Elastic wave element, module, and communication device

Abstract

In the present invention, a composite substrate has a piezoelectric layer and a low-acoustic-velocity film. The low-acoustic-velocity film spreads along the bottom surface of the piezoelectric layer, and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer. A reverse-velocity surface of acoustic waves propagating in the piezoelectric layer is concave.

Description

Technical Field

[0001] The present disclosure relates to a composite substrate and an elastic wave device including the composite substrate, and also to a module and a communication device including the elastic wave device.

Background Art

[0002] An elastic wave device has, for example, a piezoelectric substrate having piezoelectricity at least on an upper surface thereof, and an IDT (Interdigital Transducer) electrode located on the upper surface of the piezoelectric substrate. When a voltage is applied to the piezoelectric substrate by the IDT electrode, an elastic wave propagating through the piezoelectric substrate is generated.

[0003] Patent Document 1 discloses a composite substrate having a piezoelectric layer, a low acoustic velocity film overlapping the lower surface of the piezoelectric layer, and a high acoustic velocity film overlapping the lower surface of the low acoustic velocity film. In Patent Document 1, the low acoustic velocity film is made of a material through which a bulk wave having a velocity lower than the velocity of the elastic wave propagating through the piezoelectric layer propagates. The high acoustic velocity film is made of a material through which a bulk wave having a velocity higher than the velocity of the elastic wave propagating through the piezoelectric layer propagates.

[0004] Patent Document 1 discloses that in the composite substrate as described above, the inverse velocity surface becomes convex (paragraph 0039 of Patent Document 1). The inverse velocity surface will be described later together with the description of the embodiments according to the present disclosure.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] A composite substrate according to an aspect of the present disclosure has a piezoelectric layer and a low acoustic velocity film. The low acoustic velocity film extends along the lower surface of the piezoelectric layer and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer. The inverse velocity surface of the elastic wave propagating through the piezoelectric layer is concave.

[0007] The elastic wave element according to one aspect of the present disclosure includes the composite substrate and the first IDT electrode. The first IDT electrode has a plurality of electrode fingers arranged along the upper surface of the piezoelectric layer.

[0008] The module according to one aspect of the present disclosure includes the elastic wave element, an antenna connected to the elastic wave element, and an integrated circuit element connected to the antenna via the elastic wave element.

[0009] The communication device according to one aspect of the present disclosure includes the elastic wave element, an antenna connected to the elastic wave element, an integrated circuit element connected to the antenna via the elastic wave element, and a housing that houses the elastic wave element and the integrated circuit element.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings. Note that the drawings are schematic, and the shapes and / or dimensions on the drawings do not necessarily match the actual ones. However, the actual shapes and / or dimensions etc. may be as shown in the drawings, or features such as shapes and / or dimensions etc. may be extracted from the drawings.

[0012] In the description of the aspects (embodiments and modifications) described relatively later, basically, only the differences from the aspects described earlier will be described. Matters not particularly mentioned may be the same as those in the aspects described earlier, or may be inferred from the aspects described earlier. The description of the aspects described earlier may be incorporated into the aspects described later as long as there are no contradictions etc. In a plurality of aspects, for members corresponding to each other, for convenience, they may be given the same reference numerals even if there are differences.

[0013] <First Embodiment> (Outline of the Embodiment) FIG. 1 is a plan view showing the configuration of a main part of the elastic wave element 1 according to the first embodiment. FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1.

[0014] The elastic wave element 1 may be oriented such that any direction can be considered as upward or downward. However, hereinafter, for convenience, the front side of the paper of FIG. 1 is regarded as upward, and terms such as the upper surface or the lower surface may be used.

[0015] The elastic wave element 1 has, for example, a composite substrate 3 and a conductor layer 5 (FIGS. 1 and 2) located on the composite substrate 3. The composite substrate 3 has, for example, a support substrate 7 (FIGS. 2 and 3), a low sound velocity film 9 (FIGS. 2 and 3) located on the support substrate 7, and a piezoelectric layer 11 located on the low sound velocity film 9. The sound velocity in the low sound velocity film 9 is lower than the sound velocity in the piezoelectric layer 11.

