WO2004070408A1

WO2004070408A1 - Magnetic sensor

Info

Publication number: WO2004070408A1
Application number: PCT/JP2004/001098
Authority: WO
Inventors: Yutaka Shimada; Junichi Hayasaka; Koichi Okamoto; Yoshiaki Ikeda
Original assignee: Nec Tokin Corporation
Priority date: 2003-02-04
Filing date: 2004-02-04
Publication date: 2004-08-19
Also published as: JPWO2004070408A1

Abstract

A small-sized, lightweight, highly-sensitive magnetic sensor with a simple sensing signal processing circuit. The sensor can be used as a portable direction sensor. The magnetic sensor comprises a piezoelectric body (102) which is provided on a major surface of a substrate (103) serving as a support and on which a magnetostrictive thin film (101) is formed. The magnetic sensor has a magnetostrictive element composed of a sensor structure (106) comprising a generally plate-shaped multilayer body having an electrode led out of the piezoelectric body (102). While the sensor structure (106) is mechanically vibrating as one piece because of the voltage applied to the piezoelectric body (102), the mechanical resonance frequency of the sensor structure (106) varies with a change of the external magnetic field (113), and the strength of the external magnetic field (113) is calculated from the amount of change of the resonance frequency.

Description

Description Magnetic sensor Technical field

The present invention relates to a small and highly sensitive magnetic sensor capable of detecting geomagnetism mounted on various industrial devices such as portable terminal devices, home electric appliances, automobiles, measuring devices, and the like. It relates to a magnetic sensor of the type that combines the method and the method. Background art

Conventionally, for example, a small and highly sensitive magnetic sensor capable of detecting a magnetic field on the order of terrestrial magnetism is an Ml sensor using a magnetic impedance element (MI element) using the skin effect in the band of several MHz to several hundred MHz, Alternatively, a flux gate sensor utilizing a change in the magnetic permeability of a soft magnetic material may be used. In the case of these magnetic sensors, the magnetic sensitivity generally tends to be significantly reduced as the size of the sensor is reduced due to the influence of the demagnetizing field of the magnetic material. Therefore, it is difficult for such an Ml sensor or a flux gate sensor to achieve both miniaturization and high sensitivity, and it is not applied to, for example, a portable direction sensor using geomagnetism.

On the other hand, as a magnetic sensor based on a principle different from the above-described MI sensor and flux gate sensor, a type combining a magnetostriction phenomenon and a piezoelectric detection method has been developed.

An example of such a type of magnetic sensor is a magnetic sensor using a magnetostrictive element disclosed in Japanese Patent Application Laid-Open No. 2000-88937, for example.

FIG. 1 is a schematic diagram showing a basic configuration of a magnetic sensor 14 according to an example of the related art. The magnetic sensor 14 is applied to current measurement in a substation or a transmission line, and a current J flowing through a conductor 15 at a distance r is expressed by a relational expression H = J / 2 π τ ( (A / m), the piezoelectric element 17 is distorted by the expansion of the magnetostrictive element 16 by combining the magnetostrictive element 16 and the piezoelectric element 17 so that the voltage can be detected. It has a function of converting, and is configured to measure the voltage value from the piezoelectric element 17 with a voltmeter 18.

That is, the basic principle of the magnetic sensor 14 disclosed in Japanese Patent Application Laid-Open No. 2000-88937 is that the elongation (shape change) of the magnetostrictive element 16 due to a change in an external magnetic field is integrated with it. This is detected as a voltage generated in the piezoelectric element 17. Therefore, the quality of the magnetic sensitivity greatly depends on the voltage generated in the piezoelectric element 17, and the generated voltage V depends on the piezoelectric stress constant g ₃₁ , the thickness t of the piezoelectric element 17, and the applied pressure P. V = g ₃ _X X t XP is represented by relational expression 1.

Further, as disclosed in Japanese Patent Application Laid-Open No. 2000-65098, a magnet that does not pole-reverse with respect to an external magnetic field, and a magnetic field strength applied to this magnet is detected as a mechanical force. Magnetic sensors having a piezoelectric element have also been developed.

