Elastic wave device

Abstract

The present invention achieves an increase in fractional bandwidth. This elastic wave device comprises: a support substrate; an acoustic multilayer film provided upward of the support substrate; a piezoelectric layer provided upward of the acoustic multilayer film; and an IDT electrode provided to the piezoelectric layer. The acoustic multilayer film includes a plurality of layers stacked in a first direction. The plurality of layers include a first layer and a second layer. The IDT electrode has a first bus bar, a second bus bar, at least one first electrode finger, and at least one second electrode finger. When the thickness of the piezoelectric layer is defined as d, the thickness of the intermediate layer is defined as dm, and the center-to-center distance between adjacent electrode fingers is defined as p, d / p is 0.5 or less and dm / p is greater than 0.3.

Description

Elastic wave device

[0001] The present invention relates to an elastic wave device.

[0002] Patent Document 1 describes an elastic wave device including an acoustic reflection layer having a low acoustic impedance layer and a high acoustic impedance layer having a higher acoustic impedance than the low acoustic impedance layer.

[0003] Japanese Patent No. 5648695

[0004] In the elastic wave device disclosed in Patent Document 1, electric field leakage to the supporting substrate during driving may cause a reduction in the fractional bandwidth.

[0005] An object of the present invention is to provide an elastic wave device capable of increasing a fractional bandwidth.

[0006] An elastic wave device according to one aspect includes: a supporting substrate; an acoustic multilayer film provided on an upper side of the supporting substrate; a piezoelectric layer provided on an upper side of the acoustic multilayer film; an IDT electrode provided on at least one of an upper side and a lower side of the piezoelectric layer; and an intermediate layer provided between the supporting substrate and the acoustic multilayer film, wherein the acoustic multilayer film includes a plurality of layers stacked in a first direction, the plurality of layers include a first layer and a second layer made of a material different from that of the first layer, the IDT electrode includes a first bus bar and a second bus bar that face each other, at least one first electrode finger having a proximal end connected to the first bus bar, and at least one second electrode finger having a proximal end connected to the second bus bar, and when a thickness of the piezoelectric layer is d, a thickness of the intermediate layer is dm, and a center-to-center distance between the adjacent first electrode finger and second electrode finger is p, d / p is 0.5 or less, and dm / p is greater than 0.3.

[0007] According to the elastic wave device of the present invention, the fractional bandwidth can be increased.

[0008] Figure 1 is a plan view showing the elastic wave apparatus of the first embodiment. Figure 2 is a cross-sectional view taken along line II-II' of Figure 1. Figure 3 is a schematic cross-sectional view illustrating the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment. Figure 4 is a schematic cross-sectional view illustrating the amplitude direction of the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment. Figure 5 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 6 is an explanatory diagram showing the relationship between d / 2p and the specific bandwidth as a resonator, where p is the distance between the centers of adjacent electrodes or the average distance between the centers, and d is the average thickness of the piezoelectric layer, in the elastic wave apparatus of the first embodiment. Figure 7 is a plan view showing an example in which a pair of electrodes are provided in the elastic wave apparatus of the first embodiment. Figure 8 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. Figure 9 is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave apparatus of the first embodiment when a large number of elastic wave resonators are configured, and the phase rotation amount of the spurious impedance normalized by 180 degrees as the spurious magnitude. Figure 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. Figure 11 shows the LiNbO when d / p approaches 0. ３ Euler angle (0°, θ) ＬＮ ψ ＬＮ This is an explanatory diagram showing a map of the relative bandwidth for ). Figure 12 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Example 1 is changed. Figure 13 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Example 2 is changed. Figure 14 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Example 3 is changed. Figure 15 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Example 4 is changed. Figure 16 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Examples 5-1 to 5-6 is changed. Figure 17 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Examples 6-1 to 6-4 is changed. Figure 18 is a graph showing the magnitude of the relative bandwidth when the dm / p of the elastic wave apparatus according to Examples 7-1 to 7-4 is changed.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited by these embodiments. Each embodiment described in the present disclosure is an example, and partial replacement or combination of configurations is allowed between different embodiments. In modified examples and from the second embodiment onward, descriptions of matters common to the first embodiment will be omitted, and only different points will be explained. In particular, similar functions and effects obtained by similar configurations will not be sequentially mentioned for each embodiment.

[0010] (First Embodiment) FIG. 1 is a plan view showing an acoustic wave device according to the first embodiment. FIG. 2 is a cross-sectional view taken along the line II-II' in FIG. 1.

[0011] As shown in FIG. 1 and FIG. 2, the acoustic wave device 10 according to the first embodiment includes a support member, a piezoelectric layer 20, and an IDT electrode 30.

[0012] (Support Member) In the first embodiment, the support member includes a support substrate 11, an intermediate layer 12 provided on an upper side of the support substrate 11, and an acoustic multilayer film 43 provided on an upper side of the intermediate layer 12. That is, the intermediate layer 12 is provided between the support substrate 11 and the acoustic multilayer film 43. In the following description, one direction along the thickness direction of the support substrate 11 may be referred to as "up", and the other direction along the thickness direction of the support substrate 11 may be referred to as "down". In addition, in the present disclosure, the expression "provided on the upper side" includes both being provided directly on a surface in contact therewith, and being provided indirectly or at an interval so as to be positioned above.

[0013] (Support Substrate) In the first embodiment, the support substrate 11 is made of at least one selected from, for example, silicon (Si), silicon oxide, silicon nitride, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, and aluminum oxide. Here, the silicon oxide may be, for example, quartz, quartz glass, or the like. The support substrate 11 is desirably high-resistance Si with a resistivity of 4 kΩ or more.

[0014] The relative permittivity of the material of the support substrate 11 is preferably 40 or less, more preferably 11.8 or less, and even more preferably less than 11.8. This allows the electric field generated from the IDT electrode 30 to concentrate in the piezoelectric layer 20, thereby increasing the relative bandwidth. In this disclosure, relative permittivity refers to the value at room temperature as defined in JIS Z 8703.

[0015] When the support substrate 11 is made of quartz, the relative permittivity of the material of the support substrate 11 is 4.43. The relative permittivity of quartz is described in the "Handbook of Elastic Wave Device Technology" (edited by the 150th Committee on Elastic Wave Device Technology of the Japan Society for the Promotion of Science, 1st edition, 1st printing, published November 1991, Ohmsha). In this disclosure, the relative permittivity of quartz described in the said document is used by reference.

[0016] When the support substrate 11 is made of quartz glass, the relative permittivity of the material of the support substrate 11 is 3.78. The relative permittivity of quartz glass is given in "Chemical Handbook: Applied Chemistry Edition" (edited by the Chemical Society of Japan, 4th revised edition, 2. Materials Edition, published October 1986, Maruzen) as silicon dioxide (SiO₂ ２ It is stated as the relative permittivity of quartz glass. In this disclosure, the relative permittivity of quartz glass described in that document is used by reference.