[0016] The electrical signal flowing through the conductor layer 5 is converted into an elastic wave propagating through the piezoelectric layer 11. Also, the elastic wave propagating through the piezoelectric layer 11 is converted into an electrical signal flowing through the conductor layer 5. Then, for example, by utilizing the resonance of the elastic wave, the resonance and / or filtering of the electrical signal is realized. The low sound velocity film 9 contributes, for example, to reflecting the elastic wave and confining the energy of the elastic wave in the piezoelectric layer 11. The support substrate 7 contributes, for example, to reinforcing the strength of the composite substrate 3.

[0017] The rectangular coordinate system XYZ shows an example of the direction of the crystal axes in the piezoelectric layer 11. That is, the X-axis, Y-axis, and Z-axis indicate the crystal axes. The rectangular coordinate system xyz shows the relationship between the piezoelectric layer 11 and the propagation direction of the elastic wave intended to be utilized. Specifically, the z-direction is a direction parallel to the normal of the upper surface of the piezoelectric layer 11. The x-direction is the propagation direction of the elastic wave intended to be utilized. The y-direction is parallel to the upper surface of the piezoelectric layer 11 and perpendicular to the x-direction. For convenience, the term "elastic wave" may refer to the elastic wave intended to be utilized (the elastic wave propagating in the x-direction) without special notice.

[0018] As can be understood from the relationship between the orthogonal coordinate system XYZ and the orthogonal coordinate system xyz, the piezoelectric layer 11 is made of, for example, a piezoelectric single crystal of so-called rotation Y-cut X-propagation. Therefore, the X-axis and the x-axis are parallel. Also, as shown in FIG. 3, the Y-axis is inclined at a cut angle c° with respect to the normal (z-axis) of the piezoelectric layer 11.

[0019] As shown in FIG. 1, let v be the velocity (phase velocity) of an elastic wave propagating in a direction inclined at an angle ψ about the z-axis with respect to the x-axis. The velocity v varies depending on the angle ψ. That is, the velocity v is a function of ψ and can be expressed as v(ψ). The reciprocal 1 / v (or 1 / v(ψ)) of the velocity v is called the inverse velocity (or slowness). Although not particularly shown, the inverse velocity 1 / v can be decomposed into a component 1 / v x in the x-direction and a component 1 / v y in the y-direction. 1 / v x = 1 / v × cos ψ, and 1 / v y = 1 / v × sin ψ. (1 / v y ) / (1 / v x ) = tan ψ.

[0020] The value obtained by dividing the inverse velocity 1 / v(ψ) by the inverse velocity 1 / v(0) when ψ = 0° is defined as the normalized inverse velocity 1 / v n (or 1 / v n (ψ)). Let the x-direction component and the y-direction component of the normalized inverse velocity 1 / v n be represented by 1 / v nx and 1 / v ny respectively. Similar to the unnormalized inverse velocity, 1 / v nx = 1 / v n × cos ψ, and 1 / v ny = 1 / v n × sin ψ, and (1 / v ny ) / (1 / v nx ) = tan ψ. When ψ = 0°, 1 / v nx = 1, and 1 / v ny = 0.

[0021] FIG. 6 shows the normalized inverse velocity 1 / v of an elastic wave propagating through the piezoelectric layer 11 in the composite substrate 3 n(ψ) is shown. In this figure, the horizontal axis represents the x-component of the normalized inverse velocity, 1 / v nx is shown. The vertical axis represents the y-component of the normalized inverse velocity, 1 / v ny is shown. Lines L1 to L3 represent the normalized inverse velocities in three embodiments. The three embodiments differ in the thickness a (Figs. 2 and 3) of the piezoelectric layer 11 from each other.

