JP2012257019A - Elastic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave device which uses plate waves and has excellent device properties.SOLUTION: An elastic wave device includes: a support body; a piezoelectric substrate; and an IDT electrode 12. A cavity part 10a is provided at the support body. The piezoelectric substrate is provided on the support body so as to overlap with the cavity part 10a. The IDT electrode 12 is provided on the piezoelectric substrate so as to overlap with the cavity part 10a. In the elastic wave device, plate waves are excited by the IDT electrode 12. An end edge part of the cavity part 10a does not include a linear part extending parallel to the propagation direction of the plate waves excited by the IDT electrode 12.

Description

  The present invention relates to an elastic wave device. In particular, the present invention is provided with a support in which a cavity is formed, a piezoelectric substrate provided on the support so as to overlap the cavity, and provided on the piezoelectric substrate so as to overlap with the cavity. The present invention relates to an elastic wave device including an IDT electrode.

  Conventionally, surface acoustic wave devices and boundary acoustic wave devices have been used as filter devices and resonators used in RF circuits such as cellular phones.

  However, in the surface acoustic wave device and the boundary acoustic wave device, it is difficult to sufficiently increase the frequency characteristics such as the resonance frequency and the pass band and stop band of the filter device. In view of this, for example, the following Patent Document 1 proposes an elastic wave device using a Lamb wave as an elastic wave device capable of increasing the frequency characteristics.

  Specifically, Patent Document 1 describes an acoustic wave device 100 as shown in FIGS. 19 and 20. The acoustic wave device 100 includes a substrate 101. The substrate 101 is provided with a cavity 101a. A laminated resonator 102 is provided on the substrate 101. The laminated resonator 102 is disposed so as to cover the cavity 101a. The laminated resonator 102 includes a lower electrode layer 103, a lower piezoelectric layer 104, an IDT electrode 105, an upper piezoelectric layer 106, and an upper electrode layer 107.

  As shown in FIG. 20, the portion of the laminated resonator 102 where the IDT electrode 105 is provided is located on the cavity 101a. The cavity 101a has a rectangular shape, and the direction in which the short side of the cavity 101a extends and the direction y in which the electrode fingers of the IDT electrode 105 extend are parallel to each other. For this reason, the direction in which the long side of the cavity 101 a extends is parallel to the propagation direction x of the elastic wave (Lamb wave) excited by the IDT electrode 105.

JP 2007-31164 A

  The elastic wave device 100 has a problem that it is difficult to obtain sufficiently excellent device characteristics because it is difficult to sufficiently suppress deterioration of device characteristics due to unnecessary waves.

  The present invention has been made in view of such a point, and an object thereof is to provide an elastic wave device using plate waves and having excellent device characteristics.

  A first acoustic wave device according to the present invention includes a support, a piezoelectric substrate, and an IDT electrode. A cavity is formed in the support. The piezoelectric substrate is provided on the support so as to overlap the cavity. The IDT electrode is provided on the piezoelectric substrate so as to overlap the cavity. In the first acoustic wave device according to the present invention, a plate wave is excited by the IDT electrode. The edge portion of the hollow portion does not include a straight portion extending in parallel with the propagation direction of the plate wave excited by the IDT electrode.

  In a specific aspect of the first acoustic wave device according to the present invention, the end edge portion of the cavity portion does not include a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave.

  In another specific aspect of the first acoustic wave device according to the present invention, the maximum value of the width in the intersecting width direction perpendicular to the propagation direction of the plate wave in the cavity is 50 of the wavelength determined by the electrode finger pitch of the IDT electrode. Is less than double.

  In another specific aspect of the first acoustic wave device according to the present invention, the IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along a cross width direction perpendicular to the propagation direction of the plate wave. And a pair of comb-like electrodes that are interleaved with each other. At least a part of the edge of the cavity is provided so as to overlap the bus bar.

  In still another specific aspect of the first acoustic wave device according to the present invention, the cavity is provided such that at least a part of the region where the plurality of electrode fingers are provided overlaps with the edge of the cavity. Yes.

  In still another specific aspect of the first acoustic wave device according to the present invention, the end edge of the cavity has a plurality of irregularities.

  In still another specific aspect of the first acoustic wave device according to the present invention, the IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along a cross width direction perpendicular to the propagation direction of the plate wave. And a pair of comb-like electrodes that are interleaved with each other. The bus bar has a portion extending in a direction inclined with respect to the propagation direction of the plate wave.

