WO2021131606A1

WO2021131606A1 - Magnetic sensor

Info

Publication number: WO2021131606A1
Application number: PCT/JP2020/045212
Authority: WO
Inventors: 笠島　多聞; 崇人福井; 郁人小野寺; 承彬林
Original assignee: Tdk株式会社
Priority date: 2019-12-27
Filing date: 2020-12-04
Publication date: 2021-07-01
Also published as: JP2021105601A

Abstract

[Problem] To reduce the 1/f size of a magnetic sensor. [Solution] A magnetic sensor according to the present invention comprising: a sensor chip 10 that includes a magnetosensitive element R; external magnetic bodies 21, 22 that form a magnetic gap G1; and a MEMS chip 30. The MEMS chip 30 includes a displacement region 31 that overlaps the magnetic gap G1, and a support region 32 that elastically supports the displacement region 31. The displacement region 31 includes a bypass magnetic body layer B, the displacement region 31 and/or the support region 32 includes a piezoelectric body layer 41, and the distance between the magnetic gap G1 and the bypass magnetic body layer B varies due to the voltage applied to the piezoelectric body layer 41. In the present invention, the sensor chip 10 and the MEMS chip 30 are separate chips, and therefore manufacturing cost can be suppressed, and 1/f size can be reduced while preventing deterioration of characteristics of the magnetosensitive element due to high-temperature processes.

Description

Magnetic sensor

The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor in which 1 / f noise is reduced by mechanically displacing the magnetic path.

Currently, magnetic sensors using magnetic sensitive elements are used in various fields, but in order to detect extremely weak magnetic fields, magnetic sensors with a high S / N ratio are required. Here, 1 / f noise can be mentioned as a factor for lowering the S / N ratio of the magnetic sensor. Since 1 / f noise becomes more prominent as the frequency component of the magnetic field to be measured becomes lower, it is necessary to reduce 1 / f noise in order to detect a magnetic field in a low frequency region such as 1 kHz or less with high sensitivity. Is important.

As a method of reducing 1 / f noise in a magnetic sensor, as described in Non-Patent Documents 1 to 3, measurement is performed by mechanically displacing the magnetic path using MEMS (Micro Electro Mechanical Systems). A method of amplitude-modulating the target magnetic field has been proposed.

For example, in Non-Patent Document 1, as shown in FIG. 14, the GMR element 4 is arranged in the magnetic gap between the magnetic path 1 and the magnetic path 2, and the GMR element 4 is covered with the variable magnetic path 3 having a MEMS structure. , A method of changing the ratio of the magnetic flux passing through the GMR element 4 by driving the variable magnetic path 3 up and down has been proposed. According to this, by driving the variable magnetic path 3 at high speed, the magnetic field to be measured is amplitude-modulated, so that 1 / f noise can be reduced.

However, the magnetic sensors described in Non-Patent Documents 1 to 3 have a complicated structure and require a large number of processes because the variable magnetic path having a MEMS structure and the magnetic sensing element are integrated on the same chip. There were problems such as high manufacturing cost, low yield, and long lead time. Moreover, in order to obtain the MEMS structure described in Non-Patent Documents 1 to 3, it is necessary to perform a high temperature process such as sputtering or milling after forming a magnetizing element such as an MR element on the wafer. There is a problem that the characteristics of the magnetosensitive element are deteriorated by the high temperature process.

Therefore, an object of the present invention is to provide a magnetic sensor capable of reducing 1 / f noise while preventing an increase in manufacturing cost and deterioration of characteristics of a magnetic sensitive element.

The magnetic sensor according to the present invention is provided in the vicinity of the first magnetic gap formed by the first and second external magnetic materials, the end of the first external magnetic material, and the end of the second external magnetic material. It is provided with a sensor chip containing the magnetically sensitive element, and a MEMS chip including a displacement region covering the ends of the first and second external magnetic materials and a support region for elastically supporting the displacement region, and the displacement region is bypass magnetism. The body layer is included, and at least one of the displacement region and the support region includes the piezoelectric layer, and the distance between the first magnetic gap and the bypass magnetic layer changes depending on the voltage applied to the piezoelectric layer.

