Magnetic Sensors

Abstract

To provide a magnetic sensor capable of detecting with high sensitivity a measurement object magnetic field generated by a weak electric current.SOLUTION: A magnetic sensor 1 includes: a sensor chip 10 having magnetic body layers 21 and 22 magnetically coupling via a magnetic gap G1 and a magneto-sensitive element 31 formed on a magnetic path formed with the magnetic gap G1; an external magnetic body 41 magnetically coupling with the magnetic body layers 21; and a measurement current coil C1 which is wound around the external magnetic body 41 and in which a current I flows for generating a measurement object magnetic field. Since the magneto-sensitive element 31 and the magnetic body layers 21 and 22 are integrated in the sensor chip 10, the magnetic gap G1 can be designed very narrow, and most of a leakage magnetic field can be applied to the magneto-sensitive element 31. Consequently, even when the current I flowing in the measurement current coil C1 is weak, the magnetic field generated by the current I can be detected with high sensitivity.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor that detects a magnetic field generated by a current that generates a weak magnetic field to be measured. [Background technology]

[0002] Patent Document 1 discloses a magnetic sensor (current sensor) that detects a magnetic field generated by a current that generates a magnetic field to be measured. The magnetic sensor described in Patent Document 1 includes an annular magnetic core having a magnetic gap, a coil wound around the annular magnetic core and through which a current that generates a magnetic field to be measured flows, and a magnetic sensing element disposed in the magnetic gap. With this configuration, a part of the leakage magnetic field that passes through the magnetic gap is applied to the magnetic sensing element, making it possible to measure the amount of current flowing through the coil by the magnetic sensing element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-128711 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, because the magnetic gap formed in the annular magnetic core is relatively large, the leakage magnetic field also spreads widely. Therefore, when the current flowing through the coil is weak, the magnetic field component applied to the magnetic sensing element is small, making it difficult to measure with high sensitivity the amount of current that generates the magnetic field to be measured.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a magnetic sensor capable of detecting a weak magnetic field to be measured with high sensitivity. [Means for solving the problem]

[0006] The magnetic sensor according to the present invention is characterized in that it comprises a sensor chip having first and second magnetic layers magnetically coupled via a magnetic gap and a magnetic sensing element arranged on a magnetic path formed by the magnetic gap, a first external magnetic body magnetically coupled to the first magnetic layer, and a first measurement current coil wound around the first external magnetic body and through which a current flows that generates a magnetic field to be measured.

[0007] According to the present invention, since the magnetic sensing element and the first and second magnetic layers are integrated on the sensor chip, the magnetic gap can be designed to be very narrow, and most of the leakage magnetic field can be applied to the magnetic sensing element. This makes it possible to detect the magnetic field to be measured with high sensitivity even if the current that generates the magnetic field to be measured flowing through the first measurement current coil is weak.

[0008] The magnetic sensor according to the present invention may further include a second external magnetic body magnetically coupled to the second magnetic layer. In this case, the magnetic field to be detected passes through the first and second external magnetic bodies via the first and second magnetic layers, so that the magnetic field can be detected with higher sensitivity. In this case, the magnetic sensor according to the present invention may further include a second measurement current coil wound around the second external magnetic body and connected in series with the first measurement current coil. In this case, it is possible to apply a larger magnetic field to the magnetic sensing element.

[0009] In the present invention, the first external magnetic body may have a first portion magnetically coupled to the first magnetic layer, a second portion magnetically coupled to the second magnetic layer, and a third portion connecting the first portion and the second portion, and the first measuring current coil may be wound around the third portion. In this way, the first and second magnetic layers are connected in a loop shape via the first external magnetic body, so that a structure close to a closed magnetic circuit can be obtained.

[0010] In the present invention, the first and second magnetic layers may have a planar shape that narrows toward the magnetic gap, which allows the magnetic field to be more concentrated on the magnetic sensing element, thereby making it possible to apply a larger magnetic field to the magnetic sensing element.

