JP2010151630A - Element and device for detecting acceleration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration detection element for detecting acceleration having a plurality of directions, and improving detection accuracy. <P>SOLUTION: The acceleration detection element includes: a piezoelectric substrate 1; a first acoustic wave element constituted of a first transmission electrode and a first reception electrode, and arranged on one main surface 3 of the piezoelectric substrate 1, for detecting a frequency change following application of an acceleration of a first surface acoustic wave propagating on one main surface 3 of the piezoelectric substrate 1 along a first virtual straight line; and a second acoustic wave element constituted of a second transmission electrode and a second reception electrode, and arranged on one main surface 3 of the piezoelectric substrate 1, for detecting a frequency change following application of an acceleration of a second surface acoustic wave propagating on one main surface 3 of the piezoelectric substrate 1 along a second virtual straight line 6 intersecting the first virtual straight line 5 in a plan view. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an acceleration detection element and an acceleration detection device that detect acceleration.

  Acceleration detectors are used for fall protection of devices equipped with hard disk drives such as portable music players and notebook computers, and for detecting acceleration in automobile navigation systems.

As a method for detecting acceleration, there is known a piezoresistive acceleration detecting device in which at least four piezoresistive elements are provided in the axial direction to be detected on a Si substrate and a bridge circuit is formed by the piezoresistive elements. When a force is applied to such an acceleration detection device, the Si substrate is mechanically deformed and the resistance value of the piezoresistor changes. The acceleration is detected by detecting this as a change in potential of the piezoresistor (see, for example, Patent Document 1).
International Publication No. 88/08522

  However, the conventional acceleration detection device using a piezoresistor has a problem that the temperature dependence of the acceleration detection result is large because the piezoresistor easily changes depending on the temperature.

  The present invention has been devised in view of the above problems, and an object of the present invention is to provide an acceleration detection element and an acceleration detection device excellent in temperature stability.

  An acceleration detecting element according to the present invention is disposed on one main surface of a piezoelectric substrate and the piezoelectric substrate, and is an acceleration of a first surface acoustic wave propagating on the one main surface of the piezoelectric substrate along a first virtual line. A first acoustic wave element that detects a change in frequency due to application; and the piezoelectric substrate along the second imaginary line that is disposed on the one main surface of the piezoelectric substrate and intersects the first imaginary line in plan view. On the other hand, a second acoustic wave element that detects a frequency change accompanying application of acceleration of the second surface acoustic wave propagating through the main surface is provided.

  In addition, the acceleration detecting element according to the present invention includes a piezoelectric substrate and a first surface acoustic wave that is disposed on one main surface of the piezoelectric substrate and propagates along the first main surface of the piezoelectric substrate along a first virtual line. A first acoustic wave element that detects a change in frequency due to application of acceleration; and a first acoustic surface of the piezoelectric substrate that is disposed at a predetermined distance from the first acoustic wave element. A second acoustic wave element that detects a frequency change accompanying the application of acceleration of a second surface acoustic wave propagating along the one principal surface of the piezoelectric substrate along the first acoustic wave when the piezoelectric substrate is viewed in plan A weight portion disposed between the element and the second acoustic wave element and disposed on the other main surface of the piezoelectric substrate facing the one main surface.

  An acceleration detection apparatus according to the present invention includes any one of the acceleration detection elements described above and an IC chip that performs signal processing on output signals of the first and second acoustic wave elements.

  According to the present invention, the first acoustic wave element and the second acoustic wave element that detect acceleration by the frequency change or phase change of the surface acoustic wave are provided on the piezoelectric substrate, so that the frequency change or phase change of the acoustic wave is achieved. Is used for acceleration detection, it is possible to obtain an acceleration detection result that is more stable with respect to temperature changes than acceleration detection using a piezoresistor.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of an acceleration detection element and an acceleration detection device of the present invention will be described in detail with reference to the drawings. The figure is schematic and does not necessarily match the actual dimensional ratio. Further, the present invention is not limited to the following embodiments, and various changes and improvements can be made without departing from the gist of the present invention.

<Acceleration detection element>
-First embodiment-
FIG. 1A is a plan view showing the acceleration detecting element 100 according to the first embodiment, and FIG. 1B is a cross-sectional view corresponding to a cross section taken along line AA ′ of FIG. It is.

  As shown in FIG. 1A, the acceleration detecting element 100 according to the present embodiment is disposed on the piezoelectric substrate 1 and the one main surface 3 of the piezoelectric substrate 1, and propagates through the one main surface 3 of the piezoelectric substrate 1. A first acoustic wave element that detects a frequency change associated with the application of acceleration of one surface acoustic wave, and a second surface acoustic wave that is disposed on one principal surface 3 of the piezoelectric substrate 1 and propagates on the one principal surface 3 of the piezoelectric substrate 1 And a second acoustic wave element for detecting a frequency change accompanying the application of acceleration.

  The piezoelectric substrate 1 has beam portions 1 a to 1 d, and a weight portion 2 is attached to the other main surface 4 of the piezoelectric substrate 1. In each of the beam portions 1a to 1d, acoustic wave elements 7 to 10 for detecting a frequency change of the surface acoustic wave accompanying the application of acceleration are formed. The beam portions 1a to 1d have a flexible portion F1 that bends when subjected to acceleration. In the first embodiment, the flexible portion F1 is a portion of the beam portions 1a to 1d that does not overlap the weight portion 2 in plan view, as shown in FIG. For example, the beam portions 1a to 1d have a length in the longitudinal direction set to 0.3 mm to 0.8 mm, and a width (a length in a direction orthogonal to the longitudinal direction) set to 0.04 mm to 0.2 mm. The thickness is set to 2 μm to 100 μm. Thus, flexibility is expressed by forming the beam portions 1a to 1d to be elongated and thin.

