The present invention relates to an acoustic wave device.
There has been known an acoustic wave device using a plate wave propagating through a piezoelectric film made of LiNbO3 or LiTaO3. For example, Japanese Unexamined Patent Application Publication No. 2012-257019 discloses an acoustic wave device using a Lamb wave as a plate wave. In the acoustic wave device, a piezoelectric substrate is provided on a support body. The piezoelectric substrate is made of LiNbO3 or LiTaO3. An IDT electrode is provided on an upper surface of the piezoelectric substrate. A voltage is applied between multiple electrode fingers of the IDT electrode connected to one side electric potential and multiple electrode fingers of the IDT electrode connected to the other side electric potential. Thus, a Lamb wave is excited. Reflectors are provided on both sides of the IDT electrode. Thus, an acoustic wave resonator using a plate wave is formed.
Japanese Unexamined Patent Application Publication No. 2011-182096 discloses an example of a ladder filter. In the ladder filter, multiple acoustic wave devices are connected by multiple wiring lines. The multiple wiring lines include a wiring line connected to a hot electric potential and a wiring line connected to a ground electric potential. The wiring line connected to the hot electric potential and the wiring line connected to the ground electric potential face each other.
In the acoustic wave resonator as described in Japanese Unexamined Patent Application Publication No. 2012-257019, an unnecessary bulk wave may be excited. The bulk wave propagates in a thickness direction of a piezoelectric substrate. Therefore, the bulk wave may be reflected in a support body. When wiring lines connected to different electric potentials face each other as in Japanese Unexamined Patent Application Publication No. 2011-182096, a signal of an unnecessary bulk wave may be picked up by one wiring line. Alternatively, a signal of an unnecessary bulk wave may be picked up by one of facing busbars. In the cases above, ripples may occur in a frequency characteristic of an acoustic wave device.
Preferred embodiments of the present invention provide acoustic wave devices that are each able to reduce or prevent ripples in a frequency characteristic.
An acoustic wave device according to a preferred embodiment of the present invention includes a support substrate, a piezoelectric layer on the support substrate, a functional electrode on the piezoelectric layer, and a first electrode film and a second electrode film on the piezoelectric layer, facing each other, and having different electric potentials from each other. When a region between the first electrode film and the second electrode film in a plan view is defined as an inter-electrode film region, and a region overlapping with the first electrode film or the second electrode film in a plan view is defined as an electrode film underlying region, a thickness of the piezoelectric layer in at least a portion of the inter-electrode film region is smaller than a thickness of the piezoelectric layer in the electrode film underlying region.
According to preferred embodiments of the present invention, it is possible to provide acoustic wave devices that are each able to reduce or prevent ripples in a frequency characteristic.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings to clarify the present invention.
Each of the preferred embodiments described in the present description is merely an example, and configurations of different preferred embodiments can be partially replaced or combined.
As illustrated in
Each acoustic wave resonator of the present preferred embodiment uses a bulk wave in a thickness shear mode as a main wave. More specifically, each acoustic wave resonator uses a bulk wave in a thickness shear first order mode as a main wave. Each acoustic wave resonator may be a resonator using a plate wave such as, for example, a Lamb wave as a main wave. On the other hand, in the present preferred embodiment, an SH wave is excited as an unnecessary bulk wave in each acoustic wave resonator.
As illustrated in
The first electrode film 28 and the second electrode film 29 face each other. Each of the first electrode film 28 and the second electrode film 29 extends from different acoustic wave resonators. Specifically, in the present preferred embodiment, the first electrode film 28 is a wiring line electrode film connecting the series arm resonator S1 and the parallel arm resonator P1. The second electrode film 29 is a wiring line electrode film connecting the parallel arm resonator P2 and the ground terminal 27. That is, each of the first electrode film 28 and the second electrode film 29 is connected to a functional electrode. Further, the first electrode film 28 is connected to a hot electric potential, and the second electrode film 29 is connected to a ground electric potential.
However, the arrangement of the first electrode film 28 and the second electrode film 29 is not limited to the above. For example, the first electrode film 28 and the second electrode film 29 may be connected to the same functional electrode. The first electrode film 28 may be connected to the ground electric potential, and the second electrode film 29 may be connected to the hot electric potential. It is sufficient that the first electrode film 28 and the second electrode film 29 are arranged to be connected to electric potentials different from each other, and to face each other.