[0011] In the present invention, the first external magnetic body may be provided at a position overlapping the first magnetic layer, which allows the magnetic field passing through the first external magnetic body to be efficiently applied to the first magnetic layer.

[0012] In the present invention, the first measurement current coil may be offset toward the sensor chip and wound around the first external magnetic body, which allows the magnetic field passing through the first external magnetic body to be efficiently applied to the first magnetic layer.

[0013] The magnetic sensor according to the present invention may further include a compensation coil that cancels the magnetic field generated by the first measurement current coil. This makes it possible to perform so-called closed-loop control. In this case, the compensation coil may be wound around the first external magnetic body. This makes it possible to ensure a sufficient number of turns of the compensation coil. Furthermore, in this case, the first measurement current coil may be wound closer to the sensor chip than the compensation coil. This makes it possible to efficiently apply the magnetic field generated by the first measurement current coil to the magnetic sensing element. The compensation coil may be integrally formed within the sensor chip. Effect of the Invention

[0014] In this way, the present invention makes it possible to provide a magnetic sensor capable of detecting a weak magnetic field to be measured with high sensitivity. [Brief description of the drawings]

[0015] [Figure 1] Fig. 1(a) is a schematic plan view showing the configuration of a magnetic sensor 1 according to a first embodiment of the present invention, and Fig. 1(b) is a schematic cross-sectional view taken along line AA shown in Fig. 1(a). [Diagram 2] FIG. 2 is a schematic cross-sectional view showing the configuration of a magnetic sensor 2 according to a second embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing the configuration of a magnetic sensor 3 according to a third embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the configuration of a magnetic sensor 4 according to a fourth embodiment of the present invention. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing the configuration of a magnetic sensor 5 according to the fifth embodiment of the present invention. [Figure 6] FIG. 6 is a schematic plan view for explaining the configuration of the sensor chip 10 used in the fifth embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view showing the configuration of a magnetic sensor 6 according to the sixth embodiment of the present invention. [Figure 8] FIG. 8 is a schematic cross-sectional view showing the configuration of a magnetic sensor 7 according to the seventh embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view showing the configuration of a magnetic sensor 8 according to an eighth embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view showing the configuration of a magnetic sensor 8a according to a modified example of the eighth embodiment. [Figure 11] FIG. 11 is a schematic cross-sectional view showing the configuration of a magnetic sensor 9 according to a ninth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] <First embodiment> Fig. 1(a) is a schematic plan view showing the configuration of a magnetic sensor 1 according to a first embodiment of the present invention, and Fig. 1(b) is a schematic cross-sectional view taken along line AA shown in Fig. 1(a).

[0018] 1, the magnetic sensor 1 according to the first embodiment includes a sensor chip 10, an external magnetic body 41 arranged so as to overlap the sensor chip 10, and a measurement current coil C1 wound around the external magnetic body 41. The sensor chip 10 includes a magnetic sensing element 31 formed on the xy plane which is the element formation surface, a protective film 11 covering the magnetic sensing element 31, magnetic layers 21 and 22 provided on the protective film 11, and a protective film 12 covering the magnetic layers 21 and 22.

[0019] The magnetic sensing element 31 is not particularly limited as long as it is an element whose electric resistance changes depending on the direction of magnetic flux, and for example, an MR element can be used. The fixed magnetization direction of the magnetic sensing element 31 is the x-direction. The magnetic layers 21 and 22 are thin films made of a high magnetic permeability material such as permalloy. The magnetic layers 21 and 22 are magnetically coupled via a magnetic gap G1 whose width direction is the x-direction. The magnetic sensing element 31 is disposed on a magnetic path formed by the magnetic gap G1, and thus, a magnetic field in the x-direction passing through the magnetic layers 21 and 22 is applied to the magnetic sensing element 31. In the present invention, it is not essential that the magnetic sensing element 31 is located between the magnetic layers 21 and 22, and it is sufficient that the magnetic sensing element 31 is disposed near the magnetic gap G1 made of the magnetic layers 21 and 22, that is, on the magnetic path formed by the magnetic gap G1. For example, the width of the magnetic gap G1 in the x direction of the magnetic sensing element 31 may be greater than the width of the magnetic gap G1 in the x direction, so that the magnetic layers 21 and 22 and the magnetic sensing element 31 overlap when viewed in the z direction.