FIG. 2 is a circuit block diagram showing a basic configuration of a magnetic detection system 1 including a magnetic sensor 2 according to another conventional example. The magnetism detection system 1 is composed of a plate-shaped piezoelectric element 21 having a back electrode 22 connected to the whole surface of one main surface, and a magnet that is not pole-reversed with respect to an external magnetic field at one end of the other main surface. By providing the magnetic sensor 23, the piezoelectric element 21 is provided with a magnetic sensor 2 configured to detect the magnetic field strength applied to the magnet 23 as a mechanical force, and also in accordance with the mechanical force applied to the piezoelectric element 21. An oscillation circuit 31 A whose oscillation frequency changes by means of an oscillator circuit, and means for measuring a change in the oscillation frequency of the oscillation circuit 31 A and displaying the magnetic field intensity detected by the magnetic sensor 2.

Also, in the magnetic detection system 1, a non-magnetic metal 24 is provided on the other side of the other main surface of the plate-shaped piezoelectric element 21 in the magnetic sensor 2, and the magnetic sensor 2 always operates at the reference frequency in a state where the external magnetic field is zero. Oscillation circuit 31 B is provided. That is, the oscillation circuit 31A is constructed by arranging the magnet 23 of the magnetic sensor 2, the piezoelectric element 21 and the CMOS inverter 32A in the feedback path, and the oscillation circuit 31B is made of non-magnetic metal. 24, the piezoelectric element 21 and the CMOS inverter 32B are arranged in the return path. Further, as a plurality of circuits (which may be collectively referred to as a detection signal processing circuit) for constructing the magnetic detection system 1, the oscillation circuit 31A CMOS inverter 32A output side is provided. Counter circuit 33 A connected to (grounded via a capacitor in the oscillation circuit 31 A), the output of the CMOS inverter 32 B of the oscillation circuit 31 B (similarly, the oscillation circuit 31 A Condensed within Counter circuit 3 3B, counter circuit 33 connected to the counter circuit 3) A subtraction circuit 3 that subtracts the difference between the number of pulses counted by the counter circuit 3 A and the number of pulses counted by the counter circuit 3 3B 4, Compensation circuit for compensating for pulse number difference 35, Calibration coefficient generation circuit 36 for generating calibration coefficient 36, Multiplication circuit 37 for multiplying output of compensation circuit 35 and calibration coefficient 37, Based on multiplied output value And a display device 38 for displaying the value of the external magnetic field detected by the magnetic sensor 2.

In short, the basic principle of the magnetic detection system 1 disclosed in Japanese Patent Application Laid-Open No. 2000-65098 is that when an external magnetic field H acts on the magnet 23 having a magnetic moment, the magnetic moment M and the external A torque T acting in the direction of the outer product (HXM) with the magnetic field H acts, and when the strength of the external magnetic field H increases, the torque T, which is a mechanical force, increases. A stress (torsional stress) is generated in the piezoelectric element 21 and the external magnetic field H is converted into a stress.

By the way, in the case of a magnetic sensor that combines the magnetostriction phenomenon and the piezoelectric detection method disclosed in Japanese Patent Application Laid-Open No. 2000-88973, the relational expression 1 shows that the generated voltage related to magnetic sensitivity is There is an inconvenience that it is proportional to the thickness and decreases as the piezoelectric element becomes thinner. In order to suppress the drop in the generated voltage, the thickness and thickness of the piezoelectric element are maintained, and even when the size of the piezoelectric element is reduced, the length and width of the piezoelectric element relative to the thickness of the piezoelectric element are reduced with the size reduction. Since the size of the piezoelectric element becomes short and the piezoelectric element itself becomes difficult to bend, the generated voltage is further reduced due to a decrease in the pressure expressed by the relational expression 1. Due to these results, there is a problem that it is difficult to satisfy both miniaturization and high sensitivity at the same time.

In addition, a magnet that does not undergo pole reversal with respect to an external magnetic field and a piezoelectric element that detects a magnetic field intensity applied to the magnet as a mechanical force disclosed in Japanese Patent Application Laid-Open No. 2000-65098 are provided. In the case of a magnetic detection system using a magnetic sensor, the torque (HXM) generated in the magnet in principle is a moment, so that a relatively large area is required in the area of the piezoelectric element in order to receive it efficiently with the piezoelectric element. I need. If the sensor is based on such an operation principle, the size of the sensor is inevitably large even when configured as a differential type, which is not suitable for miniaturization. . Therefore, an object of the present invention is to solve such problems, and An object of the present invention is to provide a high-sensitivity magnetic sensor which can be applied to a position sensor or the like and which is provided with a simple detection signal processing circuit and which is reduced in size and weight. Disclosure of the invention

According to the present invention, the sensor structure includes a sensor structure which is a magnetostrictive element, and the sensor structure is in a state where the sensor structure is mechanically vibrating as a unit, and the sensor structure is changed with an external magnetic field change. The mechanical resonance frequency changes, and a magnetic sensor that calculates the external magnetic field amount from the change amount of the resonance frequency is obtained.