[0022] Taking line L1 among lines L1 to L3 as an example, line L1 represents the normalized inverse velocity 1 / v n (ψ) when ψ is changed. The intersection point of line L1 and the horizontal axis ((1 / v nx , 1 / v nx ) = (1, 0)) corresponds to the inverse velocity at ψ = 0°. Line L1 extends away from the above intersection point as ψ increases from 0°, and in the illustrated example, it exhibits a curve. As understood from the ratio (= tanψ) between 1 / v nx and 1 / v ny at the large-ψ ends of lines L1 to L3, in Fig. 6, generally, the normalized inverse velocity 1 / v n (ψ) is shown when ψ is 0° or more and 20° or less.

[0023] Each of such lines L1 to L3 is an example of an "inverse velocity surface (or inverse velocity curved surface)". That is, the "inverse velocity surface" refers to a line obtained by plotting the normalized inverse velocity 1 / v nx and 1 / v ny (or physical quantities corresponding thereto) on a plane with two axes (horizontal axis and vertical axis) orthogonal to each other, the normalized inverse velocity 1 / v n (ψ) (or a physical quantity corresponding thereto) when ψ is changed. As is also clear from Fig. 6, the ratio of 1 / v nx to a predetermined length on the paper surface and the ratio of 1 / v ny to the above predetermined length may be the same as each other or different from each other.

[0024] Although not particularly shown, the normalized inverse velocity 1 / v nThe line indicating (ψ) is, for example (or generally), symmetric with respect to the horizontal axis (ψ = 0°) within a range centered on the horizontal axis (for example, -15° < ψ < 15°), presenting a shape that is line-symmetric to the shape of the illustrated line (ψ > 0°). In the description of the embodiments, for convenience, while only the range of ψ > 0° is illustrated, there may be expressions as if the range of ψ < 0° is also illustrated. Also, for convenience, without particular notice, only the case of ψ > 0° (from another perspective, the +1 / v ny side) is taken as an example for explanation, or sometimes the cases of ψ > 0° and ψ < 0° (from another perspective, the +1 / v ny side and the -1 / v ny side) are explained without distinction.

[0025] Moreover, the inverse velocity surface in the range centered on ψ = 180° (for example, 165° < ψ < 195°) is, for example (or generally), of the same shape as the inverse velocity surface in the range centered on ψ = 0° (for example, -15° < ψ < 15°) (however, the positive and negative of 1 / v x are reversed). In the following, for convenience, without particular notice, only the inverse velocity surface near ψ = 0° (from another perspective, the +1 / v x side) is taken as an example for explanation, or sometimes the cases of ψ = 0° and ψ = 180° (from another perspective, the +1 / v x side and the -1 / v x side) are explained without distinction.

[0026] Line L1 is an example of a so-called convex inverse velocity surface. Also, lines L2 and L3 are examples of so-called concave inverse velocity surfaces. As can be understood from the comparison between the former and the latter, the convex inverse velocity surface generally presents a convex shape with the inverse velocity at ψ = 0° (from another perspective, the intersection with the horizontal axis) as the vertex within a range centered on ψ = 0° (for example, -15° < ψ < 15°). On the other hand, the concave inverse velocity surface generally presents a concave shape with the inverse velocity at ψ = 0° as the lowest point within a range centered on ψ = 0°. Note that within the illustrated range (roughly -20° < ψ < 20°), the illustrated concave inverse velocity surfaces (lines L2 and L3) may be regarded as having a shape where the top of the convex shape is concave.

[0027] From another perspective, when a convex reverse velocity surface appears, in the range centered around ψ = 0° (for example, -15° < ψ < 15°), basically, as the absolute value of ψ increases from 0°, the absolute value of 1 / v nx decreases, and the absolute value of 1 / v ny increases. When a concave reverse velocity surface appears, in the range centered around ψ = 0°, basically, as the absolute value of ψ increases from 0°, the absolute value of 1 / v nx increases, and the absolute value of 1 / v ny increases. In the illustrated range (generally -20° < ψ < 20°), when the absolute value of ψ further increases, the absolute value of 1 / v nx turns to decrease.