  In another specific aspect of the first acoustic wave device according to the present invention, the bus bar does not include a straight line portion extending in parallel with the propagation direction of the plate wave.

  In still another specific aspect of the first acoustic wave device according to the present invention, the bus bar does not have a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave.

  The second acoustic wave device according to the present invention includes a support, a piezoelectric substrate, and an IDT electrode. A cavity is formed in the support. The piezoelectric substrate is provided on the support so as to overlap the cavity. The IDT electrode is provided on the piezoelectric substrate so as to overlap the cavity. In the second acoustic wave device according to the present invention, a plate wave is excited by the IDT electrode. The IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along an intersecting width direction perpendicular to the plate wave propagation direction, and includes a pair of comb-like electrodes that are interleaved with each other. The bus bar has a portion extending in a direction inclined with respect to the propagation direction of the plate wave.

  In a specific aspect of the second acoustic wave device according to the present invention, the bus bar does not include a straight line portion extending in parallel with the propagation direction of the plate wave.

  In another specific aspect of the second elastic wave device according to the present invention, the bus bar does not have a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave.

  ADVANTAGE OF THE INVENTION According to this invention, it is an elastic wave apparatus using a plate wave, Comprising: The elastic wave apparatus which has the outstanding device characteristic can be provided.

It is a partial notch schematic perspective view of the elastic wave device concerning a 1st embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. It is a schematic plan view illustrating a Lamb wave of S ₀ mode. It is a schematic plan view illustrating a Lamb wave of S ₁ mode. It is a schematic plan view illustrating a Lamb wave of A ₀ mode. It is a schematic plan view illustrating a Lamb wave of A ₁ mode. It is a schematic plan view for explaining an SH wave of SH ₀ mode. It is a schematic plan view for demonstrating SH wave of SH ₁ mode. It is a schematic plan view of the cavity part and IDT electrode in 1st Embodiment. It is a schematic plan view of the cavity part and IDT electrode in 2nd Embodiment. It is a schematic plan view of the cavity part and IDT electrode in 3rd Embodiment. It is a schematic plan view of the cavity part and IDT electrode in 4th Embodiment. It is a typical top view of a cavity part and IDT electrode in a 5th embodiment. It is a schematic plan view of the cavity part and IDT electrode in 6th Embodiment. It is a schematic plan view of the cavity part and IDT electrode in 7th Embodiment. It is a typical sectional view showing a part of hollow part in the 1st modification. It is a typical sectional view showing a part of hollow part in the 2nd modification. It is a typical sectional view showing a part of hollow part in the 3rd modification. 1 is a schematic cross-sectional view of an acoustic wave device described in Patent Document 1. FIG. 1 is a schematic plan view of an elastic wave device described in Patent Document 1. FIG.

  Hereinafter, an example of the preferable form which implemented this invention is demonstrated. However, the following embodiment is merely an example. The present invention is not limited to the following embodiments.

  Moreover, in each drawing referred in embodiment etc., the member which has a substantially the same function shall be referred with the same code | symbol. The drawings referred to in the embodiments and the like are schematically described, and the ratio of the dimensions of the objects drawn in the drawings may be different from the ratio of the dimensions of the actual objects. The dimensional ratio of the object may be different between the drawings. The specific dimensional ratio of the object should be determined in consideration of the following description.

(First embodiment)
FIG. 1 is a partially cutaway schematic perspective view of an acoustic wave device according to a first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG.

As shown in FIGS. 1 and 2, the elastic wave device 1 includes a support 10. The constituent material of the support 10 is not particularly limited. Specific examples of the constituent material of the support 10 that is preferably used include LiNbO ₃ , LiTaO ₃ , quartz, silicon, glass, sapphire, alumina, ceramic, and the like.

  The support 10 is provided with a cavity 10 a that opens to the main surface 10 b of the support 10. A piezoelectric substrate 11 is provided on the main surface 10 b of the support 10. The piezoelectric substrate 11 is provided so as to overlap the cavity 10a in the z direction (stacking direction).

  The maximum value of the width in the intersecting width direction y perpendicular to the plate wave propagation direction x of the cavity 10 a is 50 times or less the wavelength determined by the IDT electrode 12.

The piezoelectric substrate 11 can be composed of an appropriate piezoelectric body. The piezoelectric substrate 11 can be composed of, for example, LiNbO ₃ , LiTaO ₃ , ZnO, AlN, quartz, or the like.