[0017] When the support substrate 11 is made of silicon, the relative permittivity of the material of the support substrate 11 is 11.8. The relative permittivity of silicon is described in the "Surface Acoustic Wave Device Material Data Book" (edited by the Japan Electronics Industry Development Association, published March 1978). In this disclosure, the relative permittivity of silicon described in the said document is used by reference.

[0018] When the support substrate 11 is made of silicon nitride, the relative permittivity of the material of the support substrate 11 is 6.5. The relative permittivity of silicon nitride is described in A. Sazonov, D. Striakhilev, Czang-Ho Lee and A. Nathan, "Low-Temperature Materials and Thin Film Transistors for Flexible Electronics," in Proceedings of the IEEE, vol. 93, no. 8, pp. 1420-1428, Aug. (2005). In this disclosure, the relative permittivity of silicon nitride described in said document is used by reference.

[0019] (Intermediate layer) The intermediate layer 12 is formed of a dielectric material. The intermediate layer 12 is thicker than each of the layers (first layers 43b, 43d and second layers 43a, 43c, 43e) included in the acoustic multilayer film described later. The material of the intermediate layer 12 is silicon dioxide (SiO₂ ｘ Preferably, the intermediate layer is at least one of the following: silicon dioxide and silicon nitride (SiN). This concentrates the electric field generated from the IDT electrode 30 on the piezoelectric layer 20, thereby increasing the specific bandwidth. Here, silicon dioxide may be, for example, quartz or quartz glass. In the following description, the thickness of the intermediate layer 12 may be described as dm. Details of the thickness dm of the intermediate layer 12 will be described later.

[0020] When the intermediate layer 12 is made of quartz, the relative permittivity of the material of the intermediate layer 12 is 4.43. The relative permittivity of quartz is described in the "Handbook of Elastic Wave Device Technology" (edited by the 150th Committee on Elastic Wave Device Technology, Japan Society for the Promotion of Science, 1st edition, 1st printing, published November 1991, Ohmsha). In this disclosure, the relative permittivity of quartz described in the said document is used by reference.

[0021] When the intermediate layer 12 is made of quartz glass, the relative permittivity of the material of the intermediate layer 12 is 3.78. The relative permittivity of quartz glass is given in "Chemical Handbook: Applied Chemistry Edition" (edited by the Chemical Society of Japan, 4th revised edition, 2. Materials Edition, published October 1986, Maruzen) as silicon dioxide (SiO₂ ２It is stated as the relative permittivity of quartz glass. In this disclosure, the relative permittivity of quartz glass described in that document is used by reference.

[0022] When the intermediate layer 12 is made of silicon nitride, the relative permittivity of the intermediate layer 12 is 6.5. The relative permittivity of silicon nitride is described in A. Sazonov, D. Striakhilev, Czang-Ho Lee and A. Nathan, "Low-Temperature Materials and Thin Film Transistors for Flexible Electronics," in Proceedings of the IEEE, vol. 93, no. 8, pp. 1420-1428, Aug. (2005). In this disclosure, the relative permittivity of silicon nitride described in said document is used by reference.

[0023] The relative permittivity of the intermediate layer 12 is preferably lower than that of the support substrate 11. That is, the materials of the support substrate 11 and the intermediate layer 12 are preferably combined such that the relative permittivity of the intermediate layer 12 is lower than that of the support substrate 11. This allows the relative bandwidth to be increased by making the intermediate layer 12 thicker. Here, the numerical values ​​of the relative permittivity of the support substrate 11 and the intermediate layer 12 can be the values ​​exemplified above. Examples of specific material combinations such that the relative permittivity of the intermediate layer 12 is lower than that of the support substrate 11 include any one of the following combinations (i) to (iii): (i) Support substrate 11: silicon Intermediate layer 12: quartz glass, crystal or silicon nitride (ii) Support substrate 11: crystal Intermediate layer 12: quartz glass (iii) Support substrate 11: silicon nitride Intermediate layer 12: quartz glass or crystal

[0024] (Acoustic Multilayer Film) The acoustic multilayer film 43 is a laminate having multiple layers. The acoustic multilayer film 43 has a laminated structure of first layers 43b, 43d and second layers 43a, 43c, 43e. In the first embodiment, the first layers 43b, 43d have a relatively higher acoustic impedance than the second layers 43a, 43c, 43e. This makes it possible to confine the bulk wave of the thickness-slip first mode within the piezoelectric layer 20.

[0025] In the example of FIG. 2, the acoustic multilayer film 43 includes three second layers 43a, 43c, 43e and two first layers 43b, 43d, and is a laminate of five layers in which the second layers 43a, 43c, 43e and the first layers 43b, 43d are alternately stacked. In the acoustic multilayer film 43 according to the example of FIG. 2, the layers are stacked in the order of the second layer 43a, the first layer 43b, the second layer 43c, the first layer 43d, and the second layer 43e from the piezoelectric layer 20 side. The number of stacked layers of the acoustic multilayer film 43 is merely an example and is not particularly limited. For example, the acoustic multilayer film 43 may include four second layers and three first layers, and be a laminate of seven layers in which the second layers and the first layers are alternately stacked. Further, for example, the acoustic multilayer film 43 may include five second layers and four first layers, and be a laminate of nine layers in which the second layers and the first layers are alternately stacked. Furthermore, in the example of FIG. 2, among the plurality of layers, the layer closest to the piezoelectric layer 20 side is the second layer 43a, and the layer closest to the support substrate 11 side is the second layer 43e; however, the present invention is not limited thereto, and at least one of the layer closest to the piezoelectric layer 20 side and the layer closest to the support substrate 11 side may be the first layer.

[0026] The first layers 43b, 43d are formed of, for example, tungsten carbide (WC), tantalum carbide (TaC), rhenium oxide (ReO ３ ), chromium silicon carbon (CrCSi), niobium carbide (NbC), zirconium carbide (ZrC), titanium nitride (TiN), lanthanum boride (LaB ６ ), vanadium carbide (VC), aluminum nitride (AlN), silicon carbide (SiC), yttrium oxide (Y ２ O ３ ), magnesium oxide (MgO), silicon nitride (Si ３ N ４ ), boron carbide (B ４ C), strontium fluoride (SrF ２ ), barium fluoride (BaF ２ ), ytterbium oxide (Yb ２ O ３ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ ), tungsten oxide (WO ３Preferably, the layers contain at least one of the following: hafnium nitride (HfN), tungsten nitride (WN), platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag). In particular, it is more preferable that the first layers 43b and 43d contain at least one of the following: platinum (Pt), tungsten (W), copper (Cu), gold (Au), and silver (Ag). This makes it possible to make the acoustic impedance of the first layers 43b and 43d greater than that of the second layers 43a, 43c, and 43e.

