Elastic wave device and filter device

Abstract

And useless waves are suppressed. A piezoelectric layer provided on the one main surface of the support member; and a functional electrode provided on at least one main surface of the piezoelectric layer such that at least a part of the functional electrode overlaps the space when viewed from a first direction, which is a direction in which the support member and the piezoelectric layer are stacked. The functional electrode includes an IDT electrode having a first bus bar, a second bus bar, a plurality of first electrode fingers, and a plurality of second electrode fingers. At least one electrode finger among the plurality of first electrode fingers and the plurality of second electrode fingers has a portion in which the width varies linearly in the second direction. In the at least one electrode finger, when the ratio of the width at the base end to the minimum width between the base end and the tip is 1 + sigma: 1-sigma, sigma is 0.01 or more and 0.054 or less.

Description

Technical Field

[0001] The present disclosure relates to an elastic wave device and a filter device. Background Art

[0002] Patent Document 1 describes an elastic wave device.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-257019 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] The elastic wave device disclosed in Patent Document 1 includes an IDT electrode. In this case, unnecessary waves may be generated, and the frequency characteristics may deteriorate.

[0008] The present disclosure is intended to solve the above-mentioned problem and aims to suppress the generation of unnecessary waves.

[0009] Technical solutions to solve problems

[0010] An elastic wave device according to one embodiment comprises: a supporting member having a space portion on one main surface; a piezoelectric layer arranged on the one main surface of the supporting member; and a functional electrode arranged on at least one main surface of the piezoelectric layer so as to overlap at least a portion of the space portion when viewed from a first direction, i.e., a stacking direction of the supporting member and the piezoelectric layer, wherein the functional electrode is an IDT electrode, and the IDT electrode comprises: a first bus bar; a second bus bar opposed to the first bus bar in a second direction intersecting the first direction; and a plurality of first electrode fingers, the base ends of which are connected to the first bus bar and the top ends of which are opposite to the first bus bar. The first bus bar is arranged in the second direction; and a plurality of second electrode fingers, whose base ends are connected to the second bus bar and whose top ends are arranged in the second direction relative to the second bus bar, the plurality of first electrode fingers and at least one electrode finger among the plurality of second electrode fingers having a portion whose width linearly changes in the second direction, and when the ratio of the width at the base end of the at least one electrode finger to the minimum width between the base end of the at least one electrode finger and the top end of the at least one electrode finger is set to 1+σ:1-σ, σ of the at least one electrode finger is greater than 0.01 and less than 0.054.

[0011] A filter device according to one aspect includes a plurality of resonators, and at least one resonator among the plurality of resonators is the elastic wave device.

[0012] Effects of the Invention

[0013] According to the present disclosure, the generation of unnecessary waves can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1A It is a perspective view showing the elastic wave device according to the first embodiment.

[0015] Figure 1B It is a plan view showing the electrode structure of the first embodiment.

[0016] Figure 2 It is along Figure 1A A cross-sectional view of a portion taken along line II-II.

[0017] Figure 3A This is a schematic cross-sectional view for explaining Lamb waves propagating through the piezoelectric layer of the comparative example.

[0018] Figure 3B This is a schematic cross-sectional view for explaining a bulk wave of a thickness shear first-order mode propagating through the piezoelectric layer of the first embodiment.

[0019] Figure 4 This is a schematic cross-sectional view for explaining the amplitude direction of the bulk wave of the thickness shear first-order mode propagating through the piezoelectric layer of the first embodiment.

[0020] Figure 5 It is an explanatory diagram showing an example of the resonance characteristics of the elastic wave device according to the first embodiment.

[0021] Figure 6 This is an explanatory diagram showing the relationship between d / 2p and the relative bandwidth of the resonator when the center-to-center distance or the average center-to-center distance of adjacent electrodes is set to p and the average thickness of the piezoelectric layer is set to d in the elastic wave device of the first embodiment.

[0022] Figure 7 This is a schematic plan view showing an example in which a pair of electrodes is provided in the elastic wave device according to the first embodiment.

[0023] Figure 8 This is a reference diagram showing an example of the resonance characteristics of the elastic wave device according to the first embodiment.

[0024] Fig. 9 This is an explanatory diagram showing the relationship between the relative bandwidth and the phase rotation amount of the impedance of the spurious normalized by 180 degrees, which is the magnitude of the spurious, when a large number of spurious wave resonators are configured in the elastic wave device according to the first embodiment.

[0025] Fig.10 It is an explanatory diagram showing the relationship among d / 2p, metallization ratio MR and relative bandwidth.

[0026] Fig.11This is an explanatory diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible.

[0027] Fig.12 This is a partially cutaway perspective view for explaining an elastic wave device according to an embodiment of the present disclosure.

[0028] Fig.13 This is a schematic plan view showing an example of the electrode structure of the elastic wave device according to the first embodiment.

[0029] Fig.14 It is a diagram for explaining the impedance characteristics of the elastic wave device according to the first embodiment.

[0030] Fig.15 This is a diagram for explaining the intensity index of the unnecessary wave with respect to the value of σ of the elastic wave device according to the first embodiment.

[0031] Fig.16 : This is a graph showing the value of FoM (Figure of Merit) with respect to the value of σ of the elastic wave device according to the first embodiment.

[0032] Fig.17 It is a diagram for explaining the admittance characteristics of the elastic wave device according to the first embodiment.

[0033] Fig.18 It is a schematic plan view showing an example of an electrode structure of an elastic wave device according to the second embodiment.

[0034] Fig.19 It is a schematic plan view showing an example of an electrode structure of an elastic wave device according to a third embodiment.

[0035] Fig. 20 This is a circuit diagram showing an example of a filter device according to the fourth embodiment. DETAILED DESCRIPTION

[0036] Hereinafter, the embodiments of the present disclosure are described in detail based on the accompanying drawings. In addition, the present disclosure is not limited to the embodiments. In addition, the various embodiments described in the present disclosure are illustrative, and partial replacement or combination of structures can be performed between different embodiments. After the modified example and the second embodiment, the description of matters common to the first embodiment is omitted, and only the differences are described. In particular, the same effects brought about by the same structure are not mentioned one by one in each embodiment.

[0037] (First embodiment)

[0038] Figure 1A It is a perspective view showing the elastic wave device according to the first embodiment. Figure 1B It is a plan view showing the electrode structure of the first embodiment.

[0039] The elastic wave device 1 of the first embodiment has a piezoelectric layer 2 including LiNbO3. The piezoelectric layer 2 may also be a piezoelectric layer including LiTaO3. The cutting angle of LiNbO3 and LiTaO3 in the first embodiment is Z-cut. The cutting angle of LiNbO3 and LiTaO3 may also be a rotated Y-cut or X-cut. Preferably, the propagation azimuth of Y propagation and X propagation is ±30°.