The thickness t of the piezoelectric substrate 11 is not particularly limited as long as a plate wave to be described in detail later is suitably excited. For example, Euler angles (0 °, 33 °, 0 °) in the case of exciting a Lamb wave of _{A 1} mode, which is described below with reference to LiTaO ₃ film, acoustic velocity 8400M / sec or more, the electromechanical coupling coefficient ^{k 2} 5. In order to set it to 8% or more, it is preferable that the thickness t of the piezoelectric substrate 11 is not more than 0.30 times the wavelength determined by the IDT electrode 12.

  On the piezoelectric substrate 11, a regular IDT electrode 12 and a pair of reflectors 13 and 14 are provided. The pair of reflectors 13 and 14 are disposed on both sides of the IDT electrode 12 in the plate wave propagation direction x. In the present embodiment, the IDT electrode 12 and the reflectors 13 and 14 are provided so as to overlap the cavity 10a in the z direction.

  The IDT electrode 12 and the reflectors 13 and 14 can be made of an appropriate conductive material. The IDT electrode 12 and the reflectors 13 and 14 are, for example, a metal selected from the group consisting of Al, Pt, Au, Ag, Cu, Ni, Ti, Cr, and Pd, or Al, Pt, Au, Ag, Cu. , Ni, Ti, Cr, and Pd can be used to form an alloy containing one or more metals selected from the group consisting of Pd. Moreover, the IDT electrode 12 and the reflectors 13 and 14 can also be comprised by the laminated body of the some electrically conductive film which consists of the said metal and an alloy.

  The IDT electrode 12 has a pair of comb-like electrodes 12a and 12b. The pair of comb-like electrodes 12a and 12b are interleaved with each other. Each of the comb-like electrodes 12a and 12b includes bus bars 12a1 and 12b1 and a plurality of electrode fingers 12a2 and 12b2. Each of the plurality of electrode fingers 12a2 extends from the bus bar 12a1 toward the bus bar 12b1 along the y direction. The plurality of electrode fingers 12a2 are arranged at an interval along the x direction. On the other hand, each of the plurality of electrode fingers 12b2 extends from the bus bar 12b1 toward the bus bar 12a1 along the y direction. The plurality of electrode fingers 12b2 are arranged at intervals from each other along the x direction.

  In the acoustic wave device 1 of the present embodiment, a plate wave is excited by the IDT electrode 12.

  Here, the “plate wave” is an elastic wave propagating in a medium sandwiched between two free boundary surfaces.

  The plate wave includes a Lamb wave and an SH wave. The Lamb wave is an elastic wave mainly composed of a component in the plate wave propagation direction x (P component) and a component in the thickness direction of the piezoelectric substrate 11 (SV component). On the other hand, the SH wave is an elastic wave mainly composed of a component (SH component) in a direction y perpendicular to the plate wave propagation direction and horizontal to the propagation surface.

The Lamb wave includes a Lamb wave in a symmetric mode (S mode) and a Lamb wave in an asymmetric mode (A mode). The S-mode Lamb wave includes an S ₀ mode Lamb wave shown in FIG. 3 in which the number of nodes in the thickness direction is 0, and an S ₁ mode Lamb wave shown in FIG. 4 in which the number of nodes in the thickness direction is 1. And are included. The A-mode Lamb wave includes an A _0- mode Lamb wave shown in FIG. 5 in which the number of nodes in the thickness direction is 0, and an A _1- mode Lamb wave shown in FIG. 6 in which the number of nodes in the thickness direction is 1. And are included. It also includes higher-order Lamb waves with a large number of nodes.

The SH wave includes an SH wave in the SH ₀ mode shown in FIG. 7 in which the number of nodes in the thickness direction is 0 and an SH wave in the SH ₁ mode shown in FIG. 8 in which the number of nodes in the thickness direction is 1. It is.

Furthermore, piezoelectric materials such as LiTaO ₃ and LiNbO ₃ exhibit elastic anisotropy because the elastic constants and piezoelectric constants differ depending on the crystal orientation, and the plate wave propagating through the anisotropic crystal has a P component, SV The component and the SH component propagate while being combined. A plate wave having a large vibration displacement of the P component and the SV component and a small vibration displacement of the SH component is also included in the Lamb wave, and a plate wave having a small vibration displacement of the P component and the SV component and a large vibration displacement of the SH component is also converted into the SH wave. Including.

  The plate wave excited by the IDT electrode 12 propagates along the plate wave propagation direction x.

