JP2015099039A - Piezoelectric acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric acceleration sensor capable of detecting acceleration applied in a Z-axis direction and achieving downsizing.SOLUTION: There is provided a piezoelectric acceleration sensor 1 that detects acceleration using a variation in resonance frequency when the acceleration is applied. In the piezoelectric acceleration sensor, a recess 2a is provided in a substrate 2 and a piezoelectric vibration element 3 having a piezoelectric film 5 is disposed at a gap formed by the recess 2a. The piezoelectric vibration element 3 is fixed to a support surface of the substrate 2. The piezoelectric vibration element 3 has the piezoelectric film, and first and second electrodes 6 and 7 provided to be in contact with the piezoelectric film. Furthermore, a neutral plane of stress caused by the acceleration applied to the piezoelectric vibration element 3 is positioned within the gap.

Description

  The present invention relates to a piezoelectric acceleration sensor used for detection of acceleration, and more particularly to a resonance frequency change type piezoelectric acceleration sensor.

  Conventionally, acceleration sensors have been used in electronic devices such as hard disk drives and vehicle airbag devices. As a sensor for detecting acceleration with high accuracy, various types of piezoelectric acceleration sensors of a resonance frequency change type have been proposed. Patent Document 1 below discloses a piezoelectric acceleration sensor having a double tuning fork type crystal vibrating element. In Patent Document 1, a double tuning fork type crystal vibrating element is bonded to a support substrate with an adhesive. The double tuning fork type crystal resonator element is housed in a vacuum sealed container.

  In Patent Document 1, when the thickness direction is the Z-axis direction, the force applied by the double tuning fork type crystal resonator element in the Z-axis direction is converted into the forces in the X-axis direction and the Y-axis direction, whereby the acceleration in the X-axis direction Can be detected.

  On the other hand, Non-Patent Document 1 below discloses a resonance frequency change type piezoelectric acceleration sensor having a double tuning fork type piezoelectric vibration element using an AlN piezoelectric thin film.

JP 2012-242343 A

Journal of Microeletromechanical Systems, Vol.18, No3, June 2009

  In the acceleration sensor described in Patent Document 1, the double tuning fork type crystal vibrating element is bonded to the support substrate with an adhesive, but it is difficult to bond with high accuracy. For this reason, there is a concern that the sensitivity may be lowered due to the misalignment. In addition, since quartz is used, it is difficult to reduce the size. Furthermore, since the surroundings of the double tuning fork type quartz vibrating element are in a vacuum, the resonance Q of the structure itself is extremely large. Therefore, there was a problem that it was easy to break.

  On the other hand, in the piezoelectric acceleration sensor described in Non-Patent Document 1, the direction of acceleration to be detected is the same as the vibration direction of the piezoelectric vibration element. Therefore, the acceleration applied in the thickness direction of the piezoelectric vibration element, that is, the Z-axis direction cannot be detected. Furthermore, the inside is housed in a vacuum sealed container, and there is a problem that the manufacturing cost is high.

  An object of the present invention is to provide a piezoelectric acceleration sensor that can detect acceleration applied in the Z-axis direction and can be miniaturized.

  The piezoelectric acceleration sensor according to the present invention is a piezoelectric acceleration sensor that detects acceleration based on a change in resonance frequency when acceleration is applied. The piezoelectric acceleration sensor according to the present invention includes a support having a support surface provided with a recess, and a gap formed by the recess with respect to the bottom surface of the recess. The support is fixed to the support surface of the support. A piezoelectric vibration element disposed with a gap therebetween, wherein the piezoelectric vibration element includes a piezoelectric film having a slit, and first and second electrodes provided so as to be in contact with the piezoelectric film. A neutral surface of stress caused by acceleration applied to the vibration element is located in the gap or the inside of the support.

  In a specific aspect of the piezoelectric acceleration sensor according to the present invention, the piezoelectric vibration element includes a vibrator main body portion and a connecting portion connected to the vibrator main body portion, and the connecting portion is provided on the support body. It is fixed to the support surface.