[0040] The thickness of the piezoelectric layer 2 is not particularly limited, but is preferably 50 nm to 1000 nm in order to effectively excite the thickness shear first-order mode.

[0041] The piezoelectric layer 2 has a first main surface 2a and a second main surface 2b that face each other in the Z direction. The electrode fingers 3 and the electrode fingers 4 are provided on the first main surface 2a.

[0042] Here, electrode finger 3 is an example of a "first electrode finger", and electrode finger 4 is an example of a "second electrode finger". Figure 1A as well as Figure 1B In the figure, the plurality of electrode fingers 3 are a plurality of "first electrode fingers" connected to the first bus bar 5. The plurality of electrode fingers 4 are a plurality of "second electrode fingers" connected to the second bus bar 6. The plurality of electrode fingers 3 and the plurality of electrode fingers 4 are interlaced with each other. Thus, an IDT (Interdigital Transducer) electrode having the electrode fingers 3, the electrode fingers 4, the first bus bar 5 and the second bus bar 6 is formed.

[0043] The electrode finger 3 and the electrode finger 4 have a rectangular shape and have a length direction. In a direction orthogonal to the length direction, the electrode finger 3 and the electrode finger 4 adjacent to the electrode finger 3 are opposed to each other. The length direction of the electrode fingers 3 and 4 and the direction orthogonal to the length direction of the electrode fingers 3 and 4 are directions intersecting the thickness direction of the piezoelectric layer 2. Therefore, it can also be said that the electrode finger 3 and the electrode finger 4 adjacent to the electrode finger 3 are opposed to each other in a direction intersecting the thickness direction of the piezoelectric layer 2. In the following description, the thickness direction of the piezoelectric layer 2 is sometimes set as the Z direction (or the first direction), the length direction of the electrode fingers 3 and the electrode fingers 4 is set as the Y direction (or the second direction), and the direction orthogonal to the electrode fingers 3 and the electrode fingers 4 is set as the X direction (or the third direction).

[0044] In addition, the length direction of the electrode fingers 3 and 4 can also be the same as Figure 1A as well as Figure 1B The length directions of the electrode fingers 3 and 4 shown are orthogonal to each other. Figure 1A as well as Figure 1BIn the embodiment, the electrode fingers 3 and 4 may be extended in the direction in which the first bus bar 5 and the second bus bar 6 extend. In this case, the first bus bar 5 and the second bus bar 6 extend in the direction in which the first bus bar 5 and the second bus bar 6 extend. Figure 1A as well as Figure 1B The electrode fingers 3 and 4 extend in the extending direction. In addition, a plurality of pairs of adjacent electrode fingers 3 and 4 connected to one potential and another potential are provided in a direction perpendicular to the longitudinal direction of the electrode fingers 3 and 4.

[0045] Here, the so-called electrode finger 3 and electrode finger 4 are adjacent to each other, which means that the electrode finger 3 and electrode finger 4 are arranged with a gap, rather than the electrode finger 3 and electrode finger 4 are arranged in direct contact. In addition, when the electrode finger 3 and electrode finger 4 are adjacent to each other, electrodes connected to the signal (hot) electrode and the ground electrode including other electrode fingers 3 and electrode fingers 4 are not arranged between the electrode finger 3 and the electrode finger 4. The number of pairs does not need to be an integer pair, and can also be 1.5 pairs, 2.5 pairs, etc.

[0046] The center-to-center distance between electrode fingers 3 and electrode fingers 4, i.e., the spacing, is preferably in the range of 1 μm or more and 10 μm or less. In addition, the center-to-center distance between electrode fingers 3 and electrode fingers 4 is the distance connecting the center of the width dimension of electrode finger 3 in the direction perpendicular to the length direction of electrode finger 3 and the center of the width dimension of electrode finger 4 in the direction perpendicular to the length direction of electrode finger 4.

[0047] Furthermore, when at least one of the electrode fingers 3 and the electrode fingers 4 has multiple electrodes (when the electrode fingers 3 and the electrode fingers 4 are set as a pair of electrode groups, when there are more than 1.5 pairs of electrode groups), the center-to-center distance of the electrode fingers 3 and the electrode fingers 4 refers to the average value of the center-to-center distances of adjacent electrode fingers 3 and the electrode fingers 4 among the more than 1.5 pairs of electrode fingers 3 and the electrode fingers 4.

[0048] In addition, the width of the electrode finger 3 and the electrode finger 4, that is, the size of the electrode finger 3 and the electrode finger 4 in the opposing direction is preferably in the range of 150 nm or more and 1000 nm or less. In addition, the so-called center-to-center distance between the electrode finger 3 and the electrode finger 4 is the distance connecting the center of the size (width dimension) of the electrode finger 3 in the direction orthogonal to the length direction of the electrode finger 3 and the center of the size (width dimension) of the electrode finger 4 in the direction orthogonal to the length direction of the electrode finger 4.

[0049] In the first embodiment, since a Z-cut piezoelectric layer is used, the direction orthogonal to the length direction of the electrode fingers 3 and 4 is a direction orthogonal to the polarization direction of the piezoelectric layer 2. This is not limited to the case where a piezoelectric body with another cutting angle is used as the piezoelectric layer 2. Here, the so-called "orthogonal" is not limited to the case of being strictly orthogonal, but may be approximately orthogonal (the angle formed by the direction orthogonal to the length direction of the electrode fingers 3 and 4 and the polarization direction is, for example, 90°±10°).

[0050] A support substrate 8 is stacked on the second main surface 2b side of the piezoelectric layer 2 via an intermediate layer 7. The support substrate 8 and the intermediate layer 7 constitute a support member. The intermediate layer 7 and the support substrate 8 have a frame-like shape. Figure 2 As shown, there are openings 7a and 8a. Thus, a space portion (air gap) 9 is formed. In addition, the space portion may be provided only in the intermediate layer 7. That is, the intermediate layer 7 may also have a recessed portion. In this case, the space portion is formed by the recessed portion.

[0051] The space portion 9 is provided so as not to hinder the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support substrate 8 is laminated on the second main surface 2b via the intermediate layer 7 at a position that does not overlap with the portion where at least one pair of electrode fingers 3 and electrode fingers 4 are provided. In addition, the intermediate layer 7 may not be provided. Therefore, the support substrate 8 may be laminated on the second main surface 2b of the piezoelectric layer 2 directly or indirectly.

[0052] The intermediate layer 7 is made of silicon oxide. However, the intermediate layer 7 may be made of a suitable insulating material other than silicon oxide, such as silicon nitride or alumina.

[0053] The supporting substrate 8 is formed of Si. The surface orientation of the Si on the side of the piezoelectric layer 2 can be (100), (110), or (111). Preferably, high-resistance Si with a resistivity of more than 4 kΩ is suitable. However, the supporting substrate 8 can also be composed of appropriate insulating materials or semiconductor materials. As the material of the supporting substrate 8, for example, piezoelectrics such as aluminum oxide, lithium tantalate, lithium niobate, and quartz, alumina, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, various ceramics, dielectrics such as diamond and glass, semiconductors such as gallium nitride, etc. can be used.

