) or the opposite direction (anti-parallel) to the Pin direction of the fixed magnetic layer 11. Therefore, the output of 1 / f noise is obtained by subtracting the saturation magnetic field signal from the second output obtained in the saturation magnetic field measurement step S2. In this case, the saturation magnetic field signal is an offset signal, and an offset correction is performed by subtracting the saturation magnetic field signal from the second output.

[0082] The magnetic field calculation step S3 calculates the measured magnetic field based on the first output measured in the magnetic field measurement step S1 and the second output measured in the saturation magnetic field measurement step S2. The first output includes the measured magnetic field signal and 1 / f noise, and the second output includes the saturation magnetic field signal and 1 / f noise. Therefore, by using the first output and the second output, the 1 / f noise can be removed from the first output.

[0083] As described above, the saturation magnetic field signal included in the second signal is known. Therefore, by further subtracting the saturation magnetic field signal from the difference between the first output and the second output, a signal of a measurement magnetic field that does not contain 1 / f noise can be obtained.

[0084] Figure 5B This is a flowchart of a magnetic measurement method according to a specific example. The magnetic measurement method shown in the figure performs a magnetic field calculation step S3' after the magnetic field measurement step S1 and the saturation magnetic field measurement step S2. In the magnetic field calculation step S3', the 1 / f noise is removed from the first output by calculating the difference between the first output and the second output, and the measured magnetic field is calculated.

[0085] Figure 8 1 is a diagram for explaining an example of the operation order (sequence) of the magnetic sensor 1, and shows the signal output from the magnetic detection unit 2. In this diagram, the order of the magnetic field measurement step S1 and the saturation magnetic field measurement step S2 is shown. Figure 5A The flowchart shown is the opposite example. After the measurement circuit of the magnetic sensor 1 is turned on, first, as a saturation magnetic field measurement step S2, a magnetic field is applied to the free magnetic layer 13 of the magnetoresistive element 10, and the measurement is performed in a saturated state to obtain the second output. Thereafter, as a magnetic field measurement step S1, the external magnetic field is measured without applying a magnetic field for saturating the free magnetic layer 13, and the first output is obtained. Then, a magnetic field calculation step S3 is performed to calculate the external magnetic field from which 1 / f noise is removed based on the first output and the second output, that is, the measurement magnetic field.

[0086] exist Figure 8 In the embodiment, the free magnetic layer 13 is saturated in the (+) direction, but the saturation magnetic field measurement step S2 may be performed in a state where the free magnetic layer 13 is saturated in the (-) direction instead. Here, the state where the free magnetic layer 13 is saturated in the (+) direction refers to a state where the free magnetic layer 13 is saturated by applying a magnetic field in the same direction (parallel) along the Pin direction, which is also appropriately referred to as (+) saturation. The state where the free magnetic layer 13 is saturated in the (-) direction refers to a state where the free magnetic layer 13 is saturated by applying a magnetic field in the opposite direction (antiparallel) along the Pin direction, which is also appropriately referred to as (-) saturation.

[0087] Fig. 91 is a diagram illustrating another example of the operation order (sequence) of the magnetic sensor 1. In the operation sequence shown in the diagram, in the saturation magnetic field measurement step S2, the free magnetic layer of the magnetoresistive element is saturated in both the (+) direction and the (-) direction, and measurement is performed in two states of (+) saturation and (-) saturation, and the second output is obtained using the two measurement results.

[0088] Fig.10 Yes Description Fig. 9 FIG. 1 is a diagram of the saturation magnetic field measurement step S2 in the operation sequence shown in FIG. Fig.10 In the method, after the free magnetic layer 13 of the magnetoresistive element 10 is first set to a (+) saturated state and measured, it is set to a (-) saturated state and measured. Since the absolute value of the signal strength of the saturated magnetic field signal is large, the absolute value of the signal strength of the measurement result in the saturated state including the saturated magnetic field signal is large in both the (+) saturated state and the (-) saturated state. However, since the saturated magnetic field signal contained in the (+) saturated measurement result and the saturated magnetic field signal contained in the (-) saturated measurement result have opposite polarities, the absolute value of the signal strength can be reduced by adding these measurement results to form the second output, or by setting the average value of the two to form the second output. Thus, the magnetic field calculation unit 4, the amplifier 5, and the analog-to-digital conversion circuit 6 (A / D conversion circuit, reference Figure 1 ) becomes smaller, which is beneficial from the perspective of improving the amplification factor of the amplifier and the resolution during A / D conversion.

