Elastic wave device

Abstract

A purpose of the invention is to increase a fractional bandwidth. This elastic wave device comprises: a support substrate; a first acoustic multilayer film provided on the upper side of the support substrate; a piezoelectric layer provided on the upper side of the first acoustic multilayer film; an IDT electrode provided on the piezoelectric layer; a second acoustic multilayer film provided on the upper side of the piezoelectric layer; and a dielectric film provided on the second acoustic multilayer film. The IDT electrode has: a first busbar; a second busbar; at least one first electrode finger; and at least one second electrode finger. If d is the thickness of the piezoelectric layer and p is the distance between centers of adjacent electrode fingers, d / p is 0.5 or less. The ratio of the dielectric film thickness to the thickness of the second acoustic multilayer film is 14.3 or less.

Description

Elastic wave apparatus

[0001] This invention relates to an elastic wave apparatus.

[0002] Patent Document 1 describes an elastic wave apparatus comprising 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] Patent No. 5648695

[0004] In some cases, a dielectric film is provided in the elastic wave apparatus shown in Patent Document 1, and the frequency is adjusted by adjusting the thickness of the dielectric film. In this case, even if the thickness of the dielectric film is changed by processing the dielectric film, it may not be possible to properly adjust the frequency characteristics, and the desired frequency characteristics may not be obtained.

[0005] The present invention aims to provide an elastic wave apparatus that can easily obtain desired frequency characteristics.

[0006] An elastic wave apparatus according to one embodiment comprises a support substrate, a first acoustic multilayer film provided on the upper side of the support substrate, a piezoelectric layer provided on the upper side of the first acoustic multilayer film, an IDT electrode provided on at least one side of the upper or lower side of the piezoelectric layer, a second acoustic multilayer film provided on the upper side of the piezoelectric layer, and a dielectric film provided on the second acoustic multilayer film, wherein the first acoustic multilayer film includes a first plurality of layers stacked in a first direction, the second acoustic multilayer film includes a second plurality of layers stacked in a first direction, and the first plurality of layers include a first layer and a material different from the first layer. The IDT electrode includes a second layer made of a different material from the third layer, and the second plurality of layers include a third layer and a fourth layer made of a different material from the third layer, and 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 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 the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 14.3 or less.

[0007] According to the elastic wave apparatus of the present invention, desired frequency characteristics can be easily obtained.

[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 diagram showing the results of the first simulation. Figure 13 is a cross-sectional view showing the elastic wave apparatus according to Comparative Example 1. Figure 14 is a cross-sectional view showing the elastic wave apparatus according to Comparative Example 2. Figure 15 is a diagram showing a graph representing the relationship between the dielectric film thickness and the resonant frequency of the elastic wave apparatus according to Example 1. Figure 16 is a diagram showing a graph representing the relationship between the dielectric film thickness and the anti-resonant frequency of the elastic wave apparatus according to Example 1. Figure 17 is a diagram showing a graph representing the relationship between the dielectric film thickness and the resonant frequency of the elastic wave apparatus according to Comparative Example 1. Figure 18 is a diagram showing a graph representing the relationship between the dielectric film thickness and the anti-resonant frequency of the elastic wave apparatus according to Comparative Example 1. Figure 19 is a diagram showing a graph representing the relationship between the dielectric film thickness and the resonant frequency of the elastic wave apparatus according to Comparative Example 2. Figure 20 is a diagram showing a graph representing the relationship between the dielectric film thickness and the anti-resonant frequency of the elastic wave apparatus according to Comparative Example 2.

[0009] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure. Each embodiment described in this disclosure is illustrative, and partial substitution or combination of configurations is possible between different embodiments. In modifications and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects and benefits due to similar configurations will not be mentioned sequentially for each embodiment.

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

[0011] As shown in Figures 1 and 2, the elastic wave apparatus 10 according to the first embodiment comprises a support member, a first acoustic multilayer film 43, a piezoelectric layer 20, an IDT electrode 30, a second acoustic multilayer film 44, a dielectric film 41, and through electrodes 51 and 52.

[0012] (Support Member) In the first embodiment, the support member comprises a support substrate 11 and an intermediate layer 12 provided on the upper side of the support substrate 11. In the following description, one direction in the thickness direction of the support substrate 11 may be described as "up," and the other direction in the thickness direction of the support substrate 11 may be described as "down." In this disclosure, "provided on the upper side" includes being provided directly on top so as to be in contact with it, and being provided indirectly or at a distance so as to be located above it.

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

[0014] (Intermediate layer) The intermediate layer 12 is formed of a dielectric material. The intermediate layer 12 is thicker than each of the first multiple layers (first layers 43b, 43d and second layers 43a, 43c, 43e) included in the first acoustic multilayer film 43, which will be described later. The material of the intermediate layer 12 is silicon dioxide (SiO₂ｘ Preferably, the material contains at least one of the following: ) and silicon nitride (SiN).

