Magnetic sensor

Abstract

To reduce the amount of current necessary for modulation in a magnetic sensor capable of sensitively detecting a magnetic field in a low-frequency region.SOLUTION: A magnetic sensor 1 includes: a sensor chip 100 having magnetic sensing elements R1 to R4; magnetic collectors 110 and 120 for collecting a magnetic field to the magnetic sensing elements R1 to R4; an excitation coil C1 wound around the magnetic collector 110; and a modulation circuit 130 for supplying an excitation current with a predetermined frequency to the excitation coil C1 so that the magnetic collector 110 is not magnetically saturated and the magnetic sensing elements R1 to R4 are periodically magnetically saturated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a magnetic sensor, and more particularly to a magnetic sensor capable of detecting magnetic fields in a low frequency range with high sensitivity. [Background technology]

[0002] Currently, magnetic sensors using magneto-sensitive elements are used in a variety of fields, but to detect extremely weak magnetic fields, magnetic sensors with a high S / N ratio are required. One factor that reduces the S / N ratio of magnetic sensors is 1 / f noise. 1 / f noise becomes more pronounced the lower the frequency component of the magnetic field being measured. Therefore, reducing 1 / f noise is important for highly sensitive detection of magnetic fields in the low-frequency range, for example, below 1 kHz.

[0003] A known magnetic sensor that reduces 1 / f noise is the magnetic sensor described in Patent Document 1. The magnetic sensor described in Patent Document 1 reduces 1 / f noise by periodically saturating the magnetic sensing element using modulation means. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2020-522696 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the magnetic sensor described in Patent Document 1, the current line for saturating the magnetic sensing element is simply placed near the magnetic sensor, which has the problem that a large current is required to saturate the magnetic sensing element.

[0006] This disclosure describes a technology for reducing the amount of current required for modulation in a magnetic sensor that can detect magnetic fields in the low frequency range with high sensitivity. [Means for solving the problem]

[0007] A magnetic sensor according to one aspect of the present disclosure includes a sensor chip having a magnetic sensing element, a magnetic collector that collects a magnetic field at the magnetic sensing element, an excitation coil wound around the magnetic collector, and a modulation circuit that supplies an excitation current having a predetermined frequency to the excitation coil so that the magnetic sensing element periodically becomes magnetically saturated without the magnetic collector becoming magnetically saturated. [Effects of the Invention]

[0008] According to the present disclosure, a technique is provided for reducing the amount of current required for modulation in a magnetic sensor capable of detecting magnetic fields in the low frequency range with high sensitivity. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic perspective view of the sensor chip 100. As shown in FIG. [Figure 3] FIG. 3 is a schematic perspective view of the magnetic collector 120. As shown in FIG. [Figure 4] FIG. 4 is a schematic plan view of the sensor chip 100. As shown in FIG. [Figure 5] FIG. 5 is a schematic cross-sectional view taken along line AA in FIG. [Figure 6] FIG. 6 is a circuit diagram for explaining the connection relationship of the magnetic sensing elements R1 to R4. [Figure 7] FIG. 7 is a circuit diagram of a closed loop circuit including magnetic sensing elements R1 to R4. [Figure 8] FIG. 8 is a schematic perspective view showing the appearance of a magnetic sensor 2 according to the second embodiment of the present disclosure. [Figure 9] FIG. 9 is a schematic plan view showing the configuration of a main part of a magnetic sensor 3 according to the third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the technology according to the present disclosure will be described in detail with reference to the accompanying drawings.

[0011] FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor 1 according to a first embodiment of the present disclosure.

[0012] As shown in Fig. 1, the magnetic sensor 1 according to the first embodiment includes a sensor chip 100 having a magnetic sensing element, magnetic collectors 110 and 120 that collect a magnetic field to the magnetic sensing element provided on the sensor chip 100, and an excitation coil C1 wound around the magnetic collector 110. The magnetic collectors 110 and 120 are both blocks made of a high-permeability material such as ferrite. The magnetic collector 110 is a rod-shaped body with its longitudinal direction in the Z direction, and its end in the +Z direction faces the sensor chip 100. An excitation coil C1 with its axial direction aligned with the Z direction is wound around the magnetic collector 110.

