JPH1096742A - Acceleration sensor, manufacture thereof, and impact detecting device utilizing the acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized acceleration sensor of which sensitivity is high extending over a wide frequency territory and dispersion of characteristic such as sensitivity is very small. SOLUTION: The main faces of piezoelectric substrates 2a, 2b having opposite two main faces and rectangular form of thickness 50μm, width 0.5mm, length 2mm, and made of LiNbO3 are joined together so that the directions of polarization axes are opposite to each other, and hence a piezoelectric element 2 is constituted. Supporting bodies 4a, 4b made of LiNbO3 are directly joined to one end of the piezoelectric element 2. Electrodes 3a, 3b made of chrome-gold of thickness 0.2μm are continuously formed on the opposite two main faces of the piezoelectric element 2 and the supporting bodies 3a, 3b, so as to constitute a bimorph type electromechanical converter 1 of cantilever construction.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor used for measuring acceleration and detecting vibration, and a method for manufacturing the same. More specifically, the present invention relates to a small and high-performance acceleration sensor and a method for manufacturing the same. Further, the present invention relates to an impact detection device using such an acceleration sensor and having a small output signal variation.

2. Description of the Related Art In recent years, miniaturization of electronic devices has progressed, and portable electronic devices such as notebook computers have become widespread. In order to secure and improve the reliability of these electronic devices against impacts, there is an increasing demand for small-sized, surface-mountable high-performance acceleration sensors. For example, if an impact is applied during a write operation to a high-density hard disk, a head displacement may occur, which may cause a data write error or damage to the head. For this reason, there is a need for a technique for detecting the impact applied to the hard disk, stopping the writing operation, and retracting the head to a safe position. Also,
In order to protect the occupants from the impact in the event of a collision of a car, demand for an acceleration sensor for impact detection of an airbag device and the like is increasing. In addition, there has been an increasing demand for mechanisms that detect the impact on small portable devices and provide mechanisms to prevent device failure and malfunction due to the impact, and to record the fact that the impact has been applied. I have. For this reason, the need for small acceleration sensors used in these devices has been increasing. Conventionally, as an acceleration sensor,
A device using a piezoelectric material such as a piezoelectric ceramic is known. If these acceleration sensors are used, high detection sensitivity can be realized by utilizing the electromechanical conversion characteristics of the piezoelectric material. A piezoelectric acceleration sensor converts a force due to acceleration or vibration into a voltage by a piezoelectric effect and outputs the voltage. As such an acceleration sensor,
There is one using a rectangular bimorph-type electromechanical transducer having a cantilever structure as disclosed in JP-A-2-248086. As shown in FIG. 26, a bimorph-type electro-mechanical transducer 50 utilizing the piezoelectric effect includes an electrode 52
The piezoelectric ceramics 51a and 51b on which a and 52b are formed are bonded together with an adhesive 53 such as an epoxy resin. As shown in FIG. 27, in the cantilever structure, one end of a bimorph-type electromechanical transducer 50 is bonded and fixed to a fixing member 55 with a conductive adhesive 54 or the like. Bimorph-type electro-mechanical transducers having a cantilever structure are used to measure acceleration having a relatively low frequency component because of its low resonance frequency. Also, when measuring acceleration in a high frequency region, as shown in FIG.
A bimorph-type electromechanical transducer 50 having a double-supported beam structure in which both ends are bonded and fixed to a fixing member 55 with a conductive adhesive 54 or the like is used. By fixing both ends of the electromechanical transducer, the resonance frequency can be made relatively high. The acceleration sensor is configured by housing the electromechanical transducer 50 in the container with the fixing member 55 fixed to the inner wall of the container. Also, the mechanical-electrical transducer 50
Generated on the electrodes 52a and 52b of the conductive adhesive 5
4 and are taken out to the external electrode.

As described above, in the conventional acceleration sensor, an adhesive made of epoxy resin or the like is used for bonding the piezoelectric ceramic, but the Young's modulus of the piezoelectric ceramic is 15 × 10 ^-12. larger the Young's modulus of the epoxy resin and 200 × 10 ^-12 m ² / N as compared to m ² / N, the machine according to the acceleration is applied - distortion of the electrical transducer is absorbed by the epoxy resin, the sensitivity is lowered Would. Further, since it is difficult to adhere the piezoelectric ceramics with the thickness of the adhesive layer being uniform, there is a problem that the characteristics of the electromechanical transducer vary.
Further, in order to stabilize the sensitivity of the rectangular bimorph-type electromechanical transducer, it is necessary to stabilize its resonance frequency. In this case, it is necessary to stabilize the fixed state of the electromechanical transducer. However, in practice, the supporting portion such as a metal or the like is mechanically or caused by stress generated by a temperature change or the like. The part supported or fixed by the fixing member is displaced. For example, when the electromechanical transducer is fixed using an adhesive, the fixing position changes depending on the application range of the adhesive, and the resonance frequency of the electromechanical transducer varies. In addition, the fixed state of the electromechanical transducer fluctuates due to a change in the temperature of the adhesive, and it becomes difficult to maintain a stable fixed state. In the case where each of the electromechanical transducers is manufactured separately and accommodated in a container, handling becomes difficult in the manufacturing process, so that downsizing of the acceleration sensor is hindered and mass productivity is reduced. There is a problem of inviting. Further, since the piezoelectric ceramic is manufactured by mixing and firing various raw materials, the variation in material constant is larger than that of a single crystal material. Therefore, when an acceleration sensor is manufactured using piezoelectric ceramics, the sensitivity and the capacitance greatly vary. In addition, when an acceleration sensor using piezoelectric ceramic is used to detect an impact applied to a portable device or the like, the sensitivity varies greatly.
The range of the magnitude of the acceleration, which is a reference for avoiding the failure of the device due to the impact, becomes large, and it becomes difficult to detect the impact with high accuracy. Further, the variation in capacitance makes it difficult to design a circuit that is connected to the acceleration sensor and amplifies the electric signal generated by the acceleration, and causes variation in the degree of amplification of the circuit. As a result, the output signal greatly varies, which hinders use in an impact detection device. The present invention has been made in order to solve the above-mentioned problems in the prior art, and provides a small-sized acceleration sensor having high sensitivity over a wide frequency range and having extremely small variation in characteristics such as sensitivity, and a method for manufacturing the same. The purpose is to: Another object of the present invention is to provide an impact detection device using such an acceleration sensor and having a small output signal variation.