[0020] The external magnetic body 41 is a rod-shaped body made of a high magnetic permeability material such as ferrite, and has a longitudinal direction in the x direction. A measuring current coil C1 through which a current I to be measured flows is wound around the central section of the external magnetic body 41. One end of the external magnetic body 41 in the x direction overlaps with the magnetic layer 21 when viewed from the z direction, and the external magnetic body 41 and the magnetic layer 21 are magnetically coupled to each other. The coil axis of the measuring current coil C1 is in the x direction, and when the current I to be measured flows through the measuring current coil C1, a magnetic field to be measured in the x direction is generated in the external magnetic body 41. The magnetic field to be measured in the x direction generated in the external magnetic body 41 is applied to the magnetic layer 21 and flows through the magnetic gap G1 to the magnetic layer 22. As a result, the magnetic sensing element 31 arranged in the magnetic gap G1 can detect the direction and strength of the magnetic field to be measured generated by the measuring current coil C1, and as a result, it becomes possible to detect the amount of the current I to be measured. That is, the magnetic sensor 1 according to the present embodiment functions as a current sensor that detects the amount of the current I to be measured.

[0021] In this way, in the magnetic sensor 1 according to this embodiment, instead of disposing a magnetic sensing element in a magnetic gap provided in a ring-shaped magnetic core, the external magnetic body 41 around which the measurement current coil C1 is wound is magnetically coupled to the magnetic layer 21, and the magnetic sensing element 31 is disposed in the magnetic gap G1 between the magnetic layer 21 and the magnetic layer 22. Since the magnetic sensing element 31 and the magnetic layers 21 and 22 are all elements integrated in the sensor chip 10, the magnetic gap G1 can be designed to be very narrow, and the positional relationship between the magnetic gap G1 and the magnetic sensing element 31 can be designed with high precision. This makes it possible to detect the magnetic field to be measured generated by the measurement current coil C1 with high sensitivity, even if the current I to be measured is weak.

[0022] <Second embodiment> FIG. 2 is a schematic cross-sectional view showing the configuration of a magnetic sensor 2 according to a second embodiment of the present invention.

[0023] 2, the magnetic sensor 2 according to the second embodiment differs from the magnetic sensor 1 according to the first embodiment in that an external magnetic body 42 and a measurement current coil C2 are added. 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 are omitted.

[0024] The external magnetic body 42 is a rod-shaped body made of the same high magnetic permeability material as the external magnetic body 41, and has a longitudinal direction in the x direction. A measurement current coil C2 is wound around the central section of the external magnetic body 42. The measurement current coil C2 is connected in series with the measurement current coil C1. Therefore, the current I to be measured also flows through the measurement current coil C2. One end of the external magnetic body 42 in the x direction overlaps with the magnetic layer 22 when viewed from the z direction, and thus the external magnetic body 42 and the magnetic layer 22 are magnetically coupled. The coil axes of the measurement current coils C1 and C2 are both in the x direction, and therefore, when the current I to be measured flows through the measurement current coils C1 and C2, a magnetic field to be measured in the x direction is generated in the external magnetic bodies 41 and 42.

[0025] In this way, the magnetic sensor 2 according to this embodiment is provided with an external magnetic body 42 that is magnetically coupled to the magnetic layer 22, and the measurement current coil C2 is wound around the external magnetic body 42, making it possible to detect the magnetic field to be measured generated by the current to be measured I with higher sensitivity.