[0013] FIG. 2 is a schematic perspective view of the sensor chip 100. As shown in FIG.

[0014] 2, the sensor chip 100 has an element forming surface 101 and a back surface 102 which are located opposite each other and form an XY plane, side surfaces 103 and 104 which are located opposite each other and form a YZ plane, and side surfaces 105 and 106 which are located opposite each other and form an XZ plane. A magnetic sensing element and magnetic layers M1 to M3, which will be described later, are formed on the element forming surface 101 of the sensor chip 100.

[0015] FIG. 3 is a schematic perspective view of the magnetic collector 120. As shown in FIG.

[0016] 3, the magnetic collector 120 has a main body 121 whose longitudinal direction is the Z direction, a pair of protrusions 122 and 123 that protrude further in the -Z direction from an end of the main body 121 in the -Z direction and have a thickness in the X direction that is thinner than that of the main body 121, an overhang 124 that protrudes in the -X direction from the end of the protrusion 122 in the -Z direction, and an overhang 125 that protrudes in the +X direction from the end of the protrusion 123 in the -Z direction. The sensor chip 100 is disposed in a space surrounded by the main body 121, the protrusions 122 and 123, and the overhangs 124 and 125.

[0017] FIG. 4 is a schematic plan view of the sensor chip 100, and FIG. 5 is a schematic cross-sectional view taken along line AA in FIG.

[0018] As shown in FIGS. 4 and 5, four magnetically sensitive elements R1 to R4 are formed on the element forming surface 101 of the sensor chip 100. The magnetically sensitive elements R1 to R4 are not particularly limited as long as they are elements whose electrical resistance changes depending on the direction of magnetic flux, and for example, MR elements can be used. The fixed magnetization directions of the magnetically sensitive elements R1 to R4 are aligned in the same direction (for example, the positive side in the X direction). The magnetically sensitive elements R1 to R4 are covered with an insulating layer 107, and magnetic layers M1 to M3 made of permalloy or the like are formed on the surface of the insulating layer 107. The magnetic layers M1 to M3 are covered with an insulating layer 108. The magnetic layer M1 is disposed approximately in the center of the element forming surface 101 in the X direction. The magnetic layers M2 and M3 are disposed on both sides of the element forming surface 101 in the X direction so as to sandwich the magnetic layer M1 in the X direction.

[0019] The magnetic layers M1 and M2 form two gaps G1 and G3 that extend in the Y direction and have the X direction as their width direction. The positions of the gaps G1 and G3 in the X direction coincide with each other, and they are aligned in the Y direction. The magnetic layers M1 and M3 form two gaps G2 and G4 that extend in the Y direction and have the X direction as their width direction. The positions of the gaps G2 and G4 in the X direction coincide with each other, and they are aligned in the Y direction. Furthermore, the gaps G1 and G4 are aligned in the X direction, and the gaps G2 and G3 are aligned in the X direction. The magnetic sensing elements R1 to R4 are positioned so as to overlap the gaps G1 to G4, respectively, in a plan view seen from the Z direction. As a result, the magnetic field in the X direction passing through the magnetic gaps G1 to G4 is applied to the magnetic sensing elements R1 to R4, respectively.

[0020] 4 and 5, the region indicated by reference numeral 110a indicates a region covered from the Z direction by the XY plane located at one end of the magnetic collector 110 in the Z direction, and the regions indicated by reference numerals 124a and 125a indicate regions covered from the Z direction by the overhanging portions 124 and 125 of the magnetic collector 120, respectively. Furthermore, the side surface 103 of the sensor chip 100 is covered from the X direction by the protruding portion 122 of the magnetic collector 120, and the side surface 104 of the sensor chip 100 is covered from the X direction by the protruding portion 123 of the magnetic collector 120. Furthermore, the back surface 102 of the sensor chip 100 is covered by the main body portion 121 of the magnetic collector 120.