[0015] (First Acoustic Multilayer Film) The first acoustic multilayer film 43 is provided on the upper side of the intermediate layer 12. The first acoustic multilayer film 43 is a laminate having a first plurality of layers. The first acoustic multilayer film 43 has a laminated structure of first layers 43b, 43d and second layers 43a, 43c, 43e as the first plurality of layers. 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.

[0016] In the example shown in Figure 2, the first acoustic multilayer film 43 has three second layers 43a, 43c, and 43e and two first layers 43b and 43d, and is a laminate of five layers in which the second layers 43a, 43c, and 43e and the first layers 43b and 43d are stacked alternately. In the first acoustic multilayer film 43 according to the example in Figure 2, the layers are stacked in the order of second layer 43a, first layer 43b, second layer 43c, first layer 43d, and second layer 43e from the piezoelectric layer 20 side. Note that the number of layers in the first acoustic multilayer film 43 is merely an example and is not particularly limited. For example, the first acoustic multilayer film 43 may have four second layers and three first layers, and may be a laminate of seven layers in which the second layers and first layers are stacked alternately. Furthermore, for example, the first acoustic multilayer film 43 may have five second layers and four first layers, and may be a laminate of nine layers in which the second layers and first layers are alternately stacked. Also, in the example of Figure 2, among the first plurality of layers, the layer closest to the piezoelectric layer 20 is the second layer 43a, and the layer closest to the support substrate 11 is the second layer 43e, but it is not limited to this, and at least one of the layer closest to the piezoelectric layer 20 and the layer closest to the support substrate 11 may be the first layer.

[0017] The first layers 43b and 43d are, for example, tungsten carbide (WC), tantalum carbide (TaC), rhenium oxide (ReO). ３ ), carbon silicon chromium (CrCSI), niobium carbide (NbC), zinc carbide (ZrC), zinc nitride (TiC), 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 ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ ), ytterbium oxide (Yb ２ O ３ ), tungsten oxide (WO ３ ), hafnium nitride (HfN), tungsten nitride (WN), platinum (Pt), tungsten (W), copper (Cu), gold (Au) and silver (Ag). Among these, it is more preferable that the first layers 43b and 43d contain at least one selected from the group consisting of platinum (Pt), tungsten (W), copper (Cu), gold (Au) and silver (Ag). This enables the acoustic impedance of the first layers 43b and 43d to be made larger than that of the second layers 43a, 43c and 43e.

[0018] The second layers 43a, 43c and 43e, for example, contain silicon oxide (SiO ｘ ) and aluminum (Al). Among these, it is preferable that the second layers 43a, 43c and 43e contain, for example, aluminum (Al). This enables the acoustic impedance of the second layers 43a, 43c and 43e to be made smaller than that of the first layers 43b and 43d.

[0019] 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.

[0020] If the first plurality of layers have a plurality of first layers, it is preferable that the thicknesses of the plurality of first layers are the same. If the first plurality of layers have a plurality of second layers, it is preferable that the thicknesses of the plurality of second layers are the same. In this disclosure, "the thicknesses of the layers are the same" means that the ratio of the absolute value of the difference between the thickness of one layer and the thickness of another layer to the average thickness of the plurality of layers is 1% or less. In other words, if the thicknesses of the plurality of layers being compared are t1 and t2, then the thicknesses of the plurality of layers being compared are the same if |t1-t2| / [(t1+t2) / 2] ≤ 0.01. If there is variation in the thickness of the layers, the average value of the thicknesses is adopted.

[0021] 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.

[0022] 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.

[0023] (IDT electrode) In the first embodiment, the IDT (Interdigital Transducer) electrode 30 is provided on the underside of the piezoelectric layer 20. This makes the first main surface 20a of the piezoelectric layer 20 flush, which facilitates the formation and thickness adjustment of the second acoustic multilayer film 44 and dielectric film 41, which will be described later. The IDT electrode 30 may be provided directly on the second main surface 20b, or it may be provided indirectly on the second main surface 20b via a dielectric film or the like. In the first embodiment, the IDT electrode 30 is provided directly on the second main surface 20b.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] (Second Acoustic Multilayer Film) The second acoustic multilayer film 44 is provided on the upper side of the piezoelectric layer 20. The second acoustic multilayer film 44 is a laminate having a second plurality of layers. The second acoustic multilayer film 44 has a laminated structure of a third layer 44b and a fourth layer 44a as the second plurality of layers. By providing the second acoustic multilayer film 44, it is possible to suppress the dielectric film 41, which will be described later, from being affected by the energy of the propagating waves from the piezoelectric layer 20 when the elastic wave device 10 is driven. As a result, it is possible to suppress the effect of the thickness of the dielectric film 41 on the frequency characteristics of the elastic wave device 10, so that the effect of fluctuations in the thickness of the dielectric film on the frequency characteristics of the elastic wave device can be set to an appropriate degree, and the desired frequency characteristics can be easily obtained. In the first embodiment, the third layer 44b has a relatively higher acoustic impedance than the fourth layer 44a. As a result, bulk waves of the thickness-slip first mode can be confined within the piezoelectric layer 20.