[0054] The plurality of electrode fingers 3, electrode fingers 4, first bus bar 5, and second bus bar 6 are made of appropriate metal or alloy such as Al, AlCu alloy, etc. In the first embodiment, the electrode fingers 3, electrode fingers 4, first bus bar 5, and second bus bar 6 have a structure in which an Al film is stacked on a Ti film. Alternatively, a bonding layer other than a Ti film may be used.

[0055] During driving, an AC voltage is applied between the electrode fingers 3 and the electrode fingers 4. More specifically, an AC voltage is applied between the first bus bar 5 and the second bus bar 6. This can obtain resonance characteristics of bulk waves using the thickness shear first-order mode excited in the piezoelectric layer 2.

[0056] In the elastic wave device 1, when the thickness of the piezoelectric layer 2 is d and the center-to-center distance between any adjacent electrode fingers 3 and 4 among the plurality of pairs of electrode fingers 3 and 4 is p, d / p is set to be 0.5 or less. Therefore, the bulk wave of the thickness shear first-order mode can be effectively excited, and good resonance characteristics can be obtained. More preferably, d / p is 0.24 or less, in which case, even better resonance characteristics can be obtained.

[0057] In addition, when there are multiple electrode fingers 3 and 4 as in the first embodiment, that is, when the electrode fingers 3 and 4 are set as a pair of electrode groups and there are more than 1.5 pairs of electrode fingers 3 and 4, the center distance between adjacent electrode fingers 3 and 4 becomes the average distance between the center distances of each adjacent electrode finger 3 and 4.

[0058] In the elastic wave device 1 of the first embodiment, since it has the above-mentioned structure, even if the number of pairs of electrode fingers 3 and 4 is reduced to achieve miniaturization, the Q value is unlikely to decrease. This is because the resonator does not require reflectors on both sides, and the propagation loss is small. In addition, the above-mentioned reflectors are not required because the bulk wave of the thickness shear first-order mode is used.

[0059] Figure 3A This is a schematic cross-sectional view for explaining Lamb waves propagating through the piezoelectric layer of the comparative example. Figure 3B This is a schematic cross-sectional view for explaining a bulk wave of a thickness shear first-order mode propagating through the piezoelectric layer of the first embodiment. Figure 4 This is a schematic cross-sectional view for explaining the amplitude direction of the bulk wave of the thickness shear first-order mode propagating through the piezoelectric layer of the first embodiment.

[0060] exist Figure 3A In the elastic wave device described in Patent Document 1, Lamb waves propagate in the piezoelectric layer. Figure 3A As shown in FIG. 1 , the wave propagates in the piezoelectric layer 201 as shown by the arrow. Here, the piezoelectric layer 201 has a first main surface 201a and a second main surface 201b, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the Z direction. The X direction is the direction in which the electrode fingers 3 and 4 of the IDT electrode are arranged. Figure 3AAs shown, for Lamb waves, the waves propagate in the X direction as shown in the figure. Since it is a plate wave, the piezoelectric layer 201 vibrates as a whole, but since the wave propagates in the X direction, reflectors are arranged on both sides to obtain resonance characteristics. Therefore, wave propagation loss occurs, and when miniaturization is achieved, that is, when the number of pairs of electrode fingers 3 and 4 is reduced, the Q value decreases.

[0061] In contrast, Figure 3B As shown, in the elastic wave device of the first embodiment, since the vibration displacement is in the thickness shear direction, the wave propagates and resonates roughly in the direction connecting the first main surface 2a and the second main surface 2b of the piezoelectric layer 2, that is, in the Z direction. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, since the resonance characteristic is obtained by the propagation of the wave in the Z direction, a reflector is not required. Therefore, no propagation loss occurs when propagating to the reflector. Therefore, even if the number of pairs of electrode pairs including the electrode fingers 3 and the electrode fingers 4 is reduced in order to promote miniaturization, it is difficult to cause a decrease in the Q value.

[0062] In addition, if Figure 4 As shown, the amplitude direction of the body wave of the thickness shear first-order mode is in the excitation area C of the piezoelectric layer 2 (refer to Figure 1B ) and the second region 252 included in the excitation region C are opposite. Figure 4 , a body wave is schematically shown when a voltage is applied between electrode finger 3 and electrode finger 4 so that electrode finger 4 has a higher potential than electrode finger 3. The first region 251 is a region between the first principal surface 2a and the imaginary plane VP1 that is orthogonal to the thickness direction of the piezoelectric layer 2 and divides the piezoelectric layer 2 into two parts in the excitation region C. The second region 252 is a region between the imaginary plane VP1 and the second principal surface 2b in the excitation region C.

[0063] Although at least one pair of electrodes including electrode fingers 3 and electrode fingers 4 is provided in elastic wave device 1, since the wave is not propagated in the X direction, the number of electrode pairs including electrode fingers 3 and electrode fingers 4 does not necessarily need to be multiple. In other words, at least one pair of electrodes is sufficient.

[0064] For example, the electrode finger 3 is an electrode connected to the signal potential, and the electrode finger 4 is an electrode connected to the ground potential. However, the electrode finger 3 may be connected to the ground potential, and the electrode finger 4 may be connected to the signal potential. In the first embodiment, as described above, at least one pair of electrodes is an electrode connected to the signal potential or an electrode connected to the ground potential, and no floating electrode is provided.

[0065] Figure 5 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave device according to the first embodiment. Figure 5The design parameters of elastic wave device 1 having the resonance characteristics shown are as follows.

[0066] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°)

[0067] Thickness of piezoelectric layer 2: 400nm

[0068] Excitation area C (refer to Figure 1B ) length: 40μm

[0069] Number of pairs of electrodes including electrode finger 3 and electrode finger 4: 21 pairs

[0070] Center-to-center distance (pitch) between electrode finger 3 and electrode finger 4: 3 μm

[0071] Width of electrode finger 3 and electrode finger 4: 500nm

[0072] d / p:0.133

[0073] Intermediate layer 7: 1 μm thick silicon oxide film

[0074] Support substrate 8: Si

[0075] In addition, the so-called excitation area C (refer to Figure 1B ), is the area where the electrode fingers 3 and 4 overlap when viewed in the X direction orthogonal to the length direction of the electrode fingers 3 and 4. The length of the excitation region C is the dimension of the excitation region C along the length direction of the electrode fingers 3 and 4. Here, the excitation region C is an example of an “intersection region”.

[0076] In the first embodiment, the center-to-center distances of the electrode pairs including the electrode fingers 3 and the electrode fingers 4 are all equal in a plurality of pairs. That is, the electrode fingers 3 and the electrode fingers 4 are arranged at equal intervals.