[0021] The regions 110a, 124a, and 125a overlap the magnetic layers M1 to M3, respectively. As a result, the magnetic layer M1 is covered from the Z direction by the magnetic collector 110, the magnetic layer M2 is covered from the Z direction by the overhanging portion 124 of the magnetic collector 120, and the magnetic layer M3 is covered from the Z direction by the overhanging portion 125 of the magnetic collector 120. The magnetic field in the Z direction, which is the magnetic field to be detected, is collected by the magnetic collector 110 and applied to the magnetic layer M1 via the magnetic collector 110. The magnetic field applied to the magnetic layer M1 is bent in the +X direction and the -X direction in the magnetic layer M1. The magnetic flux component bent in the +X direction in the magnetic layer M1 is supplied to the magnetic layer M2 via the gaps G1 and G3, and then flows to the overhanging portion 124 of the magnetic collector 120, the protrusion 122, and the main body portion 121. At this time, part of the magnetic flux passing through gaps G1 and G3 in the +X direction is applied to magnetic sensing elements R1 and R3. Meanwhile, the magnetic flux component bent in the -X direction in magnetic layer M1 is supplied to magnetic layer M3 via gaps G2 and G4, and then flows to overhang portion 125, protrusion 123, and main body portion 121 of magnetic collector 120. At this time, part of the magnetic flux passing through gaps G2 and G4 in the -X direction is applied to magnetic sensing elements R2 and R4.

[0022] Although it is not essential to provide the overhanging portions 124, 125 on the magnetic collector 120, by covering the magnetic layers M2, M3 with the overhanging portions 124, 125, respectively, it is possible to significantly reduce the magnetic resistance between the magnetic collector 110 and the magnetic collector 120. Furthermore, even if the magnetic collector 120 does not have the overhanging portions 124, 125, it is possible to reduce the magnetic resistance between the magnetic collector 110 and the magnetic collector 120 by covering the side surfaces 103, 104 of the sensor chip 100 with the protruding portions 122, 123 of the magnetic collector 120. Furthermore, by covering the back surface 102 of the sensor chip 100 with the main body portion 121 of the magnetic collector 120, it is possible to efficiently apply the magnetic field in the Z direction to be detected to the magnetic sensing elements R1 to R4.

[0023] FIG. 6 is a circuit diagram for explaining the connection relationship of the magnetic sensing elements R1 to R4.

[0024] As shown in Figure 6, magnetic sensing elements R1 to R4 are bridge-connected between the power supply Vcc and ground GND. That is, magnetic sensing elements R1 and R2 are connected in series between the power supply Vcc and ground GND, and magnetic sensing elements R4 and R3 are connected in series between the power supply Vcc and ground GND. The potential difference between the potential Va appearing at the connection point between magnetic sensing elements R1 and R2 and the potential Vb appearing at the connection point between magnetic sensing elements R4 and R3 is used as the output signal ΔV (= Va - Vb). In this way, magnetic sensing elements R1 to R4 form a differential bridge circuit, and the change in the electrical resistance of magnetic sensing elements R1 to R4 according to the magnetic flux density appears as the level of the output signal ΔV.

[0025] As shown in Fig. 1, a modulation circuit 130 is connected to an excitation coil C1 wound around a magnetic collector 110. The modulation circuit 130 applies an excitation magnetic field to the magnetic sensing elements R1 to R4 via the magnetic collector 110 by supplying an excitation current i1 having a predetermined frequency to the excitation coil C1. When the excitation current i1 is passed through the excitation coil C1, the magnetic sensing elements R1 to R4 become magnetically saturated at least at the timing when the excitation current i1 becomes maximum. The excitation current i1 has a predetermined frequency, which causes the magnetic sensing elements R1 to R4 to become magnetically saturated periodically.

