Magnetic sensor and magnetic measurement method

Abstract

To measure a small magnetic field with high accuracy by removing 1 / f noise.SOLUTION: A magnetic detector including a magnetoresistance effect element having an intermediate layer formed between a fixed magnetic layer and a free magnetic layer, a magnetic field calculator that calculates a measurement magnetic field based on an output of the magnetic detector, and a saturation magnetic field applicator that applies a magnetic field to the free magnetic layer along a direction of the measurement magnetic field to magnetically saturate the free magnetic layer, A signal of the measurement magnetic field is obtained using a first output including a signal of the measurement magnetic field and noise, a known saturation magnetic field signal which is a signal in a state in which the free magnetic layer is magnetically saturated, and a second output which is an output of the magnetic detector when the saturation magnetic field applying unit applies a magnetic field in one direction of the first direction to all of the free magnetic layers of the four magnetoresistance effect elements having the full-bridge circuit.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a magnetic sensor including a magnetoresistive element and a magnetic measurement method. [Background technology]

[0002] Some magnetic sensors that detect and measure magnetic fields include those equipped with magnetoresistive elements that utilize the GMR (giant magnetoresistance) effect or the TMR (tunneling magnetoresistance) effect. The magnetoresistive elements in these magnetic sensors are configured with a fixed magnetic layer, a non-magnetic intermediate layer, and a free magnetic layer stacked in this order. When an external magnetic field to be measured is applied to the magnetoresistive element, the magnetization direction of the free magnetic layer changes, causing a resistance change according to the angle between the magnetization direction of the free magnetic layer and the magnetization direction of the fixed magnetic layer. A magnetic sensor equipped with a magnetoresistive element can detect a magnetic field using the resistance change of the magnetoresistive element.

[0003] Magnetic sensors equipped with magnetoresistive elements have 1 / f noise that cannot be removed by filters. 1 / f noise is inversely proportional to frequency, becoming larger as the frequency decreases, so it can be an obstacle to high-precision measurements. For this reason, various methods are used to remove 1 / f noise.

[0004] Patent Document 1 discloses an even-function magnetic sensor that removes 1 / f noise 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 that, when measuring the Hall electromotive force of a semiconductor sample, shifts the frequency band of the voltage difference Vm to the lower frequency side in order to remove noise caused by a Schottky barrier that occurs between an electrode and a sample, thereby removing the frequency band of the voltage difference Vm that is significantly affected by 1 / f noise.

[0006] Patent document 3 discloses a magnetic field sensing device that samples bridge signals at a first current and a second current by switching between two sample holds, and determines the value of the magnetic field from the difference between the sampled first and second bridge signals.

[0007] Patent Document 4 discloses a sensor device that uses a modulator to switch the positive and negative sides of a sensor signal and take the difference between the modulated signals in order to remove 1 / f noise from the output signal. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2018-115972 [Patent Document 2] Japanese Patent Publication No. 2020-148727 [Patent Document 3] Special Publication No. 2012-518788 [Patent Document 4] Special Publication No. 2009-544004 Summary of the Invention [Problem to be solved by the invention]

[0009] A magnetic sensor equipped with a magnetoresistive element has a problem in that 1 / f noise in the low frequency range reduces the detection accuracy of the magnetic sensor, and various devices and methods have been proposed to solve this problem. The object of the present invention is to provide a magnetic sensor equipped with a magnetoresistive element and a magnetic measurement method that can remove 1 / f noise using a configuration different from conventional ones and measure small magnetic fields with high accuracy. [Means for solving the problem]

[0010] In one aspect, the present invention is a magnetic sensor comprising: a magnetic detection unit having a magnetoresistive element having a pinned magnetic layer, a free magnetic layer, and an intermediate layer formed between the pinned magnetic layer and the free magnetic layer; a magnetic field calculation unit that calculates a measured magnetic field based on the output of the magnetic detection unit; and a saturation magnetic field application unit that applies a magnetic field to the free magnetic layer along the direction of the measured magnetic field to magnetically saturate the free magnetic layer, wherein 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.

[0011] The magnetic field calculation section may calculate the measured magnetic field based on a difference between the first output and the second output.

[0012] The first output includes the output of the measured magnetic field and 1 / f noise, and the second output includes the output when the free magnetic layer is magnetically saturated 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, the 1 / f noise can be removed from the first output by using the difference between the first output and the second output. Furthermore, since the output when the free magnetic layer is magnetically saturated is known, the measured magnetic field from which the influence of the 1 / f noise has been removed can be obtained from the first output based on the first output, the second output, and the known output.

[0013] The magnetization direction of the pinned magnetic layer is fixed in a first direction, the magnetization direction of the free magnetic layer when the magnetic field is not applied is perpendicular to the first direction, and the direction of the measured magnetic field may be parallel or anti-parallel to the first direction.

[0014] With this configuration, the relationship between the magnetization direction of the free magnetic layer and the magnetization direction of the pinned magnetic layer varies depending on the direction of the magnetic field to be measured. Therefore, the resistance value of the magnetoresistive element changes in the opposite direction depending on whether the direction of the magnetic field to be measured is parallel or antiparallel to the first direction. Therefore, the relationship between the magnetic field to be measured and the resistance of the magnetoresistive element is an odd function, making it possible to measure the magnitude and direction of the magnetic field to be measured.