  Thus, the piezoelectric substrate 1 having the beam portions 1a to 1d is made of a piezoelectric material such as lithium niobate or lithium tantalate, which is an isotropic crystal polarized in the thickness direction. Among them, 36 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal, 42 ° ± 3 ° Y-cut X-propagating lithium tantalate single crystal, 64 ° ± 3 ° Y-cut X-propagating lithium niobate single crystal, 41 ° ± The 3 ° Y-cut X-propagating lithium single crystal and the 45 ° ± 3 ° X-cut Z-propagating lithium tetraborate single crystal are more suitable as materials for the piezoelectric substrate 1 because of their large electromechanical coupling coefficient and small frequency temperature coefficient. It is.

  In addition, if the piezoelectric substrate 1 is a piezoelectric crystal material whose pyroelectricity is reduced by solid solution of oxygen defects, Fe, or the like, it is possible to prevent discharge breakdown between IDT electrodes due to the pyroelectric effect. It is preferable in terms of reliability. In the first embodiment, the piezoelectric substrate 1 having the beam portions 1a to 1d can be manufactured by processing, for example, by irradiating a laser or etching a wafer made of the above piezoelectric material.

  When acceleration is applied to such an acceleration detection element 100, a force corresponding to the acceleration acts on the weight portion 2, and the weight portion 2 is displaced, so that the flexible portion F1 of the beam portions 1a to 1d bends. Yes. By providing the weight portion 2, when the acceleration is applied to the acceleration detecting element 100, the amount of bending of the flexible portion F1 can be further increased. The weight portion 2 is disposed at the central portion of the piezoelectric substrate 1.

The weight part 2 has a substantially circular planar shape when viewed in plan, and the length of the radius is set to 0.12 mm to 0.25 mm, for example. Moreover, the thickness of the weight part 2 is set to 0.2 mm-0.625 mm, for example. The planar shape of the weight portion 2 is not limited to a circle, and can be any shape such as a square or a rectangle. The weight part 2 is fixed to the one main surface 3 of the piezoelectric substrate 1 with an adhesive after processing silicon, SiO ₂ or the like into a desired shape. The weight portion 2 may be formed integrally with the piezoelectric substrate 1.

  Further, a frame-shaped fixing portion 50 is provided so as to surround the weight portion 2. The fixed portion 50 has a substantially square planar shape, the length of one side thereof is set to 1.4 mm to 3.0 mm, for example, and the arm width (direction orthogonal to the longitudinal direction of the arm) constituting the fixed portion 50 For example) is set to 0.3 mm to 1.8 mm. Moreover, the thickness of the fixing part 50 from the bottom surface to the top surface of the piezoelectric substrate 1 is set to 0.2 mm to 0.625 mm, for example. Such a fixing portion 50 may be integrally formed by processing the piezoelectric substrate 1 when forming the beam portions 1a to 1d, or another material may be attached with an adhesive.

  Next, the acoustic wave elements 7 to 10 formed on the flexible part F1 will be described.

  FIG. 2 is an enlarged plan view of the acoustic wave element 7 formed on the beam portion 1a. The acoustic wave element 7 illustrated in FIG. 2 includes a transmission electrode 7a and a reception electrode 7b corresponding to the transmission electrode 7a. The transmission electrode 7a and the reception electrode 7b are formed by IDT (Inter Digital Transducer) electrodes. The IDT electrode has a structure in which comb-like electrodes are intertwined. When a voltage is applied, the surface of the piezoelectric substrate 1 on which such an IDT electrode is disposed is distorted, and the frequency according to the electrode finger interval of the IDT electrode. The surface acoustic wave can be generated. Reflectors 7c are arranged on both sides of the transmitting electrode 7a and the receiving electrode 7b. The reflector 7c is composed of striped electrode fingers, and in particular, the reflection efficiency can be improved by making the period of the striped electrode fingers coincide with the period of the electrode finger interval of the transmitting electrode 7a. After a voltage is applied to the transmitting electrode 7a and a surface acoustic wave is transmitted, the surface acoustic wave propagates through the piezoelectric substrate 1 and is repeatedly reflected from the reflector 7c to generate a resonant wave. By detecting the resonance wave with the reception electrode 7b, the resonance frequency of the resonance wave can be detected. The shape of the IDT electrode and reflector shown in the figure is an example, and the shape is not limited to this, and any IDT electrode and reflector shape may be used as long as they have the same effect. The number of electrode fingers of the IDT electrode and the reflector may be several to several hundreds, but these are simplified in the figure.

  The transmitting electrode 7a, the receiving electrode 7b, and the reflector 7c are made of Al or an Al alloy (Al—Cu type, Al—Ti type) or the like, and formed by a thin film forming method such as a vapor deposition method, a sputtering method, or a CVD method. Thereafter, it is formed by patterning into a desired shape by etching or the like. The thickness of these electrodes is preferably about 0.5 to 5 μm for obtaining characteristics as an acoustic wave element. The other acoustic wave elements 8 to 10 have the same configuration as the acoustic wave element 7.

Outgoing electrode 7a~10a and receiving electrode 7b~10b is covered by _{SiO 2,} SiN x, Si, the protective film 51 made of _Al 2 _{O 3} or _the like as shown in FIG. 1 (b). Thereby, it is possible to prevent energization due to the conductive foreign matter, improve power resistance, and prevent contact between electrode fingers of the IDT electrodes when the piezoelectric substrate 1 is bent.