[0077] Depend on Figure 5 It is clear that, despite the absence of a reflector, a good resonance characteristic with a relative bandwidth of 12.5% ​​is obtained.

[0078] In addition, when the thickness of the piezoelectric layer 2 is d and the center-to-center distance between the electrode fingers 3 and 4 is p, in the first embodiment, d / p is 0.5 or less, and more preferably 0.24 or less. Figure 6 Explain it.

[0079] and got Figure 5 The elastic wave devices having the same resonant characteristics as those shown above are obtained by changing d / 2p. Figure 6This is an explanatory diagram showing the relationship between d / 2p and the relative bandwidth of the resonator when the center-to-center distance or the average center-to-center distance of adjacent electrodes is set to p and the average thickness of the piezoelectric layer 2 is set to d in the elastic wave device of the first embodiment.

[0080] like Figure 6 As shown in the figure, if d / 2p exceeds 0.25, that is, when d / p>0.5, even if d / p is adjusted, the relative bandwidth is less than 5%. In contrast, when d / 2p≤0.25, that is, d / p≤0.5, if d / p is changed within this range, the relative bandwidth can be set to more than 5%, that is, a resonator with a high coupling coefficient can be constructed. In addition, when d / 2p is less than 0.12, that is, when d / p is less than 0.24, the relative bandwidth can be increased to more than 7%. Moreover, if d / p is adjusted within this range, a resonator with a wider relative bandwidth can be obtained, and a resonator with a higher coupling coefficient can be realized. Therefore, it can be seen that by setting d / p to less than 0.5, a resonator with a high coupling coefficient that utilizes the body wave of the above-mentioned thickness shear first-order mode can be constructed.

[0081] In addition, at least one pair of electrodes may be one pair, and in the case of one pair of electrodes, the above p is set to the distance between the centers of adjacent electrode fingers 3 and 4. In the case of more than 1.5 pairs of electrodes, the average distance between the centers of adjacent electrode fingers 3 and 4 may be set to p.

[0082] Furthermore, regarding the thickness d of the piezoelectric layer 2 , even when the piezoelectric layer 2 has thickness variations, an average value of the thicknesses may be used.

[0083] Figure 7 1 is a schematic top view showing an example in which a pair of electrodes is provided in the elastic wave device of the first embodiment. In the elastic wave device 101, a pair of electrodes including electrode fingers 3 and electrode fingers 4 are provided on the first principal surface 2a of the piezoelectric layer 2. Figure 7 K in is the crossing width. As described above, in the elastic wave device of the present disclosure, the number of pairs of electrodes may be 1 pair. In this case as well, as long as the above d / p is 0.5 or less, the body wave of the thickness shear first-order mode can be effectively excited.

[0084] In the elastic wave device 1, it is preferred that the metallization ratio MR of any adjacent electrode fingers 3 and electrode fingers 4 in the plurality of electrode fingers 3 and electrode fingers 4 with respect to the excitation region C satisfies MR≤1.75(d / p)+0.075, and the excitation region C is a region where the adjacent electrode fingers 3 and electrode fingers 4 overlap when viewed in opposite directions. In this case, the stray can be effectively reduced. Figure 8 as well as Fig. 9Explain it.

[0085] Figure 8 This is a reference diagram showing an example of the resonance characteristics of the elastic wave device of the first embodiment. The spurious signal indicated by arrow B appears between the resonance frequency and the antiresonance frequency. In addition, d / p=0.08 is set, and the Euler angles of LiNbO3 are set to (0°, 0°, 90°). In addition, the metallization ratio MR is set to 0.35.

[0086] Reference Figure 1B To illustrate the metallization ratio MR. Figure 1B In the electrode structure, when focusing on one pair of electrode fingers 3 and electrode fingers 4, it is assumed that only the one pair of electrode fingers 3 and electrode fingers 4 are provided. In this case, the portion surrounded by the single-dot chain line becomes the excitation region C. The so-called excitation region C refers to the region of the electrode fingers 3 overlapping with the electrode fingers 4, the region of the electrode fingers 4 overlapping with the electrode fingers 3, and the region between the electrode fingers 3 and the electrode fingers 4 overlapping with the electrode fingers 3 and the electrode fingers 4 when the electrode fingers 3 and the electrode fingers 4 are observed in the direction perpendicular to the length direction of the electrode fingers 3 and the electrode fingers 4, that is, in the opposite direction. And, the area of ​​the electrode fingers 3 and the electrode fingers 4 in the excitation region C relative to the area of ​​the excitation region C becomes the metallization ratio MR. That is, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the excitation region C.

[0087] When a plurality of pairs of electrode fingers 3 and electrode fingers 4 are provided, the ratio of the total area of ​​the metallized portions included in all the excitation regions C to the excitation regions C may be defined as MR.

[0088] Fig. 9 This is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave device of the first embodiment, when a plurality of elastic wave resonators are formed, and the phase rotation amount of the impedance of the spurious signal normalized by 180 degrees as the magnitude of the spurious signal. In addition, the relative bandwidth is variously changed and adjusted by changing the film thickness of the piezoelectric layer 2 and the dimensions of the electrode fingers 3 and 4. In addition, Fig. 9 These are the results obtained when the piezoelectric layer 2 including Z-cut LiNbO 3 is used; however, the same tendency is observed when the piezoelectric layer 2 having other cut angles is used.

[0089] exist Fig. 9 In the area surrounded by ellipse J, the spurious value is as large as 1.0. Fig. 9 It is clear that if the relative bandwidth exceeds 0.17, that is, if it exceeds 17%, even if the parameters constituting the relative bandwidth are changed, large spurious with a spurious level of 1 or more will appear in the passband. Figure 8As shown in the resonance characteristics, large spurious signals indicated by arrow B appear in the frequency band. Therefore, the relative bandwidth is preferably 17% or less. In this case, spurious signals can be reduced by adjusting the film thickness of the piezoelectric layer 2, the size of the electrode fingers 3 and 4, and the like.

[0090] Fig.10 This is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and relative bandwidth. In the elastic wave device 1 according to the first embodiment, various elastic wave devices 1 having different d / 2p and MR were constructed, and the relative bandwidth was measured. Fig.10 The portion marked with shade on the right side of the dotted line D is an area where the relative bandwidth is less than 17%. The boundary between the shaded area and the unshaded area is represented by MR=3.5(d / 2p)+0.075. That is, MR=1.75(d / p)+0.075. Therefore, it is preferred that MR≤1.75(d / p)+0.075. In this case, it is easy to set the relative bandwidth to less than 17%. More preferably, Fig.10 The area on the right side of MR=3.5(d / 2p)+0.05 indicated by the dashed line D1 in FIG. 1. That is, if MR≤1.75(d / p)+0.05, the relative bandwidth can be reliably set to 17% or less.