[0015] The magnetic sensor may include a plurality of the magnetoresistive effect elements, and the plurality of magnetoresistive effect elements may form a bridge circuit. By using a bridge circuit formed by a plurality of magnetoresistive effect elements, the output corresponding to the measured magnetic field becomes larger than when a single magnetoresistive effect element is used, thereby improving the measurement accuracy of the magnetic sensor.

[0016] The magnetization direction of the pinned magnetic layer may be fixed in a first direction, the magnetization direction of the free magnetic layer may be perpendicular to the first direction when the magnetic field is not applied, the direction of the measured magnetic field may be the first direction, and in each of the multiple magnetoresistive effect elements, the direction in which the magnetic field is applied to the free magnetic layer by the saturation magnetic field application unit may be parallel or anti-parallel to the first direction.

[0017] With this configuration, the multiple magnetoresistive elements that make up the bridge circuit have the same resistance value when the free magnetic layer of each magnetoresistive element is saturated. As a result, the second output from the bridge circuit contains only 1 / f noise, with the known output in the saturated magnetic field state removed. In addition, the voltage value obtained as the second output from the bridge circuit is small, simplifying the calculation to determine the measured magnetic field.

[0018] The saturation magnetic field applying section may be a coil, a current line, or a magnet. By applying a magnetic field using a coil, a current line, or a magnet, the free magnetic layer can be magnetically saturated.

[0019] In another aspect, the present invention provides a magnetic measurement method for measuring a measurement magnetic field based on the output of a magnetic detection unit that includes 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, characterized in that the magnetic measurement method includes a magnetic field measurement step for obtaining a first output of the magnetic detection unit when the measurement magnetic field is applied, a saturation magnetic field measurement step for applying a magnetic field along the direction of the measurement magnetic field and obtaining a second output of the magnetic detection unit when the free magnetic layer is saturated, and a magnetic field calculation step for calculating the measurement magnetic field based on the first output and the second output.

[0020] The magnetic field calculation step may calculate the measured magnetic field based on a difference between the first output and the second output.

[0021] By calculating the measured magnetic field based on the first output acquired in the magnetic field measurement step and the second output acquired in the saturation magnetic field measurement step, the measured magnetic field from which the 1 / f noise of the magnetoresistive element has been removed can be obtained. 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. [Effects of the Invention]

[0022] According to the present invention, since 1 / f noise can be removed from the measured magnetic field, it is possible to provide a magnetic sensor and a magnetic measurement method with high magnetic resolution that can measure a small magnetic field with high accuracy. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a block diagram of a magnetic sensor according to an embodiment. [Figure 2] FIG. 2 is a perspective view schematically showing a layered structure of a magnetoresistive element. [Figure 3] FIG. 10 is a perspective view schematically showing a laminated structure of a magnetoresistive effect element according to a modified example. [Figure 4]10 is a graph showing the relationship between 1 / f noise generated in a magnetoresistive element and the output of a magnetic detection unit. [Figure 5A] 1 is a flowchart of a magnetic measurement method according to an embodiment. [Figure 5B] 1 is a flowchart of a magnetic measurement method according to one embodiment. [Figure 6] 5A to 5C are schematic diagrams illustrating the magnetic state of the magnetoresistive element and the output of the magnetic detection unit in each step of the magnetic measurement method according to the embodiment. [Figure 7] 10 is a graph showing the relationship between the magnetic field applied to the free magnetic layer and the output of the magnetic detection unit. [Figure 8] FIG. 10 is a diagram illustrating an example of an operation sequence of the magnetic sensor. [Figure 9] FIG. 10 is a diagram illustrating another example of the operation sequence of the magnetic sensor. [Figure 10] FIG. 10 is a diagram illustrating a saturation magnetic field measurement step in the operation sequence shown in FIG. [Figure 11] FIG. 10 is a block diagram of a magnetic sensor according to a modified example. [Figure 12] FIG. 1 is a block diagram of a full-bridge circuit used as a magnetic detection unit of a magnetic sensor. [Figure 13] 13 is a block diagram showing a state in which a magnetic field is applied to the full bridge circuit of FIG. 12 and the free magnetic layer is saturated. FIG. [Figure 14A] 10 is a graph showing a first output in a simulation. [Figure 14B] 10 is a graph showing the relationship between the frequency of the first output and noise in a simulation. [Figure 15A] 10 is a graph showing a second output in the simulation. [Figure 15B] 10 is a graph showing the relationship between the frequency of the second output and noise in a simulation. [Figure 16A] 10 is a graph showing the measured magnetic field output in a simulation. [Figure 16B] 10 is a graph showing the relationship between the frequency of the output of the measured magnetic field and noise in a simulation. [Figure 17] FIG. 10 is a block diagram showing a modified example of a full-bridge circuit. [Figure 18] FIG. 10 is a block diagram showing a modified example of a full-bridge circuit. [Figure 19] FIG. 10 is a block diagram showing a modified example of a full-bridge circuit. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each drawing, the same components are designated by the same reference numerals, and their description will be omitted. Reference coordinates are indicated in each drawing as appropriate to indicate the positional relationship of each component.

[0025] 1 is a block diagram of a magnetic sensor 1 according to this embodiment. As shown in the figure, the magnetic sensor 1 according to this 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-to-digital conversion circuit 6, and a control unit 7.