[0028] Note that the reverse velocity surface extends from 0° to 360°. However, in the description of this embodiment, when it is said that the reverse velocity surface is concave or convex, as described above, it means that the reverse velocity surface exhibits a concave shape or a convex shape generally centered around ψ = 0°. In other words, the reverse velocity surface focused on in this embodiment is within a relatively narrow range generally centered around ψ = 0°. The relatively narrow range is, for example, -15° < ψ < 15° or -10° < ψ < 10°. The expression of "generally" centered around ψ = 0° and the like is because the center of the concave shape or convex shape and the x-direction (the direction of ψ = 0°) do not necessarily have to coincide. For example, the two may deviate by less than 5°. Of course, there may be a deviation as a tolerance.

[0029] As a result of intensive studies, the inventor of the present application has found that in the composite substrate 3 having the structure shown in FIGS. 2 and 3, not only a convex reverse velocity surface but also a concave reverse velocity surface can be realized. When the reverse velocity surface is concave, for example, compared with the aspect where the reverse velocity surface is convex, the probability of spurious occurring between the resonance frequency fr (FIG. 4) and the anti-resonance frequency fa (FIG. 4) described later can be reduced.

[0030] More specifically, for example, when the following formula (1) is satisfied, a concave reverse velocity surface is realized. -3.36797a + 2.582139a 2 -1.02894b + 1.487276b 2 -0.02411c + 0.000309c 2 +0.432673ab - 0.00517ac + 0.000873bc + 0.272652 < -1(1) Here, a is the normalized thickness of the piezoelectric layer 11, which is the value obtained by dividing the thickness a′ (μm) of the piezoelectric layer 11 by the wavelength λ (μm) of the elastic wave. b is the normalized thickness of the low-velocity sound film 9, which is the value obtained by dividing the thickness b′ (μm) of the low-velocity sound film 9 by the wavelength λ (μm). c is the cut angle (°) as described above.

[0031] The above is the outline of the first embodiment. Hereinafter, the first embodiment will be described schematically in the following order. 1. Composite substrate 3 (excluding the configuration for realizing the concave inverse velocity surface) 1.1. Piezoelectric layer 11 1.2. Low-velocity sound film 9 1.3. Support substrate 7 2. Conductor layer 5 2.1. IDT electrode 2.2. Reflector 3. Other configurations of the elastic wave element 4. Action and characteristics of the elastic wave element (Figure 4) 5. Configuration for realizing the concave inverse velocity surface (Figures 4 to 10) 5.1. Method for specifying the inverse velocity surface 5.2. Example of simulation calculation 5.3. Equation showing the conditions for realizing the inverse velocity surface 5.4. Consideration of the conditions for realizing the inverse velocity surface 6. Summary of the first embodiment

[0032] (1. Composite substrate) As described above, the composite substrate 3 is configured by sequentially stacking a piezoelectric layer 11, a low acoustic velocity film 9, and a support substrate 7 from above. In the present embodiment, these layers acoustically overlap directly with each other. That is, between these layers, there is no layer (for example, the high acoustic velocity film 13 (FIG. 11) in the second embodiment described later) that acoustically affects the elastic wave propagating through the piezoelectric layer 11.

[0033] Note that when expressing that two layers directly overlap acoustically as described above, when viewed more microscopically, other layers that hardly acoustically affect the elastic wave propagating through the piezoelectric layer 11 may be interposed between the two layers. Examples of other layers include, for example, a bonding layer that contributes to the bonding of the two. Whether two layers directly overlap acoustically with each other may be reasonably determined in light of common technical knowledge and the like. The above other layer (for example, the bonding layer) has a thickness such that it hardly acoustically affects the elastic wave propagating through the piezoelectric layer 11. Such a thickness varies depending on the material of the other layer and the like, but specific examples include 0.005λ or less or 0.001λ or less. In the description of the embodiment, the existence of the bonding layer is basically ignored.