[0035] In the example shown in Figure 2, the second acoustic multilayer film 44 has one fourth layer 44a and one third layer 44b, and is a laminate of two layers in which the fourth layer 44a and the third layer 44b are alternately stacked. In the second acoustic multilayer film 44 according to the example in Figure 2, the layers are stacked in the order of second layer 43a and first layer 43b from the piezoelectric layer 20 side. The number of stacked second layers in the second acoustic multilayer film 44 is merely an example and is not particularly limited. In the example in Figure 2, the layer closest to the piezoelectric layer 20 is the fourth layer 44a and the layer furthest from the piezoelectric layer 20 is the third layer 44b, but this is not limited to this, and at least one of the layer closest to the piezoelectric layer 20 and the layer closest to the support substrate 11 may be the first layer.

[0036] The third layer 44b is, for example, tungsten carbide (WC), tantalum carbide (TaC), rhenium oxide (ReO ３ ), carbon silicon chromium (CrCSI), niobium carbide (NbC), zinc carbide (ZrC), zinc nitride (TiC), 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 N４ ), boron carbide (B ４ C), Strontium fluoride (SrF ２ ), barium fluoride (BaF ２ ), tantalum oxide (Ta ２ O ５ ), hafnium oxide (HfO ２ ), ytterbium oxide (Yb ２ O ３ ), tungsten oxide (WO ３ It is preferable that the third layer 44b contains 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 third layer 44b contains 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 third layer 44b greater than that of the fourth layer 44a.

[0037] The fourth layer 44a is, for example, silicon dioxide (SiO₂ ｘ Preferably, the material contains at least one of the following: ) and aluminum (Al). In particular, the fourth layer 44a preferably contains aluminum (Al). This makes it possible to make the acoustic impedance of the fourth layer 44a lower than that of the third layer 44b.

[0038] The materials for the third layer 44b and the fourth layer 44a are not limited to those described above. They can be made of any suitable material as long as the acoustic impedance relationship described above is satisfied. For example, the materials for the third layer 44b may be different from each other, and the materials for the fourth layer 44a may be different from each other. Furthermore, the materials for the third layer 44b and the fourth layer 44a are not limited to being made of one type of material, but may be layers of mixtures containing multiple materials.

[0039] Furthermore, if the second set of layers includes a plurality of third layers, it is preferable that the thickness of the plurality of third layers is the same. If the second set of layers includes a plurality of fourth layers, it is preferable that the thickness of the plurality of fourth layers is the same.

[0040] The dielectric film 41 is provided on the upper side of the second acoustic multilayer film 44. Since the frequency characteristics of the elastic wave device 10 according to this embodiment depend on the thickness of the dielectric film 41, the frequency characteristics of the elastic wave device 10 can be adjusted by adjusting the thickness of the dielectric film 41 by grinding or other means.

[0041] Here, the dielectric film 41 and the layers included in the second acoustic multilayer film 44 are distinguished in the following way. First, if the uppermost layer among the layers above the piezoelectric layer 20 is made of a dielectric, then that layer is the dielectric film 41. In this case, if there are multiple layers other than electrodes between that layer and the piezoelectric layer 20, then those multiple layers are multiple layers of the second acoustic multilayer film 44. Also, if the uppermost layer among the layers above the piezoelectric layer 20 is made of something other than a dielectric, then if the layers above the piezoelectric layer 20 include a layer made of a dielectric, and the thickness of the uppermost dielectric layer among those dielectric layers is not the same as the thickness of any of the other layers between the piezoelectric layer 20 and the dielectric layer, excluding the electrodes, then that uppermost dielectric layer is the dielectric film 41. In this case, if there are multiple other layers other than electrodes between the piezoelectric layer 20 and the dielectric layer, then those other layers are multiple layers included in the second acoustic multilayer film 44.

[0042] The dielectric film 41 is made of a dielectric material. The material of the dielectric film 41 is silicon dioxide (SiO₂). ｘ ), tantalum oxide (Ta ２ O ５ ), silicon nitride (Si ３ N ４ Preferably, it contains at least one of the following: ), aluminum nitride (AlN). That is, the dielectric film 41 may contain multiple types of the above materials, for example, silicon dioxide (SiO₂). ｘ ) and silicon nitride (Si ３ N ４ It may also be silicon oxynitride (SiON), which contains ). This makes it easy to grind the dielectric film 41 and allows the ratio of the change in the resonant frequency and anti-resonant frequency with respect to the change in the thickness of the dielectric film 41 to be of an appropriate magnitude, so that the resonant frequency and anti-resonant frequency of the elastic wave device 10 can be easily adjusted.