The acoustic wave device 10 includes a piezoelectric substrate 12. The piezoelectric substrate 12 includes a support member 13 and the piezoelectric layer 14. In the present preferred embodiment, the support member 13 includes only a support substrate. The support substrate is, for example, a silicon substrate in the present preferred embodiment. However, the material of the support substrate is not limited to the above, and, for example, sapphire or the like may be used, for example.
The piezoelectric layer 14 includes a first main surface 14a and a second main surface 14b. The first main surface 14a and the second main surface 14b are opposed to each other. Of the first main surface 14a and the second main surface 14b, the second main surface 14b is a main surface on the support member 13 side. The multiple wiring line electrode films are provided on the first main surface 14a. In the present preferred embodiment, the piezoelectric layer 14 is, for example, a lithium niobate layer. More specifically, the piezoelectric layer 14 is, for example, a LiNbO3 layer. However, the piezoelectric layer 14 may be a lithium tantalate layer such as a LiTaO3 layer, for example.
The acoustic wave device 10 includes an electrode film underlying region. The electrode film underlying region is a region overlapping with the first electrode film 28 or the second electrode film 29 in a plan view. More specifically, the electrode film underlying region includes a first electrode film underlying region E1 and a second electrode film underlying region E2. The first electrode film underlying region E1 is a region overlapping with the first electrode film 28 in a plan view. The second electrode film underlying region E2 is a region overlapping with the second electrode film 29 in a plan view. Further, the acoustic wave device 10 includes an inter-electrode film region E3. The inter-electrode film region E3 is a region positioned between the first electrode film 28 and the second electrode film 29 in a plan view. More specifically, the inter-electrode film region E3 is a region positioned between the first electrode film 28 and the second electrode film 29 adjacent to each other. In the present preferred embodiment, the inter-electrode film region E3 is not provided with an electrode film.
In the following description, a thickness of the piezoelectric layer 14 in the first electrode film underlying region E1 is denoted as d1, a thickness of the piezoelectric layer 14 in the second electrode film underlying region E2 is denoted as d2, and a thickness of the piezoelectric layer 14 in the inter-electrode film region E3 is denoted as d3.
In the present preferred embodiment, the thickness d3 in the inter-electrode film region E3 is smaller than the thickness d1 in the first electrode film underlying region E1 and the thickness d2 in the second electrode film underlying region E2. However, it is sufficient that the thickness d3 in at least a portion of the inter-electrode film region E3 is smaller than the thickness of the piezoelectric layer 14 in the electrode film underlying region. That is, it is sufficient that the thickness d3 in at least a portion of the inter-electrode film region E3 is smaller than at least one of the thickness d1 in the first electrode film underlying region E1 and the thickness d2 in the second electrode film underlying region E2. Thus, in the acoustic wave device 10, it is possible to reduce or prevent the influence of an unnecessary bulk wave on a frequency characteristic, and to reduce or prevent ripples in the frequency characteristic. Advantageous effects described above will be illustrated below by comparing the present preferred embodiment with a comparative example.
The comparative example is different from the first preferred embodiment in that the thicknesses of the piezoelectric layers in the first electrode film underlying region, the second electrode film underlying region, and the inter-electrode film region are the same or substantially the same. In the first preferred embodiment, a reflection characteristic as the frequency characteristic between the first electrode film and the second electrode film was measured. Similarly, in the comparative example, a reflection characteristic between a first electrode film and a second electrode film was measured.
As shown in
For example, when an unnecessary bulk wave propagates from the first electrode film 28 to the second electrode film 29, a portion of the bulk wave passes through a portion of the piezoelectric layer 14 positioned in the first electrode film underlying region E1. Another portion of the bulk wave passes through a portion of the piezoelectric layer 14 positioned in the first electrode film underlying region E1 and a portion of the piezoelectric layer 14 positioned in the inter-electrode film region E3. In the first preferred embodiment, the thickness d1 of the piezoelectric layer 14 in the first electrode film underlying region E1 is different from the thickness d3 of the piezoelectric layer 14 in the inter-electrode film region E3. With this, the electromechanical coupling coefficients may be made different from each other in the first electrode film underlying region E1 and in the inter-electrode film region E3. Therefore, the propagation modes of an unnecessary bulk wave may be made different from each other in the first electrode film underlying region E1 and in the inter-electrode film region E3. The relationship between the second electrode film underlying region E2 and the inter-electrode film region E3 is also the same as the relationship between the first electrode film underlying region E1 and the inter-electrode film region E3. Therefore, it is possible to reduce or prevent an unnecessary bulk wave to uniformly propagate between the first electrode film 28 and the second electrode film 29. Accordingly, it is possible to reduce or prevent the influence of an unnecessary bulk wave on a reflection characteristic, and to reduce or prevent ripples in the reflection characteristic as a frequency characteristic.