Further, according to the present invention, in the above magnetic sensor, a magnetic sensor comprising a magnetostrictive thin film as the magnetostrictive element is obtained.

Furthermore, according to the present invention, in the above magnetic sensor, a magnetic sensor is obtained in which the magnetostrictive element is formed of a laminated body including a magnetostrictive thin film and a support. In this magnetic sensor, the support is one of a piezoelectric plate made of a piezoelectric material, a silicon plate, and a non-magnetic metal plate, and the support is a cantilever structure, a doubly supported structure, or a diaphragm structure. It is preferable to have any one of the support structures.

In addition, according to the present invention, in the magnetic sensor, the magnetostrictive element includes a piezoelectric body having a magnetostrictive thin film laminated on one main surface of a support as a sensor structure. While the sensor structure is mechanically vibrating integrally with the applied voltage, the mechanical resonance frequency of the sensor structure changes with an external magnetic field change, and the resonance A magnetic sensor that calculates the external magnetic field amount from the frequency change amount is obtained.

Further, according to the present invention, in the above magnetic sensor, the sensor structure includes a substantially plate-shaped laminate having electrodes on the other main surface of the support, and a voltage is applied between the magnetostrictive thin film and the electrodes. Is obtained.

On the other hand, according to the present invention, in any one of the above magnetic sensors, the change in the mechanical resonance frequency of the sensor structure is obtained by changing the Young's modulus of the magnetostrictive thin film with a change in the external magnetic field. A sensor is obtained.

On the other hand, according to the present invention, in any one of the above magnetic sensors, a magnetic field applying means for applying an external magnetic field is provided in advance in a width direction of the magnetostrictive thin film, A magnetic sensor is obtained in which the direction is set at about 40 to 50 degrees with respect to the width direction of the magnetostrictive thin film. In this magnetic sensor, the magnetic field applying means is preferably a permanent magnet or an electromagnet.

Further, according to the present invention, in any one of the magnetic sensors described above, a detection signal processing circuit for detecting a mechanical resonance frequency of the sensor structure is provided, and the detection signal processing circuit includes the sensor structure A self-excited oscillation circuit that includes a sensor unit, an amplification circuit, and a phase shift circuit; and an oscillation frequency that is connected between the amplification circuit and the phase shift circuit and that is output from the self-excited oscillation circuit, is converted to a voltage. Thus, a magnetic sensor including a frequency-voltage conversion circuit unit that performs the above-described operation is obtained.

Further, according to the present invention, in any one of the magnetic sensors described above, the magnetic sensor further includes a detection signal processing circuit for detecting a mechanical resonance frequency of the sensor structure. A self-excited oscillation circuit section comprising a sensor section, an amplifier circuit, and a phase shift circuit, which are included as a sensor structure, and a laminate made of a non-magnetostrictive thin film or a laminate made of a non-magnetostrictive thin film and a support A second sensor structure that oscillates at a constant reference frequency without changing a mechanical resonance frequency in response to an external magnetic field change, a sensor unit including the second sensor structure, and an amplifier circuit. , And a second self-excited oscillation circuit including a phase shift circuit; an oscillation frequency output from the first self-excited oscillation circuit; a reference frequency output from the second self-excited oscillation circuit; Amplifying the difference between Thus, a magnetic sensor including a differential amplifier circuit that outputs a differential signal and a frequency Z voltage conversion circuit that converts the differential frequency output from the differential amplifier circuit to a voltage can be obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic diagram showing a basic configuration of a magnetic sensor according to a conventional example, and FIG. 2 is a circuit block diagram showing a basic configuration of a magnetic detection system including a magnetic sensor according to another conventional example. And

3 (a), 3 (b) and 3 (c) are side sectional views showing a basic configuration of a magnetic sensor according to an embodiment of the present invention.