According to the present invention, since the sensor chip and the MEMS chip are separate chips, the manufacturing cost is suppressed and the characteristics of the magnetic sensitive element by the high temperature process are suppressed as compared with the case where the variable magnetic path and the magnetic sensitive element are integrated on the same chip. It is possible to reduce 1 / f noise while preventing deterioration.

In the present invention, the support region may include a first connecting portion connected to one end of the displacement region and a second connecting portion connected to the other end of the displacement region. According to this, since the displacement region has a double-sided structure in which the displacement region is supported from at least two places, the displacement region can be stably supported.

In the present invention, the MEMS chip may have a membrane structure in which the thickness in the displacement region and the support region is selectively reduced. According to this, it is possible to increase the displacement amount in the displacement region.

In the present invention, the displacement region is located in the region defined by the plurality of first slits formed in the membrane portion of the MEMS chip, and the support region is formed in the membrane portion of the MEMS chip so as to surround the displacement region. It may be located in an area partitioned by a plurality of second slits arranged in. According to this, it is possible to secure a sufficient amount of displacement in the displacement region.

In the present invention, the piezoelectric layer may be provided in both the displacement region and the region of the support region sandwiched between the first slit and the second slit. According to this, it is possible to increase the amount of displacement in the displacement region.

In the present invention, the sensor chip further includes the first and second magnetic material layers, and the magnetic sensitive element is formed by the end portion of the first magnetic material layer and the end portion of the second magnetic material layer. The first external magnetic material overlaps the first magnetic material layer without overlapping the second magnetic material layer, and the second external magnetic material is the first magnetic material layer. It may overlap with the second magnetic material layer without overlapping with. According to this, since the magnetic flux can be more concentrated on the magnetic sensing element, it is possible to obtain higher detection sensitivity.

As described above, according to the present invention, since the sensor chip and the MEMS chip are separate chips, the manufacturing cost is suppressed and the feeling due to the high temperature process is suppressed as compared with the case where the variable magnetic path and the magnetic sensing element are integrated on the same chip. It is possible to reduce 1 / f noise while preventing deterioration of the characteristics of the magnetic element.

FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor according to a preferred embodiment of the present invention. FIG. 2 is a schematic perspective view showing a state in which the MEMS chip 30 is removed from the magnetic sensor. FIG. 3 is a schematic perspective view showing a state in which the external

magnetic bodies

21 and 22 and the MEMS chip 30 are removed from the magnetic sensor. FIG. 4 is a schematic perspective view showing a state in which the magnetic material layers M1 and M2 are removed from the sensor chip 10. FIG. 5 is an xz cross-sectional view showing a main part of the sensor chip 10. FIG. 6 is a schematic perspective view showing the structure of the MEMS chip 30 as viewed from the back surface side. FIG. 7 is a schematic plan view showing the structure of the MEMS chip 30 as viewed from the main surface side. FIG. 8 is a schematic diagram for explaining the positional relationship between the MEMS chip 30, the external

magnetic materials

21 and 22, the magnetic material layers M1 and M2, and the magnetic sensing element R. FIG. 9 is a cross-sectional view for explaining the structure of the piezoelectric structure P. FIG. 10 is a schematic perspective view showing a state in which the displacement region 31 is displaced. FIG. 11 is a schematic plan view showing the structure of the MEMS chip 30A according to the first modification. FIG. 12 is a schematic perspective view showing the structure of the MEMS chip 30B according to the second modification. FIG. 13 is a schematic perspective view showing the structure of the MEMS chip 30C according to the third modification. FIG. 14 is a schematic view of a conventional magnetic sensor having a MEMS structure.

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

FIG. 1 is a schematic perspective view showing the appearance of a magnetic sensor according to a preferred embodiment of the present invention.