Hereinafter, the configuration of the present preferred embodiment will be described in more detail.
As illustrated in
Each parallel arm resonator is connected to the ground electric potential via any ground terminal 27 illustrated in
In the present preferred embodiment, the functional electrode of each acoustic wave resonator is, for example, an IDT electrode. This configuration is illustrated below.
An IDT electrode 11 is provided on the first main surface 14a of the piezoelectric layer 14. With this, the series arm resonator S1 is configured. The IDT electrode 11 includes a first busbar 16, a second busbar 17, multiple first electrode fingers 18, and multiple second electrode fingers 19. The first busbar 16 and the second busbar 17 face each other. The first busbar 16 and the second busbar 17 are connected to different wiring line electrode films. The first busbar 16 and the second busbar 17 have different electric potentials from each other.
The first electrode finger 18 is a first electrode. The multiple first electrode fingers 18 are periodically arranged. Each of one ends of the multiple first electrode fingers 18 is connected to the first busbar 16. The second electrode finger 19 is a second electrode. The multiple second electrode fingers 19 are periodically arranged. Each of one ends of the multiple second electrode fingers 19 is connected to the second busbar 17. The multiple first electrode fingers 18 and the multiple second electrode fingers 19 are interdigitated with each other. The IDT electrode 11 may include a single-layer metal film or a multilayer metal film.
In the series arm resonator S1, an acoustic wave is excited by applying an alternating voltage to the IDT electrode 11. As described above, in the first preferred embodiment, the series arm resonator S1 and each of the other acoustic wave resonators use a bulk wave in the thickness shear mode as a main wave. The series arm resonator S1 and each of the other acoustic wave resonators may be resonators using a plate wave such as a Lamb wave as a main wave. On the other hand, in the first preferred embodiment, an SH wave is excited as an unnecessary bulk wave in each acoustic wave resonator.
Here, a direction in which the first electrode finger 18 and the second electrode finger 19 face each other in a plan view is defined as an electrode finger facing direction. The plan view is a direction viewed from above as in
Further, the series arm resonator S1 includes multiple excitation regions C. The excitation region C is also a region in which adjacent electrode fingers overlap with each other when viewed in the electrode finger facing direction. Each excitation region C is a region between electrode fingers in one pair. More specifically, the excitation region C is a region from a center of one side electrode finger in the electrode finger facing direction to a center of the other side electrode finger in the electrode finger facing direction. Therefore, the overlap region D includes multiple excitation regions C. The bulk wave in the thickness shear mode is excited in each excitation region C. On the other hand, when the series arm resonator S1 uses a plate wave, the overlap region D is an excitation region.
In the first preferred embodiment, the support member 13 includes only a support substrate. However, the support member 13 may be a multilayer body including the support substrate and an insulation layer. In the case above, the piezoelectric layer 14 is provided on the insulation layer. As a material of the insulation layer, a silicon oxide, silicon nitride, tantalum oxide, or the like may be used, for example.
As indicated by a broken line in
However, the hollow portion is not limited to a through-hole. The hollow portion may be a cavity portion, for example. The cavity portion includes a recess provided in a support member, for example. More specifically, the cavity portion is provided by sealing the recess with a piezoelectric layer or the like. Alternatively, the piezoelectric layer may be provided with a recess opening on the support member side. With this, a hollow portion may be provided. In the case above, the support member need not include a recess or a through-hole.
The multiple acoustic wave resonators in the acoustic wave device 10 share the piezoelectric substrate 12. Each acoustic wave resonator other than the series arm resonator S1 includes an IDT electrode, similar to the series arm resonator S1. Further, the support member 13 includes multiple hollow portions. Each hollow portion overlaps with at least a portion of the IDT electrode of each acoustic wave resonator in a plan view.
Referring back to
As illustrated in
As described above, it is sufficient that the thickness d3 in at least a portion of the inter-electrode film region E3 is smaller than at least one of the thickness d1 in the first electrode film underlying region E1 and the thickness d2 in the second electrode film underlying region E2. For example, when the inter-electrode film region E3 includes the overlap region D of any acoustic wave resonators, the thickness of the piezoelectric layer 14 in the overlap region D may be the same or substantially the same as the thicknesses d1 and d2.