Fig. 4 shows the resonance frequency for the external magnetic field in the magnetic sensor shown in Fig. 3 (b). This shows the output characteristics expressed as a number

Fig. 5 is a schematic diagram showing the basic configuration and operation functions when the magnetic sensor shown in Fig. 3 (b) is provided with a function of discriminating the sign of the magnetic detection direction, and (a) shows the external magnetic field. (B) relates to the case where the external magnetic field is applied in the positive direction, (c) relates to the case where the external magnetic field is applied in the negative direction, and FIG. FIG. 7 is a circuit block diagram showing the basic configuration of a detection signal processing circuit for detecting the mechanical resonance frequency of the sensor structure of the magnetic sensor shown in FIG. 3 (b). FIG. 4 is a circuit block diagram illustrating a basic configuration of another detection signal processing circuit for detecting a mechanical resonance frequency of a sensor structure of the magnetic sensor illustrated in FIG. BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference to the accompanying drawings. In the case of the magnetic sensor of the present invention, a brief description of the technical outline of the magnetic sensor is that the magnetic sensor is composed of a sensor structure, which is a magnetostrictive element, and the sensor structure integrally vibrates mechanically. In this state, the mechanical resonance frequency of the sensor structure changes with the change of the external magnetic field, and the amount of the external magnetic field is calculated from the change of the resonance frequency. However, the magnetostrictive element here may be composed of a magnetostrictive thin film (or a laminate thereof) or a laminate of a magnetostrictive thin film and a support.

FIGS. 3 (a) and 3 (b) are side sectional views showing a basic configuration of the magnetic sensor according to the first embodiment of the present invention. The magnetic sensor shown in FIG. 3 (a) includes a piezoelectric body 102 in which a magnetostrictive thin film 101 is laminated on one main surface of a substrate 103 as a support, and an electrode is formed from the piezoelectric body 102. It has a sensor structure 106 composed of a substantially plate-like laminate that is drawn out, and the sensor structure 106 is mechanically vibrated as a body by the voltage applied to the piezoelectric body 102. The mechanical resonance frequency of the sensor structure 106 changes with the change of the external magnetic field 113, and the amount of the external magnetic field 113 changes from the change in the resonance frequency. Is calculated.

As shown in FIG. 3 (b), the substrate 103 here is made up of the piezoelectric body 102 itself. In this case, the sensor structure 106 has a magnetostrictive thin film 101 laminated on one main surface of the piezoelectric body 102 and a voltage is applied to the piezoelectric body 102 on the other main surface. The magnetostrictive element is configured as a substantially plate-shaped magnetostrictive element including an electrode 104 for performing the operation, and a voltage is applied between the magnetostrictive thin film 101 and the electrode 104.

In the case of these magnetic sensors, when an external magnetic field 113 is applied, the Young's modulus of the magnetostrictive thin film 101 (the so-called elongation elastic modulus, the longitudinal elastic modulus) is accompanied by the magnetostrictive effect of the magnetostrictive thin film 101. ) Changes (due to the ΔΕ effect of the ferromagnetic material described later), and as a result, the resonance frequency of the sensor structure 106 having the magnetostrictive thin film 101 and the piezoelectric material 102 changes.

That is, the sensor structure 106 can be considered as a composite beam of the magnetostrictive thin film 101 and the piezoelectric thin film of the piezoelectric body 102, and its resonance frequency f. The change amount Δf of the magnetostrictive thin film 101 is t _f , the Young's modulus of the magnetostrictive thin film 101 is E _f , and the density of the magnetostrictive thin film 101 is p. the thickness of the thin film) t _s, the Young's modulus of the piezoelectric 1 02 E _s, when the density p _s of the piezoelectric body 1 02, Δ f = (t f · f 0/2 t s) X [(3E _f / E _s )-(p _f / p _s )] = a '(b' · E "c ').

However, here, a '= a _{_{t f · f 0/2 t}} s relational expression 3, b' = 3 / and E _s relational expression _{4, c '= p f Zp} s relational expression 5 and is satisfied I do.

From the above relational expressions 2 to 5, when the Young's modulus E _f of the magnetostrictive thin film 101 composed of the magnetostrictive thin film 101 and the piezoelectric body 102 changes due to the external magnetic field 113, Accordingly, the resonance frequency f of the composite beam. It can be seen that the variation Δf of the resonance frequency changes (the effect of the variation Δf of the resonance frequency f ₀ is large).