  When a potential is applied to the electrode fingers 12a2 and 12b2 of the IDT electrode 12, mechanical distortion occurs in the piezoelectric substrate 11, and plate waves are excited at various portions of the electrode fingers 12a2 and 12b2. These plate waves are considered to be element waves excited by a point wave source. According to Huygens' principle, an element wave of a plate wave is radiated on an arc and overlaps with surrounding element waves to form a wavefront parallel to the intersecting width direction y.

  Since the length of the electrode fingers 12a2 and 12b2 of the IDT electrode 12 is finite, a part of the plate wave leaks outside the ends of the electrode fingers 12a2 and 12b2. At least a part of the leaked plate wave is reflected at a location where the acoustic impedance is mismatched. Examples of the location where the acoustic impedance is mismatched include the end of the bus bar and the edge of the cavity constituting the membrane. In particular, in the case of a plate wave, since a plate wave cannot exist outside the cavity 10a, a large reflection occurs at the edge of the cavity 10a.

  For example, in the conventional acoustic wave device 100 shown in FIGS. 19 and 20, the cavity portion 101a is rectangular, and the edge portions 101a1 and 101a2 on the long side of the cavity portion 101a are parallel to the plate wave propagation direction x. The plate wave excited and leaked by the IDT electrode 105 is reflected at the edge portions 101a1 and 101a2 at the same reflection angle as the incident angle. Therefore, when reflected by a parallel reflecting surface, it leaks at the same angle as when leaked from the IDT electrode 105. After re-incidence, the signal is received by the IDT electrode 105. That is, the phase of the plate wave reflected at the edge portions 101a1 and 101a2 of the cavity 101a matches the main mode. Therefore, the frequency characteristics of the acoustic wave device 100 are deteriorated by the reflected wave.

  Further, since the edge portion 101a1 and the edge portion 101a2 are parallel, the plate wave is repeatedly reflected and resonated between the edge portion 101a1 and the edge portion 101a2, and the edge portion 101a1 and the edge portion 101a2 are resonated. A standing wave is generated between the two. This standing wave interferes with the main mode, and the frequency characteristics of the acoustic wave device 100 are greatly deteriorated. Since the wavelength of the plate wave leaking from the IDT electrode 105 fluctuates depending on the operating frequency of the acoustic wave device 100, the wavelength of the standing wave also changes and is superposed in the main mode, so that a large number of spurious responses and ripple responses near the main mode. Produce.

  On the other hand, in the present embodiment, as shown in FIG. 9, the edge portion of the cavity portion 10 a does not have a linear portion extending in parallel with the propagation direction x of the plate wave excited by the IDT electrode 12. For this reason, it is difficult for the phase of the reflected wave at the edge of the cavity 10a to match the phase of the main mode. Therefore, even if a plate wave is reflected at the edge of the cavity 10a, the frequency characteristics of the acoustic wave device 1 are unlikely to deteriorate. That is, the acoustic wave device 1 having excellent device characteristics can be realized.

  Note that if the cavity is made sufficiently large with respect to the IDT electrode, the area of the drive area becomes relatively small even when the phases of the reflected waves are matched, so that the leakage wave from the IDT electrode is used as the excitation source. The amplitude of the standing wave becomes smaller, and the deterioration of the frequency characteristics due to the reflected wave can be suppressed. However, in order to enlarge the hollow portion, it is necessary to enlarge the support, or it is necessary to increase the interval between the constituent members, so that the elastic wave device is increased in size.

  On the other hand, when the shape of the edge of the cavity 10a is set to a predetermined shape as in the present embodiment to suppress deterioration of the frequency characteristics caused by the reflected wave, the cavity 10a is necessarily enlarged. There is no need. Therefore, the elastic wave device 1 having excellent device characteristics and a small size can be realized.

  In particular, when the maximum value of the width in the intersecting width direction y of the cavity portion 10a is 50 times or less of the wavelength determined by the IDT electrode 12, the frequency characteristics are likely to deteriorate due to the reflected wave. For this reason, the technique of this embodiment is particularly useful for a small acoustic wave device in which the maximum value of the width in the intersecting width direction y of the cavity 10a is 50 times or less the wavelength determined by the IDT electrode 12.

  Moreover, in this embodiment, since the IDT electrode 12 can be comprised by a regular type IDT electrode, deterioration of Q value can be suppressed compared with the case where the IDT electrode which gave the apodization weighting is used, for example.