As shown in FIG. 1, the magnetic sensor according to the present embodiment includes a circuit board 6 whose main surface is the xz surface, and sensor chips 10, first and second external surfaces mounted on the main surface of the circuit board 6. It includes

magnetic materials

21 and 22, and a MEMS chip 30. FIG. 2 shows a state in which the MEMS chip 30 is removed, and the tip portion of the first external magnetic body 21 in the x direction and the tip portion of the second external magnetic body 22 in the x direction are the first. It forms a magnetic gap G1.

Further, as shown in FIG. 3 in which the first and second external

magnetic bodies

21 and 22 and the MEMS chip 30 are removed, the sensor chip 10 has an element forming surface 11 constituting an xy surface. As shown in FIG. 3, a magnetic sensitive element R, magnetic material layers M1 and M2, and terminal electrodes T11 to T14 are formed on the element forming surface 11. The magnetic sensing element R is provided at a position overlapping the second magnetic gap G2 formed by the magnetic material layers M1 and M2 (when viewed from the z direction) in a plan view. With this configuration, the magnetic field in the x direction is selectively magnetized, and the magnetic field collected is applied to the magnetic sensing element R.

The external

magnetic materials

21 and 22 play a role of collecting magnetic flux on the sensor chip 10, and all of them are made of a high magnetic permeability material such as ferrite. The external

magnetic bodies

21 and 22 are all plate-shaped bodies having the x direction as the longitudinal direction. The external

magnetic bodies

21 and 22 are separate members from the sensor chip 10, and are fixed to the circuit board 6 together with the sensor chip 10. Further, the tip portions of the external

magnetic bodies

21 and 22 are provided with notches so as not to interfere with the terminal electrodes T11 to T14. Of the external

magnetic materials

21 and 22, the external magnetic material 21 covers a part of the magnetic material layer M1 without covering the magnetic material layer M2, and the external magnetic material 22 does not cover the magnetic material layer M1 and covers the magnetic material layer M2. It covers a part of. The distance between the sensor chip 10 and the external

magnetic materials

21 and 22 in the z direction is preferably as small as possible, and more preferably in close contact with each other. In order to bring the sensor chip 10 and the external

magnetic bodies

21 and 22 into close contact with each other, an adhesive is used with the sensor chip 10 and the external

magnetic materials

21 and 22 in close contact with each other, instead of interposing an adhesive between them. It is preferable to fix these to the substrate 6.

FIG. 4 is a schematic perspective view showing a state in which the magnetic material layers M1 and M2 are removed from the sensor chip 10.

As shown in FIG. 4, the magnetic sensitive element R extends in the y direction on the element forming surface 11, one end thereof is connected to the terminal electrode T11 via the wiring L1, and the other end is connected to the terminal electrode T11 via the wiring L2. It is connected to the electrode T12. The magnetic sensing element R is not particularly limited as long as it is an element whose electrical resistance changes depending on the direction of magnetic flux, and for example, an MR element or the like can be used. The fixed magnetization direction of the magnetic sensing element R is the x direction. The terminal electrodes T13 and T14 are connected to a compensation coil (not shown). The compensation coil is used to perform so-called closed-loop control by canceling the magnetic field applied to the magnetic sensing element R.

FIG. 5 is an xz cross-sectional view showing a main part of the sensor chip 10.

As shown in FIG. 5, a magnetic sensing element R is formed on the element forming surface 11 of the sensor chip 10. The magnetic sensing element R is covered with an insulating layer 12, and magnetic layers M1 and M2 made of permalloy or the like are formed on the surface of the insulating layer 12. Then, in a plan view (viewed from the z direction), the magnetic sensing element R is located between the magnetic material layer M1 and the magnetic material layer M2. As a result, a magnetic field passing through the magnetic gap G2 is applied to the magnetic sensing element R.