  In the present embodiment, for example, the first acoustic wave element is the acoustic wave element 8 disposed on the flexible part F1 of the beam part 1b, and the second acoustic wave element is on the flexible part F1 of the beam part 1c. It is the acoustic wave element 9 formed in the. Hereinafter, the acoustic wave element 8 is referred to as “first acoustic wave element 8”, the acoustic wave element 9 is referred to as “second acoustic wave element 9”, the transmission electrode 8a of the acoustic wave element 8 is referred to as “first transmission electrode 8a”, and reception. The electrode 8b is referred to as "first receiving electrode 8b", the transmitting electrode 9a of the acoustic wave element 9 is referred to as "second transmitting electrode 9a", and the receiving electrode 9b is referred to as "second receiving electrode 9b".

  The 1st acoustic wave element 8 is an element for detecting the frequency change of the 1st surface acoustic wave accompanying application of acceleration. Here, the first surface acoustic wave is a surface acoustic wave that propagates on the one principal surface 3 of the piezoelectric substrate 1 along the first imaginary straight line 5 drawn on the beam portion 1b in a direction parallel to the beam portion 1b. The first transmitting electrode 8a transmits a first surface acoustic wave, and the first receiving electrode 8b receives the first surface acoustic wave transmitted by the first transmitting electrode 8a.

  The 2nd acoustic wave element 9 is an element for detecting the frequency change of the 2nd surface acoustic wave accompanying application of acceleration. Here, the second surface acoustic wave is a surface acoustic wave that propagates on the one principal surface 3 of the piezoelectric substrate 1 along the second virtual straight line 6 drawn on the beam portion 1c in a direction parallel to the beam portion 1c. The second transmission electrode 9a transmits a second surface acoustic wave, and the second reception electrode 9b receives the second surface acoustic wave transmitted from the second transmission electrode 9a.

  Hereinafter, an acceleration detection method when acceleration parallel to the XY plane is applied in the thus configured acceleration detection element 100 will be described. FIG. 3A is a schematic diagram showing a state in which acceleration parallel to the XY plane is applied in a direction inclined 45 degrees from the beam portion 1a to the beam portion 1d side of the acceleration detecting element 100. FIG. In addition, the white arrow in a figure shows the direction of acceleration. FIG. 3B is a cross-sectional view of FIG. 3A corresponding to a cross section taken along the line AA ′ of FIG. FIG. 3C is a cross-sectional view of FIG. 3A corresponding to a cross section taken along line BB ′ of FIG.

  In FIGS. 3B and 3C, the arrows pointing outwards indicate tensile stresses, and the arrows pointing inward indicate compressive stresses. Further, in one main surface 3 of the beam portions 1a to 1d in FIGS. 3B and 3C, for example, a region R1 of the beam portion 1c shows a region where only compressive stress is applied, and a region R4 of the beam portion 1a shows only tensile stress. Such a region is shown. Similarly, the other regions R2, R3, R5 to R8 indicate regions where stress in the same direction is applied to the one principal surface 3 of the beam portion. The first transmitting electrode 8a and the first receiving electrode 8b constituting the first acoustic wave element 8 are disposed in the region R8. The second transmitting electrode 9a and the second receiving electrode 9b constituting the second acoustic wave element 9 are disposed in the region R1.

  By applying an acceleration as shown in FIG. 3A, a compressive stress is applied to the region R8 where the first acoustic wave element 8 is formed. Since the upper surface of the beam portion 1b in the region R8 bends in the direction of contraction due to the compressive stress, the electrode finger interval of the first transmitting electrode 8a formed in the region R8 is narrowed, and the first transmitted from the first transmitting electrode 8a. The surface acoustic wave changes to the high frequency side.

  Further, by applying the acceleration in this direction, a compressive stress is also applied to the beam portion 1c on which the second acoustic wave element 9 is formed. Since the upper surface of the beam portion 1c in the region R1 bends in the direction of contraction due to compressive stress, the distance between the electrode fingers of the second transmitting electrode 9a formed in the region R1 is narrowed, and the second transmitted from the second transmitting electrode 9a. The surface acoustic wave also changes to the high frequency side.

  At this time, the frequency change is made by comparing the frequency changed by applying the acceleration of the first surface acoustic wave and the second surface acoustic wave with the frequency of the first surface acoustic wave and the second surface acoustic wave before the change. The amount can be determined. Since the frequency change amount is substantially proportional to the acceleration, the magnitude of the acceleration can be obtained. This will be described with reference to FIG.

  FIG. 4 is a diagram for explaining the principle of obtaining the frequency variation of the surface acoustic wave. In this figure, the horizontal axis represents the frequency f, and the vertical axis represents the amplitude intensity I of the surface acoustic wave. Here, f0 in the figure is the frequency before the surface acoustic wave changes. When the electrode finger interval is narrowed, the frequency of the surface acoustic wave changes to the high frequency side and the frequency becomes f1, so the frequency change amount Δf1 is | f1-f0 |. On the other hand, when the electrode finger interval is wide, the frequency of the surface acoustic wave is changed to the low frequency side and the frequency becomes f2, so the frequency change amount Δf2 is | f0−f2 |. Since the frequency change amounts Δf1 and Δf2 are values that change substantially in proportion to the magnitude of the acceleration, the magnitude of the acceleration can be obtained by obtaining the frequency change amount.

  The frequency f0 before the change of the first surface acoustic wave and the second surface acoustic wave may be referred to as appropriate by recording the surface acoustic wave frequency calculated from the computer simulation or the like when designing the electrode finger.

  Moreover, the direction of acceleration can be detected by detecting whether the frequency of the first acoustic wave element 8 and the second acoustic wave element 9 has changed to the high frequency side or the low frequency side. In the first acoustic wave element 8, since the frequency of the first surface acoustic wave is changed to the high frequency side, it can be seen that the electrode finger interval of the first transmitting electrode 8a is narrowed. From this, it can be determined that a compressive stress is applied to the beam portion 1b on which the first transmission electrode 8a is disposed. On the other hand, since the frequency of the 2nd surface acoustic wave also changed to the high frequency side, it turns out that the electrode finger interval of the 2nd transmitting electrode 9a became narrow. From this, it can be determined that a compressive stress is applied to the beam portion 1c on which the second transmission electrode 9a is disposed. In this way, by detecting whether the frequency of the first acoustic wave element 8 and the second acoustic wave element 9 has changed to the high frequency side or the low frequency side due to the application of acceleration, the beam portions 1b, 1c The direction of the stress can be detected, and the direction of the acceleration applied to the acceleration detecting element 100 can be detected based on the detected direction. Note that by synthesizing the measured biaxial acceleration vectors, the direction of the actually applied acceleration can be known.