In order to achieve the above object, a first configuration of an acceleration sensor according to the present invention is such that the main surfaces of at least two piezoelectric substrates having two opposing main surfaces are directly bonded to each other. A piezoelectric element comprising a piezoelectric element configured as described above, electrodes formed on two opposing main surfaces of the piezoelectric element, and a support for supporting the mechanical-electric converter. It is. According to the first configuration of the acceleration sensor, the electromechanical transducer is formed by directly bonding the piezoelectric substrate without using an adhesive layer such as an adhesive, and therefore, the electromechanical transducer is configured by acceleration. When bending vibration occurs, there is no one that absorbs the bending vibration. For this reason, stress is generated in the piezoelectric substrate without loss, and a large starting force is obtained. As a result, an acceleration sensor having high sensitivity can be realized. Also, since the bonding of the piezoelectric substrates becomes uniform, the mechanical
Variations in the resonance frequency and sensitivity of the electric transducer become extremely small. Further, since no adhesive layer is interposed between the piezoelectric substrates, the vibration characteristics of the electromechanical transducer do not change due to a temperature change. In the first configuration of the acceleration sensor according to the present invention, the main surfaces of the two piezoelectric substrates are
It is preferable that the constituent atoms of the two piezoelectric substrates are joined to each other by bonding to each other via at least one selected from the group consisting of oxygen and a hydroxyl group. According to this preferred example, it is possible to realize a state in which the main surfaces of the two piezoelectric substrates are firmly and directly joined at the atomic level.
In the first configuration of the acceleration sensor according to the present invention, it is preferable that the two piezoelectric substrates are joined so that the directions of the polarization axes are opposite to each other. According to this preferred example, electric charges of the same polarity are generated in the two piezoelectric substrates even though the stress generated in the two piezoelectric substrates is different from the compressive stress and the tensile stress. That is, electromotive force is generated in the two piezoelectric substrates in the same direction. For this reason,
A signal reflecting the magnitude of acceleration can be obtained from the electrodes formed on both surfaces of the electromechanical transducer. In the first configuration of the acceleration sensor according to the present invention, it is preferable that the two piezoelectric substrates are directly joined via a buffer layer. According to this preferred example, even when the joint surface has undulations or irregularities, or when foreign matter such as dust is attached to the joint surface, the irregularities and the like are absorbed by the buffer layer. Is obtained. In addition, even when a material that does not easily form an oxygen or a hydroxyl group on the surface by the hydrophilic treatment is bonded, a strong direct bonding surface can be obtained by bonding via a buffer layer. In the first configuration of the acceleration sensor according to the present invention, it is preferable that one end of the electromechanical transducer is supported by a support. According to this preferred example, it is possible to realize an acceleration sensor having a cantilever structure. Further, in the first configuration of the acceleration sensor according to the present invention, it is preferable that both ends of the electromechanical transducer are supported by a support. According to this preferred example, an acceleration sensor having a doubly supported structure can be realized. Then, even if the electromechanical transducers have the same length and the same thickness, the resonance frequency is higher than in the case of the cantilever structure, so that it is possible to measure the acceleration in a higher frequency region. In the first configuration of the acceleration sensor according to the present invention, the piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of 3m group, and the crystal axes of the single-crystal piezoelectric material are defined as an X axis, a Y axis, and a Z axis. At this time, the angle between the main surface of the piezoelectric substrate and the Y axis is perpendicular to the axis of + 129 ° to + 152 ° and includes the X axis, and the line connecting the center of gravity of the piezoelectric substrate and the center of the supporting portion is the X axis. It is preferably perpendicular to. According to this preferred example, the piezoelectric constant of the piezoelectric substrate is 90, which is the maximum value.
１００100%, and there is no problem due to sensitivity deterioration. In the first configuration of the acceleration sensor according to the present invention, the piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of 3m group, and the crystal axis of the single-crystal piezoelectric material is X-axis.
When the Y-axis and the Z-axis are used, the angle between the main surface of the piezoelectric substrate and the Y-axis is perpendicular to the axis of −26 ° to + 26 °, and includes the X-axis. It is preferable that the line connecting the center is parallel to the X axis. According to this preferred example, the piezoelectric constant of the piezoelectric substrate is a value of 90 to 100% of the maximum value, and there is no problem due to deterioration in sensitivity. In the first configuration of the acceleration sensor according to the present invention, the piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of Group 32, and the crystal axes of the single-crystal piezoelectric material are defined as an X axis, a Y axis, and a Z axis. In some cases, the main surface of the piezoelectric substrate is perpendicular to the X axis, and the line connecting the center of gravity of the piezoelectric substrate and the center of the support is +52 from the Z axis.
It is preferable to form an angle of ゜ to + 86 °. According to this preferred example, the piezoelectric constant of the piezoelectric substrate is 90 to 10 which is the maximum value.
The value is 0%, and there is no problem due to sensitivity deterioration. In the first configuration of the acceleration sensor according to the present invention, the piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of Group 32, and the crystal axes of the single-crystal piezoelectric material are X-axis, Y-axis,
When the Z-axis is set, the angle formed by the main surface of the piezoelectric substrate and the X-axis is perpendicular to the axis of −26 ° to + 26 °, includes the Y-axis, and defines the center of gravity of the piezoelectric substrate and the center of the supporting portion. Preferably, the connecting lines are parallel to the Y axis. According to this preferred example,
The piezoelectric constant of the piezoelectric substrate is 90% to 100% of the maximum value, and there is no problem due to deterioration of sensitivity. Also,
In the first configuration of the acceleration sensor according to the present invention, when the piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of Group 32, and the crystal axes of the single-crystal piezoelectric material are X, Y, and Z axes, The angle between the main surface of the piezoelectric substrate and the X axis is + 52 ° or more.
It is preferable that a line perpendicular to the axis of + 68 °, including the Z axis, and connecting the center of gravity of the piezoelectric substrate and the center of the supporting portion is perpendicular to the Z axis. According to this preferred example, the piezoelectric constant of the piezoelectric substrate is a value of 90 to 100% of the maximum value, and there is no problem due to deterioration in sensitivity. In a second configuration of the acceleration sensor according to the present invention, a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces is opposed to the piezoelectric element. A mechanical-electrical transducer comprising electrodes formed on two main surfaces, and a support for supporting the mechanical-electrical transducer,
The electromechanical transducer is directly bonded to the support. According to the second configuration of the acceleration sensor, since the electromechanical transducer is directly joined to the support without using an adhesive, the variation in the support position of the electromechanical transducer is reduced. As a result, it is possible to realize an acceleration sensor having a small variation in the resonance frequency. In addition, since the electromechanical transducer is directly bonded to the support without using an adhesive, the acceleration is not lost and the electromechanical transducer is not lost.
It is transmitted to the electric transducer. Further, since the adhesive layer is not interposed between the electromechanical transducer and the support, the support state does not change due to a change in temperature. Further, in the second configuration of the acceleration sensor according to the present invention, the piezoelectric substrate and the support constituting the electromechanical transducer are configured such that the constituent atoms of the piezoelectric substrate and the constituent atoms of the support are oxygen and hydroxyl groups. It is preferable that they are joined by bonding to each other via at least one selected from the group consisting of: Further, in the second configuration of the acceleration sensor of the present invention, a mechanical
It is preferable that the piezoelectric substrate and the support constituting the electric transducer are directly joined via the buffer layer. In the second configuration of the acceleration sensor according to the present invention, it is preferable that the piezoelectric substrate and the support are made of the same material. According to this preferred example, since there is no influence of distortion due to temperature, it is possible to realize an acceleration sensor that is extremely stable against a temperature change. In the second configuration of the acceleration sensor according to the present invention, it is preferable that one end of the electromechanical transducer is supported by a support. Further, in the second configuration of the acceleration sensor of the present invention, a mechanical
Preferably, both ends of the electric transducer are supported by a support. Further, a third configuration of the acceleration sensor according to the present invention includes:
A mechanical-electrical device comprising a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and electrodes formed on the two opposing main surfaces of the piezoelectric element. It has a converter, a support for supporting the electromechanical transducer, and a container for accommodating the electromechanical transducer, wherein the support is directly joined to the container. According to the third configuration of the acceleration sensor, since the support of the electromechanical transducer is directly bonded to the container without using an adhesive, the support is firmly bonded to the container. . As a result, it is possible to realize a highly sensitive acceleration sensor capable of transmitting the acceleration generated on the mounting surface to the support through the container without loss. Further, in the third configuration of the acceleration sensor according to the present invention, the container and the support are connected via at least one selected from the group consisting of oxygen and a hydroxyl group in which the constituent atoms of the container and the constituent atoms of the support are formed. It is preferred that they are joined by bonding to each other. Further, in the third configuration of the acceleration sensor according to the present invention, it is preferable that the container and the support are directly joined via a buffer layer. In the third configuration of the acceleration sensor according to the present invention, it is preferable that the container and the support are made of the same material. In a fourth configuration of the acceleration sensor according to the present invention, a piezoelectric element configured by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces is opposed to the piezoelectric element. A mechanical-electrical transducer comprising electrodes formed on two main surfaces, a support for supporting the mechanical-electrical transducer, and a container for accommodating the mechanical-electrical transducer; The electromechanical transducer is supported by directly joining the piezoelectric substrate to the container. According to the fourth configuration of the acceleration sensor, since the piezoelectric substrate forming the piezoelectric element is directly bonded to the container without using an adhesive, the state in which the electromechanical transducer is firmly bonded to the container. Becomes As a result, since the acceleration received by the container can be transmitted to the electromechanical transducer without loss, a highly sensitive acceleration sensor can be realized. Further, since the container plays the role of the support member, the number of constituent members can be reduced. Further, in the fourth configuration of the acceleration sensor according to the present invention, the piezoelectric substrate and the container are connected via at least one selected from the group consisting of oxygen and a hydroxyl group. It is preferred that they are joined by bonding to each other. Further, in the fourth configuration of the acceleration sensor according to the present invention, it is preferable that the piezoelectric substrate and the container are directly joined via the buffer layer. In the fourth configuration of the acceleration sensor according to the present invention, it is preferable that the piezoelectric substrate and the container are made of the same material. Also,
The fifth configuration of the acceleration sensor according to the present invention
A piezoelectric element configured by joining the main surfaces of at least two piezoelectric substrates having two main surfaces, and a mechanical-electrical transducer including electrodes formed on two opposing main surfaces of the piezoelectric element. , A support for supporting the electromechanical transducer, and a container comprising at least two parts for accommodating the electromechanical transducer, wherein each part constituting the container is directly joined to each other. . According to the fifth configuration of the acceleration sensor, the respective parts constituting the container are firmly joined without using an adhesive, and thus the heat resistance of the joint surface is increased. As a result, even when solder reflow or the like is performed, no gas is generated from the joint portion, and each part constituting the container is in a state of being hermetically sealed,
An acceleration sensor having high reliability without deteriorating characteristics can be obtained. Further, in the fifth configuration of the acceleration sensor according to the present invention, the respective parts constituting the container are mutually connected via at least one of the constituent atoms of the container selected from the group consisting of oxygen and a hydroxyl group. It is preferable that they are joined by. Further, in the fifth configuration of the acceleration sensor according to the present invention, it is preferable that the respective parts constituting the container are directly joined via a buffer layer. Further, a first method of manufacturing the acceleration sensor according to the present invention.
Is composed of a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer, and a support for supporting the mechanical-electrical transducer, wherein the piezoelectric elements are directly bonded to each other by directly joining the main surfaces of the two piezoelectric substrates. Forming an element. According to the first configuration of the method for manufacturing the acceleration sensor, the mechanical-electrical transducer is formed by directly bonding the piezoelectric substrates without using an adhesive layer such as an adhesive, and thus the mechanical-electrical transducer is formed by the acceleration. An acceleration sensor that does not absorb bending vibration generated in the electric transducer can be obtained. In the first configuration of the method for manufacturing an acceleration sensor according to the present invention, the main surfaces of the two piezoelectric substrates subjected to the hydrophilization treatment are joined to each other, and then, the two substrates are subjected to a heat treatment. Preferably, the main surfaces are directly joined. According to this preferred example, it is possible to realize a state where the main surfaces of the two piezoelectric substrates are firmly and directly bonded at the atomic level via oxygen or hydroxyl groups.
Further, a second configuration of the method for manufacturing an acceleration sensor according to the present invention includes a piezoelectric element configured by joining the main surfaces of at least two piezoelectric substrates having two main surfaces facing each other; A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising electrodes formed on two main surfaces facing each other; and a support for supporting the mechanical-electrical transducer. It is characterized in that it is directly bonded to the piezoelectric substrate constituting the piezoelectric element. According to the second configuration of the method for manufacturing the acceleration sensor, since the electromechanical transducer is directly joined to the support without using an adhesive, the variation in the support position of the electromechanical transducer is reduced. A small acceleration sensor is obtained. As a result, it is possible to realize an acceleration sensor having a small variation in the resonance frequency. Further, in the second configuration of the method for manufacturing an acceleration sensor according to the present invention, the support is bonded directly to the piezoelectric substrate by performing a heat treatment after bonding the support subjected to the hydrophilic treatment to the piezoelectric substrate. Joining is preferred. Also,
A third configuration of the method for manufacturing the acceleration sensor according to the present invention includes:
A mechanical-electrical device comprising a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and electrodes formed on the two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor comprising a transducer, a support for supporting the electromechanical transducer, and a container for housing the electromechanical transducer, wherein the support is directly joined to the container. It is characterized by the following. According to the third configuration of the method for manufacturing the acceleration sensor, the support can be firmly joined to the container. As a result, the acceleration generated on the mounting surface can be transmitted to the support through the container without loss, so that a highly sensitive acceleration sensor can be realized. Further, in the third configuration of the method for manufacturing an acceleration sensor according to the present invention, after the support subjected to the hydrophilic treatment and the container are joined, the support is directly joined to the container by performing a heat treatment. Is preferred. Further, a fourth configuration of the method for manufacturing an acceleration sensor according to the present invention includes a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two main surfaces facing each other; A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising electrodes formed on two opposing main surfaces; and a container accommodating the mechanical-electrical transducer, wherein the piezoelectric element is formed. A piezoelectric substrate to be bonded directly to the container. According to the fourth configuration of the method for manufacturing the acceleration sensor, the electromechanical transducer can be firmly joined to the container. As a result, since the acceleration received by the container can be transmitted to the electromechanical transducer without loss, a highly sensitive acceleration sensor can be realized. Further, since the role of the support member can be performed by the container, the number of constituent members can be reduced, and the manufacturing process can be simplified. Further, in the fourth configuration of the method for manufacturing an acceleration sensor according to the present invention, after bonding the container with the piezoelectric substrate subjected to the hydrophilic treatment,
It is preferable that the piezoelectric substrate is directly bonded to the container by performing a heat treatment. In a fifth configuration of the method for manufacturing an acceleration sensor according to the present invention, the piezoelectric element is formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces; , An electromechanical transducer comprising electrodes formed on two opposite main surfaces, a support for supporting the electromechanical transducer, and at least two parts accommodating the electromechanical transducer. A method for manufacturing an acceleration sensor including a container,
The parts of the container are directly joined to each other. According to the fifth configuration of the method for manufacturing the acceleration sensor, the respective parts constituting the container can be firmly joined without using an adhesive, so that the heat resistance of the joint surface can be improved. As a result, even when solder reflow or the like is performed, no gas is generated from the joint portion, and each part constituting the container is in a state of being hermetically sealed, so that high reliability without deterioration of characteristics is achieved. Can be realized. Further, in the fifth configuration of the method for manufacturing an acceleration sensor according to the present invention, the respective parts of the container are subjected to a heat treatment after the respective parts of the container subjected to the hydrophilic treatment are joined, and then the respective parts of the container are directly joined to each other. Is preferred. In a sixth configuration of the method for manufacturing an acceleration sensor according to the present invention, the piezoelectric element is formed by joining the main surfaces of at least two piezoelectric substrates having two main surfaces facing each other; A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising electrodes formed on two main surfaces opposed to each other; and a container accommodating the mechanical-electrical transducer, comprising: Forming a plurality of piezoelectric elements by directly joining at least two piezoelectric substrates on which a portion or a doubly-supported portion is patterned, and forming a container having a concave portion in a portion corresponding to the piezoelectric element on the piezoelectric substrate. The method includes a step of direct joining and a step of separating into individual acceleration sensors including the piezoelectric element.