[0089] As described above, by using the measurement results in the (+) saturation and (-) saturation states, the absolute value of the signal strength of the second output can be reduced. However, the second output sometimes includes an offset signal caused by the deviation of the magnetoresistive element 10. When the second output includes the offset signal, an offset correction is performed to remove the offset signal.

[0090] Fig.11 1 is a block diagram of a magnetic sensor 8 according to a modified example. The magnetic sensor 8 according to the modified example amplifies the first output and the second output from the magnetic detection unit 2 in the amplifier 5, performs A / D conversion in the analog-to-digital conversion circuit 6 to obtain digital signals, and then calculates the measured magnetic field in the magnetic field calculation unit 4. Each unit in the magnetic sensor may be configured to obtain the measured magnetic field based on the first output and the second output, and is not limited to Figure 1 as well as Fig.11 Example shown.

[0091] Fig.12 The magnetic sensor 1 is used as the magnetic detection unit 2 (refer to Figure 1) is a schematic diagram of a full-bridge circuit 15. As shown in the figure, the full-bridge circuit 15 includes magnetoresistance effect elements 10a, 10b, 10c and 10d (when these are not distinguished, they are appropriately referred to as magnetoresistance effect elements 10). The four magnetoresistance effect elements 10 can be provided on the same substrate (single chip).

[0092] The full bridge circuit 15 is configured by connecting a half bridge circuit 21a and a half bridge circuit 21b in parallel between a power supply point, namely a power terminal Vdd and a ground terminal Gnd. The half bridge circuit 21a connects the magnetoresistance effect elements 10a and 10b in series, and the half bridge circuit 21b connects the magnetoresistance effect elements 10c and 10d in series.

[0093] The half-bridge circuit 21a includes an output terminal Va between the magnetoresistance effect element 10a and the magnetoresistance effect element 10b. In addition, the half-bridge circuit 21b includes an output terminal Vb between the magnetoresistance effect element 10c and the magnetoresistance effect element 10d. The magnitude of the external magnetic field applied from the outside as the measurement magnetic field can be quantitatively measured by the potential difference (Va-Vb, midpoint potential difference) output from these two output terminals Va and Vb.

[0094] Regarding the pair of magnetoresistive effect elements 10a and 10b forming the half-bridge circuit 21a, the magnetization direction (Pin direction) of the fixed magnetic layer 11 is the Y1 direction and the Y2 direction in this order. In addition, regarding the pair of magnetoresistive effect elements 10c and 10d forming the half-bridge circuit 21b, the magnetization direction (Pin direction) of the fixed magnetic layer 11 is the Y2 direction and the Y1 direction in this order.

[0095] In the half-bridge circuit 21a and the half-bridge circuit 21b, the pin directions of the magnetoresistance effect elements 10a and 10c on the power supply terminal Vdd side are opposite (anti-parallel) and the pin directions of the magnetoresistance effect elements 10b and 10d on the ground terminal Gnd side are opposite (anti-parallel).

[0096] Furthermore, in the four magnetoresistive effect elements 10 a , 10 b , 10 c , and 10 d , the magnetization directions of the free magnetic layers 13 in a state where no external magnetic field is applied are the same X1 direction.

[0097] According to the above structure, as the magnitude of the measured magnetic field in the Y-axis direction changes, the output changes in the opposite directions at the output terminal Va from the half-bridge circuit 21a and the output terminal Vb from the half-bridge circuit 21b. Therefore, as the potential difference between the two output terminals Va and Vb, a large output can be obtained. Therefore, by using the full-bridge circuit 15 as the magnetic detection unit 2, the measured magnetic field can be measured with high accuracy. In addition, the half-bridge circuits 21a, 21b and the magnetoresistive effect element 10 can be used as the magnetic detection unit 2 instead of the full-bridge circuit 15.