[0027] The second layers 43a, 43c, and 43e are made of, for example, silicon dioxide (SiO₂ ｘ Preferably, the material contains at least one of the following: ) and aluminum (Al). In particular, the second layers 43a, 43c, and 43e preferably contain aluminum (Al). This makes it possible to make the acoustic impedance of the second layers 43a, 43c, and 43e smaller than that of the first layers 43b and 43d.

[0028] The materials for the first layers 43b, 43d and the second layers 43a, 43c, 43e are not limited to those shown above. They can be made of any suitable material as long as the above acoustic impedance relationship is satisfied. For example, the materials for the first layers 43b, 43d may be different from each other, and the materials for the second layers 43a, 43c, 43e may be different from each other. Also, the materials for the first layers 43b, 43d and the second layers 43a, 43c, 43e are not limited to being made of one type of material, but may be layers of mixtures containing multiple materials.

[0029] The piezoelectric layer 20 is a flat plate-shaped layer provided on the upper side of the support member. The piezoelectric layer 20 has a first main surface 20a which is the upper surface and a second main surface 20b which is the lower surface. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) is formed of ). Alternatively, the piezoelectric layer 20 is lithium tantalate (LiTaO ３ ) may consist of . LiNbo ３ ya LiTaO ３ The cut angle is, for example, a Z-cut. LiNbO ３ ya LiTaO ３The cut angle may be a rotational Y-cut or an X-cut, and a propagation direction of ±30° for Y propagation and X propagation (i.e., X propagation -30° or more and X propagation +30° or less) is preferred. Furthermore, the piezoelectric layer 20 is preferably a 120°±10° rotational Y-cut or a 90°±10° rotational Y-cut. In other words, the piezoelectric layer 20 is preferably a rotational Y-cut with a cut angle of 110° or more and 130° or less or 80° or more and 100° or less.

[0030] The thickness of the piezoelectric layer 20 is not particularly limited, but to effectively excite the thickness-sliding primary mode, a thickness of 50 nm to 1000 nm is preferred.

[0031] (IDT electrode) The IDT (Interdigital Transducer) electrode 30 is provided on the upper side of the piezoelectric layer 20. This increases the distance between the IDT electrode 30 and the support substrate 11, thereby suppressing electric field leakage when the elastic wave device is driven. The IDT electrode 30 may be provided directly on the first main surface 20a, or it may be provided indirectly on the first main surface 20a via a dielectric layer or the like. In the first embodiment, the IDT electrode 30 is provided directly on the first main surface 20a.

[0032] As shown in Figure 1, the IDT electrode 30 has a first electrode finger 31, a second electrode finger 32, a first busbar 33, and a second busbar 34. The multiple first electrode fingers 31 extend in the Y direction, and one end in the extending direction is connected to the first busbar 33. The multiple second electrode fingers 32 extend in the Y direction, and the other end in the extending direction is connected to the second busbar 34. The multiple first electrode fingers 31 and the multiple second electrode fingers 32 are arranged alternately in the X direction with spacing between them. The first busbar 33 and the second busbar 34 each extend in the X direction and are arranged opposite each other in the Y direction. The multiple first electrode fingers 31 and the multiple second electrode fingers 32 are arranged between the first busbar 33 and the second busbar 34.

[0033] Furthermore, the IDT electrode 30 is not limited to a configuration having a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32, and may also include a configuration with at least one first electrode finger 31 whose base end is connected to a first busbar 33 and at least one second electrode finger 32 whose base end is connected to a second busbar 34.

[0034] In the following description, the thickness direction of the piezoelectric layer 20 may be referred to as the Z direction, the extension direction of the first electrode finger 31 and the second electrode finger 32 as the Y direction, and the alignment direction of the first electrode finger 31 and the second electrode finger 32 as the X direction. In this disclosure, the Z direction is an example of the "first direction". In the first embodiment, the X direction is a direction perpendicular to the extension direction of the first electrode finger 31 and the second electrode finger 32. In this disclosure, the X direction is an example of the "width direction of the first electrode finger and the second electrode finger". Also, in the following description, "up" refers to the direction from the support substrate 11 toward the piezoelectric layer 20, and "down" refers to the direction from the piezoelectric layer 20 toward the support substrate 11.

[0035] The distance between the centers of the first electrode finger 31 and the second electrode finger 32 (electrode pitch) is not particularly limited, but is preferably in the range of 1 μm to 10 μm. Here, the electrode pitch refers to the distance between the center line of the dimensions of the first electrode finger 31 in the direction perpendicular to the extending direction (Y direction) of the first electrode finger 31 (X direction) and the center line of the dimensions of the second electrode finger 32 in the direction perpendicular to the extending direction (Y direction) of the second electrode finger 32 (X direction). In addition, the width of the first electrode finger 31 and the second electrode finger 32 (electrode width), that is, the dimensions in the direction perpendicular to the extending direction (Y direction) of the first electrode finger 31 and the second electrode finger 32 (X direction), is not particularly limited, but is preferably in the range of 150 nm to 1000 nm.

[0036] When there are multiple first electrode fingers 31 and second electrode fingers 32, that is, when the first electrode fingers 31 and second electrode fingers 32 are considered as a pair of electrode sets, there are 1.5 or more pairs of electrode sets, the arithmetic mean of the center-to-center distances of adjacent first electrode fingers 31 and second electrode fingers 32 among the 1.5 or more pairs of first electrode fingers 31 and second electrode fingers 32 may be described as the average center-to-center distance between the first electrode fingers 31 and second electrode fingers 32 (average electrode pitch).

[0037] In the first embodiment, the electrode spacing between electrode pairs consisting of a first electrode finger 31 and a second electrode finger 32 was made equal for all pairs. That is, the first electrode finger 31 and the second electrode finger 32 were arranged at equal pitches.

[0038] In the first embodiment, the IDT electrode 30, i.e., the first electrode finger 31, the second electrode finger 32, the first busbar 33, and the second busbar 34, is made of a suitable metal or alloy such as Al or AlCu alloy. Alternatively, the IDT electrode 30 may be a laminate in which an Al film is laminated on an adhesion layer such as a titanium (Ti) film. Note that an adhesion layer other than a Ti film may also be used.

[0039] Here, the crossing region C (excitation region) shown in Figure 1 is the region where the first electrode finger 31 and the second electrode finger 32 overlap when viewed in the X direction. The length of the crossing region C is the dimension in the extending direction of the first electrode finger 31 and the second electrode finger 32 in the crossing region C. In this embodiment, the length of the crossing region C is, for example, 30 μm.

[0040] During operation, an AC voltage is applied between a plurality of first electrode fingers 31 and a plurality of second electrode fingers 32. More specifically, an AC voltage is applied between a first busbar 33 and a second busbar 34. This makes it possible to obtain resonance characteristics using the bulk wave of the thickness-slip first mode excited in the piezoelectric layer 20.