[0026] <Third embodiment> FIG. 3 is a schematic cross-sectional view showing the configuration of a magnetic sensor 3 according to a third embodiment of the present invention.

[0027] 3, the magnetic sensor 3 according to the third embodiment differs from the magnetic sensor 1 according to the first embodiment in the shape of the external magnetic body 41. Since the other basic configurations are the same as those of the magnetic sensor 1 according to the first embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0028] In this embodiment, the external magnetic body 41 has first to third parts 41a to 41c. The first part 41a is a part that overlaps with the magnetic layer 21 and is magnetically coupled to the magnetic layer 21, and the second part 41b is a part that overlaps with the magnetic layer 22 and is magnetically coupled to the magnetic layer 22. The third part 41c is a part that connects the first part 41a and the second part 41b, and the measurement current coil C1 is wound around the third part 41c. The first to third parts 41a to 41c may be integral, or may be formed by bonding or bonding different members to each other.

[0029] With this configuration, a loop-shaped magnetic path close to a closed magnetic path is formed by the external magnetic body 41 and the magnetic layers 21, 22, so that even if the current I to be measured is weak, the magnetic field to be measured generated by the current I to be measured can be efficiently applied to the magnetic sensing element 31.

[0030] <Fourth embodiment> FIG. 4 is a schematic cross-sectional view showing the configuration of a magnetic sensor 4 according to a fourth embodiment of the present invention.

[0031] 4, the magnetic sensor 4 according to the fourth embodiment differs from the magnetic sensor 3 according to the third embodiment in that the external magnetic body 41 is substantially ring-shaped. Since the other basic configurations are the same as those of the magnetic sensor 3 according to the third embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0032] According to this embodiment, the flow of the magnetic field in the external magnetic body 41 becomes smoother, so that the magnetic field to be measured generated by the current I to be measured can be applied to the magnetic sensing element 31 more efficiently.

[0033] <Fifth embodiment> Fig. 5 is a schematic cross-sectional view showing the configuration of a magnetic sensor 5 according to a fifth embodiment of the present invention. Fig. 6 is a schematic plan view for explaining the configuration of a sensor chip 10 used in the fifth embodiment. The cross section shown in Fig. 5 corresponds to the cross section taken along line AA in Fig. 6.

[0034] 5 and 6, the magnetic sensor 5 according to the fifth embodiment differs from the magnetic sensor 1 according to the first embodiment in the structure of the sensor chip 10 and the longitudinal direction of the external magnetic body 41. 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.

[0035] The sensor chip 10 used in the fifth embodiment has four magnetic sensing elements 31-34 and three magnetic layers 21-23. The fixed magnetization directions of the magnetic sensing elements 31-34 are aligned in the same direction (for example, the positive side in the x direction). The magnetic layer 21 is disposed so as to be sandwiched between the magnetic layer 22 and the magnetic layer 23. Two magnetic gaps G1, G2 are formed between the magnetic layer 21 and the magnetic layer 22, and two magnetic gaps G3, G4 are formed between the magnetic layer 21 and the magnetic layer 23. The magnetic sensing elements 31-34 are disposed on the magnetic paths formed by the magnetic gaps G1-G4, respectively.

[0036] Furthermore, in this embodiment, the longitudinal direction of the external magnetic body 41 is the z direction, and one end of the external magnetic body 41 is arranged to overlap with the magnetic layer 21. The coil axis of the measurement current coil C1 wound around the external magnetic body 41 is in the z direction. As a result, when a current I to be measured flows through the measurement current coil C1, a magnetic field to be measured in the z direction is generated in the external magnetic body 41. The magnetic field in the z direction generated in the external magnetic body 41 is applied to the magnetic layer 21, half of which flows through the magnetic gaps G1 and G2 to the magnetic layer 22, and the remaining half flows through the magnetic gaps G3 and G4 to the magnetic layer 23. The magnetic fields passing through the magnetic gaps G1 to G4 are applied to the magnetic sensing elements 31 to 34, respectively.