[0026] The magnetic detection unit 2 detects an external magnetic field as a measurement target and is configured by a magnetoresistive effect element 10 (see FIG. 2), a full-bridge circuit 15 configured by a plurality of magnetoresistive effect elements 10, and half-bridge circuits 21a and 21b (see FIG. 12).

[0027] FIG. 2 is a perspective view schematically illustrating the structure of the magnetoresistive element 10 included in the magnetic detection unit 2. The magnetoresistive element 10 may be, for example, a GMR element (giant magnetoresistive element) or a TMR element (tunneling magnetoresistive element), and has a configuration in which a pinned magnetic layer 11, an intermediate layer 12, and a free magnetic layer 13 are stacked in this order. The resistance value of the magnetoresistive element 10 varies depending on the relative relationship between the magnetization directions of the pinned magnetic layer 11, whose magnetization direction is fixed, and the free magnetic layer 13, whose magnetization direction changes in response to an external magnetic field. The magnetic sensor 1 can measure the direction and strength of the external magnetic field to be measured based on the change in the resistance value of the magnetoresistive element 10. Hereinafter, the magnetization direction of the pinned magnetic layer 11 will also be referred to as the Pin direction, as appropriate.

[0028] When the magnetoresistance effect element 10 is a GMR element, the pinned magnetic layer 11 is formed using a ferromagnetic layer such as a CoFe alloy (cobalt-iron alloy). The intermediate layer 12 is formed using a non-magnetic intermediate layer such as Cu. The free magnetic layer 13 is formed using a soft magnetic material such as a CoFe alloy or a NiFe alloy (nickel-iron alloy) and has a single-layer structure, a laminated structure, a laminated ferrimagnetic structure, or the like.

[0029] To stabilize the output of the magnetic sensor 1, a bias magnetic field is applied to the free magnetic layer 13 in a direction perpendicular to the sensitivity axis, i.e., the direction of the external magnetic field (measurement magnetic field) to be measured (Y-axis direction, indicated by a double-sided arrow in FIG. 2 ), thereby aligning the magnetization direction of the soft magnetic material forming the free magnetic layer 13 when no magnetic field is applied.

[0030] The magnetization direction of the pinned magnetic layer 11 of the magnetoresistive element 10 is fixed in a first direction (the Y1 direction of the Y axis indicated by the white arrow in FIG. 2). The magnetization direction of the free magnetic layer 13 when no magnetic field is applied is a direction perpendicular to the first direction (the X2 direction of the X axis indicated by the black arrow in FIG. 2).

[0031] Therefore, the resistance value of the magnetoresistive element 10 changes in opposite directions depending on whether the direction of the measured magnetic field, indicated by the double-headed arrow in the figure, is the Y1 direction or the Y2 direction along the Y axis. The sign of the resistance value is reversed depending on whether the direction of the measured magnetic field is the Y1 direction or the Y2 direction along the Y axis, which is the first direction. In other words, because the resistance value is an odd function of the measured magnetic field, the direction and magnitude of the measured magnetic field can be measured continuously.

[0032] A TMR element may be used instead of the above-mentioned GMR element as the magnetoresistive effect element 10. In this case, the intermediate layer 12 is an insulating barrier layer made of MgO, Al2O3, titanium oxide, or the like.

[0033] 1 applies a magnetic field to the magnetoresistive element 10 included 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 magnetoresistive element 10, a spin transfer torque (STT) can be used as a means for saturating the free magnetic layer 13 instead of a coil, a current line, or a magnet.

[0034] The magnetic field calculation unit 4 calculates the measured magnetic field based on the output of the magnetic detection unit 2, and is configured, for example, by a CDS (Correlated Double Sampling) circuit. The magnetic field calculation unit 4 calculates the measured magnetic field based on a first output when the measured magnetic field is applied to the free magnetic layer 13 and a second output when the free magnetic layer 13 is magnetically saturated. For example, by calculating the difference between the first output and the second output, 1 / f noise can be removed from the first output.

[0035] In the magnetic sensor 1, after the magnetic field calculation unit 4 calculates the magnetic field to be measured, the signal corresponding to the calculated magnetic field to be measured is amplified by the amplifier 5 and then converted into digital data by the analog-to-digital conversion circuit 6. The control unit 7 controls each component constituting the magnetic sensor 1, and is configured as a CPU (Central Processing Unit), a program, and the like.

[0036] Fig. 3 is a perspective view schematically showing the layered structure of a magnetoresistive effect element 20 according to a modified example. The magnetoresistive effect element 20 shown in Fig. 3 differs from the magnetoresistive effect element 10 shown in Fig. 2 in the relative relationship between the magnetization direction of the pinned magnetic layer 11 and the magnetization direction of the free magnetic layer 13. That is, when no saturation magnetic field is applied to the free magnetic layer 13 of the magnetoresistive effect element 20, the magnetization direction is the X2 direction of the X axis, which is the same as the magnetization direction of the pinned magnetic layer 11.

[0037] The resistance value of the magnetoresistive element 20 changes in the same way when the direction of the measured magnetic field, indicated by the double-headed arrow in the figure, is the Y1 direction or the Y2 direction along the Y axis. That is, the resistance value of the magnetoresistive element 20 changes in the same way regardless of the direction of the measured magnetic field, and is an even function of the measured magnetic field. For this reason, the magnetoresistive element 10 of FIG. 2 is preferable to the magnetoresistive element 20 of FIG. 3 in that it provides a larger signal and an output with excellent linearity.