[0098] A free magnetic layer 13 (see Figure 2 ) The saturation magnetic field applying parts 22a, 22b, 22c, 22d for applying a magnetic field. The saturation magnetic field applying parts 22a, 22b, 22c, 22d are respectively composed of, for example, a coil, a current line, a magnet, etc. Fig.12 In the embodiment, the saturation magnetic field applying parts 22a, 22b, 22c, and 22d are connected so that a saturation magnetic field in the same direction can be applied to the magnetoresistance effect element 10a and the magnetoresistance effect element 10c, and a saturation magnetic field in the opposite direction to the magnetoresistance effect element 10a can be equally applied to the magnetoresistance effect element 10b and the magnetoresistance effect element 10d.

[0099] Fig.13 Yes Fig.12 The block diagram of the full bridge circuit 15 is a state in which the free magnetic layer 13 is saturated by applying a saturation magnetic field to the magnetic sensor 1. In the example shown in the figure, the free magnetic layer 13 in each magnetoresistance effect element 10a, 10b, 10c and 10d is saturated in a direction parallel to the magnetization direction of the fixed magnetic layer 11. Therefore, the resistance values ​​of each magnetoresistance effect element 10a, 10b, 10c and 10d are equal.

[0100] The half-bridge circuit 21a and the half-bridge circuit 21b constituting the full-bridge circuit 15 are provided with the magnetoresistance effect element 10 which makes the relative relationship of the magnetization direction of the free magnetic layer 13 and the fixed magnetic layer 11 the same when the free magnetic layer 13 is magnetically saturated. Therefore, the second output obtained based on the output from the output terminals Va and Vb does not contain the saturation magnetic field signal, but only contains 1 / f noise. Therefore, the measurement magnetic field can be obtained based on the first output and the second output only without using the known saturation magnetic field signal when the free magnetic layer 13 is saturated. Furthermore, by setting the magnetoresistance effect elements 10 in the state where the free magnetic layer 13 is saturated to the same resistance value, there is also an advantage that the output from the full-bridge circuit 15 becomes smaller and the subsequent signal processing becomes easier.

[0101] (simulation)

[0102] right Fig.13 The simulation is performed on the magnetic sensor 1 which is composed of four magnetoresistive effect elements 10 forming a full bridge circuit 15. Fig.14A as well as Fig. 14B A graph showing the first output obtained by simulation and a graph showing the relationship between frequency and noise are shown. Fig.15A as well as Fig. 15B A graph showing the second output obtained by simulation and a graph showing the relationship between frequency and noise are shown. Fig.16A as well as Fig. 16BA graph showing outputs based on the first output and the second output in this embodiment and a graph showing the relationship between the frequency and noise in the outputs are shown.

[0103] like Fig.15A As shown, the second output is obtained as a signal with a small absolute value of signal intensity. This is because the saturation magnetic field signal is canceled in the second output in a state where the free magnetic layer 13 of the magnetoresistive element 10 constituting the full bridge circuit 15 is saturated.

[0104] When the magnetoresistance effect elements 10a, 10b, 10c, and 10d constituting the full-bridge circuit 15 are in an ideal state where they are completely identical except for the Pin direction and the direction in which the saturation magnetic field is applied, the second output contains only 1 / f noise and does not contain a saturation magnetic field signal. However, when there is a deviation among the magnetoresistance effect elements 10a, 10b, 10c, and 10d, the second output from the full-bridge circuit 15 contains an offset signal caused by the deviation in addition to the 1 / f noise. When the second output contains an offset signal, an offset correction is performed to remove the offset signal.