[0037] Furthermore, by connecting the magnetic sensing elements 31-34 in a full bridge configuration, it is possible to detect the magnetic field generated by the current I to be measured with higher sensitivity than when a single magnetic sensing element 31 is used. Moreover, in this embodiment, the magnetic layers 21-23 have a planar shape that narrows toward the magnetic gaps G1-G4, so that the magnetic field is more concentrated on the magnetic sensing elements 31-34. This makes it possible to apply a larger magnetic field to the magnetic sensing elements 31-34. Alternatively, two magnetic sensing elements (for example, the magnetic sensing elements 31 and 33) may be used and connected in a half bridge configuration.

[0038] Sixth embodiment FIG. 7 is a schematic cross-sectional view showing the configuration of a magnetic sensor 6 according to the sixth embodiment of the present invention.

[0039] 7, the magnetic sensor 6 according to the sixth embodiment differs from the magnetic sensor 5 according to the fifth embodiment in that external magnetic bodies 42 and 43 are added. Since the other basic configurations are the same as those of the magnetic sensor 5 according to the fifth embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0040] The external magnetic bodies 42, 43 each cover the back and side surfaces of the sensor chip 10, and have protrusions 42a, 43a that overlap and magnetically couple with the magnetic layers 22, 23, respectively. This allows the magnetic field flowing from the external magnetic body 41 to the magnetic layers 22, 23 via the magnetic layer 21 to be efficiently applied to the external magnetic bodies 42, 43, thereby reducing the leakage magnetic field and allowing a larger magnetic field to be applied to the magnetic sensing elements 31-34.

[0041] Seventh embodiment FIG. 8 is a schematic cross-sectional view showing the configuration of a magnetic sensor 7 according to the seventh embodiment of the present invention.

[0042] 8, the magnetic sensor 7 according to the seventh embodiment differs from the magnetic sensor 6 according to the sixth embodiment in that an integrated external magnetic body 44 is added instead of the external magnetic bodies 42 and 43, and a measurement current coil C2 is added. Since the other basic configurations are the same as those of the magnetic sensor 6 according to the sixth embodiment, the same elements are given the same reference numerals and redundant explanations will be omitted.

[0043] The external magnetic body 44 covers the back and side surfaces of the sensor chip 10, and has protrusions 42a, 43a that overlap and magnetically couple with the magnetic layers 22, 23. The external magnetic body 44 extends in the z direction and has a rod-shaped portion having approximately the same thickness as the external magnetic body 41, and a measurement current coil C2 is wound around this rod-shaped portion. The measurement current coil C2 is connected in series with the measurement current coil C1, so that a measurement target current I flows through it.

[0044] In this way, the magnetic sensor 7 according to the present embodiment can detect the magnetic field to be measured generated by the current I to be measured with higher sensitivity because the measurement current coils C1 and C2 are wound around the external magnetic bodies 41 and 44, respectively. Moreover, in the present embodiment, both the measurement current coils C1 and C2 are wound offset toward the sensor chip 10. That is, instead of winding the measurement current coils C1 and C2 around the central portion in the axial direction of the external magnetic bodies 41 and 44, the measurement current coil C1 is wound offset in the -z direction so as to be closer to the sensor chip 10, and the measurement current coil C2 is wound offset in the +z direction so as to be closer to the sensor chip 10. This reduces the leakage magnetic field that is not applied to the magnetic sensing elements 31 to 34, and therefore makes it possible to efficiently apply the magnetic field passing through the external magnetic bodies 41 and 44 to the magnetic sensing elements 31 to 34.

[0045] <Eighth embodiment> FIG. 9 is a schematic cross-sectional view showing the configuration of a magnetic sensor 8 according to an eighth embodiment of the present invention.