[0038] 4 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 equipped with one magnetoresistive element 10. The 1 / f noise included in the output from the magnetic detection unit 2 increases as the frequency decreases, so low-frequency signals are buried in the 1 / f noise. For this reason, it has been difficult to measure small magnetic fields using the magnetic sensor 1 equipped with the magnetoresistive element 10.

[0039] 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 has been 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 when the free magnetic layer 13 is saturated, it is possible to remove the 1 / f noise from the first output, which includes the measured magnetic field, and measure small magnetic fields with high accuracy.

[0040] Fig. 5A is a flowchart of the magnetic measurement method according to this embodiment, and Fig. 5B is a flowchart of a magnetic measurement method according to a specific example. Fig. 6 is a schematic diagram showing the magnetic state of the magnetoresistive element 10 and the output of the magnetic detection unit in each step of the magnetic measurement method according to this embodiment. In the figure, the left side shows the magnetization state of the fixed magnetic layer 11 and the free magnetic layer 13 of the magnetoresistive element 10 in each step, and the right side shows the output of the magnetic detection unit 2 (see Fig. 1) equipped with one magnetoresistive element 10.

[0041] As shown in Figure 5A, 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 through these steps, it is possible to remove 1 / f noise from the first output obtained in the magnetic field measurement step S1 and obtain a measured magnetic field. Because the magnetic measurement method of the present invention can remove 1 / f noise, it becomes possible to measure small, low-frequency magnetic fields with high accuracy.

[0042] Either the magnetic field measurement step S1 or the saturation magnetic field measurement step S2 can be performed first. The magnetic field calculation step S3 uses the first output obtained in the magnetic field measurement step S1 and the second output obtained in the saturation magnetic field measurement step S2 to calculate the measured magnetic field. Therefore, the magnetic field calculation step S3 must be performed after the magnetic field measurement step S1 and the saturation magnetic field measurement step S2.

[0043] The measurements in the magnetic field measurement step S1 and the saturation magnetic field measurement step S2 may each be performed multiple times, and the first output and the second output may be calculated based on the multiple measurement results. For example, the first output and the second output may be calculated as the average of the multiple measurement results obtained by the multiple measurements. Alternatively, the maximum and minimum values ​​of the multiple measurement results obtained by the multiple measurements may be excluded, and the remaining measurement results may be averaged to calculate the first output and the second output.

[0044] In the magnetic field measurement step S1, a first output of the magnetic detection unit 2 is measured while a measurement magnetic field is applied to the free magnetic layer 13 (see FIG. 2). The first output obtained by this measurement includes signals of the measurement magnetic field and 1 / f noise.

[0045] The magnetic field measured in the magnetic field measurement step S1 may be a magnetic field in only one direction or in multiple directions. Magnetic fields in multiple directions include, for example, magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction in an XYZ coordinate system, which are orthogonal to each other. When measuring magnetic fields in multiple directions, the measurements may be performed simultaneously or sequentially.

[0046] In the saturation magnetic field measurement step S2, a magnetic field is applied to the free magnetic layer 13 by the saturation magnetic field application unit 3, and the second output of the magnetic detection unit 2 is measured when the free magnetic layer 13 is magnetically saturated. When the free magnetic layer 13 is magnetically saturated, the resistance value of the magnetoresistive effect element 10 does not change even if the magnetic field increases further. The saturation magnetic field Hs applied by the saturation magnetic field application unit 3 is of a magnitude sufficient to saturate the free magnetic layer 13, and is applied in a direction parallel or anti-parallel to the direction of the magnetic field to be measured.

[0047] FIG. 7 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. Using this graph, we will explain the saturation magnetic field Hs that magnetically saturates the free magnetic layer 13. Ideally, as shown by the dashed-dotted line in the graph, the output of the magnetic detection unit 2 changes until the magnetic field applied to the free magnetic layer 13 reaches the saturation magnetic field Hs or −Hs, and remains constant when the external magnetic field is in a range above the saturation magnetic field +Hs and below the saturation magnetic field −Hs. However, in reality, as shown by the solid line in the graph, the output of the magnetic detection unit 2 changes gradually around the saturation magnetic field +Hs and −Hs, and then changes slightly after the external magnetic field reaches the saturation magnetic field +Hs or −Hs.

[0048] In this embodiment, "the free magnetic layer is magnetically saturated" refers to a state in which a magnetic field equal to or greater than the saturation magnetic field +Hs or equal to or less than the saturation magnetic field -Hs that magnetically saturates the free magnetic layer 13 is applied to the free magnetic layer. Here, the 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 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.

[0049] In reality, the magnetic detection unit 2 has some sensitivity even when the free magnetic layer 13 is magnetically saturated. Therefore, sensitivity correction (offset correction in the saturation magnetic field measurement step S2 described below) of the magnetic detection unit 2 is performed so that the output is constant above the saturation magnetic field +Hs and below the saturation magnetic field -Hs. Therefore, as shown in Figure 7, 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.

[0050] The second output obtained in the saturation magnetic field measurement step S2 includes a signal indicating that the free magnetic layer 13 is magnetically saturated (hereinafter also referred to as the saturation magnetic field signal, as appropriate) and a 1 / f noise signal. The saturation magnetic field signal is a known signal that is determined by whether the magnetically saturated direction of the free magnetic layer 13 is the same direction (parallel) or opposite direction (anti-parallel) to the pin direction of the fixed magnetic layer 11. Therefore, the 1 / f noise output 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 to subtract the saturation magnetic field signal from the second output.