According to the sixth configuration of the method for manufacturing the acceleration sensor, since the electromechanical transducer is patterned from the piezoelectric substrate, the variation in the shape of the electromechanical transducer is small. In addition, since the electromechanical transducer is formed at the same time as the support portion, the variation in the support state of the electromechanical transducer is small.
For this reason, the variation in the length of the cantilever beam or the doubly supported beam is reduced, so that it is possible to realize an acceleration sensor with extremely small variation in characteristics such as the resonance frequency. Also,
Since the mechanical-electrical transducer, the support member, and the container can be formed of the same material, an acceleration sensor excellent in stability can be realized without being affected by distortion due to temperature or the like. Further, since a large number of acceleration sensors are manufactured on one substrate at a time, an acceleration sensor excellent in mass productivity can be realized. In a sixth configuration of the method for manufacturing an acceleration sensor according to the present invention,
After forming the piezoelectric element, it is preferable to form electrodes on two opposite main surfaces of the piezoelectric element. According to this preferred example, since the piezoelectric element is already formed, positioning of the mask at the time of forming the electrode becomes easy, and
Electrodes can be formed with high precision only on the piezoelectric element. As a result, a highly accurate electromechanical transducer can be obtained. In this case, it is preferable to form a conductive layer on the piezoelectric substrate at the same time as forming the electrodes on the two opposing main surfaces of the piezoelectric element. According to this preferred example, the manufacturing process is simplified. In the sixth configuration of the method of manufacturing an acceleration sensor according to the present invention, it is preferable that after the electrodes are formed on the piezoelectric substrate, the cantilever portion or the double-supported beam portion is patterned. According to this preferred example, the electromechanical transducer can be manufactured without accurately aligning the electrodes. When the piezoelectric element is thin, if an electrode is formed after the beam portion is pattern-formed,
Although the front and rear electrodes may be short-circuited, according to this preferred example, this problem can be avoided. In this case, it is preferable to form a conductive layer on the piezoelectric substrate at the same time as forming the electrodes. Further, a seventh configuration of the method for manufacturing an acceleration sensor according to the present invention includes a piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces; A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising electrodes formed on two main surfaces opposed to each other; and a container accommodating the mechanical-electrical transducer, wherein at least two piezoelectric substrates are provided. Forming a plurality of piezoelectric elements by patterning a plurality of cantilever portions or a doubly supported beam portion, and forming a container having a concave portion in a portion corresponding to the piezoelectric element into the piezoelectric substrate. Bonding directly to the
Separating the acceleration sensor into individual acceleration sensors including the piezoelectric element. Further, in the seventh configuration of the method for manufacturing an acceleration sensor according to the present invention, it is preferable that after forming the piezoelectric element, electrodes are formed on two opposing main surfaces of the piezoelectric element. In this case, it is preferable to form a conductive layer on the piezoelectric substrate at the same time as forming the electrodes on the two opposing main surfaces of the piezoelectric element. In the seventh configuration of the method for manufacturing an acceleration sensor according to the present invention, it is preferable that after the electrodes are formed on the piezoelectric substrate, the cantilever portion or the double-supported beam portion is patterned. In this case, it is preferable to form a conductive layer on the piezoelectric substrate at the same time as forming the electrodes. Further, the configuration of the impact detection device according to the present invention includes a piezoelectric element configured by joining the main surfaces of at least two piezoelectric substrates having two main surfaces facing each other, and two opposing piezoelectric elements of the piezoelectric element. A mechanical-electrical transducer comprising electrodes formed on the main surface, an acceleration sensor including a support for supporting the mechanical-electrical transducer, and a signal output from the acceleration sensor,
An amplification circuit for amplifying, a comparison circuit for comparing a signal output from the amplification circuit with a reference signal, a control circuit for controlling a device incorporating the acceleration sensor, and a storage device for recording a shock It is a thing. According to the configuration of the impact detection device, the sensitivity variation of the acceleration sensor,
Since there is no variation in capacitance, the measurement accuracy of acceleration is high, and it is possible to make accurate judgments using the comparison circuit with respect to the reference value when detecting an impact, and to detect the impact by detecting the impact. It is possible to realize an impact detection device capable of instructing an operation of recording or protecting an apparatus from an impact by judging by a control circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to embodiments. <First Embodiment> FIG. 1 is a perspective view showing a mechanical-electrical transducer used for an acceleration sensor according to a first embodiment of the present invention. As shown in FIG. 1, piezoelectric substrates 2 a and 2 b made of rectangular lithium niobate (LiNbO ₃ ) having a thickness of 50 μm, a width of 0.5 mm, and a length of 2 mm having two opposing main surfaces are connected to each other. Are directly joined, and the piezoelectric element 2 is thus configured. here,
The piezoelectric substrates 2a and 2b are joined so that the directions of the polarization axes are opposite to each other. On opposite two main surfaces of the piezoelectric element 2, electrodes 3a and 3b made of chromium-gold having a thickness of 0.2 μm are formed, respectively. Thereby, the bimorph type electromechanical transducer 1 is configured. Hereinafter, an example of a method for manufacturing the electromechanical transducer having the above-described configuration will be described. FIG. 2 is an explanatory view showing the interface state of the piezoelectric substrate at each stage of the direct bonding in the method of manufacturing the electromechanical transducer used for the acceleration sensor according to the first embodiment of the present invention. In FIG. 2, L ₁ ,
L ₂ and L ₃ indicate the distance between the piezoelectric substrates. First, both surfaces of two LiNbO ₃ substrates, which are the piezoelectric substrates 2a and 2b, were mirror-polished. Next, these piezoelectric substrates 2a, 2b
Is washed with a mixed solution of ammonia, hydrogen peroxide and water (ammonia water: hydrogen peroxide solution: water = 1: 1: 6 (volume ratio)), so that the piezoelectric substrates 2a and 2b are subjected to a hydrophilic treatment. did. As shown in FIG. 2A, the surfaces of the piezoelectric substrates 2a and 2b washed with the mixed liquid were terminated with hydroxyl groups (-OH groups) and became hydrophilic (the state before joining). Then
As shown in FIG. 2B, two piezoelectric substrates (LiNbO ₃ ) 2a and 2b that have been subjected to a hydrophilization treatment are joined such that the directions of the polarization axes are opposite to each other (L ₁ >).
L _2). As a result, dehydration occurs and the piezoelectric substrate (LiN
bO ₃ ) 2a and the piezoelectric substrate (LiNbO ₃ ) 2b
They were attracted and joined by attractive forces such as H polymerization and hydrogen bonding. Next, the piezoelectric substrate (Li
NbO ₃ ) 2a and 2b were subjected to a heat treatment at a temperature of 450 ° C. Thereby, as shown in FIG. 2C, the constituent atoms of the piezoelectric substrate (LiNbO ₃ ) 2a and the piezoelectric substrate (LiNbO ₃ )
O ₃ ) and the constituent atoms of 2b are covalently bonded via oxygen (O) (L ₂ > L ₃ ), and the piezoelectric substrates 2a, 2b
b was directly bonded firmly at the atomic level. That is, a bonding state in which an adhesive layer such as an adhesive did not exist at the bonding interface was obtained. Alternatively, the constituent atoms of the piezoelectric substrate (LiNbO ₃ ) 2a and the constituent atoms of the piezoelectric substrate (LiNbO ₃ ) 2b are in a state of being covalently bonded via a hydroxyl group, and the piezoelectric substrates 2a and 2b are firmly directly joined at the atomic level. It may be done. The Curie point of LiNbO ₃ is 1210 ° C., and the characteristic deteriorates due to a temperature history close to this,
The heat treatment temperature is desirably below the Curie point. Bonding that occurs directly between interfaces without the intervention of an adhesive layer such as an adhesive by bringing the mirror-polished surfaces of the members to be bonded into contact with each other after surface treatment is called "direct bonding". Generally, by performing the heat treatment, a strong bond at the atomic level, such as a covalent bond or an ionic bond, becomes a bond due to intermolecular force. Next, a directly bonded piezoelectric substrate (LiNbO ₃ )
2a, 2b, that is, chromium-gold is deposited on two opposing main surfaces of the piezoelectric element 2 by a vacuum deposition method,
a, 3b were formed (see FIG. 1). Finally, the resultant was cut into strips of a predetermined size using a dicing saw, thereby producing a bimorph-type electromechanical transducer 1. As shown in FIG. 3, the direct bonding can be performed via a buffer layer 46 made of a silicon oxide thin film or the like. That is, a buffer layer 46 made of a 0.1 μm-thick silicon oxide thin film or the like is formed on one main surface of the piezoelectric substrate 2a, and the buffer layer 46 and the other piezoelectric substrate 2b are subjected to a hydrophilic treatment. The heat treatment is performed by overlapping the piezoelectric substrates 2b with each other.
And the constituent atoms of the buffer layer 46 are bonded via oxygen or a hydroxyl group. Even if the joint surface has undulations or irregularities, or even if foreign matter such as dust adheres to the joint surface, the buffer layer 46 absorbs the irregularities and the like,
Direct joining can be easily performed. Further, even in the case where a material in which oxygen or a hydroxyl group is unlikely to be formed on the surface by the hydrophilic treatment is bonded, direct bonding can be easily performed by bonding via the buffer layer 46. in this case,
The buffer layer may be provided only on one side of the surface to be joined, or may be provided on both surfaces. As a material for the buffer layer, for example, silicon nitride, metal silicide, or the like can be used in addition to silicon oxide. FIG. 4 is a perspective view showing a bimorph type mechanical-electrical converter having a cantilever structure according to the first embodiment of the present invention, and FIG. 5 is a sectional view thereof. FIG.
As shown in FIG. 5, a thickness 5 having two opposing main surfaces
0 μm, 0.5 mm wide, 2 mm long rectangular LiN
The main surfaces of the piezoelectric substrates 2a and 2b made of bO ₃ are directly bonded to each other, and thus the piezoelectric element 2 is formed. Here, the piezoelectric substrates 2a and 2b are joined so that the directions of the polarization axes are opposite to each other.
One end of the piezoelectric element 2 has a support 4 made of LiNbO _3.
a, 4b and fixed. here,
The piezoelectric element 2 is directly joined to the supports 4a, 4b. In this case, direct bonding between the piezoelectric element 2 and the supports 4a and 4b can be performed via a buffer layer made of a silicon oxide thin film or the like. An electrode 3 made of chromium-gold having a thickness of 0.2 μm is provided on two opposite main surfaces of the piezoelectric element 2.
a, 3b are formed respectively, and these electrodes 3
a, 3b are also formed continuously on the supports 4a, 4b. Thus, a bimorph-type electromechanical transducer 1 having a cantilever structure is formed. FIG. 6 is an exploded perspective view showing an example of the acceleration sensor according to the first embodiment of the present invention. As shown in FIG. 6, a bimorph-type electro-mechanical transducer 1 having a cantilever structure having the structure shown in FIGS.
Is housed in a container 10b made of LiNbO ₃ having a depression formed in the center by a method such as etching. That is, while the portions other than the supports 4a and 4b of the bimorph-type electromechanical transducer 1 are held on the depressions, the supports 4a and 4a of the bimorph-type electromechanical transducer 1 are held.
b is fixed to the container 10b by conductive pastes 5a and 5b (5a is not shown). A container 10a made of LiNbO ₃ having a depressed portion formed in the center is also superimposed and adhered to the container 10b. As a result, the entirety of the bimorph type electromechanical transducer 1 is
b. Inside the container 10b, silver-
Conductive layers 7a and 7b made of palladium are formed, and one ends of conductive layers 7a and 7b are connected to conductive pastes 5a and 5b.
b, they are electrically connected to the electrodes 3a, 3b of the bimorph-type electromechanical transducer 1 respectively. External electrodes 9a and 9b made of nickel are formed on both end surfaces of the containers 10a and 10b, and the other ends of the conductive layers 7a and 7b are electrically connected to the external electrodes 9a and 9b, respectively. That is, the electrodes 3a and 3b of the bimorph type electromechanical transducer 1 are electrically connected to the external electrodes 9a and 9b via the conductive pastes 5a and 5b and the conductive layers 7a and 7b, respectively. Thereby, bimorph type machine
Electric charges generated in the electric transducer 1 can be taken out. Thus, the acceleration sensor 100 is configured. When acceleration is applied to the object to which the acceleration sensor 100 shown in FIG. 6 is attached, a force proportional to the acceleration is transmitted to the electromechanical transducer 1 through the containers 10a and 10b and the supports 4a and 4b. Vertical direction (arrow direction in FIG. 4)
When the acceleration occurs, the electromechanical transducer 1 bends in the up-down direction, and bending vibration occurs. This situation is shown in FIG.
Shown in Considering the case where the electromechanical transducer 1 composed of the piezoelectric substrates 2a and 2b is bent downward (solid line in FIG. 7),
Since the piezoelectric substrate 2a is positioned above the center axis of the electromechanical transducer 1, the piezoelectric substrate 2a is distorted so that the piezoelectric substrate 2a is extended by a tension. On the other hand, since the piezoelectric substrate 2b is located below the central axis of the electromechanical transducer 1, a compressive force acts on the piezoelectric substrate 2b so that the piezoelectric substrate 2b contracts.
In the case of a conventional electromechanical transducer manufactured by bonding a piezoelectric ceramic substrate, the electromechanical transducer bends vertically because a softer adhesive than the piezoelectric substrate is interposed between the piezoelectric substrates. At this time, the bending vibration is absorbed by the adhesive, and the stress generated in the piezoelectric substrate is reduced. For this reason,
The electromotive force generated on the piezoelectric substrate is also reduced. However, the electromechanical transducer 1 according to the present embodiment includes the piezoelectric substrates 2a, 2b
Of the piezoelectric substrates 2a and 2b, there is no adhesive layer such as an adhesive between the piezoelectric substrates 2a and 2b.
That is, when bending vibration occurs in the electromechanical transducer 1 due to acceleration, there is no one that absorbs the bending vibration. Therefore, stress is generated in the piezoelectric substrates 2a and 2b without loss, and a large electromotive force is obtained. As a result, an acceleration sensor having high sensitivity can be realized.
In addition, since the bonding state of the piezoelectric substrates 2a and 2b becomes uniform, variations in the resonance frequency and sensitivity of the electromechanical transducer 1 become extremely small. Further, since the adhesive layer is not interposed between the piezoelectric substrates 2a and 2b, the vibration characteristics of the electromechanical transducer 1 do not change due to a temperature change. In addition, since the supports 4a and 4b are firmly joined to the electromechanical transducer 1 at the atomic level, the acceleration applied to the object to which the containers 10a and 10b are attached is reduced without any loss. Is transmitted to In the piezoelectric substrates 2a and 2b made of LiNbO ₃ or the like, electric charges corresponding to the compressive stress and the tensile stress are generated on the upper and lower surfaces of the piezoelectric substrates 2a and 2b, but the directions of the polarization axes of the piezoelectric substrates 2a and 2b are mutually different. Since the bonding is performed in the opposite direction, the piezoelectric substrate 2
Although the stresses a and b are different from the compressive stress and the tensile stress, electric charges of the same polarity are generated on the piezoelectric substrate 2a and the piezoelectric substrate 2b. That is, an electromotive force is generated on the piezoelectric substrate 2a and the piezoelectric substrate 2b in the same direction (see FIG. 7). Therefore, signals reflecting the magnitude of the acceleration can be obtained from the electrodes 3a and 3b formed on both surfaces of the electromechanical transducer 1. The thickness direction of the LiNbO ₃ substrate is Y ′
When the axial direction and the longitudinal direction are set in the Z′-axis direction, compressive stress and tensile stress act in the Z′-axis direction, and electric charges are generated in the Y′-axis direction. In this case, the amount of generated electric charge largely depends on the piezoelectric constant d ₂₃ ′. Also, this piezoelectric constant d
The size of ₂₃ 'greatly changes depending on the direction of the Y' axis and the Z 'axis with respect to the crystal axis. That is, the sensitivity of the acceleration sensor greatly changes depending on the directions of the Y ′ axis and the Z ′ axis. The Y 'axis and the Z' axis are appropriately set, and the piezoelectric constant d
_{When the} cut angle is selected so that the absolute value of the size of ₂₃ 'is the largest, an acceleration sensor with the highest sensitivity can be obtained. FIG. 8 shows the relationship between the crystal axis and the cut angle of the LiNbO ₃ substrate. In FIG. 8, the X, Y, and Z axes are Li
The direction of the crystal axis of NbO ₃ is shown, and the X ′ axis (= X axis),
The Y 'axis and the Z' axis indicate orthogonal axes when the Y axis is rotated by an angle θ about the X axis. That is, the X ′ axis (= X
Axis), the Y ′ axis, and the Z ′ axis indicate the cutting direction of the LiNbO ₃ substrate. As shown in FIG. 8, when the direction of each axis is set, when the thickness direction of the LiNbO ₃ substrate is set to the X′-axis direction and the longitudinal direction is set to the Y′-axis direction, the piezoelectric constant d ₁₂ ′
Greatly affects the sensitivity of the acceleration sensor. In addition, LiN
When the thickness direction of the bO ₃ substrate is set in the X′-axis direction and the longitudinal direction is set in the Z′-axis direction, the piezoelectric constant d ₁₃ ′ greatly affects the sensitivity of the acceleration sensor. When the thickness direction of the LiNbO ₃ substrate is set to the Y′-axis direction and the longitudinal direction is set to the X′-axis direction, the piezoelectric constant d ₂₁ ′ greatly affects the sensitivity of the acceleration sensor. When the thickness direction of the LiNbO ₃ substrate is set to the Y′-axis direction and the longitudinal direction is set to the Z′-axis direction, the piezoelectric constant d ₂₃ ′ greatly affects the sensitivity of the acceleration sensor. When the thickness direction of the LiNbO ₃ substrate is set in the Z′-axis direction and the longitudinal direction is set in the X′-axis direction, the piezoelectric constant d ₃₁ ′ greatly affects the sensitivity of the acceleration sensor. When the thickness direction of the LiNbO ₃ substrate is set in the Z′-axis direction and the longitudinal direction is set in the Y′-axis direction, the piezoelectric constant d ₃₂ ′ greatly affects the sensitivity of the acceleration sensor. FIG.
4 shows the relationship between the cut angle of the bO ₃ substrate and the piezoelectric constant. FIG.
As shown in the figure, when the cut angle is 140 °, the piezoelectric constant d
₂₃ 'has the largest value. The experimental results in the case where the mechanical-electrical converter was actually manufactured by changing the cut angle are shown in the following (Table 1) and FIG.