  In another specific aspect of the piezoelectric acceleration sensor according to the present invention, the connecting portion is connected to one end and the other end of the vibrator main body in the length direction.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, the vibrator body is a vibrator body that vibrates in a contour vibration mode.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, the vibrator main body has a rectangular planar shape having a length direction, and the slit is provided to extend in the length direction. It has been.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, a mass adding portion for adding mass is connected to one of the connecting portions.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, the mass adding portion is configured integrally with the support.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, in the piezoelectric vibration element, the first electrode and the second electrode overlap with each other through at least a part of the layer of the piezoelectric thin film. Are arranged as follows.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, the piezoelectric vibration element is a double tuning fork type piezoelectric vibration element.

  In still another specific aspect of the piezoelectric acceleration sensor according to the present invention, the first and second electrodes have a plurality of electrode fingers that are interleaved with each other to form an interdigital electrode.

  According to the piezoelectric acceleration sensor according to the present invention, the piezoelectric vibration element is disposed so as to be separated from the bottom surface of the concave portion with a gap formed by the concave portion of the support, and the acceleration is applied to the piezoelectric vibration element. Since the neutral plane of the stress is located in the gap or in the support, the acceleration applied in the Z-axis direction, that is, the thickness direction of the piezoelectric vibration element can be detected. Further, the size can be reduced.

1 is a perspective view of a piezoelectric acceleration sensor according to a first embodiment of the present invention. (A) is a top view of the piezoelectric acceleration sensor of the 1st Embodiment of this invention, (b) is sectional drawing in alignment with the AA in (a), (c) is (a) It is sectional drawing which follows the BB line in the inside. It is a top view for demonstrating the dimension of each part of the piezoelectric type acceleration sensor of the 1st Embodiment of this invention. It is a figure which shows the impedance characteristic of the piezoelectric acceleration sensor of the 1st Embodiment of this invention. It is a figure which shows the Example of the piezoelectric acceleration sensor of the 1st Embodiment of this invention, and the acceleration and frequency shift amount of the piezoelectric acceleration sensor of a comparative example. It is a top view of the piezoelectric acceleration sensor which concerns on the 2nd Embodiment of this invention. It is a top view of the piezoelectric acceleration sensor which concerns on the 3rd Embodiment of this invention. It is a perspective view of the piezoelectric acceleration sensor which concerns on the 4th Embodiment of this invention. It is a perspective view of the piezoelectric acceleration sensor which concerns on the 5th Embodiment of this invention.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a perspective view of a piezoelectric acceleration sensor according to the first embodiment of the present invention, and FIG. 2A is a plan view of the piezoelectric acceleration sensor. 2 (b) and 2 (c) are cross-sectional views along the lines AA and BB in FIG. 2 (a).

  The piezoelectric acceleration sensor 1 is a piezoelectric acceleration sensor that detects acceleration based on a change in resonance frequency when acceleration is applied.

  In the piezoelectric acceleration sensor 1, as shown in FIG. 2A, the length direction is the X-axis direction, one direction in the X-axis direction is the direction X1, and the other direction is the direction X2. The width direction is defined as the Y-axis direction, one direction in the Y-axis direction is defined as direction Y1, and the other direction is defined as direction Y2. And as shown in FIG.2 (b), let the thickness direction be a Z-axis direction.

The piezoelectric acceleration sensor 1 of the present embodiment has a support 2. The support 2 has a rectangular shape in plan view. The support 2 is made of silicon in the present embodiment. However, the support 2 may have a structure including a Si substrate and an insulating film such as a SiO ₂ film provided on the Si substrate.

  Moreover, the support body 2 has the main-body part 2b. The main body 2b has a rectangular planar shape and has an upper surface 2c. On the upper surface 2 c of the support 2, a concave portion 2 a opened upward is formed.

  As shown in FIG.2 (c), the support beam 2d is provided in the lower surface of the main-body part 2b in the edge part by the side of the said direction X2 of the main-body part 2b of the support body 2. As shown in FIG. The support beam 2d is used to support the piezoelectric acceleration sensor 1 from the outside.

  However, the support beam 2d may not be provided. That is, you may support from the exterior in any part of the edge part of the said direction side of the support body 2. As shown in FIG. The piezoelectric acceleration sensor 1 is fixed to the outside at the end on the X2 direction side and is supported by a cantilever beam.

  At the end of the main body 2b on the X1 direction side, a mass adding portion 2e is provided on the lower surface of the main body 2b. The mass addition part 2e functions as a weight that urges the end of the support 2 on the X1 direction side downward.