[0051] The magnetic field calculation step S3 calculates a 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 contains a signal of the measured magnetic field and 1 / f noise, and the second output contains a 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.

[0052] As described above, the saturation magnetic field signal contained in the second signal is known, so by further subtracting the saturation magnetic field signal from the difference between the first output and the second output, a signal of the measured magnetic field that does not include 1 / f noise can be obtained.

[0053] 5B is a flowchart of a magnetic measurement method according to a specific example. The magnetic measurement method shown in the figure includes a magnetic field measurement step S1, a saturation magnetic field measurement step S2, and then a magnetic field calculation step S3'. In the magnetic field calculation step S3', the difference between the first output and the second output is calculated to remove 1 / f noise from the first output, thereby calculating the measured magnetic field.

[0054] FIG. 8 is a diagram illustrating an example of the operation sequence of the magnetic sensor 1, showing the signal output from the magnetic detection unit 2. This diagram illustrates an example in which the order of the magnetic field measurement step S1 and the saturation magnetic field measurement step S2 is reversed from that of the flowchart shown in FIG. 5A. After the measurement circuit of the magnetic sensor 1 is turned on, a magnetic field is first applied to the free magnetic layer 13 of the magnetoresistive effect element 10 in the saturation magnetic field measurement step S2, and measurement is performed in a saturated state to obtain a second output. Then, in the magnetic field measurement step S1, an external magnetic field is measured without applying a magnetic field to saturate the free magnetic layer 13, and a first output is obtained. Then, in the magnetic field calculation step S3, the external magnetic field from which 1 / f noise has been removed, i.e., the measured magnetic field, is calculated based on the first and second outputs.

[0055] 8, the free magnetic layer 13 is saturated in the (+) direction, but instead, the saturation magnetic field measurement step S2 may be performed in a state saturated in the (-) direction. Here, the state saturated in the (+) direction refers to a state in which a magnetic field is applied in the same direction (parallel) as the Pin direction to saturate the free magnetic layer 13, and is also referred to as (+) saturation where appropriate. The state saturated in the (-) direction refers to a state in which a magnetic field is applied in the opposite direction (antiparallel) to the Pin direction to saturate the free magnetic layer 13, and is also referred to as (-) saturation where appropriate.

[0056] 9 is a diagram illustrating another example of the operation sequence of the magnetic sensor 1. In the operation sequence shown in the figure, in the saturated magnetic field measurement step S2, the free magnetic layer of the magnetoresistive element is saturated in both the (+) direction and the (-) direction, and measurements are performed in two states, (+) saturation and (-) saturation, and a second output is obtained using the two measurement results obtained.

[0057] FIG. 10 is a diagram illustrating the saturation magnetic field measurement step S2 in the operational sequence shown in FIG. 9. In FIG. 10, the free magnetic layer 13 of the magnetoresistive element 10 is first measured in a (+) saturated state and then in a (-) saturated state. Because the saturation magnetic field signal has a large absolute value of signal strength, the measurement results in the saturated state, including the saturation magnetic field signal, have a large absolute value of signal strength in both the (+) saturated state and the (-) saturated state. However, because the saturation magnetic field signal included in the (+) saturated measurement result and the saturation magnetic field signal included in the (-) saturated measurement result have opposite polarities, the absolute value of the signal strength can be reduced by adding these measurement results to obtain the second output or by averaging the two. This reduces the absolute value of the signal strength processed by the magnetic field calculation unit 4, amplifier 5, and analog-to-digital conversion circuit 6 (A / D conversion circuit, see FIG. 1), which is advantageous from the perspectives of increasing the amplification factor of the amplifier and improving the resolution during A / D conversion.

[0058] 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 may contain an offset signal due to variations in the magnetoresistive element 10. If the second output contains an offset signal, an offset correction is performed to remove the offset signal.

[0059] 11 is a block diagram of a magnetic sensor 8 according to a modified example. In the magnetic sensor 8 according to the modified example, the first output and the second output from the magnetic detection unit 2 are amplified by the amplifier 5, and are converted into digital signals by the analog-to-digital conversion circuit 6, after which the measured magnetic field is calculated by the magnetic field calculation unit 4. Each part of the magnetic sensor is not limited to the examples shown in FIGS. 1 and 11 as long as it is configured to be able to determine the measured magnetic field based on the first output and the second output.

[0060] 12 is a schematic diagram of a full-bridge circuit 15 used as the magnetic detection unit 2 (see FIG. 1) of the magnetic sensor 1. As shown in the figure, the full-bridge circuit 15 includes magnetoresistive effect elements 10a, 10b, 10c, and 10d (when not distinguishing between them, they will be referred to as magnetoresistive effect elements 10 as appropriate). The four magnetoresistive effect elements 10 may be provided on the same substrate (one chip).

[0061] The full-bridge circuit 15 is configured such that a half-bridge circuit 21a and a half-bridge circuit 21b are connected in parallel between a power supply terminal Vdd, which is a power supply feeding point, and a ground terminal Gnd. The half-bridge circuit 21a has magnetoresistive effect elements 10a and 10b connected in series, and the half-bridge circuit 21b has magnetoresistive effect elements 10c and 10d connected in series.