[0043] In this embodiment, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 14.3 or less. This reduces the amount of grinding required to adjust the resonant and anti-resonant frequencies of the elastic wave device 10 to desired values. Furthermore, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 0.0034 or more. This suppresses the influence on the frequency characteristics due to variations in the dielectric film 41 that occur during the process of grinding the dielectric film 41 to adjust the resonant and anti-resonant frequencies of the elastic wave device 10 to desired values ​​when manufacturing the elastic wave device 10. As described above, by setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to the above range, the frequency characteristics can be easily adjusted by the dielectric film 41, and the desired frequency characteristics can be easily obtained.

[0044] When the dielectric film 41 contains silicon oxide, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 7.33 or less, and more preferably 3.33 or less. Furthermore, when the dielectric film 41 contains silicon oxide, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 0.0034 or more. This makes the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed to a more appropriate level, making it easier to adjust the frequency characteristics with the dielectric film 41 and easier to obtain the desired frequency characteristics.

[0045] When the dielectric film 41 contains tantalum oxide, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 7.66 or less, and more preferably 5.33 or less. Furthermore, when the dielectric film 41 contains tantalum oxide, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 0.0034 or more. This makes the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed to a more appropriate level, making it easier to adjust the frequency characteristics with the dielectric film 41 and easier to obtain the desired frequency characteristics.

[0046] When the dielectric film 41 contains silicon nitride, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 14.3 or less, and more preferably 6.00 or less. Furthermore, when the dielectric film 41 contains silicon nitride, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 0.0034 or more. This makes the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed to a more appropriate level, thus making it easier to adjust the frequency characteristics with the dielectric film 41 and to obtain the desired frequency characteristics more easily.

[0047] When the dielectric film 41 contains aluminum nitride, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 14.3 or less, and more preferably 3.33 or less. Furthermore, when the dielectric film 41 contains aluminum nitride, the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is preferably 0.0034 or more. This makes the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed to a more appropriate level, making it easier to adjust the frequency characteristics with the dielectric film 41 and easier to obtain the desired frequency characteristics.

[0048] The magnitude of the change in the resonant frequency and anti-resonant frequency of the elastic wave apparatus 10 with respect to a change in the thickness of the dielectric film 41 is preferably 0.5 MHz / nm or more and 8.0 MHz / nm or less, more preferably 1.0 MHz / nm or more and 2.5 MHz / nm or less, and even more preferably 1.1 MHz / nm or more and 1.4 MHz / nm. By satisfying the upper limit of these ranges, the amount of grinding required to set the resonant frequency and anti-resonant frequency of the elastic wave apparatus 10 to desired values ​​can be reduced. By satisfying the lower limit of these ranges, the amount of additional grinding required for the dielectric film 41 in the process of grinding the dielectric film 41 to set the resonant frequency and anti-resonant frequency of the elastic wave apparatus 10 to desired values ​​can be increased to a manageable level. This makes it easier to adjust the frequency characteristics by the dielectric film 41 and easily obtain the desired frequency characteristics. In the following description, the magnitude of the change in resonant frequency with respect to a change in the thickness of the dielectric film may be described as the frequency sensitivity to dielectric film thickness.

[0049] The through electrodes 51 and 52 are wiring electrodes that provide an electrical connection to the IDT electrode 30. The material of the through electrodes 51 and 52 is a conductor such as metal. In the example of Figure 1, the through electrode 51 is provided so as to be in contact with the first bus bar 33 and the second bus bar 34, and the through electrode 52 is provided so as to be in contact with the first bus bar 33 and the second bus bar 34. In the example of Figure 2, the through electrodes 51 and 52 penetrate the dielectric film 41 and the second acoustic multilayer film 44 in the Z direction. Note that the through electrodes 51 and 52 are not an essential component, and the electrical connection to the IDT electrode 30 may be provided, for example, by the first bus bar 33 and the second bus bar 34 exposed by providing an opening that penetrates the dielectric film 41 and the second acoustic multilayer film 44 in the Z direction in a region that overlaps with the first bus bar 33 and the second bus bar 34 when viewed in plan in the Z direction, or by the first bus bar 33 and the second bus bar 34 extended in the Y direction.

[0050] 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.

[0051] 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.

[0052] 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 can be 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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

[0058] As is clear from Figure 5, despite the absence of a reflector, a good resonance characteristic with a relative bandwidth of 12.5% ​​has been obtained.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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).

[0071] (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)

[0072] 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.