  In this embodiment, the mass addition part 2e is integrally comprised with the same material as the main-body part 2b. But the mass addition part 2e may be comprised with another material. In that case, what is necessary is just to join the mass addition part 2e to the lower surface of the main-body part 2b of the support body 2. FIG.

  Although the main body 2b has a rectangular planar shape as described above, the above-described recess 2a is formed on the upper surface 2c. The recess 2a is not particularly limited, but has a rectangular planar shape and reaches both ends in the Y1 direction and the Y2 direction as shown in FIGS. 2 (a) and 2 (b). That is, the recesses 2 a are formed so as to reach both ends of the support 2 of the piezoelectric acceleration sensor 1 in the width direction.

  A piezoelectric vibration element 3 is fixed to the upper surface 2c of the support 2 as an acceleration detection element. The piezoelectric vibration element 3 has a vibrator body 3X. The vibrator main body 3X has a rectangular planar shape whose length direction is the X-axis direction. The vibrator body 3X is formed with a first slit 8a and a second slit 8b. The first slit 8a and the second slit 8b have an elongated rectangular planar shape whose length direction is the X-axis direction.

  Outside the first slit 8a, a first drive unit 3a is provided so as to extend in parallel with the first slit 8a. The outside of the second slit 8b is the second drive unit 3b. The second driving unit 3b also extends in parallel with the second slit 8b.

  The lengths of the first drive unit 3a and the second drive unit 3b are equal to the first and second slits 8a and 8b. That is, both ends in the length direction of the first drive unit 3a and the second drive unit 3b are equal to both ends in the length direction of the first and second slits 8a and 8b. And the connection parts 3d and 3e are provided so that it may connect with the length direction both ends of the 1st drive part 3a and the 2nd drive part 3b. The connecting portions 3d and 3e are provided so as to reach both ends of the piezoelectric acceleration sensor 1 in the width direction.

  The connecting portions 3d and 3e have a rectangular shape extending in the width direction. A vibrator central portion 3c extending in the length direction at the center in the width direction is provided in parallel with the first and second drive portions 3a and 3b.

  A first connecting portion 3d is provided so as to connect one end in the length direction of the first and second driving portions 3a, 3b and the vibrator central portion 3c, that is, the X-axis direction. On the other hand, the second connecting portion 3e is provided so as to connect the other ends in the length direction of the first driving portion 3a, the second driving portion 3b, and the vibrator central portion 3c, that is, the X-axis direction. .

  The first and second connection portions 3 d and 3 e are provided so as to reach both ends in the width direction of the piezoelectric acceleration sensor 1.

  In the present embodiment, the vibrator main body 3X is constituted by the first and second drive parts 3a and 3b, the vibrator center part 3c, and the connection parts 3d and 3e. The vibrator body 3X has a rectangular outer shape.

  On the other hand, first and second connecting portions 3f and 3g are provided at the centers of the outer edges of the first and second connecting portions 3d and 3e, respectively. Here, the outside means the side away from the center of the vibrator body 3X. The outer end of the first connecting portion 3f is connected to the first support portion 3h. The first support portion 3h is provided so as to reach both ends in the width direction. Similarly, the outer end of the second connecting portion 3g is connected to the second support portion 3i. The 1st support part 3h and the 2nd support part 3i are parts joined to the upper surface 2c of the support body 2 mentioned above.

  By the way, the vibrator main body 3X, the first and second connecting portions 3f and 3g, and the first and second support portions 3h and 3i are integrally configured using a piezoelectric thin film. More specifically, in the present embodiment, a first AlN film 4 as a holding film and a second AlN film 5 as a film using a piezoelectric effect are stacked. A first electrode 6 is laminated between the first AlN film 4 and the second AlN film 5. The first electrode 6 is provided so as to reach the entire region of the vibrator main body 3X, the first and second connection portions 3f and 3g, and the first and second support portions 3h and 3i.

  On the other hand, in the drive units 3 a and 3 b, the second electrode 7 is laminated on the upper surface of the second AlN film 5. The second AlN film 5 is oriented in the C axis and is polarized in the thickness direction.

  The operation of the piezoelectric acceleration sensor 1 of this embodiment will be described.