[0105] like Fig.16A As shown, by taking Fig.14A The first output shown is Fig.15A The difference of the second output shown in FIG. 1 can obtain a measurement magnetic field with less noise. Fig. 16B As shown in the figure, the spectrum after noise removal is Fig. 14B The spectrum of the first output shown in FIG. 1 includes noise components in the low-frequency region, and the noise is reduced as a whole. In this way, the present invention can reduce the 1 / f noise included in the measurement magnetic field.

[0106] (Variation)

[0107] Fig.17 Yes means Fig.13 1 is a block diagram of a full bridge circuit 16 of a modified example of a state in which the free magnetic layer 13 is saturated. In the example shown in the figure, the free magnetic layer 13 in each magnetoresistive element 10a, 10b, 10c and 10d is saturated in a direction antiparallel to the magnetization direction of the fixed magnetic layer 11.

[0108] Fig.18 1 is a block diagram showing a full bridge circuit 17 according to a modification. In the example shown in the figure, the free magnetic layers 13 of the magnetoresistance effect elements 10a and 10c are saturated in a direction parallel to the magnetization direction of the fixed magnetic layer 11, and the free magnetic layers 13 of the magnetoresistance effect elements 10b and 10d are saturated in a direction antiparallel to the magnetization direction of the fixed magnetic layer 11. In order to realize this structure, in the full bridge circuit 17, the connection method of the saturation magnetic field applying parts 22a, 22b, 22c, and 22d is different from that of the full bridge circuit 15.

[0109] Fig.19 1 is a block diagram showing a full-bridge circuit 18 according to a modified example. The full-bridge circuit 18 shown in this example has the same circuit structure as the full-bridge circuit 17, but the power supply direction to the saturation magnetic field applying parts 22a, 22b, 22c, and 22d is opposite. As a result, the free magnetic layer 13 in the magnetoresistance effect elements 10a and 10c is saturated in a direction antiparallel to the magnetization direction of the fixed magnetic layer 11. Then, the free magnetic layer 13 in the magnetoresistance effect elements 10b and 10d is saturated in a direction parallel to the magnetization direction of the fixed magnetic layer 11.

[0110] about Figure 17 to Figure 19 The full bridge circuits 16 to 18, the half bridge circuits 21a and the half bridge circuits 21b of the modified examples shown are also composed of the magnetoresistance effect element 10 in which the free magnetic layer 13 and the fixed magnetic layer 11 have the same relative magnetization direction when the free magnetic layer 13 is in the magnetic saturation state. Therefore, Fig.13 The full bridge circuit 15 also does not contain a saturation magnetic field signal in the outputs from the output terminals Va and Vb. Therefore, as the difference between the outputs from the output terminals Va and Vb, a second output containing no saturation magnetic field signal in a saturated state of the free magnetic layer 13 and containing 1 / f noise can be obtained.

[0111] The embodiments disclosed in this specification are illustrative in all points and are not limited to the embodiments. The scope of the present invention is not shown by the description of the above-mentioned embodiments alone, but by the claims, and is intended to include all changes in the meaning and scope equivalent to the claims. For example, in the above description, the saturation magnetic field is applied to the magnetoresistive effect elements 10a, 10b, 10c, 10d by the saturation magnetic field application units 22a, 22b, 22c, 22d, but it is not limited to this. For example, in the case where the magnetic sensor 1 measures the induced magnetic field generated by the measured current flowing through the current line arranged near the magnetic sensor 1, a large current can also flow through the current line to generate an induced magnetic field that magnetically saturates the free magnetic layer 13.

[0112] Industrial Applicability

[0113] The present invention is useful as a magnetic sensor and a magnetic measurement method that can detect low-frequency magnetism with high sensitivity and have high magnetic resolution.