The ΔΕ effect of a ferromagnetic material can be calculated as follows: According to the well-known document “Kanaku, Physics of Ferromagnetic Materials (Bottom), Kyobo Sho, p. As a result, extra elongation is generated due to the rotation of spontaneous magnetization due to tension, thereby lowering the Young's modulus E _f This effect is called the ΔΕ effect, and the ΔE effect is caused by the presence of magnetostriction λ. It is proportional to. "

Considering the magnetic sensor of the present invention, when an external magnetic field 113 is applied to the sensor structure 106, the spontaneous magnetization rotates along the direction of the external magnetic field 113. Therefore, the magnetostrictive thin film 101 elongates, and the Young's modulus E _f decreases accordingly. For this reason, when the external magnetic field 113 changes, the resonance frequency of the composite beam of the sensor structure 106 decreases according to the relational expression 3. The change in the resonance frequency f ₀ of the composite beam here is also caused by the shape change due to the magnetostriction of the magnetostrictive thin film 101, and the resonance frequency f as the sensor output. The amount of change △ f is caused by the integral vibration change of the sensor structure 106. In order to improve the sensor sensitivity △ f ZH _ex of the magnetic sensor, it is necessary to increase the value of a ′ shown in the relational expression 3 in the sensor design, that is, the thickness t _f of the magnetostrictive thin film 101 and the piezoelectric thin film of the piezoelectric body 102 The ratio t _f Zt _s to the thickness t _s of the sensor structure 106 and the resonance frequency f of the composite beam of the sensor structure 106. Must be increased. The resonance frequency f of the composite beam of the sensor structure 106. In order to enhance itself, for example, when the fundamental mode of the piezoelectric body 102 is longitudinal vibration, the length of the piezoelectric body 102 is reduced, and when the fundamental mode of the piezoelectric body 102 is thick vibration, In this case, the thickness of the vibrator (piezoelectric body 102) may be reduced.

In the magnetic sensor of the present invention as well, as long as a magnetic thin film is used, the influence of a demagnetizing field cannot be avoided in principle. However, compared to conventional Ml sensors and fluxgate sensors, the sensor sensitivity △ i / H _ex Is considered to have a small effect. That is, as shown in the above-mentioned relational expression 2, even if the variation of the term of the Young's modulus E _f of the magnetostrictive thin film 101 related to the demagnetizing field is small, the thickness t _s of the piezoelectric thin film and the thickness of the magnetostrictive thin film 101 are small. the percentage t _f Zt _s and the resonant frequency f Q is or sufficiently large with t _f, or is higher, it is possible to maintain a high sensor sensitivity Δ fZHex.

When manufacturing the magnetic sensor shown in Fig. 3 (b), first, RF sputtering or the like is performed on a piezoelectric substance 102 on a-18.5 degree X-Cut quartz plate (corresponding to the substrate 103) with a thickness of about 50 m. A Co—Fe—Zr-based magnetostrictive thin film 101 having a thickness of about 1 m is deposited by using the film forming technique described above. Here, Co- Fe- Z r based stoichiometric composition of the magnetostrictive film 101, for example, 50: 35: 15 and the magnetostriction constant lambda s at that time are 25X 10_ about ^6, used as the piezoelectric 102 Yes— 18.5 degrees X—Cut Let the fundamental vibration mode of the quartz plate (corresponding to substrate 103) be longitudinal vibration.

Next, the electrode 104 is formed on the entire opposite surface of the 18.5 degree X-Cut quartz plate to form the sensor structure 106, and its resonance frequency f. Is roughly the sensor structure 1 It is determined by the length of 06. For example, if the length of the piezoelectric body 102 (the length of the sensor structure 106) is about 12 mm, the resonance frequency f ₀ of the sensor structure 106 is about 200 (kHz).