  As described above, the acceleration detecting element 100 can detect acceleration parallel to the biaxial directions of the XY plane.

  Examples of a method for detecting a frequency change include a method for detecting an intensity change of a certain frequency before and after application of acceleration, a method for detecting a change in frequency spectrum, and the like.

  In such an acceleration detecting element 100, the first acoustic wave element 8 and the second acoustic wave element 9 are formed on the same main surface, so that the acceleration detecting element 100 is located above and below the beam like a conventional external force sensor using a surface acoustic wave. Compared with the case where a transmission electrode and a reception electrode for transmitting and receiving a surface acoustic wave are provided, the amount of bending of the beam can be increased when an external force is applied, so that the detection sensitivity can be improved.

  In the acceleration detection element 100 described above, when the frequency change amount is obtained, the frequency value of the surface acoustic wave before the frequency change needs to be obtained in advance, but the state before the change (no external force is applied). It is not easy to determine whether or not the state is), and in the above-described example, the example of obtaining the frequency of the surface acoustic wave before being changed by simulation has been described. As a means for solving this problem, as shown in FIG. 1, reference acoustic wave elements 7 ′ to 10 ′ are formed on one main surface 3 of a region F <b> 2 that overlaps the weight portion 2 or the fixing portion 50 when viewed in plan. There is a way to arrange. The reference acoustic wave element 7 'includes a reference transmission electrode 7a' that transmits a reference surface acoustic wave and a reference reception electrode 7b 'that receives the reference surface acoustic wave transmitted from the reference transmission electrode 7a'.

  That is, the reference acoustic wave element 7 ′ is disposed on the region F <b> 2 that overlaps the weight portion 2 of the beam portion 1 a when viewed in plan, and the region F <b> 2 is restrained by the weight portion 2 and is not easily bent. Therefore, even if acceleration is applied, the electrode finger interval of the reference acoustic wave element 7 'in the region F2 hardly changes. Therefore, the reference acoustic wave element 7 ′ can be used as a reference surface acoustic wave frequency in which the frequency of the surface acoustic wave hardly changes even when the acceleration is applied and the weight portion 2 is displaced. If the shape of the IDT electrode of the reference acoustic wave elements 7 ′ to 10 ′ is the same as that of the acoustic wave elements 7 to 10, the frequency of the reference surface acoustic wave of the reference acoustic wave elements 7 ′ to 10 ′ and the acoustic wave element The frequency of the surface acoustic waves of 7 to 10 is almost the same frequency. Therefore, when the weight part 2 is displaced by application of acceleration, the frequency change amount is obtained by comparing the frequency of the surface acoustic wave of the acoustic wave elements 7 to 10 with the frequency of the reference surface acoustic wave that hardly changes. It can be easily obtained.

  In FIG. 1, reference acoustic wave elements 7 ′ to 10 ′ corresponding to the acoustic wave elements 7 to 10 are used. However, when the reference acoustic wave elements have the same reference surface acoustic wave frequency, only one is provided. You may do it.

  Moreover, as shown in FIG. 1, it is preferable that the cavity part 55 opened to the other main surface 4 side of the weight part 2 is formed. By forming the cavity portion 55 in this way, for example, the reference surface acoustic wave generated on the one main surface 3 can be reflected to the one main surface 3 side at the interface between the other main surface 4 and air, Loss of the reference surface acoustic wave that is dissipated in the thickness direction of the piezoelectric substrate 1 can be reduced. Furthermore, by providing the cavity portion 55 in the weight portion 2, the condition in which the reference acoustic wave elements 7 ′ to 10 ′ are installed is made closer to the acoustic wave elements 7 to 10 in which the space below the piezoelectric substrate 1 is a gap. Can do. Thereby, the frequency of the surface acoustic wave before changing by application of the acceleration of the actual acoustic wave elements 7 to 10 and the frequency of the reference surface acoustic wave can be made closer. From this, it is possible to accurately detect the acceleration with the acoustic wave elements 7 to 10 using the frequency of the reference surface acoustic waves of the reference acoustic wave elements 7 'to 10'.

Note that an acoustic reflector may be provided instead of the cavity 55 or the weight portion 2 to reflect the surface acoustic wave at the interface between the other main surface 4 and the acoustic reflector. The acoustic reflector is formed by alternately laminating low specific acoustic impedance layers and high specific acoustic impedance layers. The high specific acoustic impedance layer is formed of tungsten, molybdenum or the like as a metal material or AlN, ZnO, Ta ₂ O ₅ , Al ₂ O ₃ or the like as a dielectric material, and the low specific acoustic impedance layer is a heat resistant resin material. It is formed of polyimide resin, fluorine resin, BCB resin or the like.

  In the above description, the first transmitting electrode 8a and the first receiving electrode 8b constituting the first acoustic wave element 8 are both described in the example arranged in the region R8. However, the present invention is not limited to this. Either the first transmitting electrode 8a or the first receiving electrode 8b may be disposed in the region R8.