However, in the present invention, it is not essential that the magnetic sensitive element R is located between the magnetic material layers M1 and M2 in a plan view, and the magnetic gap G2 is in the vicinity of the magnetic gap G2 composed of the magnetic material layers M1 and M2. It suffices if the magnetic sensing element R is arranged on the formed magnetic path. Further, the relationship between the width of the magnetic gap G2 and the width of the magnetic sensing element R is not particularly limited. In the example shown in FIG. 5, the width Gx of the magnetic gap G2 in the x direction is narrower than the width Rx of the magnetic sensor R in the x direction, whereby the magnetic material layers M1 and M2 and the magnetic sensor R are viewed from the z direction. Have an overlapping OV.

FIG. 6 is a schematic perspective view showing the structure of the MEMS chip 30 as viewed from the back surface side. Further, FIG. 7 is a schematic plan view showing a structure of the MEMS chip 30 as viewed from the main surface side. FIG. 8 is a schematic diagram for explaining the positional relationship between the MEMS chip 30, the external

magnetic materials

21 and 22, the magnetic material layers M1 and M2, and the magnetic sensing element R.

The MEMS chip 30 is a chip made of silicon or the like, and as shown in FIGS. 6 to 8, the main surface 30a constituting the xy surface is located on the opposite side of the main surface 30a, and the membrane portion 30c is formed. It has a back surface 30b. The membrane portion 30c is a region where the thickness in the z direction is selectively reduced. With such a membrane structure, the membrane portion 30c can be displaced in the z direction.

The membrane portion 30c includes a displacement region 31 partitioned by two slits SL11 and SL12, and a support region 32 partitioned by four slits SL21 to SL24 surrounding the displacement region 31. Four slits SL31 to SL34 are formed on the outer side of the support area 32, and the area partitioned by the slits SL31 to SL34 also constitutes a part of the support area 32. With such a structure, the displacement region 31 is elastically supported by the support region 32 and can be displaced in the z direction. Further, the support region 32 includes a first connecting portion 32a connected to one end of the displacement region 31 in the x direction and a second connecting portion 32b connected to the other end of the displacement region 31 in the x direction. As a result, the displacement region 31 is elastically supported at two points. With such a double-sided structure, the support region 32 can stably support the displacement region 31.

On the main surface 30a side of the MEMS chip 30, a laminate BP of the piezoelectric structure P and the bypass magnetic material layer B is formed at a position overlapping the displacement region 31, and a plurality of piezoelectric structures P are formed at a position overlapping the support region 32. It is formed. The structure of the piezoelectric structure P is as shown in FIG. 9, and is composed of a piezoelectric layer 41 made of a piezoelectric material such as PZT and

electrode layers

42 and 43 formed on both sides thereof. The bypass magnetic material layer B is a metal foil made of a high magnetic permeability material such as permalloy, and is laminated on the surface of the piezoelectric structure P to form a laminated body BP. The piezoelectric structure P and the bypass magnetic material layer B can be formed on the main surface 30a of the MEMS chip 30 by using a semiconductor process. That is, after forming the piezoelectric structure P and the bypass magnetic material layer B on the main surface 30a side of the chip made of silicon or the like by using a semiconductor process, the membrane portion 30c is formed by etching from the back surface 30b, and further. The MEMS chip 30 can be manufactured by forming a plurality of slits SL11, SL12, SL21 to SL24, and SL31 to SL34.

The MEMS chip 30 having such a structure is fixed on the substrate 6 so that the laminated body BP provided in the displacement region 31 overlaps with the magnetic gap G1. The distance between the MEMS chip 30 and the external

magnetic materials

21 and 22 in the z direction is preferably as small as possible, and more preferably in close contact with each other. In order to bring the MEMS chip 30 and the external

magnetic materials

21 and 22 into close contact with each other, an adhesive is used with the MEMS chip 30 and the external

magnetic materials

21 and 22 in close contact with each other, instead of interposing an adhesive between them. It is preferable to fix these to the substrate 6. Further, it is preferable that the laminated body BP is formed so that the bypass magnetic material layer B is on the upper side, whereby the bypass magnetic material layer B and the external

magnetic materials

21 and 22 are brought into close contact with each other.