The magnetic sensor according to Example 2 shown in FIG. 3C has a sensor structure 106 formed by laminating a magnetostrictive thin film 101 on one main surface of a substrate 103 as a support. Substrate 103 is a support, a quartz plate, a piezoelectric ceramic plate typified by PZT, L INb_〇 ₃ plate, a silicon substrate, or stainless steel and T i, Cu, C r, Au, non-magnetic metal plate such as A 1 It is desirable that

When a silicon substrate or a non-magnetic metal plate is used, the mechanical resonance state can be reduced if any one of a cantilever structure (a cantilever structure), a cantilever structure, and a diaphragm structure is employed. In order to generate it, it can be easily driven by an electrostatic, electromagnetic, or thermal excitation method such as an electrostatic drive method or a light detection method. Even when the piezoelectric material is used as a support, not only a flat plate but also one of a cantilever structure, a doubly supported structure, and a diaphragm structure is employed. It is desirable to generate a mechanical resonance state (the driving method technology for these various structures is well known, and thus description thereof is omitted). However, in this case, it is preferable that the electrode is directly provided on the magnetostrictive thin film 101 or the substrate 103 as a support, or is directly drawn out.

FIG. 4 shows the resonance frequency f with respect to the external magnetic field _Hex in the magnetic sensor described above. It shows the output characteristics (sensor output) expressed by the relationship.

According to FIG. 4, the sensor output changes at the resonance frequency f with respect to the change of the external magnetic field 113. And a nearly linear relationship is obtained.

Also, in general, the relationship between the magnetostriction and the Young's modulus of the ferromagnetic material is proportional, in order to increase the sensor sensitivity delta f ZH _ex magnetic sensor, it may be preferable to apply a material having a large magnetostriction constant Can be Therefore, for example, a TbDyFe alloy having a high magnetostriction constant has recently been developed. However, these materials are generally not preferable because the magnetic bias point where the magnetostriction phenomenon occurs is as high as several hundred Oe or more.

On the other hand, magnetic materials such as Fe-Si-B, Fe-Co, or Fe-Ni-based thin films have not only high absolute values of magnetostriction constant but also high magnetic permeability. In addition, it has a high magnetostriction constant on the low magnetic field side of several 〇e or less, and can reduce the magnetic bias point. Therefore, it is suitable for the magnetic sensor material of the present invention.

FIG. 5 is a schematic diagram showing a basic configuration and an operation function when the magnetic sensor described above has a function of determining whether the magnetic detection direction is positive or negative. FIG. 5 (a) shows a case where an external magnetic field is not applied. Fig. 2 (b) shows the case where the external magnetic field 113 is applied in the positive direction, and Fig. 2 (c) shows the case where the external magnetic field 120 is applied in the negative direction. .

Here, the width of the magnetostrictive thin film 1 22 in the sensor structure 124 equivalent to the sensor structure 16 is provided so that the magnetic sensor of the above embodiment has a function of discriminating the sign of the magnetic detection direction. Permanent magnets (or electromagnetic coils) for applying an external magnetic field in advance in the direction are provided, and a bias magnetic field is applied to the magnetostrictive thin film 122. The configuration is such that the vibration direction 1 18 of 1 23 is set at 45 degrees with respect to the width direction of the magnetostrictive thin film 1 22.

To explain the principle of the method of discriminating the sign of the magnetic detection direction in such a configuration, first, as shown in FIG. 5 (a), when no external magnetic field is applied (when there is no magnetic signal due to the external magnetic field), According to 14 and 1 16, the rotational magnetization 1 17 is almost oriented in the width direction of the magnetostrictive thin film 1 2 2, and the vibration direction 1 18 of the piezoelectric body 1 2 3 is in the direction of the magnetostrictive thin film 1 2 2 It is in a state of tilting 45 degrees. This state is due to the magnetostriction phenomenon caused by the application of the magnetic bias in the width direction of the magnetostrictive thin film 122 compared with the case where the permanent magnets 114 and 116 described in FIG. 3 are not provided. Although the Young's modulus E _f of the magnetostrictive film 1 is low, the magnetostriction direction of the magnetostrictive thin film 1 2 2 is inclined by 45 degrees with respect to the vibration direction 1 1 8 of the piezoelectric material 1 2 3. It can be said that the Young's modulus E _f in the vibration direction 1 18 of ₂₃ is increasing. Therefore, in this configuration, the resonance frequency f ₀ is higher than in the configuration shown in FIG.

Next, when an external magnetic field 113 is applied in the positive direction as shown in Fig. 5 (b), the direction of the rotational magnetization 119 is parallel to the vibration direction 118 of the piezoelectric body 123. Accordingly, the magnetostriction of the magnetostrictive thin film 122 in the vibration direction 118 of the piezoelectric body 123 increases, and the Young's modulus E _f further decreases. Therefore, in this case Resonant frequency f. Will decrease.