[0091] Fig.11 This is an explanatory diagram showing a map of the relative bandwidth with respect to the Euler angle (0°, θ, ψ) of LiNbO 3 when d / p is made as close to 0 as possible. Fig.11 The portion indicated by hatching is a region where a relative bandwidth of at least 5% is obtained. If the range of the region is approximated, it becomes a range represented by the following equations (1), (2), and (3).

[0092] (0°±10°, 0°~20°, arbitrary ψ) …Formula (1)

[0093] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, {180°-60°(1-(θ-50) 2 / 900) 1 / 2}~180°) …Formula (2)

[0094] (0°±10°, {180°-30° (1-(ψ-90) 2 / 8100) 1 / 2}~180°, any ψ) …Formula (3)

[0095] Therefore, in the case of the Euler angle range of the above-mentioned formula (1), formula (2) or formula (3), the relative bandwidth can be sufficiently widened, which is preferable.

[0096] Fig.12 FIG. 1 is a partially cutaway perspective view for explaining an elastic wave device according to an embodiment of the present disclosure. Fig.12 In FIG. 1 , the outer periphery of the space portion 9 is shown by a dotted line. The elastic wave device disclosed in the present invention may also be an elastic wave device using plate waves. In this case, Fig.12 As shown, the elastic wave device 301 has reflectors 310 and 311. The reflectors 310 and 311 are arranged on both sides of the electrode fingers 3 and 4 of the piezoelectric layer 2 in the direction of propagation of the elastic wave. In the elastic wave device 301, by applying an alternating electric field to the electrode fingers 3 and 4 on the space portion 9, Lamb waves as plate waves can be excited. At this time, since the reflectors 310 and 311 are arranged on both sides, the resonance characteristics caused by the Lamb waves as plate waves can be obtained.

[0097] As described above, in the elastic wave devices 1 and 101, the bulk wave of the thickness shear first-order mode is used. In addition, in the elastic wave devices 1 and 101, the first electrode finger 3 and the second electrode finger 4 are adjacent electrodes, and when the thickness of the piezoelectric layer 2 is d and the center distance between the first electrode finger 3 and the second electrode finger 4 is p, d / p is set to be less than or equal to 0.5. Thus, even if the elastic wave device is miniaturized, the Q value can be improved.

[0098] In the elastic wave device 1, 101, the piezoelectric layer 2 is formed of lithium niobate or lithium tantalate. On the first principal surface 2a or the second principal surface 2b of the piezoelectric layer 2, there are first electrode fingers 3 and second electrode fingers 4 facing each other in a direction intersecting the thickness direction of the piezoelectric layer 2, and the first electrode fingers 3 and the second electrode fingers 4 are preferably covered with a protective film.

[0099] Fig.13 FIG. 1 is a schematic plan view showing an example of an electrode structure of the elastic wave device according to the first embodiment. Fig.13 As shown in FIG. 1 , the functional electrode of the elastic wave device 1A according to the first embodiment is an IDT electrode including electrode fingers 3A and 4A and bus bars 5 and 6 . Fig.13 In the example, the functional electrode is provided on the first principal surface 2a of the piezoelectric layer 2. In the following description, among the ends in the Y direction of the electrode fingers 3A and 4A, one end connected to the bus bar 5 and 6 is set as the base end, and one end not connected to the bus bar 5 and 6 is set as the top end.

[0100] like Fig.13As shown, the electrode fingers 3A and 4A have a portion whose width changes linearly in the Y direction. In other words, in the electrode fingers 3A and 4A, there is a portion whose position in the Y direction and the width of the electrode fingers 3A and 4A have a linear relationship. In the first embodiment, all the electrode fingers 3A and 4A are shaped such that their width changes linearly in the Y direction. In addition, the shape of the electrode fingers 3A and 4A is a trapezoid. That is, the shape of the electrode fingers 3A and 4A is a shape such that the width changes linearly in the Y direction from the base end to the top end. Fig.13 In the example of FIG. 1 , when viewed from above in the Z direction, the shape of the electrode fingers 3A and 4A is an isosceles trapezoid whose width decreases from the base end to the tip. That is, the shape of the electrode fingers 3A and 4A is symmetrical in the X direction. In addition, the width of the electrode fingers 3A and 4A is the largest at the base end and the smallest at the tip.

[0101] In the following description, the width at the base end of the electrode finger 3A, 4A is set to W1 (1 + σ), and the minimum width between the base end and the top end of the electrode finger 3A, 4A is set to W1 (1-σ). That is, the ratio of the width at the base end of the electrode finger 3A, 4A to the minimum width between the base end and the top end of the electrode finger 3A, 4A is 1 + σ: 1-σ. In addition, W1 can be said to be the average length of the width at the base end of the electrode finger 3A, 4A and the width at the top end of the electrode finger 3A, 4A.

[0102] σ is greater than or equal to 0.001 and less than or equal to 0.054, and preferably greater than or equal to 0.03. This makes it possible to suppress the generation of unnecessary waves without deteriorating the FoM (Figure of Merit). The so-called FoM is an index indicating the performance of an oscillator, and is the product of the coupling coefficient and the Q value.

[0103] An example of the elastic wave device according to the first embodiment has been described above, but the elastic wave device according to the first embodiment is not limited to Fig.13 For example, the shape of electrode fingers 3A and 4A is an isosceles trapezoid, but it is not limited to this, and it can also be a non-isosceles trapezoid, and the width decreases from the base end to the top end. In addition, as long as at least one electrode finger among the electrode fingers of the IDT electrode has a portion where the width changes linearly in the Y direction.

[0104] Hereinafter, examples according to the first embodiment will be described. Note that the present invention is not limited to the following examples.

[0105] (Comparative Example 1)

[0106] The elastic wave device according to Comparative Example 1 is an elastic wave device in which σ is 0. That is, the elastic wave device according to Comparative Example 1 is an elastic wave device in which the electrode fingers 3 and 4 are rectangular in shape and have a constant width.

[0107] (Example 1)

[0108] The elastic wave device according to Example 1 is an elastic wave device in which all electrode fingers have an isosceles trapezoidal shape and the width thereof decreases linearly from the base end to the tip end. In Example 1, σ is 0.05.

[0109] (Examples 2 and 3)

[0110] The elastic wave device according to Example 2 is the same as that of Example 1 except that σ is 0.01. The elastic wave device according to Example 3 is the same as that of Example 1 except that σ is 0.03.

[0111] (Examples 4 and 5)

[0112] The elastic wave device according to Example 4 is the same as that of Example 1 except that σ is 0.027. The elastic wave device according to Example 5 is the same as that of Example 1 except that σ is 0.054.

[0113] (Comparative Example 2)

[0114] The elastic wave device according to Comparative Example 2 is the same as the elastic wave device of Example 1 except that σ is 0.108.