[0041] In the elastic wave apparatus 10, when the thickness of the piezoelectric layer 20 is d and the average electrode pitch is p, the ratio d / p is set to 0.5 or less. Therefore, the bulk wave of the thickness-slip first mode described above is effectively excited, and good resonance characteristics can be obtained. More preferably, the ratio d / p is 0.24 or less, in which case even better resonance characteristics can be obtained. Regarding the thickness d of the piezoelectric layer 20, if the piezoelectric layer 20 has thickness variations, the average value of its thickness is adopted.

[0042] The inventors of the elastic wave apparatus according to this disclosure have found that the reduction in the relative bandwidth in an elastic wave apparatus equipped with an acoustic multilayer film 43 is due to leakage of the electric field to the support substrate 11 when the elastic wave apparatus 10 is driven. From this, the inventors have found through diligent research that by setting the ratio dm / p of the thickness dm of the intermediate layer 12 to the average electrode pitch p to a predetermined range, it is possible to suppress leakage of the electric field to the support substrate 11 and increase the relative bandwidth.

[0043] In the elastic wave apparatus 10 according to the first embodiment, dm / p is 0.3 or more. Preferably, dm / p is 0.5 or more, and more preferably 0.6 or more. This suppresses leakage of the electric field to the support substrate 11 when the elastic wave apparatus 10 is driven, thereby increasing the relative bandwidth. Also, it is preferable that dm / p is 0.9 or less. This allows for a sufficiently large relative bandwidth while reducing the size of the elastic wave apparatus in the Z direction.

[0044] The thickness dm of the intermediate layer 12 is preferably 0.3 μm or more and 2 μm or less. By setting dm / p within the above range, leakage of the electric field to the support substrate 11 during the operation of the elastic wave device 10 can be sufficiently suppressed, thereby effectively increasing the specific bandwidth.

[0045] The average electrode pitch p is preferably 4.5 μm or less, more preferably 1.5 μm to 4.5 μm, and even more preferably 1.5 μm to 3 μm. By setting dm / p within the above range, leakage of the electric field to the support substrate 11 during the operation of the elastic wave device 10 can be sufficiently suppressed, thereby effectively increasing the specific bandwidth.

[0046] In the elastic wave device 10 of the first embodiment, a bulk wave of the first-order thickness-slip mode is used. This reduces propagation loss, and even if the logarithm of the first electrode finger 31 and the second electrode finger 32 is reduced in an attempt to miniaturize the device, a decrease in the Q value is less likely to occur.

[0047] Figure 3 is a schematic cross-sectional view illustrating the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment. Figure 4 is a schematic cross-sectional view illustrating the amplitude direction of the bulk wave of the first-order thickness-slip mode propagating through the piezoelectric layer of the first embodiment.

[0048] As shown in Figure 3, in the elastic wave device 10 of the first embodiment, since the vibration displacement is in the thickness sliding direction, the wave propagates almost entirely in the direction connecting the first main surface 20a and the second main surface 20b of the piezoelectric layer 20, i.e., in the Z direction, and resonates. That is, the X-direction component of the wave propagation direction is significantly smaller than the Z-direction component. And since the resonance characteristics are obtained by the propagation of this Z-direction wave, a reflector is not required. Therefore, no propagation loss occurs when the wave propagates to the reflector. Accordingly, even if the number of electrode pairs consisting of the first electrode finger 31 and the second electrode finger 32 is reduced in an attempt to miniaturize the device, a decrease in the Q value is unlikely to occur.

[0049] In the first embodiment, the amplitude direction of the bulk wave in the thickness-slip primary mode is approximately opposite in the first region 251 and the second region 252, both included in the intersection region C (see Figure 1) of the piezoelectric layer 20, as shown in Figure 4. Figure 4 schematically shows the bulk wave when a voltage is applied between the first electrode finger 31 and the second electrode finger 32 such that the second electrode finger 32 is at a higher potential than the first electrode finger 31. Here, the virtual plane VP1 is a plane that is perpendicular to the thickness direction of the piezoelectric layer 20 and divides the piezoelectric layer 20 into two. The first region 251 is the region between the virtual plane VP1 and the first main surface 20a within the intersection region C. The second region 252 is the region between the virtual plane VP1 and the second main surface 20b within the intersection region C.

[0050] In the elastic wave device 10, at least one pair of electrodes consisting of a first electrode finger 31 and a second electrode finger 32 are arranged. However, since waves are not propagated in the X direction, it is not necessarily required that there be multiple pairs of electrodes consisting of the first electrode finger 31 and the second electrode finger 32. In other words, it is sufficient that at least one pair of electrodes is provided.

[0051] For example, the first electrode finger 31 is an electrode connected to a hot potential, and the second electrode finger 32 is an electrode connected to a ground potential. However, the first electrode finger 31 may be connected to a ground potential and the second electrode finger 32 may be connected to a hot potential. In the first embodiment, at least one pair of electrodes are either connected to a hot potential or to a ground potential, as described above, and no floating electrodes are provided.

[0052] Figure 5 is an explanatory diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. The design parameters of the elastic wave apparatus 10 that obtained the resonance characteristics shown in Figure 5 are as follows.

[0053] Piezoelectric layer 20: LiNbO with Euler angles (0°, 0°, 90°) ３ Thickness of piezoelectric layer 20: 400 nm Support substrate 11: Si Length of cross region C: 40 μm Number of electrode pairs consisting of first electrode finger 31 and second electrode finger 32: 21 pairs Average electrode pitch between first electrode finger 31 and second electrode finger 32: 3 μm Width of first electrode finger 31 and second electrode finger 32: 500 nm d / p: 0.133

[0054] As is clear from Figure 5, good resonance characteristics with a relative bandwidth of 12.5% ​​are obtained despite the absence of a reflector.

[0055] By the way, if the thickness of the piezoelectric layer 20 is d and the average (average distance) of the electrode pitch between the first electrode finger 31 and the second electrode finger 32 is p, then in the first embodiment, d / p is 0.5 or less, more preferably 0.24 or less. This will be explained with reference to Figure 6.

[0056] Figure 6 is an explanatory diagram showing the relationship between d / 2p and the specific bandwidth of the resonator in the elastic wave apparatus of the first embodiment, where p is the distance between the centers of adjacent electrodes or the average distance between the centers, and d is the average thickness of the piezoelectric layer. In Figure 6, multiple elastic wave apparatuses were obtained in the same manner as the elastic wave apparatus that obtained the resonance characteristics shown in Figure 5, except that d / 2p was changed.

[0057] As shown in Figure 6, when d / 2p exceeds 0.25, i.e., d / p > 0.5, the relative bandwidth is less than 5% even when d / p is adjusted. In contrast, when d / 2p ≤ 0.25, i.e., d / p ≤ 0.5, the relative bandwidth can be increased to 5% or more by changing d / p within that range, i.e., a resonator with a high coupling coefficient can be constructed. Furthermore, when d / 2p is 0.12 or less, i.e., when d / p is 0.24 or less, the relative bandwidth can be increased to 7% or more. In addition, by adjusting d / p within this range, a resonator with an even wider relative bandwidth can be obtained, and a resonator with an even higher coupling coefficient can be realized. Therefore, it can be seen that by setting d / p to 0.5 or less, a resonator with a high coupling coefficient can be constructed using the bulk wave of the thickness-slip first mode described above.