  Specifically, in the present embodiment, the edge portion of the cavity portion 10a includes a pair of edge portions 10a1 and 10a2 extending along the intersecting width direction y, the plate wave propagation direction x, and the intersecting width direction y, respectively. Edge portions 10a3 to 10a6 extending in a direction inclined with respect to each other. Here, the edge portion 10a3 and the edge portion 10a5 are provided at the same position in the plate wave propagation direction x. And edge part 10a3 and edge part 10a5 are non-parallel. That is, the edge portion 10a3 and the edge portion 10a5 are not opposed to each other. Further, the edge portion 10a4 and the edge portion 10a6 are provided at the same position in the plate wave propagation direction x. And edge part 10a4 and edge part 10a6 are non-parallel. That is, the edge part 10a4 and the edge part 10a6 are not opposed. Moreover, although the edge part 10a3 and the edge part 10a6 are parallel, since the position in the plate wave propagation | transmission direction x differs, it is not facing. Similarly, the edge portion 10a4 and the edge portion 10a5 are parallel, but do not face each other because the positions in the plate wave propagation direction x are different. Therefore, in this embodiment, the width along the intersecting width direction y of the cavity 10a is not constant in the plate wave propagation direction x.

  Thus, in this embodiment, the edge part of the cavity part 10a does not have a pair of linear part which opposes in directions other than the plate wave propagation | transmission direction x. For this reason, the plate wave reflected by the edge portions 10a3 to 10a6 of the cavity portion 10a is less likely to cause resonance with a strong amplitude. Therefore, it is possible to more effectively suppress the deterioration of the frequency characteristics of the elastic wave device 1.

  Hereinafter, other examples of preferred embodiments of the present invention will be described. In the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second Embodiment)
FIG. 10 is a schematic plan view of the cavity and the IDT electrode in the second embodiment. In FIG. 10 and FIGS. 11 to 15 below, the electrode fingers 12a2 and 12b2 are not drawn.

  The elastic wave device according to the second and second embodiments has a configuration substantially similar to that of the first embodiment except that the shape of the cavity 10a is different.

  As shown in FIG. 10, in the second embodiment, the cavity 10 a is formed in an elliptical shape whose longitudinal direction is along the plate wave propagation direction x. For this reason, also in this embodiment, the edge part of the cavity part 10a does not include the linear part extended in parallel with the plate wave propagation | transmission direction x. Moreover, the edge part of the cavity part 10a does not contain a pair of linear part which opposes in directions other than the plate wave propagation direction x. Therefore, as in the first embodiment, an elastic wave device having excellent device characteristics and a small size can also be realized in this embodiment.

(Third embodiment)
FIG. 11 is a schematic plan view of the cavity and the IDT electrode in the third embodiment.

  The elastic wave device according to the third embodiment has substantially the same configuration as that of the first embodiment except that the shape of the cavity 10a is different.

  As shown in FIG. 11, in the third embodiment, the cavity 10 a is formed in a rectangular shape whose longitudinal direction extends in a direction inclined with the plate wave propagation direction x. For this reason, also in this embodiment, the edge part of the cavity part 10a does not include the linear part extended in parallel with the plate wave propagation | transmission direction x. Moreover, the edge part of the cavity part 10a does not contain a pair of linear part which opposes in directions other than the plate wave propagation direction x. Therefore, as in the first embodiment, an elastic wave device having excellent device characteristics and a small size can also be realized in this embodiment.

(Fourth and fifth embodiments)
FIG. 12 is a schematic plan view of the cavity and the IDT electrode in the fourth embodiment. FIG. 13 is a schematic plan view of the cavity and the IDT electrode in the fifth embodiment.

  Each of the elastic wave device according to the fourth embodiment and the elastic wave device according to the fifth embodiment is substantially the same as the first embodiment except that the shape of the cavity 10a is different. It has a configuration.

  In the fourth and fifth embodiments, the size of the cavity 10a with respect to the IDT electrode 12 is smaller than that in the first embodiment. Specifically, in the fourth embodiment, the cavity 10a is provided such that at least a part of the bus bars 12a1, 12b1 overlaps the edge portions 10a3, 10a4, 10a5, 10a6 of the cavity 10a. For this reason, reflection of the plate wave at the outer edge of the crossing width direction y of the bus bars 12a1 and 12b1 can be suppressed. Therefore, more excellent device characteristics can be realized.

  In the fifth embodiment, the cavity 10a is provided such that the region where the plurality of electrode fingers 12a2 and 12b2 are provided overlaps at least a part of the edge portions 10a3, 10a4, 10a5 and 10a6 of the cavity 10a. Yes. For this reason, the reflection of the plate wave in the electrode finger region inside the cross width direction y of the bus bars 12a1 and 12b1 is suppressed together with the reflection of the plate wave at the outer edge portion in the cross width direction y of the bus bars 12a1 and 12b1. Can do. Therefore, further excellent device characteristics can be realized.