[0115] Fig.14 1 is a diagram illustrating the impedance characteristics of the elastic wave device according to the first embodiment. More specifically, it is a diagram illustrating the unwanted waves of the elastic wave devices according to the comparative example 1 and the embodiment 1. Fig.14 As shown in the figure, in Example 1 where the width of the electrode fingers 3A and 4A varies linearly in the Y direction, the size of the unnecessary wave indicated by the arrow B1 is suppressed compared to Comparative Example 1 where the width of the electrode fingers 3A and 4A is fixed in the Y direction. It can be seen that the generation of the unnecessary wave can be suppressed by linearly varying the width of the electrode fingers 3A and 4A in the Y direction. In the following description, the minimum value of the impedance of the unnecessary wave indicated by the arrow B1 is set to Z. min (Ω), set the maximum value to Z max (Ω), the minimum value Z min (Ω) and maximum value Z max The difference in decibels (Ω) is used as an indicator of the intensity of unwanted waves. Z That is, d Z =log 10 (Z max / Z min ).

[0116] Fig.15 : is a diagram illustrating the intensity index of the unwanted wave with respect to the value of σ of the elastic wave device according to the first embodiment. More specifically, Fig.15σ and the unnecessary wave intensity index d normalized by the unnecessary wave intensity index according to Comparative Example 1 are shown. Z The relationship between the values ​​of Fig.15 As shown, in Examples 1 to 3 where σ is 0.001 or more, the intensity index d of the unwanted wave is greater than that of Comparative Example 1 where σ is 0. Z In Examples 2 and 3 where σ is greater than 0.03, the intensity index d of the unwanted wave is Z This is less than half of that in Comparative Example 1 in which σ is 0. This shows that the generation of unnecessary waves can be suppressed by setting σ to 0.001 or more, and the generation of unnecessary waves can be further suppressed by setting σ to 0.03 or more.

[0117] Fig.16 : is a graph showing the value of FoM (Figure of Merit) with respect to the value of σ of the elastic wave device according to the first embodiment. More specifically, Fig.16 : is a graph showing the relationship between σ and the value of FoM normalized by the value of FoM according to Comparative Example 1. Fig.17 1 is a diagram for explaining the admittance characteristics of the elastic wave device according to the first embodiment. Fig.16 As shown in FIG. 1 , in Examples 4 and 5 where σ is greater than or equal to 0.001 and less than or equal to 0.054, FoM is improved compared to Comparative Example 1 where σ is 0 and Comparative Example 2 where σ is greater than or equal to 0.054. Fig.17 As shown, in Examples 4 and 5 where σ is greater than or equal to 0.001 and less than or equal to 0.054, the generation of the unnecessary wave indicated by the arrow B2 is suppressed compared to Comparative Example 1 where σ is 0. This shows that by setting σ to greater than or equal to 0.001 and less than or equal to 0.054, the degradation of the FoM can be suppressed while suppressing the generation of the unnecessary wave.

[0118] As described above, the elastic wave device according to the first embodiment includes: a support member having a space portion 9 on one main surface; a piezoelectric layer 2 provided on one main surface of the support member; and a functional electrode provided on at least one main surface of the piezoelectric layer 2 so as to overlap at least a portion of the space portion 9 when viewed in the first direction, which is the stacking direction of the support member and the piezoelectric layer 2. The functional electrode is an IDT electrode, and the IDT electrode includes: a first bus bar 5; a second bus bar 6 opposed to the first bus bar 5 in a second direction intersecting the first direction; a plurality of first electrode fingers 3A having base ends connected to the first bus bar 5 and having top ends provided in the second direction relative to the first bus bar; and a plurality of second electrode fingers 4A having base ends connected to the second bus bar 6 and having top ends provided in the second direction relative to the second bus bar 6. At least one of the plurality of first electrode fingers 3A and the plurality of second electrode fingers 4A has a portion whose width changes linearly in the second direction. When the ratio of the width at the base end of at least one electrode finger to the minimum width between the base end of at least one electrode finger and the top end of at least one electrode finger is set to 1+σ:1-σ, σ of at least one electrode finger is greater than 0.01 and less than 0.054. Thus, the intensity index of the useless wave can be reduced while suppressing the degradation of FoM, so the generation of the useless wave can be suppressed.

[0119] As a preferred embodiment, σ is equal to or greater than 0.03. This can further reduce the intensity index of the unnecessary wave, and thus further suppress the generation of the unnecessary wave.

[0120] As a preferred embodiment, all of the plurality of first electrode fingers 3A and the plurality of second electrode fingers 4A have portions whose widths change linearly in the second direction. This can further suppress the generation of unnecessary waves.

[0121] As a preferred embodiment, when the film thickness of the piezoelectric layer 2 is d and the center-to-center distance between adjacent first electrode fingers 3 and second electrode fingers 4 is p, d / p is equal to or less than 0.5. This can effectively excite bulk waves of the thickness shear first-order mode.

[0122] As a preferred embodiment, the piezoelectric layer 2 includes lithium niobate or lithium tantalate. This can provide an elastic wave device that can obtain good resonance characteristics.

[0123] As a preferred embodiment, the Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer 2 are within the range of the following formula (1), formula (2) or formula (3). In this case, the relative bandwidth can be reliably set to 17% or less.

[0124] (0°±10°, 0°~20°, arbitrary ψ) …Formula (1)

[0125] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, {180°-60°(1-(θ-50) 2 / 900) 1 / 2}~180°) …Formula (2)

[0126] (0°±10°, {180°-30° (1-(ψ-90) 2 / 8100) 1 / 2}~180°, any ψ) …Formula (3)

[0127] As a preferred embodiment, the structure is such that a bulk wave of a thickness shear mode can be utilized. Thus, an elastic wave device having a high coupling coefficient and capable of obtaining good resonance characteristics can be provided.

[0128] As a preferred embodiment, when the film thickness of the piezoelectric layer 2 is d and the center-to-center distance between adjacent first electrode fingers 3 and second electrode fingers 4 is p, d / p is equal to or less than 0.24. This can more effectively excite bulk waves of the thickness shear first-order mode.

[0129] As a preferred method, when the overlapping region of the adjacent first electrode fingers 3 and second electrode fingers 4 when viewed in opposite directions is set as the excitation region, when the metallization ratio of the plurality of first electrode fingers 3 and second electrode fingers 4 relative to the excitation region is set as MR, MR≤1.75(d / p)+0.075 is satisfied. Thus, the stray light can be effectively reduced.

[0130] As a preferred embodiment, the structure is such that plate waves can be utilized. Thus, an elastic wave device capable of obtaining good resonance characteristics can be provided.