[0114] Explanation of symbols

[0115] 1: Magnetic sensor

[0116] 2: Magnetic detection unit

[0117] 3: Saturation magnetic field application section

[0118] 4: Magnetic field calculation unit

[0119] 5: Amplifier

[0120] 6: Analog-digital conversion circuit

[0121] 7: Control Department

[0122] 8: Magnetic sensor

[0123] 10: Magnetoresistance effect element

[0124] 10a: Magnetoresistive element

[0125] 10b: Magnetoresistive element

[0126] 10c: Magnetoresistive element

[0127] 10d: Magnetoresistive element

[0128] 11: Fixed magnetic layer

[0129] 12: Middle layer

[0130] 13: Free magnetic layer

[0131] 15: Full bridge circuit

[0132] 16: Full bridge circuit

[0133] 17: Full-bridge circuit

[0134] 18: Full bridge circuit

[0135] 20: Magnetoresistance effect element

[0136] 21a: Half-bridge circuit

[0137] 21b: Half-bridge circuit

[0138] 22a: Saturation magnetic field applying section

[0139] 22b: Saturation magnetic field applying section

[0140] 22c: Saturation magnetic field applying section

[0141] 22d: Saturation magnetic field applying section

[0142] Hs: saturation magnetic field

[0143] +Hs: saturation magnetic field

[0144] -Hs: saturation magnetic field

[0145] +Ps: Saturation point

[0146] -Ps: Saturation point

[0147] +LP: Parallel Lines

[0148] -LP: Parallel Lines

[0149] L0: Tangent

[0150] Vdd: power supply terminal

[0151] Gnd: Ground terminal

[0152] Va: Output terminal

[0153] Vb: output terminal.

Claims

1. A magnetic sensor, characterized in that: have: A magnetic detection unit including a magnetoresistance effect element having a fixed magnetic layer, a free magnetic layer, and an intermediate layer formed between the fixed magnetic layer and the free magnetic layer; a magnetic field calculation unit that calculates a measurement magnetic field based on the output of the magnetic detection unit; and a saturation magnetic field applying unit for applying a magnetic field to the free magnetic layer along the direction of the measurement magnetic field to magnetically saturate the free magnetic layer; The magnetic field calculation unit calculates the measurement magnetic field based on a first output of the magnetic detection unit when the measurement magnetic field is applied to the free magnetic layer and a second output of the magnetic detection unit when the free magnetic layer is magnetically saturated.

2. The magnetic sensor according to claim 1, wherein: The magnetic field calculation unit calculates the measurement magnetic field based on a difference between the first output and the second output.

3. The magnetic sensor according to claim 1, wherein: The fixed magnetic layer fixes the magnetization direction in a first direction. In the free magnetic layer, the magnetization direction when the magnetic field is not applied is a direction orthogonal to the first direction, The direction of the measurement magnetic field is parallel or antiparallel to the first direction.

4. The magnetic sensor according to claim 1, wherein: The magnetic sensor includes a plurality of magnetoresistive effect elements. The plurality of magnetoresistive effect elements constitute a bridge circuit.

5. The magnetic sensor according to claim 4, wherein: The fixed magnetic layer fixes the magnetization direction in a first direction. In the free magnetic layer, the magnetization direction when the magnetic field is not applied is a direction orthogonal to the first direction, The direction of the measured magnetic field is the first direction, In each of the plurality of magnetoresistive effect elements, a direction in which the magnetic field is applied to the free magnetic layer by the saturation magnetic field applying section is parallel or antiparallel to the first direction.

6. The magnetic sensor according to claim 1, wherein: The saturation magnetic field applying unit is a coil, a current line, or a magnet.

7. A magnetic measurement method, comprising measuring a magnetic field based on an output of a magnetic detection unit, wherein the magnetic detection unit comprises a magnetoresistive element having a fixed magnetic layer, a free magnetic layer, and an intermediate layer formed between the fixed magnetic layer and the free magnetic layer, The magnetic measurement method is characterized by comprising: A magnetic field measuring step, obtaining a first output of the magnetic detection unit when the measuring magnetic field is applied; a saturation magnetic field measuring step of applying a magnetic field along the direction of the measuring magnetic field to obtain a second output of the magnetic detection unit in a state where the free magnetic layer is saturated; and The magnetic field calculation step calculates the measurement magnetic field based on the first output and the second output.

8. The magnetic measurement method according to claim 7, wherein: In the magnetic field calculation step, the measurement magnetic field is calculated based on a difference between the first output and the second output.

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