  In driving, an alternating electric field is applied between the first electrode 6 and the second electrode 7. Accordingly, the vibrator main body 3X of the piezoelectric vibration element 3 vibrates in the contour mode, and resonance characteristics are obtained.

  In the first embodiment, since it can be driven in a mode similar to the contour vibration, it can be driven at a frequency of 1 MHz or more. Also, the electromechanical coupling coefficient is good. Therefore, it can be easily vibrated in the atmosphere.

  On the other hand, when a force due to acceleration acts on the piezoelectric acceleration sensor 1, the resonance characteristic changes. The acceleration can be detected by the change in the resonance characteristics.

  The change in the resonance characteristics is not particularly limited, but may be an appropriate change such as a change in the impedance value at the resonance frequency, a change in the frequency position of the resonance frequency, a change in the impedance at the antiresonance frequency, or a change in the position of the antiresonance frequency. Changes in factors can be used.

  When the acceleration acts in the Z-axis direction, that is, in the thickness direction of the piezoelectric vibration element 3, the piezoelectric vibration element 3 expands and contracts. That is, according to the present embodiment, the piezoelectric vibration element 3 is fixed to the support 2 with the gap based on the recess 2 a as described above. Further, the piezoelectric vibration element 3 is arranged with a gap based on the concave portion 2a, and a neutral plane of stress due to acceleration in the Z-axis direction applied to the piezoelectric acceleration sensor 1 is located in the gap. . Therefore, compressive stress or tensile stress is applied to the piezoelectric vibrator 3, and expansion and contraction occurs in the piezoelectric vibration element 3, and acceleration in the Z-axis direction can be detected.

  Note that the neutral surface of the stress due to the acceleration in the Z-axis direction applied to the piezoelectric acceleration sensor 1 may be located not in the gap but in the main body 2 b of the support 2, that is, in the support 2. Even in this case, compressive stress or tensile stress is applied to the piezoelectric vibrator 3, and the piezoelectric vibration element 3 expands and contracts, and acceleration in the Z-axis direction can be detected.

  In the present embodiment, the piezoelectric acceleration sensor 1 vibrates in an in-plane vibration mode such as contour vibration. Therefore, even when the gap due to the recess 2 a is small, the piezoelectric vibration element 3 is difficult to contact the main body 2 b of the support 2. Therefore, it is possible to configure the piezoelectric acceleration sensor 1 that can detect the acceleration in the Z-axis direction by using a so-called MEMS structure.

  Furthermore, when the contour vibration is used, the piezoelectric vibration element 3 can be vibrated in the atmosphere without requiring a vacuum package. For example, even when contour vibration having a resonance frequency of 1 MHz or more is used, it can be easily vibrated in the atmosphere. Therefore, it is not necessary to store the piezoelectric vibration element 3 in the vacuum package. Therefore, the manufacturing cost can be reduced. In addition, downsizing is possible.

  In addition, in this embodiment, since the said mass addition part 2e is provided, a measurement sensitivity can be improved much more effectively. But the mass addition part 2e does not necessarily need to be provided.

In the present embodiment, the first AlN film 4 is used as a holding film. However, the holding film is not necessarily formed of a piezoelectric material such as AlN. That is, it is the second AlN film 5 sandwiched between the first electrode 6 and the second electrode 7 that actively uses the piezoelectric action. Therefore, the first AlN film 4 positioned below the first electrode 6 can be formed of an appropriate material such as another dielectric material of SiO ₂ film or another piezoelectric material.

  Next, an acceleration detection test between the example of the above embodiment as a specific simulation example and a comparative example will be described. FIG. 3 shows the dimensions of each part related to the piezoelectric acceleration sensor 1 according to the embodiment prepared as an example, and these dimensions are set as shown in Table 1 below.

  FIG. 4 is a diagram illustrating resonance characteristics when no acceleration is applied in the piezoelectric acceleration sensor 1 of the present embodiment. FIG. 4 shows that the resonance frequency is 17.4 MHz and the electromechanical coupling coefficient is about 6.5%. Therefore, it can be seen that the resonance characteristics are good.

  FIG. 5 shows the relationship between the acceleration when the acceleration is applied in the Z-axis direction and the frequency shift amount Δf (Hz) of the resonance frequency in the piezoelectric acceleration sensor of the above embodiment.