As illustrated in
In the present preferred embodiment, an unnecessary bulk wave propagates through the piezoelectric layer 34 and the support member 13 in the first electrode film underlying region E1 and the second electrode film underlying region E2. On the other hand, an unnecessary bulk wave propagates only through the support member 13 in the inter-electrode film region E3. Therefore, also in the present preferred embodiment, the same as or similar to the first preferred embodiment, the propagation modes of an unnecessary bulk wave may be made different from each other in the first electrode film underlying region E1 and in the inter-electrode film region E3. The relationship between the second electrode film underlying region E2 and the inter-electrode film region E3 is also the same as the relationship between the first electrode film underlying region E1 and the inter-electrode film region E3. Accordingly, it is possible to reduce or prevent the influence of an unnecessary bulk wave on a frequency characteristic and to reduce or prevent ripples in the frequency characteristic.
The present preferred embodiment is different from the second preferred embodiment in that a dielectric film 45 is provided on the support member 13 in the inter-electrode film region E3. Except for the point described above, the acoustic wave device of the present preferred embodiment has the same or substantially the same configuration as that of the acoustic wave device of the second preferred embodiment.
In the present preferred embodiment, the piezoelectric layer 34 and the support member 13 are laminated in the first electrode film underlying region E1 and the second electrode film underlying region E2. On the other hand, in the inter-electrode film region E3, the dielectric film 45 and the support member 13 are laminated. With this, the electromechanical coupling coefficient may be made different from each other in a portion in the first electrode film underlying region E1 through which an unnecessary bulk wave propagates and in a portion in the inter-electrode film region E3 through which an unnecessary bulk wave propagates. Therefore, the propagation modes of an unnecessary bulk wave may be made different from each other in the first electrode film underlying region E1 and in the inter-electrode film region E3. The relationship between the second electrode film underlying region E2 and the inter-electrode film region E3 is also the same as the relationship between the first electrode film underlying region E1 and the inter-electrode film region E3. Accordingly, it is possible to reduce or prevent the influence of an unnecessary bulk wave on a frequency characteristic and to reduce or prevent ripples in the frequency characteristic.
In a plan view, the dielectric film 45 is provided in an entire or substantially an entire portion where the piezoelectric layer 34 is not provided, in the inter-electrode film region E3. In a plan view, it is sufficient that the dielectric film 45 is provided in at least a portion of a portion where the piezoelectric layer 34 is not provided, in the inter-electrode film region E3.
The Young's modulus of the dielectric film 45 is preferably smaller than the Young's modulus of the support substrate. Thus, an unnecessary bulk wave may effectively be attenuated. Accordingly, ripples in the frequency characteristic may effectively be reduced or prevented. As the material of the dielectric film 45, for example, silicon oxide, silicon nitride, or resin is preferably used. Thus, an unnecessary bulk wave may more reliably be attenuated. However, the material of the dielectric film 45 is not limited to the above.
As in the first preferred embodiment illustrated in
As illustrated in
However, the thickness of the dielectric film 45, the shape of the first surface 45a, and the like are not limited to the above. Hereinafter, there will be described first to fourth modifications of the third preferred embodiment that are different from the third preferred embodiment only in the thickness of the dielectric film or the shape of the first surface. Also in the first to fourth modifications, similar to the third preferred embodiment, ripples in the frequency characteristic may be reduced or prevented.
In the first modification illustrated in
In the second modification illustrated in
In the third modification illustrated in
In the fourth modification illustrated in
In the first to third preferred embodiments, examples are described in which the influence of a signal of an unnecessary bulk wave may be reduced or prevented when the signal of the unnecessary bulk wave propagates between wiring line electrode films in a filter device. However, the acoustic wave device according to the present invention may be an acoustic wave resonator. In the case above, the first electrode film and the second electrode film may be a first electrode finger and a second electrode finger, for example. In the case above, the inter-electrode film region is positioned between the first electrode finger and the second electrode finger. The first electrode film underlying region is a region overlapping with the first electrode finger in a plan view, and the second electrode film underlying region is a region overlapping with the second electrode finger in a plan view. Alternatively, for example, the first electrode film and the second electrode film may be a first busbar and a second busbar, respectively. In the case above, the inter-electrode film region is positioned between the first busbar and the second busbar. The first electrode film underlying region is a region overlapping with the first busbar in a plan view, and the second electrode film underlying region is a region overlapping with the second busbar in a plan view.