[0062] Half-bridge circuit 21a has an output terminal Va between magnetoresistive element 10a and magnetoresistive element 10b. Half-bridge circuit 21b has an output terminal Vb between magnetoresistive element 10c and magnetoresistive element 10d. The magnitude of the external magnetic field applied from the outside as the magnetic field to be measured can be quantitatively measured from the potential difference (Va-Vb, midpoint potential difference) between the outputs of these two output terminals Va and Vb.

[0063] The pair of magnetoresistive effect elements 10a and 10b forming the half-bridge circuit 21a have the magnetization directions (Pin directions) of the pinned magnetic layers 11 set to the Y1 direction and the Y2 direction, respectively. The pair of magnetoresistive effect elements 10c and 10d forming the half-bridge circuit 21b have the magnetization directions (Pin directions) of the pinned magnetic layers 11 set to the Y2 direction and the Y1 direction, respectively.

[0064] In the half-bridge circuits 21a and 21b, the pin directions of the magnetoresistive effect elements 10a and 10c on the power supply terminal Vdd side are opposite (anti-parallel), and the pin directions of the magnetoresistive effect elements 10b and 10d on the ground terminal Gnd side are opposite (anti-parallel).

[0065] In the four magnetoresistance effect elements 10a, 10b, 10c, and 10d, the magnetization direction of the free magnetic layer 13 is the same X1 direction when no external magnetic field is applied.

[0066] With the above-described configuration, as the magnitude of the measured magnetic field in the Y-axis direction changes, the outputs from the output terminal Va from the half-bridge circuit 21a and the output terminal Vb from the half-bridge circuit 21b change in opposite directions. Therefore, a large output is obtained as the potential difference between the two output terminals Va and Vb. Therefore, by using the full-bridge circuit 15 as the magnetic detector 2, the measured magnetic field can be detected with high accuracy. Instead of the full-bridge circuit 15, the half-bridge circuits 21a and 21b or the magnetoresistance effect element 10 can also be used as the magnetic detector 2.

[0067] Saturation magnetic field applying units 22a, 22b, 22c, and 22d that apply a magnetic field to the free magnetic layer 13 (see FIG. 2) are provided near the magnetoresistive elements 10a, 10b, 10c, and 10d, respectively. Each of the saturation magnetic field applying units 22a, 22b, 22c, and 22d is configured, for example, by a coil, a current line, or a magnet. In FIG. 12, the saturation magnetic field applying units 22a, 22b, 22c, and 22d are connected so that a saturation magnetic field in the same direction is applied to the magnetoresistive elements 10a and 10c, and a saturation magnetic field in the opposite direction to that of the magnetoresistive element 10a is equally applied to the magnetoresistive elements 10b and 10d.

[0068] Fig. 13 is a block diagram of a full-bridge circuit 15 showing a state in which a saturation magnetic field is applied to the magnetic sensor 1 of Fig. 12 and the free magnetic layer 13 is saturated. In the example shown in the figure, the free magnetic layer 13 in each of the magnetoresistive elements 10a, 10b, 10c, and 10d is saturated in a direction parallel to the magnetization direction of the pinned magnetic layer 11. Therefore, the resistance values ​​of the magnetoresistive elements 10a, 10b, 10c, and 10d are equal.

[0069] The half-bridge circuits 21a and 21b constituting the full-bridge circuit 15 include magnetoresistive elements 10 in which the relative relationship between the magnetization directions of the free magnetic layer 13 and the pinned magnetic layer 11 is the same when the free magnetic layer 13 is magnetically saturated. Therefore, the second output obtained based on the outputs from the output terminals Va and Vb does not include a saturation magnetic field signal, but only 1 / f noise. Therefore, the measured magnetic field can be determined based only on the first and second outputs, without using a known saturation magnetic field signal when the free magnetic layer 13 is saturated. Furthermore, by setting the resistance values ​​of the magnetoresistive elements 10 to the same value when the free magnetic layer 13 is saturated, the output from the full-bridge circuit 15 is reduced, which has the advantage of facilitating subsequent signal processing.

[0070] (simulation) A simulation was performed on the magnetic sensor 1 in which a full-bridge circuit 15 is formed by four magnetoresistance effect elements 10 shown in FIG. 13. FIGS. 14A and 14B show graphs illustrating the first output obtained by the simulation and a graph illustrating the relationship between frequency and noise. FIGS. 15A and 15B show graphs illustrating the second output obtained by the simulation and a graph illustrating the relationship between frequency and noise. FIGS. 16A and 16B show graphs illustrating the output based on the first output and the second output in this example and a graph illustrating the relationship between frequency and noise for the output.

[0071] 15A, the second output is obtained as a signal having a small absolute value of signal intensity, because the saturation magnetic field signal is canceled out in the second output when the free magnetic layer 13 of the magnetoresistive element 10 constituting the full-bridge circuit 15 is saturated.

[0072] In an ideal state where the magnetoresistive elements 10a, 10b, 10c, and 10d constituting the full-bridge circuit 15 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, if there is variation in the magnetoresistive elements 10a, 10b, 10c, and 10d, the second output from the full-bridge circuit 15 contains an offset signal resulting from the variation in addition to the 1 / f noise. If the second output contains an offset signal, offset correction is performed to remove the offset signal.