[0034] The elastic wave that is intended to be used in the elastic wave element 1 and that propagates through the piezoelectric layer 11 may be appropriate. For example, the elastic wave may be a surface acoustic wave, a bulk wave, a plate wave (Lamb wave), or it may not be possible to make the above distinctions. The elastic wave used varies depending on, for example, the material of the piezoelectric layer 11, the cut angle (not limited to the cut angle c described above), and the thickness, the configuration on the lower surface side of the piezoelectric layer 11 (the configuration of the low acoustic velocity film 9, etc.), and the configuration on the upper surface side of the piezoelectric layer 11 (the configuration of the conductor layer 5, etc.).

[0035] (1.1. Piezoelectric Layer) The piezoelectric layer 11 is composed of, for example, a single crystal having piezoelectricity. Examples of materials constituting such a single crystal include lithium tantalate (LiTaO3, hereinafter sometimes abbreviated as LT), lithium niobate (LiNbO3, hereinafter sometimes abbreviated as LN), and quartz (SiO2). Note that the piezoelectric layer 11 may be composed of polycrystals.

[0036] The material, cut angle, and thickness of the piezoelectric layer 11 affect the realization of the concave inverse velocity surface. In this embodiment, taking the aspect where the material of the piezoelectric layer 11 is LT of rotation Y-cut X-propagation as an example, specific values of the cut angle and thickness at which the concave inverse velocity surface is realized are exemplified. However, as will be described later, even when the material of the piezoelectric layer 11 is other than LT of rotation Y-cut X-propagation, if the cut angle and thickness of the piezoelectric layer 11 and the conditions of other layers are appropriately set, the concave inverse velocity surface can be realized.

[0037] The cut angle c and the normalized thickness a of the piezoelectric layer 11 may be values that satisfy the formula (1) as described above. Also, whether the formula (1) is satisfied or not, the lower limit and the upper limit of the normalized thickness a when a concave inverse velocity surface is realized may be appropriately set. For example, the normalized thickness a may be 0.05 or more or 0.1 or more. With such a thickness, for example, an elastic wave propagating through the piezoelectric layer 11 can be utilized. Also, for example, the normalized thickness a may be 0.2 or more or 0.3 or more. As shown by the simulation results and the like described later (Figs. 6 to 10), the present inventors have confirmed that a concave inverse velocity surface is realized at such a thickness. Also, for example, the normalized thickness a may be 1.0 or less. In this case, if anisotropy is ignored, within one wavelength of the vibration excited on the upper surface of the piezoelectric layer 11 and propagating downward, a layer (the low sound velocity film 9 in this embodiment) overlapping the lower surface of the piezoelectric layer 11 is positioned to define a boundary condition. Therefore, the characteristics of the laminated structure of the piezoelectric layer 11 and the low sound velocity film 9 are likely to appear. Also, for example, the normalized thickness a may be 0.6 or less. As shown by the simulation results and the like described later (Figs. 6 to 10), the present inventors have confirmed that a concave inverse velocity surface is realized at such a thickness. The above-mentioned lower limit and upper limit may be combined arbitrarily with each other.

[0038] (1.2. Low sound velocity film) The low sound velocity film 9 extends along the lower surface of the piezoelectric layer 11. When expressed in this way, the low sound velocity film 9 may directly overlap the lower surface of the piezoelectric layer 11 acoustically as in this embodiment, or may indirectly overlap acoustically as in the second embodiment described later (see Fig. 11).

[0039] The material of the low sound velocity film 9 is arbitrary as long as the sound velocity in the low sound velocity film 9 is lower than the sound velocity in the piezoelectric layer 11. Physical property values (such as density, Young's modulus, and acoustic impedance) that interact with the sound velocity may also be arbitrarily set.