The functional electrode is not limited to the IDT electrode. Hereinafter, another example in which the acoustic wave device is an acoustic wave resonator will be described.
As illustrated in
As illustrated in
The first electrode film 58 and the second electrode film 59 face each other. In the present preferred embodiment, the first electrode film underlying region E1, the second electrode film underlying region E2, and the inter-electrode film region E3 in the piezoelectric layer 14 are provided, similar to the configuration of the first preferred embodiment illustrated in
BAW (Bulk Acoustic Wave) such as in the acoustic wave device of the present preferred embodiment may be applied to the filter device illustrated in
Hereinafter, a thickness shear mode and a plate wave will be described in detail. A support member in the following example corresponds to the support substrate.
An acoustic wave device 1 includes a piezoelectric layer 2 made of, for example, LiNbO3. The piezoelectric layer 2 may be made of, for example, LiTaO3. The cut-angle of LiNbO3 or LiTaO3 is, for example, a Z-cut, but may be a rotated Y-cut or an X-cut. Although the thickness of the piezoelectric layer 2 is not particularly limited, in order to effectively excite a thickness shear mode, the thickness of the piezoelectric layer 2 is, for example, preferably about 40 nm or more and about 1000 nm or less, and more preferably about 50 nm or more and about 600 nm or less. The piezoelectric layer 2 has a first main surface 2a and a second main surface 2b opposed to each other. An electrode 3 and an electrode 4 are provided on the first main surface 2a. Here, the electrode 3 is an example of the “first electrode”, and the electrode 4 is an example of the “second electrode”. In
Further, since the acoustic wave device 1 uses a Z-cut piezoelectric layer, the direction orthogonal or substantially orthogonal to the longitudinal direction of the electrodes 3 and 4 is orthogonal or substantially orthogonal to a polarization direction of the piezoelectric layer 2. This is not the case when a piezoelectric body having another cut-angle is used as the piezoelectric layer 2. Here, “orthogonal” is not limited only to being strictly orthogonal but may be substantially orthogonal (an angle formed by the direction orthogonal to the longitudinal direction of the electrodes 3 and 4 and the polarization direction is within a range of about 90°±10°, for example).
A support member 8 is laminated on the piezoelectric layer 2 on the second main surface 2b side via an insulation layer 7. The insulation layer 7 and the support member 8 have a frame shape, and include through-holes 7a and 8a as illustrated in
The insulation layer 7 is made of, for example, silicon oxide. However, for example, in addition to silicon oxide, an appropriate insulation material such as silicon oxynitride, alumina or the like may be used. The support member 8 is made of, for example, Si. The plane orientation of the surface of Si on the piezoelectric layer 2 side may be (100), (110), or (111). Si of the support member 8 preferably has high resistance of about 2 kΩ or more in resistivity, and more preferably has high resistance of about 4 kΩ or more in resistivity, for example. However, the support member 8 may also be made using an appropriate insulation material or semiconductor material.
The multiple electrodes 3 and 4, and the first busbar 5 and the second busbar 6 are made of an appropriate metal or alloy such as, for example, Al, an AlCu alloy or the like. In the present preferred embodiment, the electrodes 3 and 4, and the first busbar 5 and the second busbar 6 have, for example, a structure in which an Al film is laminated on a Ti film. An adhesion layer other than the Ti film may be used.
At the time of driving, an alternating voltage is applied between the multiple electrodes 3 and the multiple electrodes 4. More specifically, an alternating voltage is applied between the first busbar 5 and the second busbar 6. Thus, it is possible to obtain a resonant characteristic using a bulk wave in a thickness shear mode excited in the piezoelectric layer 2. Further, in the acoustic wave device 1, when the thickness of the piezoelectric layer 2 is denoted as d and the distance between centers of any adjacent electrodes 3 and 4 of the multiple pairs of electrodes 3 and 4 is denoted as p, d/p is about 0.5 or less, for example. Therefore, the bulk wave in a thickness shear mode is effectively excited, and a preferable resonant characteristic may be obtained. More preferably, d/p is, for example, about 0.24 or less, and in that case, an even better resonant characteristic may be obtained.