[0058] Figure 7 is a plan view showing an example in which a pair of electrodes is provided in the elastic wave apparatus of the first embodiment. In the elastic wave apparatus 10, a pair of electrodes having a first electrode finger 31 and a second electrode finger 32 are provided on the first main surface 20a of the piezoelectric layer 20. In Figure 7, K is the crossover width. As mentioned above, in the elastic wave apparatus 10 of this disclosure, the number of electrode finger pairs may be one. Even in this case, if the above d / p is 0.5 or less, the bulk wave of the thickness-slip first mode can be effectively excited.

[0059] In the elastic wave apparatus 10, it is preferable that the metallization ratio MR of the adjacent first electrode finger 31 and second electrode finger 32 with respect to the crossing region C satisfies MR ≤ 1.75 (d / p) + 0.075. In this case, spurious emissions can be effectively reduced. This will be explained with reference to Figures 7 and 8.

[0060] Figure 8 is a reference diagram showing an example of the resonance characteristics of the elastic wave apparatus of the first embodiment. As shown in Figure 8, the spurious signal indicated by arrow B appears between the resonant frequency and the anti-resonant frequency. Note that d / p = 0.08 and LiNbO ３ The Euler angles were set to (0°, 0°, 90°). Furthermore, the metallization ratio MR was set to 0.35.

[0061] The metallization ratio MR will be explained with reference to Figure 1. In the electrode structure of Figure 1, if we focus on a pair of first electrode fingers 31 and second electrode fingers 32, we assume that only this pair of first electrode fingers 31 and second electrode fingers 32 are provided. In this case, the area enclosed by the dashed line becomes the intersection region C. This intersection region C is the area on the first electrode finger 31 that overlaps with the second electrode finger 32 when viewed in a direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, i.e., in an opposing direction, the area on the first electrode finger 31 that overlaps with the first electrode finger 32, the area on the second electrode finger 32 that overlaps with the first electrode finger 31, and the area between the first electrode finger 31 and the second electrode finger 32 that overlaps. The area of ​​the first electrode finger 31 and the second electrode finger 32 within the intersection region C relative to the area of ​​the intersection region C is the metallization ratio MR. In other words, the metallization ratio MR is the ratio of the area of ​​the metallized portion to the area of ​​the cross region C.

[0062] Furthermore, if multiple pairs of first electrode fingers 31 and second electrode fingers 32 are provided, the ratio of the metallized portion to the total area of ​​the cross region C should be defined as MR.

[0063] Figure 9 is an explanatory diagram showing the relationship between the relative bandwidth of the elastic wave device of the first embodiment, when a large number of elastic wave resonators are configured, and the phase rotation amount of the spurious impedance normalized to 180 degrees as the spurious magnitude. The relative bandwidth was adjusted by changing various aspects such as the thickness of the piezoelectric layer 20 and the dimensions of the first electrode fingers 31 and the second electrode fingers 32. Also, Figure 9 shows the Z-cut LiNbO ３ The results shown are for the case where a piezoelectric layer 20 consisting of the above is used, but a similar trend is observed when piezoelectric layers 20 with other cut angles are used.

[0064] In the region enclosed by the ellipse J in Figure 9, the spurious emission is large at 1.0. As is clear from Figure 9, when the relative bandwidth exceeds 0.17, that is, when it exceeds 17%, large spurious emissions with a spurious emission level of 1 or more appear within the passband, even if the parameters constituting the relative bandwidth are changed. In other words, as shown in the resonance characteristics in Figure 7, large spurious emissions indicated by arrow B appear within the bandwidth. Therefore, it is preferable that the relative bandwidth be 17% or less. In this case, the spurious emissions can be reduced by adjusting the thickness of the piezoelectric layer 20 and the dimensions of the first electrode finger 31 and the second electrode finger 32.

[0065] Figure 10 is an explanatory diagram showing the relationship between d / 2p, the metallization ratio MR, and the relative bandwidth. In the elastic wave apparatus 10 of the first embodiment, various elastic wave apparatuses 10 with different d / 2p and MR were configured, and the relative bandwidth was measured. The hatched area to the right of the dashed line D in Figure 10 is the region where the relative bandwidth is 17% or less. The boundary between this hatched region and the unhatched region is represented by MR = 3.5(d / 2p) + 0.075. That is, MR = 1.75(d / p) + 0.075. Therefore, preferably, MR ≤ 1.75(d / p) + 0.075. In that case, it is easy to keep the relative bandwidth at 17% or less. More preferably, it is the region to the right of MR = 3.5(d / 2p) + 0.05, shown by the dashed line D1 in Figure 10. In other words, if MR ≤ 1.75 (d / p) + 0.05, the relative bandwidth can be reliably reduced to 17% or less.

[0066] Figure 11 shows LiNbO when d / p approaches 0. ３ Euler angle (0°, θ) ＬＮ ψ ＬＮ This is an explanatory diagram showing a map of the relative bandwidth for ). The hatched area in Figure 11 is the region where a relative bandwidth of at least 5% is obtained. Approximating the range of the region, it is the range expressed by the following equations (1), (2), and (3).

[0067] (0°±10°, 0°~20°, any ψ) ＬＮ )...Equation (1) (0°±10°, 20°~80°, 0°~60°(1-(θ ＬＮ -50)２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ) ＬＮ -50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°−30°(1−(ψ ＬＮ -90) ２ ( / 8100) １／２ ] ~180°, any ψ ＬＮ )...Formula (3)

[0068] Therefore, in the case of the Euler angle range of equation (1), equation (2), or equation (3) above, the relative bandwidth can be made sufficiently wide, which is preferable.

[0069] As described above, the elastic wave apparatus 10 according to the first embodiment comprises a support substrate 11, an acoustic multilayer film 43 provided on the upper side of the support substrate 11, a piezoelectric layer 20 provided on the upper side of the acoustic multilayer film 43, an IDT electrode 30 provided on at least one side of the upper or lower side of the piezoelectric layer 20, and an intermediate layer 12 provided between the support substrate 11 and the acoustic multilayer film 43. The acoustic multilayer film 43 includes a plurality of layers (first layers 43b, 43d and second layers 43a, 43c, 43e) stacked in a first direction. The plurality of layers include the first layers 43b, 43d and the second layers 43a, 43c, 43e made of a different material from the first layers 43b, 43d. The IDT electrode 30 has a first busbar 33 and a second busbar 34 facing each other, at least one first electrode finger 31 whose base end is connected to the first busbar 33, and at least one second electrode finger 32 whose base end is connected to the second busbar 34. When the thickness of the piezoelectric layer 20 is d, the thickness of the intermediate layer 12 is dm, and the distance between the centers of adjacent first electrode fingers 31 and second electrode fingers 32 is p, then d / p is 0.5 or less and dm / p is greater than 0.3. As a result, leakage of the electric field to the support substrate 11 can be suppressed when the elastic wave device 10 is driven, so the relative bandwidth can be increased.