[0131] (Second embodiment)

[0132] Fig.18 FIG. 1 is a schematic plan view showing an example of an electrode structure of an elastic wave device according to the second embodiment. Fig.18 As shown, the elastic wave device according to the second embodiment is different from the first embodiment in that the electrode fingers 3B and 4B have two or more portions 3Ba, 3Bb, 4Ba, and 4Bb whose widths change linearly in the Y direction. Fig.18In the example, the electrode fingers 3B and 4B have portions 3Ba and 4Ba whose widths decrease from the base end to the top end, and portions 3Bb and 4Bb whose widths increase from the base end to the top end. The shapes of the portions 3Ba, 4Ba, 3Bb and 4Bb are isosceles trapezoidal shapes when viewed from above in the Z direction. That is, the electrode fingers 3B and 4B are hexagonal shapes whose sides opposite to each other in the Y direction are parallel and whose two angles between the base end and the top end are greater than 180°. In this case, the width between the base end and the top end of the electrode fingers 3A and 4A is the smallest between the portions 3Ba and 4Ba and the portions 3Bb and 4Bb in the Y direction.

[0133] The electrode structure of the elastic wave device according to the second embodiment is not limited to Fig.18 For example, the electrode finger may include three or more portions whose width varies linearly in the Y direction. For example, the electrode finger may include a first portion whose width decreases from the base end to the top end, and a second portion whose width decreases from the base end to the top end and whose taper is different from that of the first portion. For example, only a part of the electrode fingers among the plurality of electrode fingers may include two or more portions whose width varies linearly in the Y direction.

[0134] As described above, in the elastic wave device according to the second embodiment, at least one electrode finger (electrode fingers 3B, 4B) has two or more portions 3Ba, 3Bb, 4Ba, 4Bb whose widths change linearly in the second direction. In this case as well, generation of unnecessary waves can be suppressed.

[0135] (Third embodiment)

[0136] Fig.19 FIG. 1 is a schematic plan view showing an example of an electrode structure of an elastic wave device according to the third embodiment. Fig.19 As shown in FIG. 1 , the elastic wave device according to the third embodiment is different from the first embodiment in that the values ​​of σ are different between the electrode fingers 3C and 4C. Fig.19 In the example, when the width at the base end of electrode finger 3C is set to W1 (1+σ1), the minimum width between the base end and the top end of electrode finger 3A is set to W1 (1-σ1), the width at the base end of electrode finger 4C is set to W2 (1+σ2), and the minimum width between the base end and the top end of electrode finger 4C is set to W2 (1-σ2), σ1 and σ2 are different.

[0137] The electrode structure of the elastic wave device according to the third embodiment is not limited to Fig.19 For example, W1 and W2 may be the same. For example, W1 may be larger than W2. For example, σ may be different in some of the electrode fingers among the plurality of electrode fingers connected to the same bus bar.

[0138] As described above, in the elastic wave device according to the third embodiment, at least two electrode fingers among the plurality of first electrode fingers 3C and the plurality of second electrode fingers 4C have portions whose widths change linearly in the second direction, and at least two electrode fingers have different σ from each other. In this case as well, generation of unnecessary waves can be suppressed.

[0139] (Fourth embodiment)

[0140] Fig. 20 : is a circuit diagram showing an example of a filter device according to a fourth embodiment. A filter device F according to the fourth embodiment includes the elastic wave device according to the first embodiment.

[0141] like Fig. 20 As shown, the filter device F is a filter having a plurality of resonators connected to each other. Fig. 20 In the example, the filter device F is a so-called ladder filter including series arm resonators SR1 to SR4 inserted in series in a signal path (first path) from an input terminal IN to an output terminal OUT, and parallel arm resonators PR1 to PR4 inserted in a signal path (second path) between a node on the first path and ground. One terminal of the series arm resonators SR1 to SR4 is electrically connected to the input terminal IN, and the other terminal is electrically connected to the output terminal OUT. One terminal of the parallel arm resonators P1 to PR4 is electrically connected to the input terminal IN, and the other terminal is electrically connected to the ground. In addition, Fig. 20 The number of resonators in the filter device F is just an example. In addition, the filter device F may be a filter other than a ladder filter.

[0142] In the fourth embodiment, in the filter device F, at least one of the series arm resonators SR1 to SR4 and the parallel arm resonators PR1 to PR4 is the elastic wave device involved in the first embodiment. That is, at least one of the series arm resonators SR1 to SR4 and the parallel arm resonators PR1 to PR4 is a resonator having an IDT electrode, and at least one of the electrode fingers of the IDT electrode has a portion whose width changes linearly in a direction orthogonal to the length direction. As a result, the generation of unnecessary waves can be suppressed, so the filter characteristics can be improved. In addition, the filter device F may include the elastic wave device involved in the second embodiment or the third embodiment instead of the elastic wave device involved in the first embodiment.

[0143] As described above, the filter device F according to the fourth embodiment includes a plurality of resonators (series arm resonators SR1 to SR4 and parallel arm resonators PR1 to PR4), and at least one of the plurality of resonators is the elastic wave device according to the first embodiment. Thus, the generation of unnecessary waves can be suppressed by the elastic wave device, so that the filter characteristics can be improved.

[0144] In addition, the above-mentioned embodiments are for easy understanding of the present disclosure, and are not intended to be interpreted in a limiting manner. The present disclosure can be changed / improved without departing from the gist thereof, and the present disclosure also includes its equivalents.

[0145] In addition, the present invention can also adopt the following structures.

[0146] <1> An elastic wave device comprising:

[0147] A supporting member having a space portion on one main surface;

[0148] a piezoelectric layer disposed on the one main surface of the support member; and

[0149] The functional electrode is provided on at least one main surface of the piezoelectric layer so that at least a portion of the functional electrode overlaps with the space portion when viewed from a first direction, which is a stacking direction of the support member and the piezoelectric layer.

[0150] The functional electrode is an IDT electrode, and the IDT electrode has: a first bus bar; a second bus bar, which is opposite to the first bus bar in a second direction intersecting the first direction; a plurality of first electrode fingers, whose base ends are connected to the first bus bar and whose top ends are arranged in the second direction relative to the first bus bar; and a plurality of second electrode fingers, whose base ends are connected to the second bus bar and whose top ends are arranged in the second direction relative to the second bus bar.

[0151] At least one electrode finger among the plurality of first electrode fingers and the plurality of second electrode fingers has a portion whose width changes linearly in the second direction.

[0152] When the ratio of the width at the base end of the at least one electrode finger to the minimum width between the base end of the at least one electrode finger and the tip of the at least one electrode finger is set to 1+σ:1-σ, σ of the at least one electrode finger is greater than or equal to 0.01 and less than or equal to 0.054.

[0153] <2> according to <1> The elastic wave device, wherein:

[0154] The above-mentioned σ is 0.03 or more.

[0155] <3> according to <1> or <2> The elastic wave device, wherein:

[0156] The at least one electrode finger has two or more portions whose width changes linearly in the second direction.

[0157] <4> according to <1> to <3> The elastic wave device according to any one of claims , wherein:

[0158] At least two of the plurality of first electrode fingers and the plurality of second electrode fingers have portions whose widths vary linearly in the second direction.