  In the fourth and fifth embodiments, since the cavity 10a can be made smaller, the acoustic wave device can be further reduced in size.

(Sixth embodiment)
FIG. 14 is a schematic plan view of the cavity and the IDT electrode in the sixth embodiment.

  The sixth embodiment has substantially the same configuration as the first embodiment except that the shapes of the IDT electrode 12 and the reflectors 13 and 14 are different.

  In this embodiment, the IDT electrode 12 is subjected to apodization weighting. For this reason, the bus bars 12a1 and 12b1 of the IDT electrode 12 have portions extending in a direction inclined with the plate wave propagation direction x. Specifically, the entire bus bars 12a1 and 12b1 extend in a direction inclined with respect to the plate wave propagation direction x. The bus bars 12a1 and 12b1 do not have a straight line portion extending in parallel with the plate wave propagation direction x. Therefore, the phase of the reflected wave at the bus bars 12a1 and 12b1 is difficult to match the phase of the main mode. Therefore, even if the plate wave is reflected by the bus bars 12a1 and 12b1, the frequency characteristics of the elastic wave device are unlikely to deteriorate. That is, more excellent device characteristics can be realized.

  Further, in the present embodiment, the bus bars 12a1 and 12b1 do not have a pair of straight portions facing each other in a direction other than the plate wave propagation direction x. Therefore, further excellent device characteristics can be realized. The plate waves reflected by the bus bars 12a1 and 12b1 are less likely to cause resonance with a strong amplitude. Therefore, excellent device characteristics can be realized.

(Seventh embodiment)
FIG. 15 is a schematic plan view of the cavity and the IDT electrode in the seventh embodiment. In the seventh embodiment, FIGS. 1 and 2 are referred to in common with the first embodiment.

The elastic wave device of this embodiment includes a support 10. The constituent material of the support 10 is not particularly limited. Specific examples of the constituent material of the support 10 that is preferably used include LiNbO ₃ , LiTaO ₃ , quartz, silicon, glass, ceramic, and the like.

  The support 10 is provided with a cavity 10 a that opens to the main surface 10 b of the support 10. A piezoelectric substrate 11 is provided on the main surface 10 b of the support 10. The piezoelectric substrate 11 is provided so as to overlap the cavity 10a in the z direction (stacking direction).

  The shape of the cavity 10a is not particularly limited. In the present embodiment, the cavity 10a has a rectangular shape whose longitudinal direction is along the plate wave propagation direction x.

  The maximum value of the width in the intersecting width direction y perpendicular to the plate wave propagation direction x of the cavity 10 a is 50 times or less the wavelength determined by the IDT electrode 12.

The piezoelectric substrate 11 can be composed of an appropriate piezoelectric body. The piezoelectric substrate 11 can be composed of, for example, LiNbO ₃ , LiTaO ₃ , ZnO, AlN, quartz, or the like.

The thickness of the piezoelectric substrate 11 is not particularly limited as long as a plate wave, which will be described in detail later, is suitably excited. For example, Euler angles (0 °, 33 °, 0 °) in the case of exciting a Lamb wave of _{A 1} mode, which is described below with reference to LiTaO ₃ film, acoustic velocity 8400M / sec or more, the electromechanical coupling coefficient ^{k 2} 5. In order to set it to 8% or more, it is preferable that the thickness t of the piezoelectric substrate 11 is not more than 0.30 times the wavelength determined by the IDT electrode 12.

  On the piezoelectric substrate 11, an apodized weighted IDT electrode 12 and a pair of reflectors 13 and 14 are provided. In the present embodiment, the IDT electrode 12 and the reflectors 13 and 14 are provided so as to overlap the cavity 10a in the z direction.

  The IDT electrode 12 and the reflectors 13 and 14 can be made of an appropriate conductive material. The IDT electrode 12 and the reflectors 13 and 14 are, for example, a metal selected from the group consisting of Al, Pt, Au, Ag, Cu, Ni, Ti, Cr, and Pd, or Al, Pt, Au, Ag, Cu. , Ni, Ti, Cr, and Pd can be used to form an alloy containing one or more metals selected from the group consisting of Pd. Moreover, the IDT electrode 12 and the reflectors 13 and 14 can also be comprised by the laminated body of the some electrically conductive film which consists of the said metal and an alloy.