Furthermore, when the external magnetic field 120 is applied in the negative direction, as shown in FIG. 5 (c), the direction of the rotational magnetization 121 is relative to the vibration direction 118 of the piezoelectric body 123. As a result, the magnetostriction of the magnetostrictive thin film 122 in the vibration direction 118 of the piezoelectric body 123 decreases, and the Young's modulus _Ef increases. Therefore, the resonance frequency f in this case. Will increase.

According to FIGS. 5 (a) to 5 (c), the permanent magnets 114 and 116 are provided so that an external magnetic field can be applied in the width direction of the magnetostrictive thin film 122, and the vibration of the piezoelectric body 123 If the direction 118 is set at 45 degrees with respect to the width direction of the magnetostrictive thin film 122, the magnetic detection direction can be determined. According to various experimental results, the vibration direction 118 of the piezoelectric body 123 is set in a direction inclined at about 40 to 50 degrees with respect to the width direction of the magnetostrictive thin film 122. It was found that the magnetic detection direction could be determined with the configuration described above.

FIG. 6 is a circuit block diagram showing a basic configuration of a detection signal processing circuit for detecting a mechanical resonance frequency of the sensor structure 106 described above. The detection signal processing system circuit here includes a self-excited oscillation circuit section including a sensor section 7 including a sensor structure 106, an amplification circuit 8, and a phase shift circuit 9, and a self-excited oscillation circuit section. A frequency Z voltage conversion circuit (FZV converter) 10 is connected between the amplification circuit 8 and the phase shift circuit 9 and converts the oscillation frequency output from the self-excited oscillation circuit into a voltage. You. An example of the configuration of the simple self-excited oscillation circuit section can be realized by disposing the sensor section 7 in the feedback circuit of the CMOS sensor.

FIG. 7 is a circuit block diagram showing a basic configuration of another detection signal processing circuit for detecting the mechanical resonance frequency of the sensor structure 106 described above. The detection signal processing system circuit here includes a first self-excited circuit including a sensor section 7 including the sensor structure 106 as a first sensor structure, an amplifier circuit 8, and a phase shift circuit 9. It consists of an oscillation circuit section 11 and a laminated body composed of a non-magnetostrictive thin film or a laminated body composed of a non-magnetostrictive thin film and a support, and has a constant reference frequency without a change in mechanical resonance frequency in response to an external magnetic field change. A second self-excited circuit comprising a schematic second sensor structure that oscillates, a sensor unit including the second sensor structure, an amplifier circuit, and a phase shift circuit. An oscillation circuit section 12 is provided. The detection signal processing system circuit is provided between the amplifier circuit 8 and the phase shift circuit 9 in the first self-excited oscillation circuit section 11, and the amplifier circuit and the phase shift circuit in the second self-excited oscillation circuit section 12. The difference between the oscillation frequency output from the first self-excited oscillation circuit section 11 and the reference frequency output from the second self-excited oscillation circuit section 12 is amplified by It has a differential amplifier circuit 13 that outputs a frequency, and a frequency Z voltage conversion circuit unit (F / V converter) 10 that converts the differential frequency output from the differential amplifier circuit 13 into a voltage. I have.

In the case of such a differential detection signal processing circuit that obtains the difference between the oscillation frequency of the first self-excited oscillation circuit 11 and the reference frequency of the second self-excited oscillation circuit 12, Since a change in shape and a change in Young's modulus of the magnetostrictive thin film 101 due to the change can be corrected, magnetic field measurement can be performed with higher accuracy. The non-magnetostrictive thin film used in the other sensor structure here is almost equal to the magnetostrictive thin film 101 to which various material constants such as heat capacity, thermal conductivity, and thermal expansion coefficient are applied in addition to the shape. It is preferable to select As an example, when the magnetostrictive thin film 101 is a Fe—Co thin film, thin films such as Au, A 1, Cu, Cr, and Ti can be cited as non-magnetostrictive thin films.