[0070] In a desirable embodiment, the relative permittivity of the intermediate layer 12 is lower than that of the support substrate 11. This allows the relative bandwidth to be increased by making the intermediate layer 12 thicker.

[0071] In a preferred embodiment, the material of the intermediate layer 12 includes at least one of silicon oxide and silicon nitride. This effectively suppresses the leakage of the electric field to the support substrate 11 when the elastic wave device 10 is driven, thereby increasing the specific bandwidth.

[0072] In a preferred embodiment, the material of the support substrate 11 includes at least one of silicon, silicon oxide, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, and aluminum oxide. This allows for a larger specific bandwidth.

[0073] In a preferred embodiment, the material of the support substrate 11 is silicon, and the material of the intermediate layer 12 is quartz glass, crystal, or silicon nitride. This allows the relative permittivity of the intermediate layer 12 to be lower than that of the support substrate 11, and by increasing the thickness of the intermediate layer 12, the relative bandwidth can be increased.

[0074] In a preferred embodiment, the material of the support substrate 11 is quartz, and the material of the intermediate layer 12 is quartz glass. This allows the relative permittivity of the intermediate layer 12 to be lower than that of the support substrate 11, and by making the intermediate layer 12 thicker, the relative bandwidth can be increased.

[0075] In a preferred embodiment, the material of the support substrate 11 is silicon nitride, and the material of the intermediate layer 12 is quartz glass or crystal. This allows the relative permittivity of the intermediate layer 12 to be lower than that of the support substrate 11, and by increasing the thickness of the intermediate layer 12, the relative bandwidth can be increased.

[0076] In a preferred embodiment, at least one of the multiple layers (first layers 43b, 43d and second layers 43a, 43c, 43e) is made of a dielectric material. This allows for a larger relative bandwidth.

[0077] In a desirable embodiment, the acoustic impedance of the first layer is higher than that of the second layer. This allows for good containment of the bulk wave of the thickness-slip first mode within the piezoelectric layer 20.

[0078] In a preferred embodiment, the first layers 43b and 43d contain at least one of the following: tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium carbon, niobium carbide, zinc carbide, zinc nitride, lanthanum boride, vanadium carbide, aluminum nitride, silicon carbide, yttrium oxide, magnesium oxide, silicon nitride, boron carbide, strontium fluoride, barium fluoride, ytterbium oxide, tantalum oxide, hafnium oxide, tungsten oxide, hafnium nitride, tungsten nitride, platinum, tungsten, copper, gold, and silver. This improves the acoustic impedance of the first layers 43b and 43d.

[0079] In a more desirable embodiment, the first layers 43b and 43d contain at least one of hafnium oxide and tungsten oxide. This improves the acoustic impedance of the first layers 43b and 43d.

[0080] In a preferred embodiment, the second layers 43a, 43c, and 43e contain silicon dioxide. This reduces the acoustic impedance of the second layers 43a, 43c, and 43e.

[0081] In a preferred configuration, the IDT electrode 30 is provided on the upper side of the piezoelectric layer 20. This increases the distance between the IDT electrode 30 and the support substrate 11, thereby suppressing electric field leakage when the elastic wave device is driven.

[0082] In a desirable configuration, the d / p ratio is 0.24 or less. This allows for even better resonance characteristics to be obtained.

[0083] A desirable configuration is one where dm / p is 0.5 or higher. This allows for a larger relative bandwidth.

[0084] In a desirable embodiment, the thickness dm of the intermediate layer 12 is greater than the thickness of each of the multiple layers (first layers 43b, 43d and second layers 43a, 43c, 43e). This allows for a larger relative bandwidth.

[0085] In a desirable embodiment, when viewed from a direction perpendicular to the extending direction of the first electrode finger 31 and the second electrode finger 32, the region where adjacent first electrode finger 31 and second electrode finger 32 overlap, and the region between the centers of adjacent first electrode finger 31 and second electrode finger 32 in a direction perpendicular to the extending direction of the first electrode finger 31 and second electrode finger 32, is defined as the excitation region, and when the metallization ratio of the first electrode finger 31 and the second electrode finger 32 with respect to the excitation region is denoted as MR, the condition MR ≤ 1.75 (d / p) + 0.075 is satisfied. This effectively reduces spurious emissions and improves resonance characteristics.

[0086] In a desirable embodiment, the Euler angle (φ) of the lithium niobate constituting the piezoelectric layer 20 is Ｓｉ , θ Ｓｉ ψ Ｓｉ ) is within the range of equation (1), equation (2), or equation (3) below. This allows the relative bandwidth to be sufficiently wide. (0°±10°, 0°~20°, any ψ Ｓｉ )...Equation (1) (0°±10°, 20°~80°, 0°~60°(1-(θ Ｓｉ -50) ２ / 900) １／２ ) or (0°±10°, 20°~80°, [180°-60°(1-(θ) Ｓｉ -50) ２ / 900) １／２ ]~180°) ...Formula (2) (0°±10°, [180°−30°(1−(ψ Ｓｉ -90) ２ ( / 8100) １／２ ] ~180°, any ψ Ｓｉ )...Formula (3)

[0087] (Examples) The following describes examples of the first embodiment. However, the embodiments are not limited to these examples.

[0088] (Example 1) The elastic wave apparatus according to Example 1 was designed as follows. Here, the acoustic multilayer film 43 according to Example 1 is a laminate consisting of a total of five layers, a first layer of two layers and a second layer of three layers, and the first layer and the second layer are stacked alternately. Piezoelectric layer 20: Single crystal LiNbO ３Layer (thickness 300 nm, Euler angles (0°, 120°, 0°)) IDT electrode 30: Al layer (thickness 100 nm) Average electrode pitch: 4.5 μm Electrode width: 0.6 μm First layer of acoustic multilayer film: HfO ２ Layer (thickness 112 nm) Second layer of acoustic multilayer film: SiO ２ Layer (thickness 121 nm) Intermediate layer 12: SiO ２ Layer support substrate 11: Single crystal silicon layer (thickness 4.0 μm)

[0089] (Example 2) The elastic wave apparatus according to Example 2 has a first layer of acoustic multilayer film with a thickness of 125 nm and made of tungsten oxide (WO ３ Aside from being a layer, the design was the same as that of the elastic wave apparatus in Example 1.

[0090] (Example 3) The elastic wave apparatus according to Example 3 is designed in the same way as the elastic wave apparatus according to Example 1, except that the acoustic multilayer film 43 is a laminate consisting of a total of seven layers, a first layer of three layers and a second layer of four layers, and the first layer and the second layer are stacked alternately.