[0073] As shown in Fig. 16A, a measured magnetic field with less noise can be obtained by taking the difference between the first output shown in Fig. 14A and the second output shown in Fig. 15A. As shown in Fig. 16B, the spectrum after noise removal has less noise overall, including noise components in the low frequency range, compared to the spectrum of the first output shown in Fig. 14B. In this way, the present invention can reduce the 1 / f noise contained in the measured magnetic field.

[0074] (Variation) Fig. 17 is a block diagram showing a modified full-bridge circuit 16 in a state where the free magnetic layer 13 of Fig. 13 is saturated. In the example shown in Fig. 17, the free magnetic layer 13 of each of the magnetoresistive elements 10a, 10b, 10c, and 10d is saturated in a direction antiparallel to the magnetization direction of the pinned magnetic layer 11.

[0075] 18 is a block diagram showing a full-bridge circuit 17 according to a modified example. In the example shown in the figure, the free magnetic layers 13 of the magnetoresistive elements 10a and 10c are saturated in a direction parallel to the magnetization direction of the pinned magnetic layer 11, and the free magnetic layers 13 of the magnetoresistive elements 10b and 10d are saturated in a direction antiparallel to the magnetization direction of the pinned magnetic layer 11. To achieve this configuration, the full-bridge circuit 17 differs from the full-bridge circuit 15 in the connection method of the saturation magnetic field application units 22a, 22b, 22c, and 22d.

[0076] 19 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 configuration as the full-bridge circuit 17, but the power supply directions to the saturation magnetic field application units 22a, 22b, 22c, and 22d are opposite. As a result, the free magnetic layers 13 in the magnetoresistive elements 10a and 10c are saturated in a direction antiparallel to the magnetization direction of the pinned magnetic layer 11. The free magnetic layers 13 in the magnetoresistive elements 10b and 10d are saturated in a direction parallel to the magnetization direction of the pinned magnetic layer 11.

[0077] 17 to 19, the half-bridge circuits 21a and 21b are also configured with magnetoresistive elements 10 in which the relative magnetization directions of the free magnetic layer 13 and the pinned magnetic layer 11 are the same when the free magnetic layer 13 is magnetically saturated. Therefore, similar to the full-bridge circuit 15 in FIG. 13, the outputs from the output terminals Va and Vb do not include a saturation magnetic field signal. Therefore, a second output that does not include a saturation magnetic field signal when the free magnetic layer 13 is saturated and includes 1 / f noise is obtained as the difference between the outputs from the output terminals Va and Vb.

[0078] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. The scope of the present invention is defined by the claims, not by the description of the above-described embodiments, and is intended to include all modifications within the meaning and scope of the claims. For example, in the above description, saturation magnetic fields are applied to the magnetoresistive elements 10a, 10b, 10c, and 10d by the saturation magnetic field application units 22a, 22b, 22c, and 22d. However, this is not limiting. For example, when the magnetic sensor 1 is used to measure an induced magnetic field generated by a current to be measured flowing through a current line located near the magnetic sensor 1, a large current may be passed through the current line to generate an induced magnetic field that magnetically saturates the free magnetic layer 13. [Industrial Applicability]

[0079] The present invention is useful as a magnetic sensor and a magnetic measurement method having high magnetic resolution, which can detect low-frequency magnetism with high sensitivity. [Explanation of symbols]

[0080] 1: Magnetic sensor 2: Magnetic detection unit 3: Saturation magnetic field application section 4: Magnetic field calculation section 5: Amplifier 6: Analog-to-digital conversion circuit 7: Control section 8: Magnetic sensor 10: Magnetoresistance effect element 10a: Magnetoresistance effect element 10b: Magnetoresistance effect element 10c: Magnetoresistance effect element 10d: Magnetoresistance effect element 11: Fixed magnetic layer 12: Middle class 13: Free magnetic layer 15: Full bridge circuit 16: Full bridge circuit 17: Full bridge circuit 18: Full bridge circuit 20: Magnetoresistance effect element 21a: Half-bridge circuit 21b: Half-bridge circuit 22a: Saturation magnetic field application section 22b: Saturation magnetic field application section 22c: Saturation magnetic field application section 22d: Saturation magnetic field application section Hs: Saturation magnetic field +Hs: Saturation magnetic field -Hs: Saturation magnetic field +Ps :Saturation point -Ps: Saturation point +LP :Parallel line -LP:Parallel line L0: Tangent Vdd: Power supply terminal Gnd: Ground terminal Va: Output terminal Vb: Output terminal

Claims

1. a magnetic detection unit including a magnetoresistive element having a pinned magnetic layer whose magnetization direction is fixed in a first direction, a free magnetic layer, and an intermediate layer formed between the pinned magnetic layer and the free magnetic layer; a magnetic field calculation unit that calculates a measured magnetic field based on an output of the magnetic detection unit; a saturation magnetic field applying unit that applies a magnetic field to the free magnetic layer in the direction of the measurement magnetic field to magnetically saturate the free magnetic layer, the magnetic detection unit includes a full-bridge circuit having four of the magnetoresistive effect elements, The magnetic field calculation unit a first output, which is an output of the magnetic detection unit when the measurement magnetic field is applied to the free magnetic layer, and which includes a signal of the measurement magnetic field and noise; a known saturation magnetic field signal that is a signal when the free magnetic layer is magnetically saturated; a second output that is an output of the magnetic detection unit when the saturation magnetic field application unit applies a magnetic field in one of the first directions to all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit; and to obtain a signal of the measured magnetic field. A magnetic sensor comprising:

2. The magnetic sensor according to claim 1 , wherein the second output includes the saturation magnetic field signal, which is an offset signal, and the noise.