  The IDT electrode 12 has a pair of comb-like electrodes 12a and 12b. The pair of comb-like electrodes 12a and 12b are interleaved with each other. Each of the comb-like electrodes 12a and 12b includes bus bars 12a1 and 12b1 and a plurality of electrode fingers 12a2 and 12b2. Each of the plurality of electrode fingers 12a2 extends from the bus bar 12a1 toward the bus bar 12b1 along the y direction. The plurality of electrode fingers 12a2 are arranged at an interval along the x direction. On the other hand, each of the plurality of electrode fingers 12b2 extends from the bus bar 12b1 toward the bus bar 12a1 along the y direction. The plurality of electrode fingers 12b2 are arranged at intervals from each other along the x direction.

  In the elastic wave device of this embodiment, a plate wave is excited by the IDT electrode 12. The plate wave excited by the IDT electrode 12 propagates along the plate wave propagation direction x.

  When a potential is applied to the electrode fingers 12a2 and 12b2 of the IDT electrode 12, mechanical distortion occurs in the piezoelectric substrate 11, and plate waves are excited at various portions of the electrode fingers 12a2 and 12b2. These plate waves are considered to be element waves excited by a point wave source. According to Huygens' principle, an element wave of a plate wave is radiated on an arc and overlaps with surrounding element waves to form a wavefront parallel to the intersecting width direction y.

  Since the length of the electrode fingers 12a2 and 12b2 of the IDT electrode 12 is finite, a part of the plate wave leaks outside the ends of the electrode fingers 12a2 and 12b2. At least a part of the leaked plate wave is reflected at a location where the acoustic impedance is mismatched. Examples of the location where the acoustic impedance is mismatched include the end of the bus bar and the edge of the cavity constituting the membrane.

  For example, in the conventional acoustic wave device 100 shown in FIGS. 19 and 20, the bus bars 105a and 105b of the IDT electrode 105 are parallel to the plate wave propagation direction x. For this reason, the phase of the plate wave reflected by the bus bars 105a and 105b matches the main mode. Therefore, the frequency characteristics of the acoustic wave device 100 are deteriorated by the reflected wave.

  Further, since the bus bar 105a and the bus bar 105b are parallel to each other, the plate wave is repeatedly reflected and resonated between the bus bar 105a and the bus bar 105b, so that the frequency characteristic of the elastic wave device 100 is greatly deteriorated by the reflected wave.

  On the other hand, in this embodiment, as shown in FIG. 15, apodization weighting is applied to the IDT electrode 12. For this reason, the bus bars 12a1 and 12b1 of the IDT electrode 12 have portions extending in a direction inclined with the plate wave propagation direction x. Specifically, the entire bus bars 12a1 and 12b1 extend in a direction inclined with respect to the plate wave propagation direction x. The bus bars 12a1 and 12b1 do not have a straight line portion extending in parallel with the plate wave propagation direction x. Therefore, the phase of the reflected wave at the bus bars 12a1 and 12b1 is difficult to match the phase of the main mode. Therefore, even if the plate wave is reflected by the bus bars 12a1 and 12b1, the frequency characteristics of the elastic wave device are unlikely to deteriorate. That is, excellent device characteristics can be realized.

  Further, in the present embodiment, the bus bars 12a1 and 12b1 do not have a pair of straight portions facing each other in a direction other than the plate wave propagation direction x. Therefore, further excellent device characteristics can be realized. The plate waves reflected by the bus bars 12a1 and 12b1 are less likely to cause resonance with a strong amplitude. Therefore, further excellent device characteristics can be realized.

(First to third modifications)
FIG. 16 is a schematic cross-sectional view showing a part of the cavity in the first modification. FIG. 17 is a schematic cross-sectional view showing a part of the cavity in the second modification. FIG. 18 is a schematic cross-sectional view showing a part of the cavity in the third modification. Specifically, FIGS. 16 to 18 are schematic cross-sectional views of a portion corresponding to the portion A of FIG. The first to third modifications can be applied to any of the first to seventh embodiments.

  As shown in FIGS. 16-18, in the 1st-3rd modification, the edge part of the cavity 10a has several unevenness | corrugation. For this reason, the plate wave is irregularly reflected at the edge of the cavity 10a. Therefore, the reflected wave does not become a standing wave and is less likely to resonate. Therefore, more excellent device characteristics can be realized.