  For example, the first acoustic wave element 8 may be disposed in the region R8 only in the first transmission electrode 8a, and may be disposed so as to overlap the weight portion 2 or the fixed portion 50 in plan view. . The first acoustic wave element 8 arranged in this manner can detect the acceleration because the frequency of the first surface acoustic wave is changed by changing the electrode finger interval of the first transmitting electrode 8a by applying the acceleration. Since the 1st receiving electrode 8b exists in the position which is hard to bend, since a 1st surface acoustic wave can be received stably, the precision of a detection result can be improved.

  On the other hand, only the first receiving electrode 8b of the first acoustic wave element 8 may be disposed in the region R8, and the first transmitting electrode 8a may be disposed so as to overlap the weight portion 2 or the fixed portion 50 in plan view. Even in the first acoustic wave element 8 arranged in this way, the frequency characteristic of the first surface acoustic wave that can be received by changing the electrode finger interval of the first receiving electrode 8b changes due to the application of acceleration. Therefore, acceleration can be detected. Since the 1st transmission electrode 8a exists in the position which is hard to bend, since a 1st surface acoustic wave can be transmitted stably, the precision of a detection result can be improved.

  As described above, the case where the weight portion 2 is attached to the other main surface 4 of the piezoelectric substrate 1 has been described, but the weight portion 2 may be attached to the one main surface 3. In the above description, the acoustic wave elements 7 to 10 and the weight portion 2 are disposed on the opposing main surfaces, but may be disposed on the same main surface. In that case, all the stresses applied to the beam portions 1a to 1d are reversed.

  In this specification, the piezoelectric substrate 1 includes not only a single piezoelectric material but also a combination of a piezoelectric material and a substrate such as Si or SOI capable of propagating surface acoustic waves. In that case, a piezoelectric material may be formed on a part of the flexible substrate, and the acoustic wave elements 7 to 10 may be formed on the piezoelectric material.

  Next, a method for detecting an acceleration component parallel to the XZ plane (or YZ plane) in such an acceleration detection element 100 will be described.

  As shown in FIG. 1, the acceleration detecting element 100 according to the present embodiment is disposed on the piezoelectric substrate 1 and the one main surface 3 of the piezoelectric substrate 1, and the one main surface 3 of the piezoelectric substrate 1 along the first virtual straight line. A first acoustic wave element that detects a change in frequency associated with the application of acceleration of the first surface acoustic wave that propagates through the piezoelectric substrate 1, and is disposed in a state where a predetermined interval is provided between the first acoustic wave element and the first principal surface 3 of the piezoelectric substrate 1. The second acoustic wave element for detecting the frequency change accompanying the application of the acceleration of the second surface acoustic wave propagating along the first principal surface 3 of the piezoelectric substrate 1 along the first virtual line and the piezoelectric substrate 1 in plan view And a weight portion 2 that is located between the first acoustic wave element and the second acoustic wave element and is disposed on the other principal surface 4 facing the one principal surface 3 of the piezoelectric substrate 1. .

  Hereinafter, a case where acceleration parallel to the Z axis is applied to the acceleration detecting element 100 will be described with reference to FIG. FIG. 5A is a schematic diagram showing a state in which acceleration parallel to the Z-axis is applied, and FIG. 5B is a cross-sectional view taken along the line AA ′ of FIG. FIG. In addition, the white arrow in a figure shows the direction where acceleration is applied.

  In such a method of detecting acceleration parallel to the XZ axis, for example, the first acoustic wave element is the acoustic wave element 9 disposed on the flexible part F1 of the beam portion 1c, and the second acoustic wave element is The acoustic wave element 7 is formed on the flexible portion F1 of the beam portion 1a. Hereinafter, the acoustic wave element 9 is referred to as “first acoustic wave element 9”, the acoustic wave element 7 is referred to as “second acoustic wave element 7”, the transmission electrode 9a of the acoustic wave element 9 is referred to as “first transmission electrode 9a”, and reception. The electrode 9b is referred to as "first receiving electrode 9b", the transmitting electrode 7a of the acoustic wave element 7 is referred to as "second transmitting electrode 7a", and the receiving electrode 7b is referred to as "second receiving electrode 7b".

  The 1st acoustic wave element 9 is an element for detecting the frequency change of the 1st surface acoustic wave accompanying application of acceleration. Here, the first surface acoustic wave is a surface acoustic wave that propagates on the one principal surface 3 of the piezoelectric substrate 1 along the first virtual straight line 6 drawn on the beam portion 1c in a direction parallel to the beam portion 1c. The first transmitting electrode 9a transmits a first surface acoustic wave, and the first receiving electrode 9b receives the first surface acoustic wave transmitted by the first transmitting electrode 9a.

  The 2nd acoustic wave element 7 is an element for detecting the frequency change of the 2nd surface acoustic wave accompanying application of acceleration. Here, the second surface acoustic wave is one of the piezoelectric substrates 1 along the first virtual straight line 6 along which the first surface acoustic wave transmitted by the first acoustic wave element 9 drawn in the direction parallel to the beam portion 1a propagates. It is a surface acoustic wave that propagates through the principal surface 3. The second transmitting electrode 7a transmits a second surface acoustic wave, and the second receiving electrode 7b receives the second surface acoustic wave transmitted by the second transmitting electrode 7a.

  As shown in FIG. 5A, compressive stress is applied to the region R7 where the first acoustic wave element 9 is formed by applying acceleration parallel to the Z-axis. Since the upper surface of the beam portion 1c in the region R7 bends in the direction of contraction due to the compressive stress, the distance between the electrode fingers of the first transmitting electrode 9a formed in the region R7 is reduced, and the first transmitted from the first transmitting electrode 9a. The surface acoustic wave changes to the high frequency side.

  Further, by applying the acceleration in this direction, a compressive stress is also applied to the region R7 where the second acoustic wave element 7 is formed. Since the upper surface of the beam portion 1a in the region R6 bends in the direction of contraction due to the compressive stress, the electrode finger interval of the second transmitting electrode 7a formed in the region R6 is narrowed, and the second transmitted from the second transmitting electrode 7a. The surface acoustic wave also changes to the high frequency side.