[0046] 9, the magnetic sensor 8 according to the eighth embodiment differs from the magnetic sensor 7 according to the seventh embodiment in that an external magnetic body 45 is provided to connect the external magnetic body 41 and the external magnetic body 44, and a measurement current coil C1 is wound around the external magnetic body 45. Since the other basic configurations are the same as those of the magnetic sensor 7 according to the seventh embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0047] In this embodiment, the external magnetic bodies 41, 44 and the magnetic layers 21-23 form a loop-shaped magnetic path that is close to a closed magnetic path, so that the magnetic field to be measured generated by the current I to be measured can be efficiently applied to the magnetic sensing elements 31-34. Here, the external magnetic bodies 41, 44, 45 may be separate members, or may be a single member. In addition, it is not essential that the external magnetic bodies 41, 44, 45 are linear, and a ring-shaped external magnetic body 46 may be used as in a modified magnetic sensor 8a shown in FIG. 10.

[0048] <Ninth embodiment> FIG. 11 is a schematic cross-sectional view showing the configuration of a magnetic sensor 9 according to a ninth embodiment of the present invention.

[0049] 11, the magnetic sensor 9 according to the ninth embodiment differs from the magnetic sensor 6 according to the sixth embodiment in that a compensation coil C3 is wound around an external magnetic body 41. Since the other basic configurations are the same as those of the magnetic sensor 6 according to the sixth embodiment, the same elements are denoted by the same reference numerals and redundant explanations will be omitted.

[0050] The compensation coil C3 cancels out the magnetic field generated by the measurement current coil C1, and a current flows in the opposite direction to that of the measurement current coil C1. By using such a compensation coil C3, it becomes possible to perform so-called closed loop control. The compensation coil C3 may be integrated into the sensor chip 10 instead of being wound around the external magnetic body 41, but by winding it around the external magnetic body 41, it becomes possible to ensure a sufficient number of turns for the compensation coil C3.

[0051] 11, by winding the measurement current coil C1 closer to the sensor chip 10 than the compensation coil C3, it becomes possible to efficiently apply the magnetic field generated by the measurement current coil C1 to the magnetic sensing elements 31 to 34. In addition, a part or the whole of the compensation coil may be integrated into the sensor chip 10.

[0052] Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention. [Explanation of symbols]

[0053] 1~9 Magnetic Sensor 10 Sensor chip 11,12 Protective film 21~23 Magnetic layer 31~34 Magnetic sensing element 41~46 External magnetic material 41a First Part 41b Second Part 41c Third Part 42a,43a Protrusion C1, C2 measuring current coil C3 Compensation coil G1~G4 Magnetic gap I Current to be measured

Claims

1. A sensor chip comprising: first and second magnetic layers provided on an element forming surface extending in a first direction and a second direction perpendicular to the first direction, the first direction being the width direction, and magnetically coupled via a magnetic gap extending in the second direction; and a magnetic sensing element provided on the element forming surface and arranged on a magnetic path formed by the magnetic gap; a rod-shaped first external magnetic body extending linearly in a third direction perpendicular to the first and second directions; a first measurement current coil wound around the first external magnetic body and through which a current flows that generates a magnetic field to be measured; a compensation coil wound around the first external magnetic body to cancel out a magnetic field generated by the first measurement current coil; the first external magnetic body is disposed such that one end in the third direction overlaps with the first magnetic layer; The magnetic sensor according to claim 1, wherein the first measurement current coil and the compensation coil are arranged coaxially such that their winding positions in the third direction are different from each other.

2. 2. The magnetic sensor according to claim 1, wherein the first and second magnetic layers have a planar shape whose width in the second direction narrows toward the magnetic gap.

3. 3. The magnetic sensor according to claim 1, wherein the first measurement current coil is wound around the first external magnetic body and offset toward the sensor chip.

4. 4. The magnetic sensor according to claim 1, wherein the first measurement current coil is wound closer to the sensor chip than the compensation coil.

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