[0026] That is, during the period when the exciting coil C1 is not excited, the magnetic sensing elements R1 to R4 can detect the magnetic field to be detected, and an output signal ΔV corresponding to the strength of the magnetic field to be detected appears. In contrast, during the period when the exciting coil C1 is excited, the magnetic sensing elements R1 to R4 are magnetically saturated, making it impossible to detect the magnetic field to be detected, and the output signal ΔV becomes zero. As a result, the output signal ΔV output from the sensor chip 100 is modulated by the frequency of the exciting current i1 supplied from the modulation circuit 130 to the exciting coil C1, thereby significantly reducing 1 / f noise.

[0027] Here, the maximum value of the excitation current i1 supplied from the modulation circuit 130 to the excitation coil C1 is less than the amount of current that magnetically saturates the magnetic collector 110. Therefore, even when the excitation current i1 having a predetermined frequency is supplied from the modulation circuit 130 to the excitation coil C1, the magnetic collector 110 does not become magnetically saturated. This reduces the amount of the excitation current i1 supplied from the modulation circuit 130, thereby not only reducing current consumption but also suppressing heat generation due to the excitation current. In this way, even when the excitation current i1 is supplied to the excitation coil C1, the magnetic collector 110 does not become magnetically saturated. Therefore, even when the excitation current i1 is supplied to the excitation coil C1, the magnetic field to be detected is collected by the magnetic collector 110 and applied to the magnetic sensing elements R1 to R4, even when the excitation current i1 is at its maximum. However, because the magnetic sensing elements R1 to R4 are magnetically saturated at this timing, the sensitivity of the magnetic sensing elements R1 to R4 is zero.

[0028] To periodically magnetically saturate the magnetic sensitive elements R1 to R4 without magnetically saturating the magnetic collector 110, the magnetic collection efficiency can be designed so that the magnetic flux density of the magnetic field flowing through the magnetic sensitive elements R1 to R4 is higher than the magnetic flux density of the magnetic field flowing through the magnetic collector 110. In other words, if the magnetic flux density of the magnetic field flowing through the magnetic collector 110 is A and the magnetic flux density of the magnetic field flowing through the magnetic sensitive elements R1 to R4 is B, the magnetic collection efficiency G, defined as B / A, can be designed to exceed 1, and the amount of excitation current i1 supplied from the modulation circuit 130 to the excitation coil C1 can be adjusted so that the magnetic flux density A is equal to or less than the saturation magnetic field of the magnetic collector 110 and the magnetic flux density B exceeds the saturation magnetic field of the magnetic sensitive elements R1 to R4. Here, the saturation magnetic field refers to a magnetic field at which the magnetization of a ferromagnetic material becomes saturated.

[0029] When the magnetic flux concentration efficiency G exceeds 1, the saturation magnetic field of the magnetic flux concentrator 110 may be lower than the saturation magnetic fields of the magnetosensitive elements R1 to R4. For example, when the saturation magnetic field of the magnetic flux concentrator 110 is a and the saturation magnetic fields of the magnetosensitive elements R1 to R4 are b, even if a < b, if b / a < G, it is possible to periodically magnetically saturate the magnetosensitive elements R1 to R4 without magnetically saturating the magnetic flux concentrator 110. As an example, when the saturation magnetic field a of the magnetic flux concentrator 110 is about 1.5 Oe and the saturation magnetic fields b of the magnetosensitive elements R1 to R4 are about 100 Oe, it may be designed such that the magnetic flux concentration efficiency G is about 67 times or more. Actually, when ferrite blocks are used as the materials of the magnetic flux concentrators 110 and 120 and permalloy thin films are used as the materials of the magnetic layers M1 to M3, the magnetic flux concentration efficiency G can be designed to be 1200 to 2000 times. Therefore, even if the saturation magnetic fields of the magnetic flux concentrator 110 and the magnetosensitive elements R1 to R4 are the above values, it is possible to periodically magnetically saturate the magnetosensitive elements R1 to R4 without magnetically saturating the magnetic flux concentrator 110.

[0030] FIG. 7 is a circuit diagram of a closed-loop circuit including the magnetosensitive elements R1 to R4.