[Table 1]As shown in the above (Table 1), Y-
Using a cut 140 ° substrate, the Z ′ axis direction is taken as the longitudinal direction.
Mechanical-electrical transducer generates the largest charge and the sensitivity is
It was confirmed that it was good. FIG.
4 shows a relationship between cut angles of the acceleration sensor. As shown in FIG.
Rotate the Y axis by 140 ° around the X axis and perpendicular to the Y 'axis
An electrode is provided on a flat surface, and the longitudinal direction is set to the Z 'axis direction.
The speed sensor showed the highest sensitivity. LiNbO_Threeof
The crystal structure is a trigonal system 3m group, with 3
Take a symmetrical structure. Therefore, they have the same piezoelectric constant
There are several cut angles. For example, as shown in FIG.
The piezoelectric constant d at a cut angle of 50 ° and 230 °₃₂’And mosquito
140 ° and 320 ° cut angle piezoelectric constant d_{twenty three}’Is the same value
Becomes This is clear considering the symmetry of the crystal.
It is. In addition, with optimal cut angle for maximum sensitivity
At close cut angles, the dependence of the piezoelectric constant on cut angle is small.
Almost the same sensitivity without strictly optimizing the cut angle
can get. If you try to strictly optimize the cut angle,
In addition, high precision of processing by strictly defining the cut angle
Processing by complicating the process to suppress increase in degree and variation
Problems with increased costs and increased unit prices due to lower yield
It becomes. Piezoelectric constant d_{twenty three}’In Figure 9
As shown, the optimal cut angle is 140 °,
If the angle is in the range of 129 ° to 152 °, the piezoelectric constant is
90 to 100% of the maximum value, due to sensitivity degradation
There is no problem. In addition, LiNbO_ThreeSubstrate thickness
When the direction is set to the Y 'axis direction and the longitudinal direction is set to the X axis direction
The sensitivity of the acceleration sensor is the piezoelectric constant d_{twenty one}’.
As shown in FIG. 9, the piezoelectric constant d _{twenty one}’Is dependent on the cut angle
Piezoelectric constant d_{twenty three}'. In this case,
If the cut angle is within the optimal cut angle ± 26 °, the piezoelectric constant
Is 90 to 100% of the maximum value.
No problem arises. Therefore, the cut angle is highly accurate
A highly sensitive acceleration sensor can be manufactured without finishing
Therefore, the processing cost can be reduced. Two pieces of pressure
If there is a difference in the cut angle of the printed circuit board, the pyroelectric effect of the piezoelectric
Charge is not canceled out,
It is preferable that the difference between the cut angles of the piezoelectric substrates is small.
Since the cut angle dependence of the constant is not large,
The difference between the cut angles of the two piezoelectric substrates constituting the commutator is 1 ° or less.
If it is inside. The length, thickness and
The width is determined in consideration of the frequency range of the acceleration to be measured.
Is determined. The frequency of the measured acceleration is a mechanical-electrical transducer
As the resonance frequency approaches, the sensitivity of the acceleration sensor increases.
It becomes. Two 50 μm thick LiNbO_ThreeSubstrate directly
Joined, length from tip to support set to 2mm
The resonant frequency of the cantilevered mechanical-electrical transducer 1 is
It was 20 kHz. The sensitivity and acceleration frequency shown in FIG.
As can be seen from the measurement results, the acceleration frequency is 10 kHz
z or more, the resonance frequency of the electromechanical transducer 1
As we approached, the sensitivity increased. Measurement frequency range
Therefore, the sensitivity of the acceleration sensor does not greatly depend on the frequency.
In order to ensure that the resonance frequency is
Need to be separated into minutes. For this, for example,
Vibration frequency is twice the maximum measurement frequency
Then, the mechanical-electrical converter 1 may be designed. I mentioned above
Thus, the resonance frequency of the electromechanical transducer 1 depends on its length and
Depends on thickness. Conventional piezoelectric ceramic
In the case of a speed sensor, the support of the electromechanical transducer uses adhesive.
Has been done through. Controlling the amount of adhesive applied
Difficult, mechanical and electrical
Large variations, such as a reduction in the actual length of the transducer
No. Therefore, acceleration sensors using conventional piezoelectric ceramics
The resonance frequency of the electromechanical transducer varies.
The sensitivity in the high-frequency range,
There is a problem that the settable frequency changes individually. Book
In the case of the embodiment, the supports 4a and 4b are
Since it is directly joined to the transducer 1, the length of the electromechanical transducer 1
The variation of the height is extremely small. As a result,
The variation of the resonance frequency of the air transducer 1 is extremely small.
The sensitivity of each acceleration sensor in the high frequency range and the measurement
Fluctuations in the frequency range are very small. As a piezoelectric material
LiNbO used_ThreeIs a single crystal, piezoelectric constant, dielectric
The variation in modulus, elastic constant, etc. is extremely small. Piezoelectric ceramic
In the case of Mick, these material constants are usually about 20%.
Has flicker. For this reason, processing using piezoelectric ceramics
The sensitivity and resonance frequency of the speed sensor vary by about 20%
Having. However, LiNbO_ThreeDirect bonding of substrates
In the acceleration sensor of the present embodiment manufactured,
In both cases, the variation could be suppressed to 5% or less.
In addition, piezoelectric ceramics change greatly with time, resulting in increased stability.
Chip. Therefore, the acceleration sensor using piezoelectric ceramic
If the sensitivity changes by 10-15% over time,
Had the problem of However, LiNbO_ThreeBoard
The accelerometer of this example fabricated by direct bonding
And the change with time was 2% or less. Piezoelectric substrate 2a,
2b is a single crystal piezoelectric material that can be directly bonded
And LiNbO_ThreeOther than lithium tantalate
(LiTaO_Three), Quartz, langasite type piezoelectric crystal, etc.
Can also be used. Langasite-type piezoelectric crystal
La_ThreeGa_FiveSiO₁₄, La_ThreeGa_5.5Nb
_0.5O₁₄, La_ThreeGa_5.5Ta_0.5O₁₄and so on. L
iTaO_ThreeHas a crystal structure of LiNbO_ThreeTrigonal as well
3m group, and its optimal cut angle is LiNbO_ThreeWhen
Is the same. In addition, the bonding of quartz and langasite-type piezoelectric crystals
The crystal structure is a trigonal system 32 group. 12 to 14
In addition, the cut angle and pressure of the quartz substrate having the crystal structure of group 32
This shows the relationship with the electric constant. FIG. 12 shows the rotation about the X axis as the rotation axis.
FIG. 13 shows the relationship between the cut angle and the piezoelectric constant when rotated.
Angle and piezoelectric constant when rotating about the axis
FIG. 14 shows the power when rotating about the Z axis as the rotation axis.
The relationship between the cut angle and the piezoelectric constant is shown. still,
Cut angle and piezo of substrate made of langasite type piezoelectric crystal
The same applies to the relationship with the constant. The following (Table 2) shows FIGS.
Single crystal piezoelectric having a group 32 crystal structure determined from FIG.
The optimum cut angle of the material is adjusted to the 3m group crystal structure described above.
It is shown together with the case of a single crystal piezoelectric material having the same.