3. The magnetic sensor of claim 2 , wherein the noise includes 1 / f noise.

4. The second output is a saturation magnetic field applied by the saturation magnetic field applying unit to all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit. a measurement result of the full bridge circuit when the magnetic field is applied in one of the first directions; a measurement result of the full bridge circuit when the magnetic field is applied in a direction antiparallel to the one of the two; 2. The magnetic sensor of claim 1, obtained using:

5. a magnetic detection unit including a magnetoresistive element having a pinned magnetic layer whose magnetization direction is fixed in a first direction, a free magnetic layer, and an intermediate layer formed between the pinned magnetic layer and the free magnetic layer; a magnetic field calculation unit that calculates a measured magnetic field based on an output of the magnetic detection unit; a saturation magnetic field applying unit that applies a magnetic field to the free magnetic layer in the direction of the measurement magnetic field to magnetically saturate the free magnetic layer, the magnetic detection unit includes a full-bridge circuit having four of the magnetoresistive effect elements, The magnetic field calculation unit a first output of the magnetic detection unit when the measurement magnetic field is applied to the free magnetic layer; a second output of the magnetic detection unit when the free magnetic layer is magnetically saturated; and The second output is a saturation magnetic field applied by the saturation magnetic field applying unit to all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit. a measurement result of the full bridge circuit when the magnetic field is applied in one of the first directions; a measurement result of the full bridge circuit when the magnetic field is applied in a direction antiparallel to the one of the two; What you can get by using A magnetic sensor comprising:

6. 6. The magnetic sensor according to claim 4, wherein the magnetic field calculation section adds two of the measurement results or sets an average value of the two measurement results as the second output.

7. the magnetization direction of the free magnetic layer when the magnetic field is not applied is perpendicular to the first direction; the direction of the measurement magnetic field is parallel or anti-parallel to the first direction; The magnetic sensor according to claim 1 .

8. the free magnetic layer has a magnetization direction perpendicular to the first direction when the magnetic field is not applied, the direction of the measurement magnetic field is the first direction, In each of the plurality of magnetoresistive effect elements, the direction in which the magnetic field is applied to the free magnetic layer by the saturation magnetic field application unit is parallel or antiparallel to the first direction.

6. The magnetic sensor according to claim 4 or claim 5.

9. The saturation magnetic field applying unit is a coil, a current wire, or a magnet. The magnetic sensor according to claim 1 .

10. 1. A magnetic measurement method for measuring a magnetic field based on an output of a magnetic detector including a magnetoresistive element having a pinned magnetic layer whose magnetization direction is fixed in a first direction, a free magnetic layer, and an intermediate layer formed between the pinned magnetic layer and the free magnetic layer, the magnetic detection unit includes a full-bridge circuit having four of the magnetoresistive effect elements, a magnetic field measuring step of obtaining a first output, which is an output of the magnetic detection unit when the measurement magnetic field is applied to the free magnetic layer; a saturation magnetic field measuring step of applying a magnetic field along the direction of the measurement magnetic field to saturate the free magnetic layer and obtaining a second output of the magnetic detection unit; a magnetic field calculation step of calculating the measured magnetic field based on the first output and the second output, the second output is an output of the magnetic detection unit when the saturation magnetic field application unit applies a magnetic field in one of the first directions to all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit, In the magnetic field measuring step, a signal of the measured magnetic field is obtained using the first output, the second output, and a known saturation magnetic field signal which is a signal when the free magnetic layer is magnetically saturated. A magnetic measurement method, comprising:

11. the first output includes a signal and noise of the measured magnetic field; The magnetic measurement method according to claim 10 , wherein the second output includes the saturation magnetic field signal, which is an offset signal, and the noise.

12. The magnetic measurement method according to claim 11 , wherein the noise includes 1 / f noise.

13. The second output is a saturation magnetic field applied by the saturation magnetic field applying unit to all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit. a measurement result of the full bridge circuit when the magnetic field is applied in one of the first directions; a measurement result of the full bridge circuit when the magnetic field is applied in a direction antiparallel to the one of the two; The magnetic measurement method according to claim 10, obtained using

14. 1. A magnetic measurement method for measuring a magnetic field based on an output of a magnetic detector including a magnetoresistive element having a pinned magnetic layer whose magnetization direction is fixed in a first direction, a free magnetic layer, and an intermediate layer formed between the pinned magnetic layer and the free magnetic layer, the magnetic detection unit includes a full-bridge circuit having four of the magnetoresistive effect elements, a magnetic field measuring step of obtaining a first output of the magnetic detection unit while the measurement magnetic field is applied; a saturation magnetic field measuring step of applying a magnetic field along the direction of the measurement magnetic field to saturate the free magnetic layer and obtaining a second output of the magnetic detection unit; a magnetic field calculation step of calculating the measured magnetic field based on the first output and the second output, The second output is for all of the free magnetic layers of the four magnetoresistive effect elements included in the full bridge circuit. a measurement result of the full bridge circuit when the magnetic field is applied in one of the first directions; a measurement result of the full bridge circuit when the magnetic field is applied in a direction antiparallel to the one of the two; What you can get by using A magnetic measurement method, comprising:

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