[0159] The at least two electrode fingers have σ different from each other.

[0160] <5> according to <1> to <4> The elastic wave device according to any one of claims , wherein:

[0161] All of the plurality of first electrode fingers and the plurality of second electrode fingers have portions whose widths change linearly in the second direction.

[0162] <6> according to <1> to <5> The elastic wave device according to any one of claims , wherein:

[0163] When the film thickness of the piezoelectric layer is denoted by d and the center-to-center distance between the adjacent first electrode fingers and the second electrode fingers is denoted by p, d / p is equal to or less than 0.5.

[0164] <7> according to <1> to <6> The elastic wave device according to any one of claims , wherein:

[0165] The piezoelectric layer includes lithium niobate or lithium tantalate.

[0166] <8> according to <7> The elastic wave device, wherein:

[0167] The Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2) or formula (3),

[0168] (0°±10°, 0°~20°, arbitrary ψ) …Formula (1)

[0169] (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, {180°-60°(1-(θ-50) 2 / 900) 1 / 2}~180°) …Formula (2)

[0170] (0°±10°, {180°-30° (1-(ψ-90)2 / 8100) 1 / 2}~180°, arbitrary ψ) …Formula (3).

[0171] <9> according to <1> to <8> The elastic wave device according to any one of claims , wherein:

[0172] The elastic wave device is configured to utilize bulk waves of a thickness shear mode.

[0173] <10> according to <6> to <9> The elastic wave device according to any one of claims , wherein:

[0174] When the film thickness of the piezoelectric layer is denoted by d and the center-to-center distance between the adjacent first electrode fingers and the second electrode fingers is denoted by p, d / p is equal to or less than 0.24.

[0175] <11> according to <1> to <10> The elastic wave device according to any one of claims , wherein:

[0176] When an area where the adjacent first electrode fingers and second electrode fingers overlap when viewed in opposite directions is defined as an excitation area, and when a metallization ratio of the first electrode fingers and the second electrode fingers relative to the excitation area is defined as MR, MR≤1.75(d / p)+0.075 is satisfied.

[0177] <12> according to <1> to <5> The elastic wave device according to any one of claims , wherein:

[0178] The elastic wave device is configured to utilize plate waves.

[0179] <13> A filter device comprises a plurality of resonators.

[0180] At least one resonator among the plurality of resonators is <1> to <12> An elastic wave device as described in any one of the above.

[0181] Description of Reference Numerals

[0182] 1.101.301 Elastic Wave Device

[0183] 2 Piezoelectric layer

[0184] 2a 1st main surface

[0185] 2b Second main surface

[0186] 3. 3A~3C electrode fingers (1st electrode finger)

[0187] 3Ba, 3Bb part

[0188] 4. 4A~4C electrode fingers (second electrode fingers)

[0189] 4Ba, 4Bb part

[0190] 5 Bus bar (Bus bar 1)

[0191] 6 Bus bar (2nd bus bar)

[0192] 7 Middle Layer

[0193] 7a Opening

[0194] 8 Support base plate

[0195] 8a Opening

[0196] 9 Space Department

[0197] 201 Piezoelectric layer

[0198] 201a 1st Main Side

[0199] 201b Second main surface

[0200] 251 Area 1

[0201] 252 Area 2

[0202] 310, 311 reflectors

[0203] C Excitation region (crossover region)

[0204] F Filter Device

[0205] VP1 Imaginary plane.

Claims

1. An elastic wave device comprising: A supporting member having a space portion on one main surface; a piezoelectric layer disposed on the one main surface of the support member; and The functional electrode is provided on at least one main surface of the piezoelectric layer so that at least a portion of the functional electrode overlaps with the space portion when viewed from a first direction, which is a stacking direction of the support member and the piezoelectric layer. The functional electrode is an IDT electrode, and the IDT electrode has: a first bus bar; a second bus bar, which is opposite to the first bus bar in a second direction intersecting the first direction; a plurality of first electrode fingers, whose base ends are connected to the first bus bar and whose top ends are arranged in the second direction relative to the first bus bar; and a plurality of second electrode fingers, whose base ends are connected to the second bus bar and whose top ends are arranged in the second direction relative to the second bus bar. At least one electrode finger among the plurality of first electrode fingers and the plurality of second electrode fingers has a portion whose width changes linearly in the second direction. When the ratio of the width at the base end of the at least one electrode finger to the minimum width between the base end of the at least one electrode finger and the tip of the at least one electrode finger is set to 1+σ:1-σ, σ of the at least one electrode finger is greater than or equal to 0.01 and less than or equal to 0.

054.

2. The elastic wave device according to claim 1, wherein: The above-mentioned σ is not less than 0.

03.

3. The elastic wave device according to claim 1, wherein: The at least one electrode finger has two or more portions whose width changes linearly in the second direction.

4. The elastic wave device according to claim 1, wherein: At least two of the plurality of first electrode fingers and the plurality of second electrode fingers have portions whose widths change linearly in the second direction. The at least two electrode fingers have σ different from each other.

5. The elastic wave device according to claim 1, wherein: All of the plurality of first electrode fingers and the plurality of second electrode fingers have portions whose widths change linearly in the second direction.

6. The elastic wave device according to claim 1, wherein: When the film thickness of the piezoelectric layer is denoted by d and the center-to-center distance between the adjacent first electrode fingers and the second electrode fingers is denoted by p, d / p is equal to or less than 0.

5.

7. The elastic wave device according to claim 1, wherein: The piezoelectric layer includes lithium niobate or lithium tantalate.

8. The elastic wave device according to claim 7, wherein: The Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within the range of the following formula (1), formula (2) or formula (3), (0°±10°, 0°~20°, arbitrary ψ) …Formula (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, {180°-60° (1-(θ-50) 2 / 900) 1 / 2 }~180°) …Formula (2) (0°±10°, {180°-30° (1-(ψ-90) 2 / 8100) 1 / 2 }~180°, arbitrary ψ) …Formula (3).

9. The elastic wave device according to claim 1, wherein: The elastic wave device is configured to utilize bulk waves of a thickness shear mode.

10. The elastic wave device according to claim 6, wherein: When the film thickness of the piezoelectric layer is denoted by d and the center-to-center distance between the adjacent first electrode fingers and the second electrode fingers is denoted by p, d / p is equal to or less than 0.

24.

11. The elastic wave device according to claim 1, wherein: When an area where the adjacent first electrode fingers and second electrode fingers overlap when viewed in opposite directions is defined as an excitation area, and when a metallization ratio of the first electrode fingers and the second electrode fingers relative to the excitation area is defined as MR, MR≤1.75(d / p)+0.075 is satisfied.

12. The elastic wave device according to claim 1, wherein: The elastic wave device is configured to utilize plate waves.

13. A filter device comprising a plurality of resonators, At least one resonator among the plurality of resonators is the elastic wave device according to any one of claims 1 to 12.

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