[0073] As described above, the elastic wave apparatus 10 according to the first embodiment includes a support substrate 11, a first 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 first 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, a second acoustic multilayer film 44 provided on the upper side of the piezoelectric layer 20, and a dielectric film 41 provided on the second acoustic multilayer film 44. The first acoustic multilayer film 43 includes a first plurality of layers (first layers 43b, 43d and second layers 43a, 43c, 43e) stacked in a first direction. The second acoustic multilayer film 44 includes a second plurality of layers (third layer 44b and fourth layer 44a) stacked in a first direction. The first plurality of layers includes first layers 43b, 43d and second layers 43a, 43c, 43e made of a different material from the first layers 43b, 43d. The first plurality of layers also includes a third layer 44b and a fourth layer 44a made of a different material from the third layer 44b. The IDT electrode 30 has a first busbar 33 facing each other, a second busbar 34, 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 and the distance between the centers of adjacent first electrode fingers 31 and second electrode fingers 32 is p, d / p is 0.5 or less. The ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 14.3 or less. This allows the amount of additional grinding required for the dielectric film 41 in the process of grinding the dielectric film 41 to achieve the desired resonant and anti-resonant frequencies of the elastic wave device 10 to be increased to a manageable level. Consequently, the frequency characteristics can be easily adjusted using the dielectric film 41, and the desired frequency characteristics can be easily obtained.

[0074] In a preferred embodiment, the dielectric film 41 includes at least one of silicon oxide, tantalum oxide, silicon nitride, and aluminum nitride. This facilitates grinding of the dielectric film 41, allowing for easy adjustment of the resonant and anti-resonant frequencies of the elastic wave apparatus 10, and thus easily obtaining the desired frequency characteristics.

[0075] In a more desirable embodiment, the dielectric film 41 contains silicon oxide. The ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 7.33 or less. This ensures that the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed is appropriate, making it easy to adjust the frequency characteristics using the dielectric film 41.

[0076] In a more desirable embodiment, the dielectric film 41 contains tantalum oxide. The ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 7.66 or less. This ensures that the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed is appropriate, making it easy to adjust the frequency characteristics using the dielectric film 41.

[0077] In a more desirable embodiment, the dielectric film 41 contains silicon nitride. The ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 14.3 or less. This ensures that the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed is appropriate, making it easy to adjust the frequency characteristics using the dielectric film 41.

[0078] In a more desirable embodiment, the dielectric film 41 contains aluminum nitride. The ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 is 14.3 or less. This ensures that the magnitude of the change in frequency characteristics when the thickness of the dielectric film 41 is changed is appropriate, making it easy to adjust the frequency characteristics using the dielectric film 41.

[0079] In a desirable embodiment, the acoustic impedance of the first layers 43b and 43d is higher than that of the second layers 43a, 43c, and 43e. The acoustic impedance of the third layer 44b is higher than that of the fourth layer 44a. This allows the bulk wave of the thickness-slip first mode to be well confined within the piezoelectric layer 20.

[0080] In a preferred embodiment, the first layer 43b, 43d and the third layer 44b 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 layer 43b, 43d, and the third layer 44b.

[0081] In a preferred embodiment, the second layers 43a, 43c, 43e and the fourth layer 44a contain at least one of silicon oxide and aluminum. This reduces the acoustic impedance of the second layers 43a, 43c, 43e and the fourth layer 44a.

[0082] In a preferred embodiment, the IDT electrode 30 is provided on the underside of the piezoelectric layer 20. This makes the surface of the piezoelectric layer 20 on the dielectric film 41 side (first main surface 20a) flush, which facilitates the formation of the second acoustic multilayer film 44 and the adjustment of the thickness of the dielectric film 41.

[0083] In a preferred embodiment, an intermediate layer 12 is further provided between the support substrate 11 and the first acoustic multilayer film 43. This allows for even better resonance characteristics to be obtained.

[0084] In a desirable configuration, the d / p ratio is 0.24 or less. This allows for even better resonance characteristics to be obtained.

[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] (First Simulation) In the first simulation, the frequency sensitivity to dielectric film thickness was investigated for the elastic wave apparatus of the following design by varying the thickness of the dielectric film 41 and the Young's modulus of the material of the dielectric film 41. Piezoelectric layer 20: Single crystal LiNbO ３Layer (thickness 300 nm, Euler angles (0°, 30°, 0°)) IDT electrode 30: Al layer (thickness 100 nm) Average electrode pitch: 3.9 μm Electrode width: 0.9 μm First layer of the first acoustic multilayer film 43: HfO ２ Layer (thickness 150 nm) Second layer of the first acoustic multilayer film 43: SiO ２ Layer (thickness 150 nm) Third layer of the second acoustic multilayer film 44: HfO ２ Layer (thickness 150 nm) Fourth layer of the second acoustic multilayer film 44: SiO ２ Layer (thickness 150 nm) Intermediate layer 12: SiO ２ Layer (thickness 175 μm) Support substrate 11: Single crystal silicon layer (thickness 7.9 μm)

[0089] Figure 12 shows the results of the first simulation. As shown in Figure 12, when the thickness of the dielectric film 41 is 4.35 μm or less, the frequency sensitivity to the dielectric film thickness sometimes exceeds 0.5 MHz / nm. In the first simulation, the thickness of the second acoustic multilayer film 44 is 300 nm, so it can be seen that by setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.3 or less, the frequency sensitivity to the dielectric film thickness increases.