[0031] The closed-loop circuit shown in FIG. 7 includes an operational amplifier 141 that receives an output signal ΔV, a compensation coil C2 connected between the output node of the operational amplifier 141 and the output terminal 140, and a resistor 142 connected between the output terminal 140 and the ground GND. The compensation coil C2 is integrated in the sensor chip 100 as shown in FIG. 2. When a compensation current i2 output from the operational amplifier 141 flows through the compensation coil C2, a canceling magnetic field is generated. As a result, when an output signal ΔV corresponding to the magnetic flux density of the detection target magnetic field is generated, a corresponding compensation current i2 flows through the compensation coil C2, a canceling magnetic field in the reverse direction is generated, and the detection target magnetic field is canceled. Then, if the output signal Vout is generated by converting the compensation current i2 into a current voltage by the resistor 142, it becomes possible to detect the strength of the detection target magnetic field. By using such a closed-loop circuit, it becomes possible to detect the magnetic field magnetically concentrated through the magnetic flux concentrators 110 and 120 with higher accuracy.

[0032] When using such a closed loop circuit, by designing the maximum value of the excitation magnetic field applied to the magnetic sensing elements R1 to R4 by the excitation coil C1 to be greater than the maximum value of the cancellation magnetic field applied to the magnetic sensing elements R1 to R4 by the compensation coil C2, it becomes possible to periodically magnetically saturate the magnetic sensing elements R1 to R4 without the excitation magnetic field being completely canceled out by the cancellation magnetic field.

[0033] Here, the excitation current i1 generated by the modulation circuit 130 may be an AC current having a sine wave or a pulsed DC current having a predetermined frequency. If a pulsed DC current having a predetermined frequency is used as the excitation current i1, a state in which the current value is zero continues for a certain period within one cycle of the excitation current i1, thereby ensuring a sufficient period during which the output signal Vout can be observed. In this case, if the excitation current i1 is designed so that the period during which the current value is zero (duty ratio) is 25% or more within one cycle of the excitation current i1, it is possible to ensure a sufficient period during which the output signal Vout can be observed.

[0034] As described above, the magnetic sensor 1 according to this embodiment includes magnetic collectors 110 and 120 that collect a weak magnetic field to be detected on the sensor chip 100, and an excitation coil C1 is wound around the magnetic collector 110. This allows the modulation circuit 130 to pass an excitation current i1 having a predetermined frequency through the excitation coil C1, thereby modulating the detection signal (ΔV or Vout) obtained from the magnetic sensing elements R1 to R4. As a result, even if the frequency of the weak magnetic field to be detected is low, it is possible to significantly reduce 1 / f noise. Furthermore, the excitation magnetic field generated by the excitation coil C1 is at a level that periodically magnetically saturates the magnetic sensing elements R1 to R4 without magnetically saturating the magnetic collector 110, thereby reducing current consumption. When a general magnetic material is used, the saturation magnetic field of the magnetic collector 110 is lower than the saturation magnetic field of the magnetic sensing elements R1 to R4. However, by designing the magnetic collection efficiency G to be large, it is possible to periodically magnetically saturate the magnetic sensing elements R1 to R4 without magnetically saturating the magnetic collector 110.

[0035] FIG. 8 is a schematic perspective view showing the appearance of a magnetic sensor 2 according to the second embodiment of the present disclosure.

[0036] 8, the magnetic sensor 2 according to the second embodiment differs from the magnetic sensor 1 according to the first embodiment in that the excitation coil C1 is wound around the magnetic collector 120. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are given the same reference numerals and redundant explanations will be omitted. As exemplified by the magnetic sensor 2 according to the second embodiment, instead of winding the excitation coil C1 around the magnetic collector 110, the excitation coil C1 may be wound around the magnetic collector 120.

[0037] FIG. 9 is a schematic plan view showing the configuration of the main part of a magnetic sensor 3 according to the third embodiment of the present disclosure, with magnetic collectors 110 and 120 omitted.