In short, in the case of the magnetic sensor of the present invention, as described with reference to FIG. 3, when the sensor structure, which is the magnetostrictive element, is mechanically vibrating integrally, Since the mechanical resonance frequency of the sensor structure changes with the change, and the external magnetic field amount is calculated from the change amount of the resonance frequency, the size and weight can be reduced, and the sensitivity is high. It has sensor characteristics. In particular, in this magnetic sensor, a magnetic field applying means for applying an external magnetic field in advance in the width direction of the magnetostrictive thin film is provided, and the vibration direction of the piezoelectric body is inclined by about 40 to 50 degrees with respect to the width direction of the magnetostrictive thin film. If the configuration is such that the magnetic detection direction can be determined as the configuration for setting the direction, it is suitable for application to various industrial equipment such as a portable direction sensor. Also, in this magnetic sensor, the detection signal processing circuit has the configuration described with reference to FIG. 6 or the differential type configuration described with reference to FIG. It can be done easily.

Claims

The scope of the claims

1. Consisting of a sensor structure that is a magnetostrictive element, in a state where the sensor structure is mechanically vibrating as a unit, and the mechanical resonance frequency of the sensor structure in accordance with an external magnetic field change Wherein the external magnetic field amount is calculated from the change amount of the resonance frequency.

2. The magnetic sensor according to claim 1, wherein the magnetostrictive element is made of a magnetostrictive thin film.

3. The magnetic sensor according to claim 1, wherein the magnetostrictive element is formed of a laminated body including a magnetostrictive thin film and a support.

4. The magnetic sensor according to claim 3, wherein the support is one of a piezoelectric plate made of a piezoelectric material, a silicon plate, and a non-magnetic metal plate.

5. The magnetic sensor according to claim 4, wherein the support has any one of a cantilever structure, a doubly supported structure, and a diaphragm structure.

6. The magnetic sensor according to claim 3, wherein the magnetostrictive element includes a piezoelectric body in which the magnetostrictive thin film is laminated on one main surface of the support as the sensor structure. When the sensor structure is mechanically vibrating as a unit by the voltage applied to the body, the mechanical resonance frequency of the sensor structure changes with an external magnetic field change, A magnetic sensor which calculates an external magnetic field amount from the change amount of the resonance frequency.

7. The magnetic sensor according to claim 3, wherein the sensor structure includes a substantially plate-shaped laminate having an electrode on the other main surface of the support, and the sensor structure includes a gap between the magnetostrictive thin film and the electrode. A magnetic sensor to which a voltage is applied.

8. The magnetic sensor according to any one of claims 2 to 7, wherein a change in a mechanical resonance frequency of the sensor structure changes a Young's modulus of the magnetostrictive thin film with a change in the external magnetic field. A magnetic sensor characterized by being obtained by:

9. The magnetic sensor according to any one of claims 2 to 8, wherein the magnetostrictive thin film is used. A magnetic field applying means for applying an external magnetic field is provided in advance in the width direction, and the vibration direction of the piezoelectric body is set to a direction inclined about 40 to 50 degrees with respect to the width direction of the magnetostrictive thin film. A magnetic sensor.

10. The magnetic sensor according to claim 9, wherein the magnetic field applying means is a permanent magnet or an electromagnet.

11. The magnetic sensor according to any one of claims 1 to 10, further comprising a detection signal processing circuit for detecting a mechanical resonance frequency of the sensor structure, wherein the detection signal processing circuit is A self-excited oscillation circuit unit including a sensor unit including the sensor structure, an amplifier circuit, and a phase shift circuit; and a frequency / voltage converter for converting an oscillation frequency output from the self-excited oscillation circuit unit to a voltage. A magnetic sensor comprising a circuit unit.

12. The magnetic sensor according to any one of claims 1 to 10, further comprising: a detection signal processing circuit for detecting a mechanical resonance frequency of the sensor structure, wherein the detection signal processing circuit A first self-excited oscillation circuit unit including a sensor unit including the sensor structure as a first sensor structure, an amplifier circuit, and a phase shift circuit; and a laminate of a non-magnetostrictive thin film or a non-magnetostrictive thin film A second sensor structure that oscillates a constant reference frequency without changing a mechanical resonance frequency in response to an external magnetic field change; and A second self-excited oscillation circuit including a sensor unit, an amplification circuit, and a phase shift circuit, the oscillation frequency output from the first self-excited oscillation circuit, and the second self-excited oscillation circuit. The reference frequency output from the oscillation circuit section A differential amplifier circuit that amplifies the difference between the differential frequencies and outputs the differential frequency as a differential frequency; and a frequency / voltage conversion circuit unit that converts the differential frequency output from the differential amplifier circuit into a voltage. A magnetic sensor characterized by the above-mentioned.