[0090] (Silicon oxide (Young's modulus: 73 GPa)) As shown in Figure 12, when the Young's modulus of the dielectric film 41 material is 73 GPa, the frequency sensitivity to dielectric film thickness is 0.5 MHz / nm or higher when the thickness of the dielectric film 41 is 2.22 μm or less, and the frequency sensitivity to dielectric film thickness is 1 MHz / nm or higher when the thickness of the dielectric film 41 is 1.19 μm or less.

[0091] Here, the Young's modulus of silicon oxide is 73 GPa, and in the first simulation, the thickness of the second acoustic multilayer film 44 is 300 nm. Therefore, when the dielectric film 41 contains silicon oxide, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.33 or less increases the frequency sensitivity to the dielectric film thickness. Furthermore, when the dielectric film 41 contains silicon oxide, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 3.33 or less increases the frequency sensitivity to the dielectric film thickness. Note that the Young's modulus of silicon oxide is merely an example. As shown in Figure 12, when the Young's modulus is near 73 GPa, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.33 or less increases the frequency sensitivity to the dielectric film thickness. More preferably, by setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.00 or less, the frequency sensitivity to the dielectric film thickness can be increased more reliably.

[0092] (Tantalum oxide (Young's modulus: 130 GPa)) As shown in Figure 12, when the Young's modulus of the dielectric film 41 material is 130 GPa, the frequency sensitivity to dielectric film thickness is 0.5 MHz / nm or higher when the thickness of the dielectric film 41 is 2.32 μm or less, and the frequency sensitivity to dielectric film thickness is 1 MHz / nm or higher when the thickness of the dielectric film 41 is 1.64 μm or less.

[0093] Here, the Young's modulus of tantalum oxide is 130 GPa, and in the first simulation, the thickness of the second acoustic multilayer film 44 is 300 nm. Therefore, when the dielectric film 41 contains tantalum oxide, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.66 or less increases the frequency sensitivity to the dielectric film thickness. Furthermore, when the dielectric film 41 contains tantalum oxide, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 5.33 or less increases the frequency sensitivity to the dielectric film thickness. Note that the Young's modulus of tantalum oxide is merely an example. As shown in Figure 12, when the Young's modulus is near 130 GPa, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.66 or less increases the frequency sensitivity to the dielectric film thickness. More preferably, by setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 7.33 or less, the frequency sensitivity to dielectric film thickness can be increased more reliably.

[0094] (Silicon nitride (Young's modulus: 290 GPa)) As shown in Figure 12, when the Young's modulus of the dielectric film 41 material is 290 GPa, the frequency sensitivity to dielectric film thickness is 0.5 MHz / nm or higher when the thickness of the dielectric film 41 is 4.26 μm or less, and the frequency sensitivity to dielectric film thickness is 1 MHz / nm or higher when the thickness of the dielectric film 41 is 1.87 μm or less.

[0095] Here, the Young's modulus of silicon nitride is 290 GPa, and in the first simulation, the thickness of the second acoustic multilayer film 44 is 300 nm. Therefore, when the dielectric film 41 contains silicon nitride, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.3 or less increases the frequency sensitivity to the dielectric film thickness. Furthermore, when the dielectric film 41 contains silicon nitride, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 6.00 or less increases the frequency sensitivity to the dielectric film thickness even further. Note that the Young's modulus of silicon nitride is merely an example. As shown in Figure 12, when the Young's modulus is near 290 GPa, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.3 or less increases the frequency sensitivity to the dielectric film thickness. More preferably, by setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.0 or less, the frequency sensitivity to the dielectric film thickness can be increased more reliably.

[0096] (Aluminum nitride (Young's modulus: 308 GPa)) As shown in Figure 12, when the Young's modulus of the dielectric film 41 material is 308 GPa, the frequency sensitivity to dielectric film thickness is 0.5 MHz / nm or higher when the thickness of the dielectric film 41 is 4.29 μm or less, and the frequency sensitivity to dielectric film thickness is 1 MHz / nm or higher when the thickness of the dielectric film 41 is 1.08 μm or less.

[0097] Here, the Young's modulus of aluminum nitride is 308 GPa, and in the first simulation, the thickness of the second acoustic multilayer film 44 is 300 nm. Therefore, it can be seen that when the dielectric film 41 contains aluminum nitride, setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.3 or less increases the frequency sensitivity with respect to the dielectric film thickness. Further, when the dielectric film 41 contains aluminum nitride, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 3.33 or less further increases the frequency sensitivity with respect to the dielectric film thickness. Note that the Young's modulus of aluminum nitride is merely an example. As shown in FIG. 12, when the Young's modulus is in the vicinity of 308 GPa, it can be seen that setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.3 or less increases the frequency sensitivity with respect to the dielectric film thickness. More preferably, setting the ratio of the thickness of the dielectric film 41 to the thickness of the second acoustic multilayer film 44 to 14.0 or less can more reliably increase the frequency sensitivity with respect to the dielectric film thickness.