[0038] 9, the magnetic sensor 3 according to the third embodiment differs from the magnetic sensor 1 according to the first embodiment in that the excitation coil C1 is integrated in the sensor chip 100 and wound around the magnetic layers M2 and M3. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are given the same reference numerals and redundant explanations will be omitted. As exemplified by the magnetic sensor 3 according to the third embodiment, instead of winding the excitation coil C1 around the magnetic collector 110, the excitation coil C1 may be wound around the magnetic layers M2 and M3 on the sensor chip 100.

[0039] The above describes the embodiments of the present disclosure, but the present disclosure is not limited to the above embodiments, and various modifications are possible within the scope of the present disclosure, and it goes without saying that these modifications are also included within the scope of the present disclosure.

[0040] The technology according to the present disclosure includes, but is not limited to, the following configuration examples.

[0041] A magnetic sensor according to one aspect of the present disclosure includes a sensor chip having a magnetic sensing element, a magnetic collector that collects a magnetic field at the magnetic sensing element, an excitation coil wound around the magnetic collector, and a modulation circuit that supplies an excitation current having a predetermined frequency to the excitation coil so that the magnetic sensing element is periodically magnetically saturated without magnetically saturating the magnetic collector. This allows the magnetic sensing element to be periodically magnetically saturated with a smaller amount of current.

[0042] In the magnetic sensor, the magnetic collector may have a lower saturation magnetic field than the magnetic sensing element, which allows the magnetic collector to be made of a general magnetic material such as ferrite.

[0043] The magnetic sensor may further include a compensation coil integrated on the sensor chip to cancel the magnetic field applied to the magnetic sensing element. This allows for closed-loop control. In this case, the maximum value of the excitation magnetic field applied to the magnetic sensing element by the excitation coil may be greater than the maximum value of the cancellation magnetic field applied to the magnetic sensing element by the compensation coil. This prevents the excitation magnetic field applied to the magnetic sensing element from being canceled by the compensation coil.

[0044] In the magnetic sensor described above, the state in which the current value is zero may continue for a certain period within one cycle of the excitation current. This makes it possible to ensure a sufficient period during which the output signal can be observed. In this case, the period during which the current value is zero may be 25% or more within one cycle of the excitation current. This makes it possible to ensure a sufficient period during which the output signal can be observed. [Explanation of symbols]

[0045] 1~3 Magnetic sensors 100 sensor chips 101 Element formation surface 102 Back side 103~106 Side 107,108 Insulating layer 110,120 Magnetic collector 110a,124a,125a area 121 Main body 122,123 Protrusion 124,125 Overhang 130 Modulation Circuit 140 output terminal 141 Operational Amplifier 142 Resistance C1 Excitation coil C2 Compensation coil G1~G4 Gap M1~M3 magnetic layer R1~R4 magnetic sensing element i1 Excitation current i2 compensation current

Claims

1. a sensor chip having a magnetic sensing element; a magnetic collector that collects a magnetic field at the magnetic sensing element; an excitation coil wound around the magnetic collector; a modulation circuit that supplies an excitation current having a predetermined frequency to the excitation coil so that the magnetic sensitive element is periodically magnetically saturated without the magnetic collector being magnetically saturated; A magnetic sensor comprising:

2. The magnetic collector has a saturation magnetic field lower than that of the magnetic sensing element. The magnetic sensor according to claim 1 .

3. Further comprising a compensation coil integrated on the sensor chip to cancel a magnetic field applied to the magnetic sensing element. The magnetic sensor according to claim 1 .

4. a maximum value of the excitation magnetic field applied to the magnetic sensing element by the excitation coil is greater than a maximum value of the cancellation magnetic field applied to the magnetic sensing element by the compensation coil; The magnetic sensor according to claim 3 .

5. A state in which the current value is zero continues for a certain period within one cycle of the excitation current. The magnetic sensor according to claim 1 .

6. Within one cycle of the excitation current, a period in which the current value is zero exists for 25% or more. The magnetic sensor according to claim 5 .

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