[Table 2]In the above (Table 2), the three numbers of Euler angles are X in order.
The rotation angles about the axis, the Y axis, and the Z axis are shown. Ma
Table 2 above also shows the maximum piezoelectric constant.
You. As shown in the above (Table 2), it has a crystal structure of group 32.
When the piezoelectric body to be rotated by 70 ° with the X axis as the rotation axis,
The maximum piezoelectric constant is d₁₃’. This means that 32
A piezoelectric body having a crystal structure of group III is rotated around the X axis as a rotation axis.
° When rotated, the X 'axis (= X axis) direction after rotation
Cut out the piezoelectric substrate vertically and extend the length of the piezoelectric substrate in the Z'-axis direction.
Indicates that sensitivity is best when hand direction is set.
doing. When the Euler angle is (0,0,0),
The maximum piezoelectric constant is d₁₂’. This means that
If the angle is (0,0,0), the X 'axis after rotation
(= X axis) Cut out the piezoelectric substrate perpendicular to the direction,
When the longitudinal direction of the piezoelectric substrate is set to
It shows that it gets better. Also, if the Euler angle is (0,
0,90), the maximum piezoelectric constant is d_{twenty one}’
You. This means that the Euler angle is (0,0,90)
Cut out the piezoelectric substrate perpendicular to the Y 'axis direction after rotation
When the longitudinal direction of the piezoelectric substrate is set in the X'-axis direction
Fig. 2 shows that the sensitivity is highest. Also, 32
Substrate with crystal structure of group III (quartz, langasite type)
D)₁₃+ 52 ° to +
Within the range of 86 °, d₁₂’Is within ± 26 °,
d₃₂’In the range of + 52 ° to + 68 °
Is 90 to 100% of the maximum value,
No problem arises. Therefore, the cut angle is highly accurate
A highly sensitive acceleration sensor can be manufactured without finishing
Therefore, the processing cost can be reduced. That's all
As described above, according to the present embodiment, an adhesive layer such as an adhesive is used.
Without directly connecting the piezoelectric substrates 2a and 2b firmly.
The mechanical-electrical transducer 1 was formed by
High sensitivity with no variation in characteristics or attenuation of vibration
Acceleration sensor can be realized. Also adhesive
Without using the electromechanical transducer 1 with the support 4a,
4b, so that the mechanical-electrical transducer
1 can be performed with high accuracy. The result
As a result, there is no variation in the length and support
Has high stability and extremely small variations in characteristics.
A speed sensor can be realized. Also use adhesive
Without the electromechanical transducer 1 being supported by the supports 4a, 4b
Direct connection to the machine.
-Transmitted to the electrical transducer 1; In this embodiment,
Using chromium-gold as the material of the electrodes 3a and 3b
But it is not necessarily limited to this.
For example, gold, chromium, silver, or an alloy material may be used. Ma
In this embodiment, the materials of the containers 10a and 10b
LiNbO as a charge _ThreeIs used, but this is not necessarily
Without limitation, for example, LiTaO_Three,water
Crystal, glass, plastic, ceramic such as alumina
Or the like may be used. In the present embodiment,
Although the mechanical-electrical conversion element 1 has a cantilever structure,
The invention is not limited to this structure,
Both ends of the conversion element 1 are directly joined to the support to support the beam
And supports the center of the electromechanical transducer 1
It may be joined directly to the body to form a central support structure. <Second Embodiment> FIG. 15 shows a second embodiment of the present invention.
FIG. 2 shows a mechanical-electrical transducer used for an acceleration sensor in a stationary state.
FIG. As shown in FIG.
Thickness 50μm, width 0.5mm, length 2mm with main surface
Rectangular LiNbO_ThreePiezoelectric substrates 2a and 2b made of
The main surfaces are directly joined to each other,
The electric element 2 is configured. Here, the piezoelectric substrate 2a and the pressure
The circuit board 2b is joined so that the direction of the polarization axis is opposite.
Have been. One end of the piezoelectric element 2 is LiNbO_ThreeFrom
Fixed between the supporting members 4a and 4b
You. Here, the piezoelectric element 2 is in direct contact with the supports 4a and 4b.
Have been combined. On two opposing main surfaces of the piezoelectric element 2,
A thickness of 0.2 is applied to portions not sandwiched between the supports 4a and 4b.
Each of the electrodes 3a and 3b made of chrome-gold
Has been established. By the above, bimorph of cantilever structure
A type of electromechanical transducer 1 is configured. Figure 16 is a book
An example of the acceleration sensor according to the second embodiment of the present invention
FIG. 17 is an exploded perspective view, and FIG. 17 is a sectional view thereof. FIG.
As shown in FIG. 17, cantilever having the structure shown in FIG.
The electromechanical transducer 1 having a beam structure has an upper surface, one end surface, and one side surface.
LiNbO with opening_ThreeContained in a container 10c made of
The supports 4a and 4b are placed directly inside the other end surface of the container 10c.
They are joined together. In this case, the supports 4a and 4b and the container
The direct junction with 10c is made of a backing made of a silicon oxide thin film or the like.
It is also possible to carry out via a pha layer. Electrodes 3a, 3b
In the state where the supports 4a, 4b and the container 10c are
One ends of the conductive layers 7c and 7d are connected to each other,
The other ends of c and 7d are exposed at the end of the container 10c.
The container 10c also contains LiNbO_ThreeContainer 10 made of
A container 10d having the same shape as c is joined. Container 10
External electrodes 9 made of nickel are provided on the outer surfaces of c and 10d.
c and 9d are formed, and the external electrodes 9c and 9d are electrically conductive.
The layers are electrically connected to the layers 7c and 7d, respectively. sand
That is, the electrodes 3a and 3b of the electromechanical transducer 1 are electrically conductive layers.
7c and 7d to the external electrodes 9c and 9d, respectively.
Connected. Thereby, the electromechanical transducer 1
Can be taken out to the outside. more than
Thus, the acceleration sensor 102 is configured. In FIG.
In the acceleration sensor 102 shown in FIG.
When it is added, the electromechanical transducer 1 swings up and down.
Move and bending vibration occurs. When bending vibration occurs, the pressure
Electric substrate (LiNbO_Three) One of 2a, 2b extends
And the other is shrunk to shrink. Here, the piezoelectric substrate 2a
And the piezoelectric substrate 2b so that the polarization axes are opposite to each other.
Due to the bonding, the reaction generated on the piezoelectric substrates 2a and 2b
Although the force is different from the compressive stress and the tensile stress,
Electric charges of the same polarity are generated on the piezoelectric substrate 2a and the piezoelectric substrate 2b.
You. That is, the piezoelectric substrate 2a and the piezoelectric substrate 2b have the same
An electromotive force is generated in the direction. Therefore, the mechanical-electrical transducer
From the electrodes 3a and 3b formed on both surfaces of
A signal reflecting the degree can be obtained. FIG. 18 shows the present invention.
14 shows another example of the acceleration sensor according to the second embodiment.
FIG. As shown in FIG.
Having two main surfaces, thickness 50 μm, width 0.5 mm, length 2
mm rectangular LiNbO_ThreeA piezoelectric substrate 2a,
2b has its main surfaces directly joined to each other,
The piezoelectric element 2 is constituted. Here, the piezoelectric substrate 2a
And the piezoelectric substrate 2b so that the polarization axes are opposite to each other.
Are joined. On two opposing main surfaces of the piezoelectric element 2
Are electrodes 3a, 3 made of chromium-gold having a thickness of 0.2 μm.
b is formed. Thereby, the electromechanical transducer 1
Is configured. One end of the mechanical-electrical transducer 1 is vertically
LiNbO with open surface and split into two_ThreeContainer 1 consisting of
0e and 10f.
A mechanical-electrical transducer 1 is supported. Here, the container 10
e, 10f and the electromechanical transducer 1 are directly joined.
Also, the containers 10e and 10f are directly joined to each other.
You. In this case, the containers 10e and 10f and the electromechanical transducer
1 or direct joining between containers 10e and 10f
Is performed through a buffer layer made of a silicon oxide thin film or the like.
It is also possible. Containers 10e, 10f
The containers 10g and 10h are fixed using an adhesive. This
Thereby, the electromechanical transducer 1 is sealed in the container.
I have. External electrodes 9 made of nickel are provided on both end surfaces of the container.
e, 9f are formed respectively, and the external electrodes 9
e and 9f are electromechanical transducers via a conductive layer (not shown).
Are electrically connected to the first electrodes 3a and 3b, respectively.
You. Thereby, the electric charge generated in the electromechanical transducer 1 is
Can be taken out. In addition, container 10g, 10h
When the mechanical-electrical transducer 1 bends, the mechanical-electrical
A depression is provided so that the transducer 1 does not contact.
You. Thus, the acceleration sensor 103 is configured.
You. The length, thickness and width of the electromechanical transducer 1 are measured
It is determined in consideration of the frequency range of the acceleration to be taken. Measurement
Is the resonance frequency of the electromechanical transducer 1
As the number approaches, the sensitivity of the acceleration sensor increases. Measurement
In the constant frequency range, the sensitivity of the acceleration sensor
To avoid significant dependence, measure the resonance frequency.
It is necessary to keep it sufficiently away from the constant frequency range. others
For example, the resonance frequency is twice as high as the highest measurement frequency.
If the mechanical-electrical transducer 1 is designed to have a frequency,
Good. LiNbO used as a piezoelectric material_ThreeIs a single crystal
Extremely small variations in piezoelectric constant, dielectric constant, elastic constant, etc.
Small. For piezoceramics, these material constants are
Usually, it has a variation of about 20%. For this reason, the piezoelectric
The sensitivity and resonance frequency of the acceleration sensor using Lamic are 2
It has a variation of about 0%. However, LiNbO_ThreeBase
The acceleration sensor of the present embodiment manufactured by directly joining the plates
Reduces variation in sensitivity and resonance frequency to 5% or less
I was able to. Furthermore, piezoelectric ceramics change over time.
Large and lacks stability. For this reason, piezoelectric ceramic
The acceleration sensor used has a sensitivity of 10 to 15 over time.
%. But L
iNbO_ThreeAcceleration of this embodiment fabricated by directly bonding substrates
The degree sensor is extremely stable and changes over time are less than 2%.
Was. As described above, according to the present embodiment, the adhesive
The piezoelectric substrates 2a and 2b are firmly fixed without using an adhesive layer of
Of electromechanical transducer 1 by direct bonding to
And there is no variation in characteristics or attenuation of vibration.
An acceleration sensor having high sensitivity can be realized.
Further, the electromechanical transducer 1 can be used without using an adhesive.
Since it is directly joined to the supports 4a and 4b,
-Positioning of the electric transducer 1 can be performed with high accuracy.
You. As a result, variations in cantilever length and support
And high stability with extremely small variation in characteristics
A small acceleration sensor can be realized. Also,
The electromechanical transducer 1 is used as a support without using an adhesive.
4a and 4b are joined directly to accelerate
The power is transmitted to the electromechanical transducer 1 without loss. Also,
The supports 4a and 4b are directly attached to the container without using an adhesive.
By making contact, the acceleration from the mounting surface
The supports 4a and 4b are firmly joined to the directly transmitted container.
Transmission of acceleration to the electromechanical transducer 1 without loss
can do. In this embodiment, the piezoelectric
LiNbO as a material for the substrates 2a and 2b_ThreeUsing
However, it is not necessarily limited to this, for example,
LiTaO _ThreeOr quartz may be used. In addition, the form of this implementation
In the embodiment, the material of the electrodes 3a, 3b is chromium-gold.
But is not necessarily limited to this.
For example, gold, chromium, silver or alloy materials may be used.
No. In the present embodiment, the material of the container is
LiNbO_ThreeBut is not necessarily limited to this
Not glass, ceramics, resin
Or the like may be used. In the present embodiment,
Fixing the supports 4a, 4b of the electromechanical transducer 1 into the container
Direct bonding is used as the fixing means and the container fixing means
However, it is not necessarily limited to this method.
The same characteristics can be exhibited even if the
Wear. Also, in the present embodiment, the mechanical-electrical conversion
The child 1 has a cantilever structure.
Without being limited, both ends of the electromechanical transducer 1
It may be directly joined to the support to form a doubly supported structure.
In addition, the center of the electromechanical transducer 1 is directly joined to the support.
A central support structure may be used. <Third Embodiment> Next, the same parts as in FIGS.
Acceleration sensor having a cantilever structure and method for manufacturing the same
Will be described. 19 and 20 show a third embodiment of the present invention.
FIG. 7 is a process chart showing a method for manufacturing the acceleration sensor in the embodiment.
You. First, as shown in FIG.
LiNbO as a and 12b _ThreePhotoresist using substrate
Sandblast method using strike pattern as masking material
Thus, cantilever portions 11a and 11b were formed. Then
As shown in FIG. 19B, a cantilever portion 11a is formed.
Piezoelectric substrate formed with a piezoelectric substrate 12a and a cantilever 11b.
The plate 12b was joined by direct joining. Direct bonding is on
The two piezoelectric substrates 12 subjected to the hydrophilic treatment as described above
a and 12b are set so that the directions of the polarization axes are opposite to each other.
, And heat-treated. In this case, the piezoelectric
The direct bonding between the substrate 12a and the piezoelectric substrate 12b is made of silicon oxide.
It can also be performed via a buffer layer consisting of a thin film, etc.
is there. Next, as shown in FIG.
Chromium-gold is deposited on both sides of the
The poles 13a and 13b were formed. With this, the cantilever structure
A bimorph-type electromechanical transducer 15 was obtained. Machine
The mechanical-electrical transducer 15 is provided with openings in the piezoelectric substrates 12a and 12b.
The periphery is supported as a support. Also, the piezoelectric substrate 1
The surface of the electrode 2a on the same side as the electrode 13a is electrically connected to the electrode 13a.
In this state, the conductive layer 14a was formed. This conductive layer 14a
Is used to transfer the charge generated at the electrode 13a to the external electrode 20a (FIG. 2).
0 (b), (c)). Further
And a cantilever on the same side of the piezoelectric substrate 12b as the electrode 13b.
On the opposite side (right side in the figure) of the beam portion and the opening of the piezoelectric substrate 12b
The conductive layer 14b was formed so as to conduct. In this case,
The conductive layer 14a or the conductive layer 14b to the electrode 13a or the electrode 13
If it is formed simultaneously with b, the manufacturing process can be simplified.
Next, as shown in FIG. 20A, another LiNbO_Three
Using a photoresist pattern as a masking material on the substrate
The concave portion 17 is formed by using a sand blast method, and the container 1 is formed.
6a and 16b were produced. The containers 16a, 16
b, the conductive layers 14a, 14 on the piezoelectric substrates 12a, 12b
a through hole 18 for electrical connection with
Was. Next, as shown in FIG.
The piezoelectric substrates 12a and 12b on which the commutators 15 are formed
The vessels 16a and 16b were joined by direct joining. to this
Thus, the electromechanical transducer 15 is placed in the containers 16a and 16b.
I contained it. In this case, the piezoelectric substrates 12a and 12b and the container
Direct bonding with 16a, 16b can be made from silicon oxide thin film
It is also possible to perform the process through a buffer layer. Cantilever
The beam is LiNbO_ThreePattern form from substrate to support at the same time
The support part may be bent because of the
LiNbO that also serves as a support part with the vessels 16a and 16b_ThreeBase
More firmly supported by the plate. Piezoelectric substrate (LiN
bO_Three) 12a, 12b and container (LiNbO)_Three) 16
a, a conductive layer (chromium-gold) 14
a, 14b, the piezoelectric substrates 12a,
It is difficult to directly join 2b and containers 16a and 16b.
However, the piezoelectric substrates 12a and 12b and the containers 16a and 16b
The bonding area is sufficiently large compared to the areas of the conductive layers 14a and 14b.
If it is strict, it can be firmly joined. Then,
The conductive layers 14a, 14b are inserted into the through holes 18 of the containers 16a, 16b.
Pour a conductive paste so as to be electrically connected to b
And fired to form through-fall conductive parts 19a, 19b