[0098] (Second Simulation) In the second simulation, for the elastic wave devices according to Example 1 and Comparative Example 1, the magnitudes of the resonance frequency and the anti-resonance frequency were investigated through a simulation in which the thickness of the dielectric film 41 was changed. Further, for the elastic wave device according to Comparative Example 2, the magnitudes of the resonance frequency and the anti-resonance frequency were investigated through a simulation in which the thickness of the support substrate 11A on the second acoustic multilayer film 44 was changed.

[0099] (Example 1) The elastic wave device according to Example 1 had the following design. Piezoelectric layer 20: single-crystal LiNbO ３ 3 layer (thickness: 300 nm, Euler angles (0°, 30°, 0°)) IDT electrode 30: Al layer (thickness: 100 nm) Average inter-electrode pitch: 3.9 µm Electrode width: 0.9 µm First layer of the first acoustic multilayer film 43: HfO ２ 2 layer (thickness: 150 nm) Second layer of the first acoustic multilayer film 43: SiO ２ 2 layer (thickness: 150 nm) Third layer of the second acoustic multilayer film 44: HfO ２ 2 layer (thickness: 150 nm) Fourth layer of the second acoustic multilayer film 44: SiO２ Layer (thickness 150 nm) Dielectric film: SiN layer Interlayer 12: SiO ２ Layer (thickness 175 μm) Support substrate 11: Single crystal silicon layer (thickness 7.9 μm)

[0100] Figure 15 is a graph showing the relationship between the thickness of the dielectric film and the resonant frequency of the elastic wave apparatus according to Example 1. Figure 16 is a graph showing the relationship between the thickness of the dielectric film and the anti-resonant frequency of the elastic wave apparatus according to Example 1. In the graphs in Figures 15 and 16, the dotted line is an approximate straight line calculated by performing linear regression based on the plots. In Figure 15, the magnitude of the slope of the approximate straight line of the plots was 1.4 MHz / nm. In Figure 16, the magnitude of the slope of the approximate curve of the plots was 1.1 MHz / nm.

[0101] (Comparative Example 1) Figure 13 is a cross-sectional view showing the elastic wave apparatus according to Comparative Example 1. Figure 13 shows a cross-section corresponding to Figure 2 described above. As shown in Figure 13, the elastic wave apparatus 10X according to Comparative Example 1 has the same design as the elastic wave apparatus according to Example 1, except that it is designed without a second acoustic multilayer film 44.

[0102] Figure 17 is a graph showing the relationship between the dielectric film thickness and the resonant frequency of the elastic wave apparatus according to Comparative Example 1. Figure 18 is a graph showing the relationship between the dielectric film thickness and the anti-resonant frequency of the elastic wave apparatus according to Comparative Example 1. In the graphs in Figures 17 and 18, the dotted line is an approximate straight line calculated by performing linear regression based on the plots. In Figure 17, the magnitude of the slope of the approximate straight line of the plots was 8.5 MHz / nm. In Figure 18, the magnitude of the slope of the approximate curve of the plots was 8.4 MHz / nm.

[0103] (Comparative Example 2) Figure 14 is a cross-sectional view showing the elastic wave apparatus according to Comparative Example 2. Figure 14 shows a cross-section corresponding to Figure 2 described above. As shown in Figure 14, in the elastic wave apparatus 10Y according to Comparative Example 2, the second acoustic multilayer film 44 consists of a total of five layers: two third layers 44b and 44d and three fourth layers 44a, 44c and 44e. In the elastic wave apparatus 10Y according to Comparative Example 2, an intermediate layer 12A identical to the intermediate layer 12 and a support substrate 11A identical to the support substrate 11 are provided on the second acoustic multilayer film 44, and the dielectric film 41 is omitted, except that the design is the same as the elastic wave apparatus according to Example 1.

[0104] Figure 19 is a graph showing the relationship between the dielectric film thickness and the resonant frequency of the elastic wave apparatus according to Comparative Example 2. Figure 20 is a graph showing the relationship between the dielectric film thickness and the anti-resonant frequency of the elastic wave apparatus according to Comparative Example 2. In the graphs in Figures 19 and 20, the dotted line is an approximate straight line calculated by performing linear regression based on the plots. In Figures 19 and 20, the magnitude of the slope of the approximate straight line of the plots was 0 MHz / nm.