  At this time, the frequency change amount of the changed first surface acoustic wave and the second surface acoustic wave is detected, and the direction and magnitude of the acceleration applied to the acceleration detecting element 100 can be obtained similarly to the first embodiment. .

  Thus, acceleration parallel to the XZ direction (or YZ direction) is detected by using the first acoustic wave element and the second acoustic wave element in which the second surface acoustic wave propagates along the first virtual line. can do.

  Alternatively, the acceleration in the triaxial direction may be detected using three or more acoustic wave elements. Of the three or more acoustic wave elements, it is preferable that at least one acoustic wave element does not overlap the virtual line of the other two acoustic wave elements. The detection method is realized by combining the detection method in the XY plane direction and the detection method in the Z-axis direction.

  In the above description, the method for detecting acceleration by using the change in the frequency of the surface acoustic wave has been described. However, the acceleration can also be detected by a phase change caused by a change in the propagation distance of the surface acoustic wave. .

  Hereinafter, a method for detecting the acceleration by the phase change of the surface acoustic wave will be described. Since the basic configuration is the same as that detected by frequency change, the same reference numerals are given to the overlapping portions, and the description thereof is omitted.

  Similar to the case where the acceleration parallel to the XY plane is detected by frequency change, compressive stress is applied to the region R8 where the first acoustic wave element 8 is formed by applying the acceleration as shown in FIG. Since the upper surface of the beam portion 1b in the region R8 bends in the direction of contraction due to the compressive stress, the first surface acoustic wave exchanged between the first transmitting electrode 8a and the first receiving electrode 8b formed in the region R8. The propagation distance is shortened and the phase of the first surface acoustic wave is changed earlier.

  Further, by applying the acceleration in this direction, a compressive stress is also applied to the beam portion 1c on which the second acoustic wave element 9 is formed. Since the upper surface of the beam portion 1c in the region R1 bends in the direction of contraction due to compressive stress, the second surface acoustic wave exchanged between the second transmitting electrode 9a and the second receiving electrode 9b formed in the region R1. The propagation distance is shortened, and the phase of the second surface acoustic wave is changed earlier.

  At this time, by comparing the phases of the first surface acoustic wave and the second surface acoustic wave changed before and after application of the acceleration, the amount of phase change can be obtained and the magnitude of the acceleration can be obtained. This is because the amount of phase change is substantially proportional to the acceleration.

  Further, the direction of acceleration can be detected by detecting whether the phase of the first acoustic wave element 8 and the second acoustic wave element 9 has changed to the faster side or the slower side. Since the first acoustic wave element 8 has changed to the side where the phase of the first surface acoustic wave becomes faster, it can be seen that the propagation distance of the first surface acoustic wave has become shorter. From this, it can be determined that compressive stress is applied to the beam portion 1b on which the first acoustic wave element 8 is disposed. On the other hand, since the phase of the second surface acoustic wave has also changed to an earlier side, it can be seen that the propagation distance of the second surface acoustic wave has become shorter. From this, it can be determined that a compressive stress is applied to the beam portion 1c on which the second acoustic wave element 9 is disposed. Thus, by detecting whether the phase of the first acoustic wave element 8 and the second acoustic wave element 9 has changed to the faster side or the slower side due to the application of acceleration, the beam portions 1b, 1c The direction of the stress can be detected, and the direction of the acceleration applied to the acceleration detecting element 100 can be detected based on the detected direction. Note that by synthesizing the measured biaxial acceleration vectors, the direction of the actually applied acceleration can be known.

  As described above, the acceleration detecting element 100 can detect acceleration parallel to the biaxial directions of the XY plane.

  In this way, in the method of detecting acceleration by phase change, the first transmitting electrode 8a and the first receiving electrode 8b constituting the first acoustic wave element 8 may be arranged as far as possible in the region R8 of the beam portion 1b. preferable. By arranging in this way, the distance of the propagating first surface acoustic wave can be increased, so that the amount of phase change due to the application of acceleration increases and the acceleration detection sensitivity can be increased.

  Furthermore, even when the electrode finger spacing of the transmitting electrodes 7a to 10a changes due to the application of acceleration, the phase of the transmitted surface acoustic wave changes. When the electrode finger interval is widened, the phase of the surface acoustic wave is advanced. On the other hand, when the electrode finger interval is narrowed, the phase of the surface acoustic wave is delayed.

In addition, as a method for detecting acceleration, a combination of a method using phase displacement and a method using frequency change is used to correct one of the acceleration detection results, thereby detecting the acceleration with high accuracy. .
-Second embodiment-
FIG. 6 shows a second embodiment. In the embodiment shown in FIG. 6, the beam portions 1e to 1h, the acoustic wave elements 11 to 14, and the reference acoustic wave elements 11 'to 14' are further increased with respect to the acceleration detection element. With such a configuration, the number of acoustic wave elements involved in detecting the acceleration increases, so that the detection accuracy can be improved. In addition, variation in detected values can be suppressed by increasing the number of acoustic wave elements that detect acceleration.

  FIG. 7 shows still another embodiment. FIG. 7A is a plan view, and FIG. 7B is a cross-sectional view taken along the line CC ′ of FIG. In the embodiments described above, the beam portion is provided as the flexible region. However, the present embodiment is different in that the beam portion is not provided. Specifically, the piezoelectric substrate 1, the first transmitting electrode 65a that transmits the first surface acoustic wave propagating on the piezoelectric substrate 1 along the first imaginary straight line, and the first surface acoustic wave are received. The acoustic wave element 65 including the first receiving electrode 65b, the second transmitting electrode 66a that transmits the second surface acoustic wave propagating on the piezoelectric substrate 1 along the first virtual straight line, and the second surface acoustic wave are received. The surface acoustic wave 66 is composed of the second receiving electrode 66b, and the weight 63 is disposed on the main surface 3. However, the weight part 63 is located between the acoustic wave element 66 and the acoustic wave element 67 when the piezoelectric substrate 1 is viewed in plan. With such a configuration, it is possible to realize a biaxial acceleration detection element that detects acceleration in the XZ direction using the same acceleration detection method as that of the embodiment described in FIG.