Then, when a driving voltage is applied to the electrode layers 42 and 43, the piezoelectric layer 41 is deformed, so that the displacement region 31 is displaced in the z direction, and the distance between the magnetic gap G1 and the bypass magnetic layer B changes. That is, when the driving voltage is not applied to the electrode layers 42 and 43, the displacement region 31 is flat, and the bypass magnetic layer B and the external

magnetic bodies

21 and 22 are in contact with each other or are very close to each other. It is kept in a state. Therefore, of the magnetic field taken in through the external

magnetic materials

21 and 22 in this state, a part is applied to the magnetic sensing element R via the magnetic material layers M1 and M2, but most of the magnetic field is in the displacement region. Bypassing the bypass magnetic material layer B formed on 31 is bypassed. That is, the magnetic gap G1 is magnetically short-circuited. Since the magnetic field component bypassed by the bypass magnetic material layer B is not applied to the magnetic sensing element R, the detection sensitivity of the magnetic sensor is lowered.

On the other hand, when a driving voltage is applied to the electrode layers 42 and 43, the piezoelectric layer 41 contracts, so that the displacement region 31 and the magnetic gap G1 are displaced in the z direction so as to be separated from each other as shown in FIG. As a result, the bypass magnetic material layer B formed on the displacement region 31 is separated from the magnetic path formed by the magnetic gap G1, so that the magnetic field taken in through the external

magnetic materials

21 and 22 is large. The portion is applied to the magnetic sensing element R, and the magnetic field passing through the bypass magnetic material layer B becomes small. Therefore, the detection sensitivity of the magnetic sensor is high.

Therefore, if a drive voltage having a predetermined frequency is applied to the electrode layers 42 and 43, the output signal of the magnetic sensing element R is amplitude-modulated with the frequency of the drive voltage as the sampling frequency. Then, by demodulating the amplitude-modulated output signal, it is possible to obtain a measurement result in which 1 / f noise is reduced. As an example, when the frequency component of the magnetic field to be measured is in a low frequency band such as 0.1 Hz to 1 kHz, the S / N ratio is lowered by 1 / f noise, so that the magnetic field to be measured is particularly weak. It becomes difficult to measure. However, if the magnetic sensor according to the present embodiment is used, the output signal can be amplitude-modulated at an arbitrary sampling frequency. Therefore, for example, by setting the sampling frequency to several kHz, the influence of 1 / f noise can be almost eliminated. It will be possible.

Here, the position where the piezoelectric structure P is formed is not particularly limited as long as the displacement region 31 can be displaced in the z direction, and may be formed only in the displacement region 31 or only in the support region 32. It doesn't matter. In the present embodiment, the amount of displacement of the displacement region 31 is increased by forming the piezoelectric structure P in both the displacement region 31 and the support region 32. In particular, in the support region 32, the region sandwiched between the slits SL11, SL12 and the slits SL21, SL22, the region sandwiched between the slits SL11, SL12 and the slits SL23, SL243, and the region sandwiched between the slits SL21, SL22 and the slit SL32. Sufficient displacement by forming the piezoelectric structure P in the region sandwiched between the slits SL23, SL24 and the slit SL34, the region sandwiched between the slit SL11 and the slit SL31, and the region sandwiched between the slit SL12 and the slit SL32, respectively. The amount is secured.

As described above, since the magnetic sensor according to the present embodiment includes the MEMS chip 30 that amplitude-modulates the output signal of the magnetic sensing element R, 1 / f noise can be reduced. Moreover, since the MEMS chip 30 is a different chip from the sensor chip 10, it is possible to prevent an increase in manufacturing cost and deterioration of the characteristics of the magnetic sensitive element R due to a high temperature process. Further, in the present embodiment, the sensor chip 10 and the MEMS chip 30 are not directly overlapped with each other, but external

magnetic bodies

21 and 22 having a magnetic gap G1 are interposed between the sensor chip 10 and the MEMS chip 30. , It is possible to greatly improve the selectivity of the magnetic field in the x direction.