Since the acoustic wave device 1 has the configuration described above, when the number of pairs of the electrodes 3 and 4 is decreased in order to achieve a reduction in size, a decrease in a Q factor is less likely to occur. This is because the propagation loss is small, even when the number of electrode fingers in the reflectors on both sides is decreased. Further, the reason why the number of the electrode fingers may be decreased is that a bulk wave in a thickness shear mode is used. The difference between a Lamb wave used in the acoustic wave device and a bulk wave in the thickness shear mode above will be described with reference to
On the other hand, as illustrated in
As illustrated in
As described above, in the acoustic wave device 1, at least one pair of electrodes including the electrode 3 and the electrode 4 is provided. However, since a wave is not propagated in the X-direction, the number of pairs of electrodes including the electrodes 3 and 4 need not be multiple. That is, it is sufficient that at least one pair of electrodes is provided.
For example, the electrode 3 is an electrode connected to a hot electric potential, and the electrode 4 is an electrode connected to a ground electric potential. However, the electrode 3 may be connected to a ground electric potential and the electrode 4 may be connected to a hot electric potential. In the present preferred embodiment, as described above, at least electrodes in one pair includes an electrode connected to a hot electric potential and an electrode connected to a ground electric potential, and do not include a floating electrode.
Piezoelectric layer 2: LiNbO3 of Euler angles (0°, 0°, 90°), thickness is about 400 nm.
When viewed in the direction orthogonal or substantially orthogonal to the longitudinal direction of the electrodes 3 and 4, a length of a region where the electrodes 3 and 4 overlap with each other, that is, a length of the excitation region C is about 40 μm, the number of pairs of electrodes 3 and 4 is 21, the distance between centers of the electrodes is about 3 μm, the width of the electrodes 3 and 4 is about 500 nm, and d/p is about 0.133.
Insulation layer 7: silicon oxide film of about 1 μm thickness.
Support member 8: Si.
The length of the excitation region C is a size of the excitation region C along the longitudinal direction of the electrodes 3 and 4.
In the present preferred embodiment, inter-electrode distances of the electrode pairs including the electrodes 3 and 4 are all made equal or substantially equal in multiple pairs. That is, the electrodes 3 and the electrodes 4 are arranged with equal or substantially equal pitches.
As is clear in
When the thickness of the piezoelectric layer 2 is denoted as d, and the distance between electrode centers of the electrodes 3 and 4 is denoted as p, d/p is, for example, preferably about 0.5 or less, and more preferably about 0.24 or less in the present preferred embodiment as described above. This will be described with reference to
In the same manner as the acoustic wave device having obtained the resonant characteristic illustrated in
As is clear in
As described above, the number of pairs of at least one pair of electrodes may be one.
For example, when the piezoelectric layer 2 has a variation in thickness, a value obtained by averaging the thickness may be used.
(0°±10°, 0° to 20°, any ψ) Expression (1)
(0°±10°, 20° to 80°, 0° to 60° (1−(θ−50)2/900)1/2) or (0°±10°, 20° to 80°, [180°−60° (1−(θ−50)2/900)1/2] to 180°) Expression (2)
(0°±10°, [180°−30° (1−(ψ−90)2/8100)1/2] to 180°, any ψ) Expression (3)
Accordingly, in a case of Euler angles in the range of Expression (1), Expression (2) or Expression (3) above, the fractional bandwidth may sufficiently be widened, and is preferable.
An acoustic wave device 81 includes a support substrate 82. The support substrate 82 includes a recess that is open to an upper surface. A piezoelectric layer 83 is laminated on the support substrate 82. Thus, the hollow portion 9 is provided. An IDT electrode 84 is provided on the piezoelectric layer 83 above the hollow portion 9. Reflectors 85 and 86 are provided on both sides of the IDT electrode 84 in an acoustic wave propagation direction. In
In the acoustic wave device 81, a Lamb wave as a plate wave is excited by applying an alternating electric field to the IDT electrode 84 above the hollow portion 9. Since the reflectors 85 and 86 are provided on both sides, a resonant characteristic caused by the Lamb wave may be obtained.
The thickness d of the piezoelectric layer 2, illustrated in
In the first preferred embodiment illustrated in
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
This application claims the benefit of priority to U.S. Provisional Application No. 63/052,149 filed on Jul. 15, 2020 and is a Continuation Application of PCT Application No. PCT/JP2021/025633 filed on Jul. 7, 2021. The entire contents of each application are hereby incorporated herein by reference.
Number | Date | Country | |
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63052149 | Jul 2020 | US |
Number | Date | Country | |
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Parent | PCT/JP2021/025633 | Jul 2021 | US |
Child | 18096621 | US |