  FIG. 8 shows still another embodiment. This embodiment is a modification of the other embodiment shown in FIG. In FIG. 8, in the configuration of FIG. 7, the second transmitting electrode 66 a that transmits the second surface acoustic wave that propagates on the piezoelectric substrate 1 along the second virtual line that intersects the first virtual line in plan view and the second transmitting electrode 66 a. An acoustic wave element 66 including a second reception electrode 66b that receives two surface acoustic waves is disposed. With such a configuration, the acceleration in the XY directions can be detected using the same acceleration detection method as that of the first embodiment described in FIG.

<Acceleration detector>
Next, the acceleration detection device will be described. FIGS. 9 and 10 show an example of an acceleration detection apparatus using the acceleration detection element 100 of FIG. 1 described above. 9 is a plan view with the lid 39 removed, FIG. 10 (a) is a cross-sectional view taken along the line DD ′ of FIG. 9, and FIG. 10 (b) is a cross-sectional view taken along the line EE ′ of FIG. It is. The acceleration detection apparatus shown in FIG. 10 includes a case 101, an acceleration detection element 100 and an IC chip 30 mounted on the case 101.

  The case 101 has a function of protecting the acceleration detection element 100 and is provided with an upper surface side cavity 110 that houses the acceleration detection element 100 and a lower surface side cavity 32 that houses the IC chip 30. The case 101 is formed by laminating a plurality of insulating layers made of a ceramic material or the like. Specifically, the insulating layer arranged at the center in the thickness direction is made of a flat plate-like member, and a predetermined number of frame-like insulating layers are laminated on both sides (upper surface side and lower surface side).

  The upper surface side cavity 110 has a stepped portion, and a plurality of substrate side electrode pads 33 are provided on the stepped portion. The substrate-side electrode pad 33 is electrically connected to an element-side electrode pad 33 ′ provided on the upper surface of the fixed portion 50 of the acceleration detecting element 100 by a metal thin wire 34 made of gold, copper, aluminum or the like. A plurality of external terminals 35 are provided on the lower surface of the case 1, and the external terminals 35 are connected to the substrate-side electrode pads 33 via via-hole conductors 36 provided inside the case 101. That is, the electrical signal of the acceleration detecting element 100 is taken out through the element side electrode pad 33 ′, the metal thin wire 34, the substrate side electrode pad 33, the via hole conductor 36, the external terminal 35, and the like.

  The acceleration detecting element 100 placed on the main surface of the case 101 is joined to the case 101 with an adhesive 38. As the adhesive 38, for example, a silicone resin or an epoxy resin can be used. In particular, it is preferable to use a silicone resin from the viewpoint of relaxing the residual stress during bonding. A spherical spacer member 37 having a predetermined diameter is mixed in the adhesive 38 so that a gap having a predetermined size is formed between the lower surface of the weight portion 2 and the main surface of the case 101. That is, the size of the gap between the lower surface of the weight portion 2 and the main surface of the substrate 1 can be controlled by the spacer member 37. The spacer member 37 is a spherical member having a predetermined hardness such as silica, silicon, divinylbenzene, and the diameter thereof is, for example, 2 to 20 μm.

  When the beam portions 1 a to 1 d are connected to the central portions of the four upper sides of the weight portion 2 as in this embodiment, the acceleration detection element 100 and the case 101 can be joined at the four corners of the fixed portion 50. preferable. Thereby, the distance between the joint location of the acceleration detection element 100 to the case 101 and the beam portions 1a to 1d is increased. Therefore, it is possible to reduce the influence of the residual stress that can be generated due to the joining by the adhesive 38 on the beam portions 1a to 1d, and to suppress the deterioration of the electrical characteristics of the acceleration detecting device.

  A lid 39 is fixed to the upper surface of the case 101 so as to close the opening of the upper surface side cavity 110 that accommodates the acceleration detection element 100, whereby the acceleration detection element 100 is hermetically sealed in the upper surface side cavity 110. Yes. The lid 39 is made of a metal plate such as 42 alloy or stainless steel, and is joined to the case 101 by a thermosetting resin such as an epoxy resin.

  On the other hand, the IC chip 30 is mounted on the lower surface side of the case 101 while being accommodated in the lower surface side cavity 32. The IC chip 30 has a function of processing the output signal of the acceleration detection element 100, and is electrically connected to the acceleration detection element 100 and the external terminal 35 via a via-hole conductor 36 or a wiring conductor provided in the case 101. It is connected to the. For example, the IC chip 30 includes an amplifier circuit that amplifies the output signal of the acceleration detection element 100, a temperature compensation circuit that corrects the temperature characteristics of the acceleration detection element 100, a noise removal circuit that removes noise, and the like. . By providing such an IC chip 30, acceleration can be detected with high accuracy.