  As a comparative example, a comparative example using only the piezoelectric vibration element 3 in which the support 2 made of Si was not used was prepared. The acceleration and frequency shift amount in this comparative example are also shown in FIG.

  As is apparent from FIG. 5, when the support 2 is not provided, the frequency shift amount changes in a quadratic function with respect to the gravitational acceleration. On the other hand, according to the embodiment, the frequency shift amount changes linearly with respect to the magnitude of the acting acceleration. Therefore, according to the embodiment, it can be understood that the acting acceleration in the Z-axis direction can be detected with high accuracy.

  In the above embodiment, an AlN film is used as the piezoelectric film, but various other piezoelectric films such as a PZT film can be used. The thickness of the piezoelectric film sandwiched between the first and second electrodes 6 and 7 is not limited to the above experimental example, and can be set to an appropriate thickness as long as it is a thin film of about 100 nm to 3 μm.

  Further, although the first and second electrodes 6 and 7 are made of molybdenum, they can be made of various metals such as tungsten, copper, aluminum, ruthenium, or alloys thereof.

  As described above, the support 2 is not limited to Si, and can be formed of various dielectrics or insulators.

  FIG. 6 is a schematic plan view of the piezoelectric acceleration sensor 21 according to the second embodiment of the present invention. In the present embodiment, the vibrator main body 23 includes a comb-shaped first electrode 25 and a comb-shaped second electrode 26. The plurality of electrode fingers of the first electrode 25 and the plurality of electrode fingers of the second electrode 26 are interleaved with each other. That is, an interdigital electrode is configured. As described above, the first and second electrodes 25 and 26 provided so as to be in contact with the piezoelectric film 24 may constitute interdigital electrodes. Even in this case, the resonance characteristic can be obtained by applying an alternating electric field between the first electrode 25 and the second electrode 26. Since the resonance characteristics change when acceleration is applied, the acceleration can be detected as in the first embodiment.

  In the second embodiment, the vibrator body 23 is configured in substantially the same manner except that the vibrator body 23 is different from the piezoelectric vibration element 3 of the first embodiment. Accordingly, the same parts are denoted by the same reference numerals, and other descriptions are omitted.

  Also in the second embodiment, the vibrator main body 23 is floated from the support 2 with a gap (not shown). The neutral plane of the stress caused by the acceleration applied to the vibrator body 23 is located in the gap. Therefore, similarly to the first embodiment, the acceleration acting in the Z-axis direction can be detected also in the second embodiment. In addition, since the MEMS structure is also adopted in this embodiment, manufacturing is easy and miniaturization is possible.

  Also in the second embodiment, the neutral surface of the stress due to the acceleration in the Z-axis direction applied to the piezoelectric acceleration sensor 21 is not located in the gap but in the main body 2b of the support 2, that is, inside the support 2. You may do it. Even in this case, compressive stress or tensile stress is applied to the piezoelectric vibrator 3, and the piezoelectric vibration element 3 expands and contracts, and acceleration in the Z-axis direction can be detected.

  In the second embodiment, since the IDT electrode is configured, it can be vibrated in the Lamb wave mode. Therefore, it can be vibrated in a high frequency range of several hundred MHz to several MHz.

  FIG. 7 is a plan view of the piezoelectric acceleration sensor 31 of the third embodiment. In the present embodiment, the vibrator main body is provided with one slit 38 extending in the length direction at the center in the width direction. Drive units 39a and 39b are provided on both sides of the slit 38, respectively. Since other structures are the same as those of the first embodiment, the same parts are denoted by the same reference numerals, and detailed description thereof is omitted.

  However, when the piezoelectric vibration element 33 shown in FIG. 7 is used, a vacuum package is required. However, even in this case, since the vibrator body is formed with a gap therebetween, and the neutral surface of the stress is located in the gap, acceleration acting in the Z-axis direction can be detected. . Furthermore, since it can process using a MEMS process, size reduction and highly accurate processing are possible.