  In addition, the unevenness | corrugation of an edge part may have a periodic structure as shown in FIG.16 and FIG.17, and may have an aperiodic structure as shown in FIG. Specifically, in the first modified example shown in FIG. 16, the end edge portion has a sawtooth shape. In the second modified example shown in FIG. 17, a plurality of semicircular convex portions are formed on the edge portion.

  In addition, the structures shown in FIGS. 9 to 15 illustrated in the present invention do not become point symmetric or line symmetric with respect to the center of the IDT electrode, so that the phase of the reflected wave from the edge portion is shifted and fixed. The response of the wave can be reduced, and spurious can be easily suppressed. Therefore, it is desirable that the IDT electrode is not point-symmetric or line-symmetric.

The hollow portion may be formed by arranging a piezoelectric body on a depression formed by excavating the support substrate, or by arranging a support substrate under the depression formed by excavating the piezoelectric body. It may be formed by forming a support substrate in which a frame is formed of a thin film made of SiO ₂ or SiN on the substrate, and a piezoelectric body may be disposed on the frame, or on the piezoelectric body. forming a piezoelectric substrate formed with the frame a thin film made of SiO ₂ or SiN, it may be formed by disposing a supporting substrate under the frame.

  In particular, the method of forming a frame with a thin film can be easily performed by using a photolithography technique, so that a complicated shape other than a rectangle as shown in FIGS. 9 to 15 or a shape as shown in FIGS. In addition, it is desirable because it can be processed with high accuracy.

DESCRIPTION OF SYMBOLS 1 ... Elastic wave apparatus 10 ... Support body 10a ... Cavity part 10a1-10a6 ... End edge part 10b ... Main surface 11 ... Piezoelectric substrate 12 ... IDT electrode 12a, 12b ... Comb-like electrode 12a1, 12b1 ... Busbar 12a2, 12b2 ... Electrode Fingers 13, 14 ... reflector

Claims (12)

A support formed with a cavity,
A piezoelectric substrate provided on the support so as to overlap the cavity,
An IDT electrode provided on the piezoelectric substrate so as to overlap the cavity,
With
An elastic wave device in which a plate wave is excited by the IDT electrode,
The edge part of the said cavity part is an elastic wave apparatus which does not contain the linear part extended in parallel with the propagation direction of the plate wave excited by the said IDT electrode.   2. The acoustic wave device according to claim 1, wherein the edge portion of the hollow portion does not include a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave.   3. The elastic wave according to claim 1, wherein a maximum value of a width in an intersecting width direction perpendicular to the propagation direction of the plate wave of the hollow portion is 50 times or less of a wavelength determined by an electrode finger pitch of the IDT electrode. apparatus. The IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along an intersecting width direction perpendicular to the propagation direction of the plate wave, and includes a pair of comb-like electrodes that are interleaved with each other. ,
The elastic wave device according to any one of claims 1 to 3, wherein at least a part of the edge of the hollow portion is provided so as to overlap the bus bar.   5. The acoustic wave device according to claim 4, wherein the hollow portion is provided so that at least a part of a region where the plurality of electrode fingers are provided overlaps a side edge portion of the hollow portion.   The edge part of the said cavity part is an elastic wave apparatus as described in any one of Claims 1-5 which has several unevenness | corrugation. The IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along an intersecting width direction perpendicular to the propagation direction of the plate wave, and includes a pair of comb-like electrodes that are interleaved with each other. ,
The elastic wave device according to any one of claims 1 to 6, wherein the bus bar has a portion extending in a direction inclined with respect to a propagation direction of the plate wave.   The elastic wave device according to claim 7, wherein the bus bar does not include a straight line portion extending in parallel with a propagation direction of the plate wave.   The elastic wave device according to claim 7 or 8, wherein the bus bar does not have a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave. A support formed with a cavity,
A piezoelectric substrate provided on the support so as to overlap the cavity,
An IDT electrode provided on the piezoelectric substrate so as to overlap the cavity,
With
An elastic wave device in which a plate wave is excited by the IDT electrode,
The IDT electrode includes a bus bar and a plurality of electrode fingers extending from the bus bar along an intersecting width direction perpendicular to the propagation direction of the plate wave, and includes a pair of comb-like electrodes that are interleaved with each other. ,
The bus bar is an acoustic wave device having a portion extending in a direction inclined with respect to a propagation direction of the plate wave.   The elastic wave device according to claim 10, wherein the bus bar does not include a straight line portion extending in parallel with a propagation direction of the plate wave.   The elastic wave device according to claim 10 or 11, wherein the bus bar does not have a pair of straight portions facing each other in a direction other than the propagation direction of the plate wave.

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