FIG. 11 is a schematic plan view showing the structure of the MEMS chip 30A according to the first modification. The MEMS chip 30A shown in FIG. 11 differs from the above-mentioned MEMS chip 30 in that slits SL41 to SL44 extending diagonally from the ends of the slits SL21 to SL24 are added. If such slits SL41 to SL44 are provided, the amount of displacement in the displacement region 31 can be further increased.

FIG. 12 is a schematic perspective view showing the structure of the MEMS chip 30B according to the second modification. The MEMS chip 30B shown in FIG. 12 is different from the above-mentioned MEMS chip 30 in that the slits SL21 to SL24 are omitted. As described above, it is not essential that the support region 32 has a double structure including a region surrounded by the slits SL21 to SL24 and a region surrounded by the slits SL31 to SL34.

FIG. 13 is a schematic perspective view showing the structure of the MEMS chip 30C according to the third modification. The MEMS chip 30C shown in FIG. 13 has slits SL51, SL52, SL61 to SL64, SL71, SL72, SL81, SL82, and the displacement region 31 is elastically supported at six points by the support region 32. As described above, the number and shape of the slits are not particularly limited as long as the displacement region 31 can be displaced in the z direction.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention, and these are also the present invention. Needless to say, it is included in the range.

1, 2 Magnetic path 3 Variable magnetic path 4 GMR element 6 Circuit board 10 Sensor chip 11 Element forming surface 12

Insulation layer

21 and 22 External

magnetic material

30, 30A to 30C MEMS chip 30a Main surface of MEMS chip 30b Back surface of MEMS chip 30c Membrane part 31 Displacement area 32

Support area

32a, 32b Connection part 41

Hydraulic material layer

42, 43 Electrode layer B Bypass magnetic material layer BP Laminated body G1, G2 Magnetic gap L1, L2 Wiring M1, M2 Magnetic material layer P piezoelectric structure R Magnetic elements SL11, SL12, SL21 to SL24, SL31 to SL34, SL41 to SL44, SL51, SL52, SL61 to SL64, SL71, SL72, SL81, SL82 Slit T11 to T14 terminal electrodes

Claims

With the first and second external magnetic materials,
A sensor chip including a magnetic sensing element provided in the vicinity of a first magnetic gap formed by an end portion of the first external magnetic material and an end portion of the second external magnetic material, and a sensor chip.
A MEMS chip including a displacement region covering the ends of the first and second external magnetic materials and a support region elastically supporting the displacement region is provided.
The displacement region includes a bypass magnetic layer.
A magnetic sensor characterized in that at least one of the displacement region and the support region includes a piezoelectric layer, and the distance between the first magnetic gap and the bypass magnetic layer changes depending on a voltage applied to the piezoelectric layer.
The first aspect of claim 1, wherein the support region includes a first connecting portion connected to one end of the displacement region and a second connecting portion connected to the other end of the displacement region. Magnetic sensor.
The magnetic sensor according to claim 1 or 2, wherein the MEMS chip has a membrane structure in which the thickness in the displacement region and the support region is selectively reduced.
The displacement region is located in a region defined by a plurality of first slits formed in the membrane portion of the MEMS chip.
3. The support region according to claim 3, wherein the support region is formed in a membrane portion of the MEMS chip and is located in a region partitioned by a plurality of second slits arranged so as to surround the displacement region. Magnetic sensor.
The magnetism according to claim 4, wherein the piezoelectric layer is provided in both the displacement region and the region of the support region sandwiched between the first slit and the second slit. Sensor.
The sensor chip further includes first and second magnetic material layers.
The magnetic sensitive element is provided in the vicinity of a second magnetic gap formed by an end portion of the first magnetic material layer and an end portion of the second magnetic material layer.
The first external magnetic material overlaps with the first magnetic material layer without overlapping with the second magnetic material layer.
The magnetic sensor according to any one of claims 1 to 5, wherein the second external magnetic material does not overlap with the first magnetic material layer but overlaps with the second magnetic material layer.