Done. Furthermore, a through hole is formed on the upper surfaces of the containers 16a and 16b.
The silver conductor is connected to the fall conductive portions 19a, 19b.
The external electrodes 20a and 20b were formed by printing ondium.
Thereby, the electrodes 13a, 1 on the electromechanical transducer 15
3b and the external electrodes 20a and 20b are electrically connected.
Was. Next, as shown in FIG.
The substrate is cut into individual acceleration sensors 104 using a
Was. The electromechanical transducer 15 has a cantilever structure,
It is firmly joined to 16a, 16b. FIG. 20 (c)
Acceleration sensor 104 applies acceleration in the vertical direction.
The mechanical-electrical transducer 15 swings up and down.
Move and bending vibration occurs. When bending vibration occurs, the pressure
One of the circuit boards 12a and 12b is distorted so as to extend, and the other is
Is distorted to shrink. Here, the piezoelectric substrate 12a and the piezoelectric substrate
12b are joined so that their polarization axes are in opposite directions to each other.
Therefore, the stress generated in the piezoelectric substrates 12a and 12b is
Despite being different from compressive stress and tensile stress, piezoelectric
Electric charges of the same polarity are generated on the substrate 12a and the piezoelectric substrate 12b.
You. That is, the piezoelectric substrates 12a and 12b have
An electromotive force is generated in the same direction. Therefore, the mechanical-electrical
The electrodes 13a and 13b formed on both sides of the commutator 15
A signal reflecting the magnitude of the speed can be obtained. machine
The length, thickness and width of the electrical transducer 15 are measured
Is determined in consideration of the frequency range of the acceleration. Measure
The frequency of acceleration becomes the resonance frequency of the electromechanical transducer 15
The sensitivity of the acceleration sensor 104 increases as approaching.
In the measurement frequency range, the sensitivity of the acceleration sensor 104 is
In order not to be very dependent on frequency,
The resonance frequency must be sufficiently separated from the measurement frequency range
It is. This can be achieved, for example, by measuring the highest resonance frequency.
Mechanical-electrical transducer 1 so that the frequency becomes twice the frequency
5 may be designed. As described above, according to the present embodiment,
If you do not use an adhesive layer such as an adhesive,
12a, 12b by joining directly firmly
-Since the electric transducer 15 is formed, variations in characteristics and vibration
Acceleration sensor 1 with high sensitivity without any dynamic attenuation
04 can be realized. Also, a mechanical-electrical transducer
15 are patterned from the piezoelectric substrate,
The variation of the shape of the air transducer 15 is small. In addition, machinery
Since the electrical transducer 15 is formed simultaneously with the support,
-Variation in the support state of the electric transducer 15 is small. this
Therefore, variations in the length of the cantilever are reduced,
Acceleration cell with extremely small variations in characteristics such as vibration frequency
Sensor can be realized. Also, a mechanical-electrical transducer
15, the support member and the containers 16a, 16b are made of the same material.
Because it can be formed, the effect of distortion due to temperature, etc.
A small acceleration sensor that is not subject to
Can be realized. In addition, a large number of
Since the acceleration sensor is manufactured at one time, mass production is possible.
Thus, it is possible to realize an acceleration sensor having excellent characteristics. Book
In the embodiment, the materials of the piezoelectric substrates 12a and 12b
As LiNbO_ThreeBut is not necessarily limited to this.
It is not specified, for example, LiTaO_ThreeAnd crystal
May be used. In the present embodiment, the container 1
LiNbO as a material for 6a, 16b _ThreeUsing
However, it is not necessarily limited to this, for example,
LiTaO_ThreeUsing quartz, silicon, glass, etc.
Good. Preferably a piezoelectric substrate constituting the electromechanical transducer 15
The same material as the plates 12a, 12b is desirable, and optimally a machine
-Of the piezoelectric substrates 12a and 12b constituting the electric transducer 15;
A material having a thermal expansion coefficient close to that of the material is desirable. In addition, this implementation
In the embodiment, the material of the electrodes 13a and 13b is
Uses rom-gold, but is not necessarily limited to this
Instead of using, for example, gold, chrome, silver or alloy materials
May be. In the present embodiment, the roof
Conductive pace as a material of the conductive portions 19a and 19b.
But not necessarily limited to this.
Instead, for example, solder or silver solder may be used. Also,
In the present embodiment, the piezoelectric substrate (LiNbO_Three) 1
Cantilever portions 11a, 11b were formed on 2a, 12b
Later, by joining these directly, bimorph type
Although the electromechanical transducer 15 is formed, the
The order is not limited, and two piezoelectric substrates (Li
NbO_Three) Cantilever after directly joining 12a and 12b
The beams 11a and 11b may be formed. In addition, this implementation
In the embodiment, the cantilever portions 11a and 11b are formed.
After that, the electrodes 13a and 13b are formed.
The order of the electrodes 13a, 13b is not limited.
After forming the cantilever portions 11a and 11b
Is also good. In the present embodiment, the piezoelectric substrate 12
a, 12b cantilever parts 11a, 11b processing method and
How to process recesses 17 and through holes 18 in containers 16a and 16b
Although the sandblast method is used as the
However, the method is not limited to
Ching, wet etching, laser processing, ion beam
Processing, machining such as dicing and wire sawing,
Turret jet machining, electric discharge machining and the like may be used. Ma
In the present embodiment, the shapes of the electrodes 13a and 13b are
Although the vacuum deposition method is used as the formation method,
It is not limited to a method, for example, a sputtering method,
Vapor phase film forming methods such as CVD, and methods such as plating and printing
May be used. Also, in the present embodiment,
Electrodes 20a and 20b are provided on the upper surfaces of containers 16a and 16b
However, it is not necessarily limited to this configuration.
The container 16a, 16b,
You may provide so that it may follow. Also, in this embodiment,
The conductive layers 14a, 14b and the external electrodes 20a, 20b
Is provided with through holes 18 in the containers 16a and 16b.
But is not necessarily limited to this method.
It is not the thing which is cut out,
It may be performed by providing. The conductive layer 14
a, 14b form the electromechanical transducer 15
Piezoelectric substrate (LiNbO)_Three) 12a, 12b and container
(LiNbO_Three) 16a, 16b with sufficient strength
If not bonded, buffer the silicon oxide film on the bonding surface.
If it is formed as a layer and bonded through this, strong bonding strength
You can get the degree. <Fourth Embodiment> FIG. 21 shows a fourth embodiment of the present invention.
FIG. 3 is an exploded perspective view showing the acceleration sensor in a state. FIG.
As shown in FIG. 1, LiNbO_ThreeContainer 27b consisting of
Is a bimorph type electromechanical transducer 21
Provided in a supported state (double-supported beam structure). Ba
The immorph type electromechanical transducer 21 is a piezoelectric substrate (Li
NbO_Three) 22a and 22b are directly joined,
It is configured. The container 27b also contains LiNbO
_ThreeIs directly joined. This place
In this case, the direct joining between the container 27a and the container 27b is made of silicon oxide.
It can also be performed via a buffer layer consisting of a thin film, etc.
is there. In addition, on the outer surfaces of the containers 27a and 27b,
External electrodes 26a and 26b (26b not shown) are formed.
The external electrodes 26a and 26b are electrically
Electrically connected to electrodes 23a and 23b of commutator 21, respectively
Have been. As a result, the voltage on the electromechanical transducer 21 is
Extracting the charges generated at the poles 23a and 23b to the outside
Can be. Thus, the acceleration sensor 105 is configured.
ing. Acceleration sensor 1 having a doubly supported structure according to the present embodiment
05 is also manufactured by the same method as in the third embodiment.
Can be built. That is, as shown in FIG.
First, two piezoelectric substrates (LiNbO_Three) 22a, 22b
And the piezoelectric substrates 22a and 22b are directly
Making bimorph type piezoelectric elements by contact bonding
I do. Next, the electrodes 23a and 23b are placed on the doubly supported beam.
To form a bimorph-type electromechanical transducer 21
You. Next, the external electrodes and the electrodes 23a and 23b are connected.
Conductive layers 24a and 24b (24b is not shown) for
To achieve. The mechanical-electrical converter 21 having the doubly supported structure has
As in the third embodiment, a large number are simultaneously formed on the substrate.
Mass productivity can be improved. Mechanical-electrical transducer 21
The third embodiment is applied to the piezoelectric substrates 22a and 22b on which
LiN with recesses and through holes formed using the same process as in the example
bO_ThreeThe substrates are directly bonded to form a container. Finally,
An external electrode and the like are provided to manufacture an acceleration sensor. Two-sided
When using a beam structure, a machine of the same length and thickness
Even with an electric conversion element, resonance is higher than in the case of a cantilever structure
Higher frequency, higher frequency acceleration
Can be measured. Of the mechanical-electrical transducer 21
Length, thickness and width are the frequency ranges of the acceleration to be measured.
It is determined in consideration of the surroundings. The frequency of the measured acceleration
As the resonance frequency of the mechanical-electrical transducer 21 approaches,
The sensitivity of the sensor 105 increases. Over the measurement frequency range
And the sensitivity of the acceleration sensor 105 is large with respect to the frequency.
In order to avoid resonance, set the resonance frequency to the measurement frequency.
It is necessary to keep it sufficiently away from the wave number range. For this
Is the frequency whose resonance frequency is twice the highest measurement frequency, for example.
It is sufficient to design the electromechanical conversion element 21 so that
No. As described above, according to the present embodiment, the adhesive
Of the piezoelectric substrates 22a and 22b without using an adhesive layer of
The strong direct bonding allows the electromechanical transducer 21
Formed, there is no variation in characteristics and no attenuation of vibration.
To realize an acceleration sensor with high sensitivity.
Wear. Further, the mechanical-electrical transducer 21 is connected to the containers 27a, 27
b, so that the mechanical-electrical transducer 2
1. High accuracy of positioning, length and support of double-supported beam
The state does not vary. As a result, the stability is high,
Measures up to high frequency range with extremely small characteristic variation
A possible small acceleration sensor can be realized. Ma
Further, the container 27a and the container 27b are directly joined.
Thereby, the container 27a and the container 27a can be used without using an adhesive.
Since the vessel 27b is firmly joined, the heat resistance of the joint surface is high.
It becomes. As a result, even if solder reflow is performed,
No gas is generated from the container 27a and the container 2
Since 7b is in a hermetically sealed state, the characteristics are degraded.
And a highly reliable acceleration sensor
You. In the present embodiment, the piezoelectric substrates 22a, 22
LiNbO as material of 2b_ThreeIs used, but always
Is not limited to this, for example, LiTaO
_ThreeOr quartz may be used. In the present embodiment,
Is LiNbO as a material of the containers 27a and 27b. _ThreeFor
Is not necessarily limited to this,
For example, LiTaO_Three, Crystal, silicon, glass, etc.
May be used. Preferably, the electromechanical transducer 21 is formed.
The same material as that of the piezoelectric substrates 22a and 22b
Includes a piezoelectric substrate 22a constituting the electromechanical transducer 21,
A material having a thermal expansion coefficient close to that of the material 22b is desirable. <Fifth Embodiment> FIG. 23 shows a fifth embodiment of the present invention.
FIG. 3 is a circuit configuration diagram of the shock detection device in the state. In FIG.
As shown, the present shock detection device includes an acceleration sensor 40,
The signal output from the acceleration sensor 40 is converted and amplified.
Amplifying circuit 41 and a signal output from amplifying circuit 41
A comparison circuit 42 for comparing a reference signal and recording a shock
A storage device 43 for displaying, a display device 44 for displaying an impact,
Controls the comparison circuit 42, the storage device 43, and the display device 44
And a control circuit 45. Control circuit 45
Therefore, the control device of the device in which the impact detection device is incorporated
Part of the device can also be used. Where the acceleration sensor
The acceleration sensor of the first embodiment (FIG.
6) is used. FIG. 24 shows the configuration of the amplifier circuit.
You. As shown in FIG. 24, the acceleration sensor 40
A resistor R is connected to the gate of the transistor (FET).₁And parallel
Are connected to the signal output from the acceleration sensor 40.
The signal is input to the gate of a field effect transistor (FET)
Is done. In the frequency characteristics of this circuit,
The toe-off frequency is determined by the resistance R₁And the capacitance of the acceleration sensor 40
Quantity C₁And f_c= 1 / 2πR₁C₁In table
Is done. Therefore, f_cAt lower frequencies, the output
Will decrease. The capacitance C of the acceleration sensor 40₁
If there is a large variation in the cutoff frequency f_cNiba
Fluctuation occurs, and the lowest measurable frequency changes. Piezoelectric
In an acceleration sensor using ceramic, the variation in capacitance
There is about 20% variation and the cut-off frequency is about the same
Get on. However, by directly bonding the piezoelectric single crystal substrate of the present invention,
In the manufactured acceleration sensor 40, the capacitance C₁Rose
Is sufficiently small as 7% or less, so that the cutoff frequency f
_cIs also stable, even at low frequency acceleration.
Output is obtained. The signal output from the acceleration sensor 40
The signal is converted and amplified by the amplifier circuit 41. Amplifier circuit
The signal output from 41 is input to comparison circuit 42.
In the comparison circuit 42, the signal output from the amplification circuit 41 is
It is determined whether the signal is larger or smaller than the reference signal. An example
For example, when a shock of 10G or more is applied, the shock is recognized.
And record or display it.
I will tell. FIG. 25 shows the acceleration cell described in the first embodiment.
The output voltage when the output of the sensor is measured by the circuit of FIG.
And the relationship between acceleration and acceleration. As shown in FIG.
Connected to the acceleration sensor 40 when an acceleration of
The magnitude of the signal output from the amplified circuit 41 is 64 mV
It is. In this case, the control circuit 45 outputs 6 as the reference signal.
4 mV is input to the comparison circuit 42. In the comparison circuit 42,
This reference signal is compared with the output signal from the amplifier circuit 41,
When the signal output from the amplification circuit 41 is larger
Generates an output signal and sends it back to the control circuit 45. This
As a result, a shock larger than the standard 10G is applied.
This can be made to be recognized by the control circuit 45. control
The circuit 45 receives a shock larger than the reference 10G.
Command to the storage device 43 to store the
it can. At this time, the magnitude of the acceleration and the date and time when the acceleration was received
Etc. can be recorded. Further, the control circuit 45
If a shock greater than the standard 10G
The display device 44 displays the magnitude and date and time of the strike.
And the display device 44 displays the information. Ma
The control circuit 45 incorporates this impact detection device.
To avoid malfunction and destruction of the entire equipment
You can also issue an order. For example, this shock detection device
If the device is installed on the hard disk,
Instantly writes information from the head to the disc
Stop so that the head does not break when hitting the disc
The head can be commanded to retract. Also,
If this shock detector is installed in a mobile phone,
Command to self-diagnose if there is no
it can. The shock sensor of the present embodiment has an acceleration sensor.
As the acceleration sensor, the acceleration sensor according to the first embodiment (FIG.
Since 6) is used, the sensitivity variation of the acceleration sensor
There is no variation in the resistance and capacitance. As a result, measurement of acceleration
Constant accuracy is high, compared to the reference value when detecting impact
That can make accurate and accurate judgments using a comparison circuit
A detection device can be realized. In addition, shock detection device
Was configured as above, so the impact was detected and recorded
Control circuit to determine the action to protect the equipment from shocks.
To provide a shock detection device capable of giving instructions
Can be.