[0105] As shown in Figures 15 and 16, in Example 1, which included the second acoustic multilayer film 44, the magnitude of the ratio of the change in the resonant frequency and anti-resonant frequency with respect to the change in the thickness of the dielectric film 41 was 8.0 MHz / nm or less. On the other hand, as shown in Figures 17 and 18, in Comparative Example 1, which did not include the second acoustic multilayer film 44, the magnitude of the ratio of the change in the resonant frequency and anti-resonant frequency with respect to the change in the thickness of the dielectric film 41 was greater than 8.0 MHz / nm. This shows that by including the second acoustic multilayer film 44, the ratio of the change in the resonant frequency and anti-resonant frequency with respect to the change in the thickness of the dielectric film 41 can be suppressed, and the frequency characteristics of the elastic wave device can be adjusted well.

[0106] As shown in Figures 15 and 16, in Example 1, in which a dielectric film 41 was provided on the upper side of the second acoustic multilayer film 44, the magnitude of the ratio of the change in the resonant frequency and anti-resonant frequency with respect to the change in the thickness of the dielectric film 41 was 1 MHz / nm or more. On the other hand, as shown in Figures 19 and 20, in Comparative Example 2, in which a dielectric film 41 was not provided on the upper side of the second acoustic multilayer film 44, the resonant frequency and anti-resonant frequency did not change even when the thickness of the support substrate 11A was changed. This shows that by providing a dielectric film 41 on the upper side of the second acoustic multilayer film 44, the resonant frequency and anti-resonant frequency can be adjusted by adjusting the thickness of the dielectric film 41, and the frequency characteristics of the elastic wave device can be adjusted well.

[0107] 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.

[0108] 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.

[0109] For example, the second acoustic multilayer film 44 and the dielectric film 41 may overlap with a portion of the piezoelectric layer 20 when viewed in plan in the Z direction. In this case, the second acoustic multilayer film 44 and the dielectric film 41 should be provided so as to overlap with at least a portion of the intersection region C when viewed in plan in the Z direction.

[0110] 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 ). In this case, the layer formed of a dielectric may be a laminate of a plurality of layers.

[0111] 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 bus bar 34 Second bus bar 41 Dielectric film 43 First acoustic multilayer film 44 Second acoustic multilayer film 51, 52 Through electrode

Claims

1. A support substrate; a first acoustic multilayer film provided on the upper side of the support substrate; a piezoelectric layer provided on the upper side of the first acoustic multilayer film; an IDT electrode provided on at least one side, either above or below the piezoelectric layer; a second acoustic multilayer film provided on the upper side of the piezoelectric layer; and a dielectric film provided on the second acoustic multilayer film, wherein the first acoustic multilayer film includes a first plurality of layers stacked in a first direction; the second acoustic multilayer film includes a second plurality of layers stacked in the first direction; the first plurality of layers includes a first layer and a second layer made of a different material from the first layer; the second plurality of layers includes a third layer and a fourth layer made of a different material from the third 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. An elastic wave apparatus in which, when the thickness of the piezoelectric layer is d and the distance between the centers of adjacent first and second electrode fingers is p, d / p is 0.5 or less, and the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 14.3 or less.

2. The elastic wave apparatus according to claim 1, wherein the dielectric film comprises at least one of silicon oxide, tantalum oxide, silicon nitride, and aluminum nitride.

3. The elastic wave apparatus according to claim 2, wherein the dielectric film contains silicon oxide, and the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 7.33 or less.

4. The elastic wave apparatus according to claim 2, wherein the dielectric film contains tantalum oxide, and the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 7.66 or less.

5. The elastic wave apparatus according to claim 2, wherein the dielectric film contains silicon nitride, and the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 14.3 or less.

6. The elastic wave apparatus according to claim 2, wherein the dielectric film contains aluminum nitride, and the ratio of the thickness of the dielectric film to the thickness of the second acoustic multilayer film is 14.3 or less.

7. The elastic wave apparatus according to any one of claims 1 to 6, wherein the acoustic impedance of the first layer is higher than the acoustic impedance of the second layer, and the acoustic impedance of the third layer is higher than the acoustic impedance of the fourth layer.

8. The elastic wave apparatus according to any one of claims 1 to 7, wherein the first and third layers include at least one of tungsten carbide, tantalum carbide, rhenium oxide, silicon chromium, 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.

9. The acoustic wave apparatus according to any one of claims 1 to 8, wherein the second layer and the fourth layer comprise at least one of silicon oxide and aluminum.

10. The elastic wave apparatus according to any one of claims 1 to 9, wherein the IDT electrode is provided below the piezoelectric layer.

11. The acoustic wave apparatus according to any one of claims 1 to 10, further comprising an intermediate layer provided between the support substrate and the first acoustic multilayer film.

12. The elastic wave apparatus according to any one of claims 1 to 11, wherein the d / p is 0.24 or less.

13. The elastic wave apparatus according to any one of claims 1 to 12, 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.

14. The acoustic wave device according to any one of claims 1 to 13, 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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