(A) is a typical top view which shows an example of embodiment of the acceleration detection element of this invention. (B) is typical sectional drawing when cut | disconnecting by the AA 'line of (a). It is a typical top view showing an example of an embodiment of an acoustic wave element concerning an acceleration detection element of the present invention. It is a figure for demonstrating the case where the acceleration parallel to an XY-axis direction is applied to the acceleration detection element shown in FIG. (A) is the schematic diagram which looked at the time of applying the acceleration of an XY-axis direction about the acceleration detection element of FIG. (B) is typical sectional drawing equivalent to the cross section cut | disconnected by the AA 'line of FIG. (C) is typical sectional drawing equivalent to the cross section cut | disconnected by the BB 'line | wire of FIG. It is a figure explaining the principle which calculates | requires the amount of frequency changes in an acoustic wave element. It is a figure for demonstrating the case where the acceleration parallel to a Z-axis direction is applied to the acceleration detection element shown in FIG. (A) is a schematic diagram when acceleration in the Z-axis direction is applied to the acceleration detection element of FIG. 1. (B) is typical sectional drawing equivalent to the cross section cut | disconnected by the AA 'line of FIG. It is a typical top view which shows an example of other embodiment of the acceleration detection element of this invention. (A) is a typical top view which shows an example of other embodiment of the acceleration detection element of this invention. (B) is typical sectional drawing when cut | disconnecting by CC 'line of (a). It is a typical top view which shows an example of other embodiment of the acceleration detection element of this invention. It is a typical top view in the state where a lid of an acceleration detecting device concerning an embodiment of the present invention was omitted. FIG. 10 is a schematic cross-sectional view of the acceleration detection device shown in FIG. 9, and (a) is a schematic cross-sectional view corresponding to a cross section taken along the line DD ′ of FIG. 9. FIG. 10B is a schematic cross-sectional view corresponding to a cross section taken along line EE ′ of FIG.

Explanation of symbols

1: Piezoelectric substrate 2: Weight part 3: One main surface 4: Other main surface 5: First virtual straight line 6: Second virtual straight line 7: Acoustic wave element 7a: Transmitting electrode 7b: Receiving electrode 7c: Reflectors 8, 9 10: Acoustic wave element 51: Protective layer 55: Cavity

Claims (11)

A piezoelectric substrate;
A first acoustic wave element that is disposed on one main surface of the piezoelectric substrate and detects a frequency change associated with application of acceleration of a first surface acoustic wave that propagates along the first main surface of the piezoelectric substrate along a first virtual line When,
Application of acceleration of a second surface acoustic wave disposed on the one principal surface of the piezoelectric substrate and propagating on the one principal surface of the piezoelectric substrate along a second imaginary line intersecting the first imaginary line in plan view An acceleration detection element comprising: a second acoustic wave element that detects a frequency change or a phase change associated with. The piezoelectric substrate has a flexible portion that bends when subjected to acceleration,
The first acoustic wave element includes a first transmission electrode that transmits the first surface acoustic wave, and a first reception electrode that receives the first surface acoustic wave,
The second acoustic wave element includes a second transmission electrode that transmits the second surface acoustic wave, and a second reception electrode that receives the second surface acoustic wave,
The acceleration detection according to claim 1, wherein at least one of the first transmission electrode and the first reception electrode and at least one of the second transmission electrode and the second reception electrode are disposed on the flexible portion. element. The acceleration detecting element according to claim 2, further comprising a weight portion disposed on the other main surface facing the one main surface of the piezoelectric substrate. A piezoelectric substrate;
A first acoustic wave element that is disposed on one main surface of the piezoelectric substrate and detects a frequency change associated with application of acceleration of a first surface acoustic wave that propagates along the first main surface of the piezoelectric substrate along a first virtual line When,
A second elastic surface disposed on the one main surface of the piezoelectric substrate with a predetermined distance from the first acoustic wave element and propagating on the one main surface of the piezoelectric substrate along the first virtual line A second acoustic wave element for detecting a frequency change associated with application of wave acceleration;
A weight part that is located between the first acoustic wave element and the second acoustic wave element when viewed in plan, and that is disposed on the other principal surface of the piezoelectric substrate that faces the one principal surface. And an acceleration detecting element. The piezoelectric substrate has a flexible portion that bends when subjected to acceleration,
The first acoustic wave element includes a first transmission electrode that transmits the first surface acoustic wave, and a first reception electrode that receives the first surface acoustic wave,
The second acoustic wave element includes a second transmission electrode that transmits the second surface acoustic wave, and a second reception electrode that receives the second surface acoustic wave,
The acceleration detection according to claim 4, wherein at least one of the first transmission electrode and the first reception electrode and at least one of the second transmission electrode and the second reception electrode are disposed on the flexible portion. element. The acceleration detecting element according to claim 3, wherein the first and second receiving electrodes are arranged in a region overlapping the weight portion of the one main surface when the piezoelectric substrate is viewed in plan. A reference transmission electrode for transmitting a reference surface acoustic wave, disposed in a region overlapping the weight portion of the one main surface when the piezoelectric substrate is viewed in plan;
The acceleration detection according to claim 3, further comprising: a reference receiving electrode that is disposed in a region overlapping with the weight portion of the one main surface when the piezoelectric substrate is viewed in plan, and that receives the reference surface acoustic wave. element. The weight portion has a hollow portion that opens to the other main surface side, and the reference transmitting electrode and the reference receiving electrode overlap with the opening surface of the hollow portion when the piezoelectric substrate is viewed in plan view. The acceleration detecting element according to claim 7, which is disposed in A frame-shaped fixing portion disposed on the piezoelectric substrate and surrounding the weight portion;
A reference transmission electrode for transmitting a reference surface acoustic wave, disposed in a region overlapping the fixed portion of the one main surface when the piezoelectric substrate is viewed in plan;
The acceleration detection according to claim 3, further comprising: a reference receiving electrode that is disposed in a region overlapping the fixed portion of the one main surface when the piezoelectric substrate is viewed in plan, and that receives the reference surface acoustic wave. element. The acceleration detecting element according to claim 1, wherein the piezoelectric substrate is made of an isotropic crystal polarized in a thickness direction. The acceleration detecting element according to any one of claims 1 to 10,
An acceleration detection apparatus comprising: an IC chip that performs signal processing on output signals of the first and second acoustic wave elements.

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