As described above, according to the present invention,
Since the mechanical-electrical transducer is configured by directly bonding the piezoelectric substrate without using an adhesive layer such as an adhesive, when the mechanical-electrical transducer flexes and vibrates due to acceleration, loss occurs in the piezoelectric substrate. Without stress. As a result, a large starting force is obtained, so that an acceleration sensor having high sensitivity can be realized.
Further, since the bonding of the piezoelectric substrates becomes uniform, variations in the resonance frequency and sensitivity of the electromechanical transducer become extremely small. Furthermore, because there is no adhesive layer between the piezoelectric substrates,
The vibration characteristics of the electromechanical transducer do not change due to the temperature change. In addition, without using an adhesive,
Since the electric transducer is directly joined to the support, the variation in the support position of the electromechanical transducer is reduced. as a result,
An acceleration sensor having a small variation in resonance frequency can be realized. In addition, without using an adhesive,
Since the electrical transducer is bonded directly to the support, acceleration is transmitted to the electromechanical transducer without loss. Further, since there is no adhesive layer between the electromechanical transducer and the support,
The supporting state does not change due to the temperature change. Moreover, since the support of the electromechanical transducer is directly joined to the container without using an adhesive, the support is firmly joined to the container. As a result, it is possible to realize a highly sensitive acceleration sensor capable of transmitting the acceleration generated on the mounting surface to the support through the container without loss. Further, the piezoelectric substrate constituting the piezoelectric element is directly joined to the container without using an adhesive, so that the electromechanical transducer is firmly joined to the container. As a result, the acceleration received by the container can be transmitted to the electromechanical transducer without loss, and a highly sensitive acceleration sensor can be realized.
Further, since the container plays the role of the support member, the number of constituent members can be reduced. In addition, since the respective parts constituting the container are firmly joined without using an adhesive, the heat resistance of the joint surface is increased. As a result, even when solder reflow or the like is performed, no gas is generated from the joint portion, and each part constituting the container is in a state of being hermetically sealed, so that high reliability without deterioration of characteristics is achieved. Can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a mechanical-electrical converter used for an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is an explanatory view showing an interface state of a piezoelectric substrate at each stage of direct bonding in a method of manufacturing a mechanical-electrical transducer used for an acceleration sensor according to a first embodiment of the present invention.