[0091] (Example 4) The acoustic wave apparatus according to Example 4 is designed in the same way as the acoustic wave apparatus according to Example 1, except that the acoustic multilayer film 43 is a laminate consisting of a total of nine layers, with four first layers and five second layers, and the first and second layers are stacked alternately.

[0092] For the elastic wave apparatuses according to Examples 1 to 4 described above, the relative bandwidth was investigated by simulations in which the dm / p ratio was changed by varying the thickness dm of the intermediate layer 12. Figures 12 to 15 are graphs showing the magnitude of the relative bandwidth when the dm / p ratio of the elastic wave apparatuses according to Examples 1 to 4 is changed.

[0093] As shown in Figures 12 to 15, when dm / p is 0.3 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.3. This shows that the relative bandwidth can be increased by setting dm / p to 0.3 or higher.

[0094] As shown in Figures 12 to 15, when dm / p is 0.5 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.5. This shows that the relative bandwidth can be increased by setting dm / p to 0.5 or higher.

[0095] As shown in Figures 12 to 15, when dm / p is 0.6 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.6. This shows that the relative bandwidth can be further increased by setting dm / p to 0.6 or higher.

[0096] (Example 5-1) The elastic wave apparatus according to Example 5-1 was designed in the same way as in Example 1.

[0097] (Example 5-2) The elastic wave apparatus according to Example 5-2 had the same design as the elastic wave apparatus according to Example 5-1, except that the average electrode pitch p was changed to 4 μm.

[0098] (Example 5-3) The elastic wave apparatus according to Example 5-3 had the same design as the elastic wave apparatus according to Example 5-1, except that the average electrode pitch p was changed to 3.5 μm.

[0099] (Example 5-4) The elastic wave apparatus according to Example 5-4 had the same design as the elastic wave apparatus according to Example 5-1, except that the average electrode pitch p was changed to 3 μm.

[0100] (Example 5-5) The elastic wave apparatus according to Example 5-5 had the same design as the elastic wave apparatus according to Example 5-1, except that the average electrode pitch p was changed to 2.5 μm.

[0101] (Example 5-6) The elastic wave apparatus according to Example 5-6 had the same design as the elastic wave apparatus according to Example 5-1, except that the average electrode pitch p was changed to 2 μm.

[0102] The relative bandwidth of the elastic wave apparatus according to Examples 5-1 to 5-6 described above was investigated by simulations in which the dm / p ratio was changed by varying the thickness dm of the intermediate layer. Figure 16 is a graph showing the magnitude of the relative bandwidth when the dm / p ratio of the elastic wave apparatus according to Examples 5-1 to 5-6 is changed.

[0103] As shown in Figure 16, when dm / p is 0.3 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.3. This shows that the relative bandwidth can be increased by setting dm / p to 0.3 or higher.

[0104] As shown in Figure 16, when dm / p is 0.5 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.5. This shows that the relative bandwidth can be increased by setting dm / p to 0.5 or higher.

[0105] As shown in Figure 16, when dm / p is 0.6 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.6. This shows that the relative bandwidth can be further increased by setting dm / p to 0.6 or higher.

[0106] As shown in Figure 16, in Examples 5-4 and 5-6, where the average electrode pitch p is greater than 2 μm and less than 3.5 μm, the relative bandwidth at dm / p ≥ 0.3 was larger compared to Examples 5-1 to 5-3, where the average electrode pitch p is 3.5 μm or more, and Example 5-6, where the average electrode pitch p is 2 μm or less. This shows that the relative bandwidth can be further increased by making the average electrode pitch p greater than 2 μm and less than 3.5 μm.

[0107] As shown in Figure 16, in Examples 5-4 and 5-6, where the average electrode pitch p is 2.5 μm or more and 3 μm, the relative bandwidth at dm / p ≥ 0.3 was larger compared to Examples 5-1 to 5-3, where the average electrode pitch p is greater than 3 μm, and Example 5-6, where the average electrode pitch p is less than 2.5 μm. This shows that the relative bandwidth can be increased by setting the average electrode pitch p to 2.5 μm or more and 3 μm.

[0108] (Example 6-1) The elastic wave apparatus according to Example 6-1 was designed as follows. Here, the acoustic multilayer film 43 according to Example 6-1 is a laminate consisting of a total of five layers, a first layer of two layers and a second layer of three layers, and the first and second layers are stacked alternately. In addition, in the simulation according to Example 6-1, the relative permittivity of the support substrate was set to 4. Piezoelectric layer 20: Single crystal LiNbO３ Layer (thickness 300 nm, Euler angles (0°, 120°, 0°)) IDT electrode 30: Al layer (thickness 100 nm) Average electrode pitch: 4.5 μm Electrode width: 0.6 μm First layer of acoustic multilayer film: HfO ２ Layer (thickness 112 nm) Second layer of acoustic multilayer film: SiO ２ Layer (thickness 121 nm) Intermediate layer 12: SiO ２ Layer support substrate 11: Si layer (thickness 4.0 μm)

[0109] (Example 6-2) The elastic wave apparatus according to Example 6-2 was designed in the same way as the elastic wave apparatus according to Example 6-1, except that the relative permittivity of the support substrate was set to 11.8.

[0110] (Example 6-3) The elastic wave apparatus according to Example 6-3 was designed in the same way as the elastic wave apparatus according to Example 6-1, except that the relative permittivity of the support substrate was set to 20.

[0111] (Example 6-4) The elastic wave apparatus according to Example 6-4 was designed in the same way as the elastic wave apparatus according to Example 6-1, except that the relative permittivity of the support substrate was set to 40.

[0112] (Example 7-1) The elastic wave apparatus according to Example 7-1 has a first layer of acoustic multilayer film made of tungsten oxide (WO) with a thickness of 125 nm. ３ Aside from being a layer, the design was the same as that of the elastic wave apparatus in Example 1.

[0113] (Example 7-2) The elastic wave apparatus according to Example 7-2 was designed in the same way as the elastic wave apparatus according to Example 7-1, except that the relative permittivity of the support substrate was set to 11.8.

[0114] (Example 7-3) The elastic wave apparatus according to Example 7-3 was designed in the same way as the elastic wave apparatus according to Example 7-1, except that the relative permittivity of the support substrate was set to 20.

[0115] (Example 7-4) The elastic wave apparatus according to Example 7-4 was designed in the same way as the elastic wave apparatus according to Example 7-1, except that the relative permittivity of the support substrate was set to 40.

[0116] For the elastic wave apparatuses according to Examples 6-1 to 6-4 and Examples 7-1 to 7-4 described above, the relative bandwidth was investigated by simulations in which the dm / p ratio was changed by varying the thickness dm of the intermediate layer 12. Figure 17 is a graph showing the magnitude of the relative bandwidth when the dm / p ratio of the elastic wave apparatuses according to Examples 6-1 to 6-4 is changed. Figure 18 is a graph showing the magnitude of the relative bandwidth when the dm / p ratio of the elastic wave apparatuses according to Examples 7-1 to 7-4 is changed.