  FIG. 8 is a perspective view of a piezoelectric acceleration sensor 41 according to the fourth embodiment of the present invention. In the present embodiment, a mass adding unit 42e is used instead of the mass adding unit 2e of the first embodiment. The mass addition part 42e has a main body part 42e1. The main body 42 e 1 is connected to one end in the length direction of the support 2. And the main-body part 42e1 is extended to the width direction both outer side exceeding the width direction full length of the support body 2. As shown in FIG.

  Further, projecting portions 42e2 and 42e3 extending in parallel with the length direction of the support 2 are connected from both ends of the main body portion 42e1. Thus, you may provide the mass addition part 42e larger than the mass addition part 2e of 1st Embodiment. In that case, since the mass addition action by the mass addition part 42e is large, the measurement sensitivity can be further enhanced.

  Further, like the piezoelectric acceleration sensor 51 shown in FIG. 9, two piezoelectric acceleration sensors 1 and 1 may be connected to each other by a mass adding portion 52e with their lengthwise ends being brought into contact with each other. In this case, each piezoelectric acceleration sensor 1, 1 may be supported by the end of the piezoelectric acceleration sensor 1, 1 that is not connected to the mass adding portion 52e.

  Furthermore, since the slit is provided as in the first embodiment, the length of vibration is easily changed, and the frequency change amount can be increased.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric acceleration sensor 2 ... Support body 2a ... Concave part 2b ... Main-body part 2c ... Upper surface 2d ... Support beam 2e ... Mass addition part 3 ... Piezoelectric vibration element 3a, 3b ... 1st, 2nd drive part 3c ... Vibrator Central part 3d, 3e ... 1st, 2nd connection part 3f, 3g ... 1st, 2nd connection part 3h, 3i ... 1st, 2nd support part 3X ... Vibrator body 4 ... 1st AlN film 5 ... 2nd AlN films 6, 7 ... 1st, 2nd electrode 8a, 8b ... 1st, 2nd slit 21 ... Piezoelectric acceleration sensor 23 ... Vibrator body 24 ... Piezoelectric film 25, 26 ... 1st , Second electrode 31 ... piezoelectric acceleration sensor 33 ... piezoelectric vibration element 38 ... slits 39a, 39b ... driving part 41 ... piezoelectric acceleration sensor 42e ... mass addition part 42e1 ... main body parts 42e2, 42e3 ... projection part 52e ... mass addition Part

Claims (10)

A piezoelectric acceleration sensor that detects acceleration by a change in resonance frequency when acceleration is applied,
A support having a support surface provided with a recess;
A piezoelectric vibration element that is fixed to a support surface of the support and is disposed with a gap formed by the recess with respect to a bottom surface of the recess;
The piezoelectric vibration element includes a piezoelectric film having a slit, and first and second electrodes provided in contact with the piezoelectric film,
A piezoelectric acceleration sensor, wherein a neutral plane of stress due to acceleration applied to the piezoelectric vibration element is located in the gap or in the support.   2. The piezoelectric vibration element according to claim 1, comprising: a vibrator main body portion; and a connecting portion connected to the vibrator main body portion, wherein the connecting portion is fixed to the support surface of the support body. Piezoelectric acceleration sensor.   3. The piezoelectric acceleration sensor according to claim 1, wherein the connecting portion is connected to one end and the other end of the vibrator main body in the length direction.   The piezoelectric acceleration sensor according to claim 1, wherein the vibrator main body is a vibrator main body that vibrates in a contour vibration mode.   The said vibrator main-body part has a rectangular planar shape which has a length direction, and the said slit is provided so that it may extend in the said length direction. Piezoelectric acceleration sensor.   The piezoelectric acceleration sensor according to claim 3, wherein a mass adding portion that adds mass is connected to one of the connecting portions.   The piezoelectric acceleration sensor according to claim 6, wherein the mass adding portion is configured integrally with the support body.   In the said piezoelectric vibration element, the said 1st electrode and the said 2nd electrode are arrange | positioned so that it may overlap through at least one part layer of the said piezoelectric thin film. A piezoelectric acceleration sensor according to 1.   The piezoelectric acceleration sensor according to claim 8, wherein the piezoelectric vibration element is a double tuning fork type piezoelectric vibration element.   8. The piezoelectric device according to claim 1, wherein the first and second electrodes have a plurality of electrode fingers that are interleaved with each other to form an interdigital electrode. 10. Type acceleration sensor.

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