FIG. 3 is a perspective view showing another example of the electromechanical transducer used for the acceleration sensor according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing a bimorph-type electro-mechanical transducer having a cantilever structure according to the first embodiment of the present invention.

FIG. 5 is a sectional view showing a bimorph-type electro-mechanical transducer having a cantilever structure according to the first embodiment of the present invention.

FIG. 6 is an exploded perspective view showing an example of the acceleration sensor according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a state where bending vibration occurs in a bimorph-type mechanical-electrical converter having a cantilever structure according to the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a relationship between a crystal axis of a piezoelectric substrate and a cut angle.

FIG. 9 is a diagram showing a relationship between a cut angle of a LiNbO ₃ substrate and a piezoelectric constant.

FIG. 10 is a frequency characteristic diagram of the acceleration sensor according to the first embodiment of the present invention.

FIG. 11 is a diagram showing a cut angle of the acceleration sensor according to the first embodiment of the present invention.

FIG. 12 is a diagram illustrating a relationship between a cut angle of a quartz substrate and a piezoelectric constant.

FIG. 13 is a diagram showing a relationship between a cut angle of a quartz substrate and a piezoelectric constant.

FIG. 14 is a diagram showing a relationship between a cut angle of a quartz substrate and a piezoelectric constant.

FIG. 15 is a cross-sectional view showing a mechanical-electrical converter used for an acceleration sensor according to a second embodiment of the present invention.

FIG. 16 is an exploded perspective view illustrating an example of an acceleration sensor according to a second embodiment of the present invention.

FIG. 17 is a sectional view illustrating an example of an acceleration sensor according to a second embodiment of the present invention.

FIG. 18 is an exploded perspective view showing another example of the acceleration sensor according to the second embodiment of the present invention.

FIG. 19 is a process chart showing a method for manufacturing an acceleration sensor according to the third embodiment of the present invention.

FIG. 20 is a process chart showing a method for manufacturing an acceleration sensor according to the third embodiment of the present invention.

FIG. 21 is an exploded perspective view illustrating an example of an acceleration sensor according to a fourth embodiment of the present invention.

FIG. 22 is an exploded perspective view showing another example of the acceleration sensor according to the fourth embodiment of the present invention.

FIG. 23 is a circuit configuration diagram of an impact detection device according to a fifth embodiment of the present invention.

FIG. 24 is a circuit diagram showing an amplifier circuit of an impact detection device according to a fifth embodiment of the present invention.

FIG. 25 is a diagram illustrating a relationship between an output and an acceleration when measured by an impact detection device according to a fifth embodiment of the present invention.

FIG. 26 is a perspective view showing a bimorph-type electromechanical transducer according to the related art.

FIG. 27 is a cross-sectional view showing a bimorph-type electro-mechanical transducer having a cantilever structure according to the related art.

FIG. 28 is a cross-sectional view showing a bimorph-type electro-mechanical transducer having a double-supported beam structure according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mechano-electric converter 2a, 2b Piezoelectric substrate 3a, 3b Electrode 5a, 5b Conductive paste 7 Conductive layer 9 External electrode 10 Container

 ──────────────────────────────────────────────────の Continued on the front page (72) Yoshihiro Tomita 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (44)

[Claims] 1. A piezoelectric element comprising at least two piezoelectric substrates having two opposing main surfaces directly joined to each other, and electrodes formed on two opposing main surfaces of the piezoelectric element. An acceleration sensor, comprising: a mechanical-electrical transducer comprising: a support for supporting the mechanical-electrical transducer. 2. The main surfaces of two piezoelectric substrates are joined by bonding the constituent atoms of the two piezoelectric substrates to each other via at least one selected from the group consisting of oxygen and a hydroxyl group. Item 2. The acceleration sensor according to item 1. 3. The acceleration sensor according to claim 1, wherein the two piezoelectric substrates are joined so that the directions of the polarization axes are opposite to each other. 4. The acceleration sensor according to claim 1, wherein the two piezoelectric substrates are directly joined via a buffer layer. 5. The acceleration sensor according to claim 1, wherein one end of the electromechanical transducer is supported by a support. 6. The acceleration sensor according to claim 1, wherein both ends of the electromechanical transducer are supported by a support. 7. A piezoelectric substrate made of a single-crystal piezoelectric material having a crystal structure of 3m group, wherein the single-crystal piezoelectric material has an X-axis and a Y-axis.
When the main surface of the piezoelectric substrate forms an angle with the Y-axis perpendicular to the axis of + 129 ° to + 152 °, and X
The acceleration sensor according to claim 1, wherein a line including an axis and connecting a center of gravity of the piezoelectric substrate and a center of the support portion is perpendicular to the X axis. 8. A piezoelectric substrate made of a single-crystal piezoelectric material having a crystal structure of 3m group, wherein the single-crystal piezoelectric material has an X-axis and a Y-axis.
When the axis and the Z axis are taken, the angle between the main surface of the piezoelectric substrate and the Y axis is perpendicular to the axis of −26 ° to + 26 °, and includes the X axis. X connecting to
The acceleration sensor according to claim 1, wherein the acceleration sensor is parallel to the axis. 9. A piezoelectric substrate made of a single-crystal piezoelectric material having a crystal structure of group 32, wherein the single-crystal piezoelectric material has an X-axis and a Y-axis.
When the axis and the Z axis are set, the main surface of the piezoelectric substrate is perpendicular to the X axis, and the line connecting the center of gravity of the piezoelectric substrate and the center of the supporting portion is Z.
The acceleration sensor according to claim 1, wherein the axis forms an angle of + 52 ° to + 86 ° with the axis. 10. The piezoelectric substrate is made of a single crystal piezoelectric material having a crystal structure of Group 32, and the crystal axis of the single crystal piezoelectric material is X-axis.
When the Y-axis and the Z-axis are used, an angle formed by the main surface of the piezoelectric substrate and the X-axis is perpendicular to an axis of −26 ° to + 26 °, and includes the Y-axis. The acceleration sensor according to claim 1, wherein a line connecting to the center is parallel to the Y axis. 11. The piezoelectric substrate is made of a single-crystal piezoelectric material having a crystal structure of Group 32, and the single-crystal piezoelectric material has an X-axis and a X-axis.
When the Y-axis and the Z-axis are set, the angle between the main surface of the piezoelectric substrate and the X-axis is perpendicular to an axis of + 52 ° to + 68 °, and includes the Z-axis. 2. The acceleration sensor according to claim 1, wherein a line connecting the right and left is perpendicular to the Z axis. 12. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on two opposing main surfaces of the piezoelectric element. An acceleration sensor, comprising: a mechanical-electrical transducer comprising: and a support for supporting the mechanical-electrical transducer, wherein the mechanical-electrical transducer is directly joined to the support. 13. The piezoelectric substrate and the support constituting the electromechanical transducer are connected via at least one of the constituent atoms of the piezoelectric substrate and the constituent atoms of the support selected from the group consisting of oxygen and hydroxyl groups. The acceleration sensor according to claim 12, wherein the acceleration sensor is joined by being connected to each other. 14. The acceleration sensor according to claim 12, wherein the piezoelectric substrate and the support constituting the electromechanical transducer are directly joined via a buffer layer. 15. The acceleration sensor according to claim 12, wherein the piezoelectric substrate and the support are made of the same material. 16. The acceleration sensor according to claim 12, wherein one end of the electromechanical transducer is supported by a support. 17. The acceleration sensor according to claim 12, wherein both ends of the electromechanical transducer are supported by a support. 18. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on two opposing main surfaces of the piezoelectric element. An acceleration sensor comprising: a mechanical-electrical transducer consisting of: . 19. The container and the support are joined by bonding the constituent atoms of the container and the constituent atoms of the support to each other via at least one selected from the group consisting of oxygen and a hydroxyl group. The acceleration sensor according to claim 18. 20. The acceleration sensor according to claim 18, wherein the container and the support are directly joined via a buffer layer. 21. The acceleration sensor according to claim 18, wherein the container and the support are made of the same material. 22. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on two opposing main surfaces of the piezoelectric element. A mechanical-electrical transducer comprising: and a container for accommodating the mechanical-electrical transducer, wherein the piezoelectric substrate constituting the piezoelectric element is directly joined to the container, whereby the mechanical-electrical transducer is Supported acceleration sensor. 23. A piezoelectric substrate and a container are joined by bonding atoms constituting the piezoelectric substrate and atoms constituting the container to each other via at least one selected from the group consisting of oxygen and a hydroxyl group. The acceleration sensor according to claim 22. 24. The acceleration sensor according to claim 22, wherein the piezoelectric substrate and the container are directly joined via a buffer layer. 25. The acceleration sensor according to claim 22, wherein the piezoelectric substrate and the container are made of the same material. 26. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A mechanical-electrical converter comprising: a support for supporting the mechanical-electrical converter; and a container comprising at least two parts for accommodating the mechanical-electrical converter. Is an acceleration sensor that is directly bonded. 27. The container according to claim 26, wherein the parts constituting the container are connected to each other by bonding the constituent atoms of the container to each other via at least one selected from the group consisting of oxygen and a hydroxyl group. Acceleration sensor. 28. The acceleration sensor according to claim 26, wherein the respective parts constituting the container are directly joined via a buffer layer. 29. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A method of manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising: A method for manufacturing an acceleration sensor, comprising forming an element. 30. The method according to claim 2, wherein after the principal surfaces of the two piezoelectric substrates subjected to the hydrophilic treatment are joined, the principal surfaces of the two piezoelectric substrates are joined directly by performing a heat treatment.
10. The method for manufacturing an acceleration sensor according to item 9. 31. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer consisting of: A method for manufacturing an acceleration sensor. 32. The method of manufacturing an acceleration sensor according to claim 31, wherein the support is bonded directly to the piezoelectric substrate by performing a heat treatment after bonding the support subjected to the hydrophilic treatment to the piezoelectric substrate. 33. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: A method for manufacturing an acceleration sensor, wherein the method is directly joined to a container. 34. The method for manufacturing an acceleration sensor according to claim 33, wherein the support is directly bonded to the container by performing a heat treatment after bonding the support subjected to the hydrophilic treatment and the container. 35. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising: A method for manufacturing an acceleration sensor. 36. The method for manufacturing an acceleration sensor according to claim 35, wherein after bonding the piezoelectric substrate subjected to the hydrophilic treatment and the container, the piezoelectric substrate is directly bonded to the container by performing a heat treatment. 37. A piezoelectric element formed by joining the main faces of at least two piezoelectric substrates having two opposing main faces, and an electrode formed on the two opposing main faces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising: a support for supporting the mechanical-electrical transducer; and a container comprising at least two parts for accommodating the mechanical-electrical transducer. And a method of manufacturing an acceleration sensor, wherein each part of the container is directly joined to each other. 38. The method of manufacturing an acceleration sensor according to claim 37, wherein the respective portions of the container are subjected to a heat treatment after the respective portions of the container subjected to the hydrophilic treatment are joined to each other to directly join the respective portions of the container. 39. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising: Directly bonding two piezoelectric substrates to form a plurality of piezoelectric elements, directly bonding a container having a concave portion formed at a portion corresponding to the piezoelectric elements to the piezoelectric substrate, and individually including the piezoelectric elements. Separating the acceleration sensor. 40. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A method for manufacturing an acceleration sensor, comprising: a mechanical-electrical transducer comprising: and a container accommodating the mechanical-electrical transducer, wherein at least two piezoelectric substrates are directly joined, and then a plurality of cantilever portions or A step of forming a plurality of piezoelectric elements by patterning a doubly-supported beam, a step of directly bonding a container having a concave portion formed at a portion corresponding to the piezoelectric element to the piezoelectric substrate, and an individual step including the piezoelectric element. Separating the acceleration sensor into a plurality of acceleration sensors. 41. An electrode is formed on the opposite main surface of the piezoelectric element after forming the piezoelectric element.
3. The method for manufacturing an acceleration sensor according to claim 1. 42. The method of manufacturing an acceleration sensor according to claim 39, wherein after forming an electrode on the piezoelectric substrate, a pattern is formed on the cantilever portion or the doubly supported beam portion. 43. The method for manufacturing an acceleration sensor according to claim 41, wherein a conductive layer is simultaneously formed on the piezoelectric substrate when forming the electrodes. 44. A piezoelectric element formed by joining the main surfaces of at least two piezoelectric substrates having two opposing main surfaces, and an electrode formed on the two opposing main surfaces of the piezoelectric element. A mechanical-electrical transducer comprising: and an acceleration sensor including a support that supports the mechanical-electrical transducer; an amplifier circuit that converts and amplifies a signal output from the acceleration sensor; and An impact detection device comprising: a comparison circuit that compares an output signal with a reference signal; a control circuit that controls a device in which the acceleration sensor is incorporated; and a storage circuit that records an impact.