[0117] As shown in Figures 17 and 18, when dm / p is 0.3 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.3. This shows that the relative bandwidth can be increased by setting dm / p to 0.3 or higher.

[0118] As shown in Figures 17 and 18, when dm / p is 0.5 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.5. This shows that the relative bandwidth can be increased by setting dm / p to 0.5 or higher.

[0119] As shown in Figures 17 and 18, when dm / p is 0.6 or higher, the relative bandwidth is larger compared to when dm / p is less than 0.6. This shows that the relative bandwidth can be further increased by setting dm / p to 0.6 or higher.

[0120] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0121] For example, in the embodiment described above, the IDT electrode 30 was described as being provided only on the upper side of the piezoelectric layer 20, but it is not limited to this configuration. The IDT electrode 30 may be provided on both the upper and lower sides of the piezoelectric layer 20, or it may be provided only on the lower side of the piezoelectric layer 20.

[0122] For example, a dielectric layer may be further provided on at least one main surface of the piezoelectric layer 20. This can suppress higher-order modes that occur in the thickness direction of the piezoelectric layer 20 and improve resonance characteristics. The dielectric layer may be provided so as to cover the IDT electrode, or it may be provided between the IDT electrode and the piezoelectric layer. The material of the dielectric layer is not particularly limited, and for example, silicon dioxide (SiO₂) ｘ ), silicon nitride (Si ３ N ４ ), aluminum nitride (AlN), aluminum oxide (Al ２ O ３ ), tantalum oxide (Ta ２ O ５ ), niobium oxide (Nb ２ O ５ ) may be at least one of the following. In this case, the dielectric layer may be a stack of multiple layers.

[0123] 10 Elastic wave device 11 Support substrate 12 Intermediate layer 20 Piezoelectric layer 20a First main surface 20b Second main surface 30 IDT electrode 31 First electrode finger 32 Second electrode finger 33 First busbar 34 Second busbar 43 Acoustic multilayer film

Claims

1. An elastic wave apparatus comprising: a support substrate; an acoustic multilayer film provided on the upper side of the support substrate; a piezoelectric layer provided on the upper side of the acoustic multilayer film; an IDT electrode provided on at least one side, either above or below the piezoelectric layer; and an intermediate layer provided between the support substrate and the acoustic multilayer film, wherein the acoustic multilayer film includes a plurality of layers stacked in a first direction, the plurality of layers include a first layer and a second layer made of a different material from the first layer, the IDT electrode has a first busbar facing each other, a second busbar, at least one first electrode finger whose base end is connected to the first busbar, and at least one second electrode finger whose base end is connected to the second busbar, and when the thickness of the piezoelectric layer is d, the thickness of the intermediate layer is dm, and the distance between the centers of adjacent first electrode fingers and second electrode fingers is p, d / p is 0.5 or less and dm / p is greater than 0.

3.

2. The elastic wave apparatus according to claim 1, wherein the relative permittivity of the intermediate layer is lower than that of the support substrate.

3. The elastic wave apparatus according to claim 1 or 2, wherein the material of the intermediate layer comprises at least one of silicon oxide and silicon nitride.

4. The elastic wave apparatus according to any one of claims 1 to 3, wherein the material of the support substrate includes at least one of silicon, silicon oxide, silicon carbide, lithium niobate, lithium tantalate, sapphire, aluminum nitride, and aluminum oxide.

5. The elastic wave apparatus according to claim 1, wherein the material of the support substrate is silicon, and the material of the intermediate layer is quartz glass, crystal, or silicon nitride.

6. The elastic wave apparatus according to claim 1, wherein the material of the support substrate is quartz, and the material of the intermediate layer is silica glass.

7. The elastic wave apparatus according to claim 1, wherein the material of the support substrate is silicon nitride, and the material of the intermediate layer is quartz glass or crystal.

8. The elastic wave apparatus according to any one of claims 1 to 7, wherein at least one of the plurality of layers is made of a dielectric.

9. The elastic wave apparatus according to any one of claims 1 to 8, wherein the acoustic impedance of the first layer is higher than the acoustic impedance of the second layer.

10. The elastic wave apparatus according to any one of claims 1 to 9, wherein the first layer comprises at least one of tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium carbon, niobium carbide, zinc carbide, zinc nitride, lanthanum boride, vanadium carbide, aluminum nitride, silicon carbide, yttrium oxide, magnesium oxide, silicon nitride, boron carbide, strontium fluoride, barium fluoride, tantalum oxide, hafnium oxide, tungsten oxide, hafnium nitride, tungsten nitride, platinum, tungsten, copper, gold, and silver.

11. The acoustic wave apparatus according to claim 10, wherein the first layer comprises at least one of hafnium oxide and tungsten oxide.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein the second layer comprises silicon oxide.

13. The elastic wave apparatus according to any one of claims 1 to 12, wherein the IDT electrode is provided on the upper side of the piezoelectric layer.

14. The elastic wave apparatus according to any one of claims 1 to 13, wherein the d / p is 0.24 or less.

15. The elastic wave apparatus according to any one of claims 1 to 14, wherein the dm / p is 0.5 or greater.

16. The elastic wave apparatus according to any one of claims 1 to 15, wherein the thickness of the intermediate layer is greater than the thickness of each of the plurality of layers.

17. The elastic wave apparatus according to any one of claims 1 to 16, wherein, when viewed from a direction perpendicular to the extending direction of the first electrode finger and the second electrode finger, the region in which adjacent first electrode finger and second electrode finger overlap, and the region between the centers of adjacent first electrode finger and second electrode finger in a direction perpendicular to the extending direction of the first electrode finger and second electrode finger is defined as the excitation region, and when the metallization ratio of the first electrode finger and second electrode finger with respect to the excitation region is denoted as MR, the condition MR ≤ 1.75 (d / p) + 0.075 is satisfied.

18. The acoustic wave device according to any one of claims 1 to 17, wherein Euler angles (φ ＬＮ , θ ＬＮ , ψ ＬＮ ) of lithium niobate constituting the piezoelectric layer fall within the range of the following formula (1), formula (2) or formula (3): (0°±10°, 0° to 20°, any ψ ＬＮ ) …Formula (1) (0°±10°, 20° to 80°, 0° to 60°(1-(θ ＬＮ -50) ２ / 900) １／２ ) or (0°±10°, 20° to 80°, [180°-60°(1-(θ ＬＮ -50) ２ / 900) １／２ to 180°] …Formula (2) (0°±10°, [180°-30°(1-(ψ ＬＮ -90) ２ / 8100) １／２ to 180°, any ψ ＬＮ ) …Formula (3)

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