[0040] The sound velocity in the comparison between the sound velocity in the low sound velocity film 9 and the sound velocity in the piezoelectric layer 11 may be, for example, the sound velocity of the bulk wave propagating through each layer. Generally speaking, the bulk wave includes three types: longitudinal wave, slow shear wave, and fast shear wave. The slow shear wave or the fast shear wave is, for example, either an SV (Shear Vertical) wave or an SH (Shear vertical) wave. The bulk wave used for comparison may be, for example, the bulk wave corresponding to the component mainly including the elastic wave that propagates through the piezoelectric layer 11 and is intended to be utilized among the above three types of bulk waves. This is because, as described above, the low sound velocity film 9 is expected to have the effect of confining the elastic wave propagating through the piezoelectric layer 11. For example, when the elastic wave in the piezoelectric layer 11 intended to be utilized mainly includes an SH wave, the sound velocity of the SH wave in the piezoelectric layer 11 and the sound velocity of the SH wave in the low sound velocity film 9 may be compared. Although the SH wave is taken as an example, the same applies to the SV wave or the longitudinal wave. Also, when the utilization of an elastic wave in which a longitudinal wave and a shear wave are combined is intended, for example, the sound velocity of the shear wave may be compared.

[0041] Note that the comparison conditions do not necessarily have to be as strict as described above. From another perspective, in the comparison of the sound velocity in the piezoelectric layer 11 and the sound velocity in the low sound velocity film 9, the sound velocities of both do not necessarily have to be precisely specified. For example, when comparing the shear wave sound velocity of the low sound velocity film 9 and the shear wave sound velocity of the piezoelectric layer 11, if the difference between the fast shear wave and the slow shear wave in the low sound velocity film 9 is relatively small (the difference between the shear wave sound velocity of the low sound velocity film 9 and the shear wave sound velocity of the piezoelectric layer 11 is relatively large), and it is clear that the shear wave sound velocity of the low sound velocity film 9 is lower than the shear wave sound velocity of the piezoelectric layer 11 even without particularly distinguishing between the fast shear wave and the slow shear wave in the low sound velocity film 9, there is no need to distinguish between the fast shear wave and the slow shear wave in the low sound velocity film 9. From another perspective, the component mainly included in the elastic wave of the piezoelectric layer 11 intended to be utilized does not necessarily have to be precisely specified.

[0042] The speed of sound in the piezoelectric layer 11 varies depending on, for example, the direction in which the speed of sound is specified (ψ from another perspective), as well as the cut angle and thickness of the piezoelectric layer 11, and is also affected by the layer on the lower surface side of the piezoelectric layer 11 (here, the low-speed film 9). The same applies to the low-speed film 9. Therefore, when comparing the speed of sound in two layers (here, the piezoelectric layer 11 and the low-speed film 9), the relationship between the speeds of sound in the two layers can vary depending on the conditions under which the comparison is made. Thus, when the speed of sound in two layers is compared, for example, the speed of sound in the x direction in two layers within the composite substrate 3 having the same configuration as the actual product may be compared. In other words, the specific speed of sound considering the influence of a specific cut angle and thickness, etc. may be compared.

[0043] However, the influence of the cut angle and thickness, etc. does not necessarily have to be considered. From another perspective, in comparing the speed of sound in two layers (here, the piezoelectric layer 11 and the low-speed film 9), the speeds of sound in both may not be precisely specified. For example, when it is clear that the speed of sound in the low-speed film 9 is lower than the speed of sound in the piezoelectric layer 11 regardless of the cut angle and / or thickness of the piezoelectric layer 11 and the thickness of the low-speed film 9, it is not necessary to specify the speed of sound in the x direction of the low-speed film 9 in the actual product. In such a case, the speed of sound may be calculated and compared from a simple theoretical formula based on density and Young's modulus, etc.

[0044] As can be understood from the description of an example of a resonator using the piston mode described below, the velocity of the elastic wave is also affected by the conductor layer 5 or the like located on the piezoelectric layer 11, and is different for each region of the elastic wave element 1. In comparing the sound velocities in two layers (here, the piezoelectric layer 11 and the low sound velocity film 9), for example, the average sound velocity in the crossover region CR (described later) in the elastic wave element 1 having the same configuration as the actual product may be used. However, for example, when it is clear that the sound velocity in the low sound velocity film 9 is lower than the sound velocity in the piezoelectric layer 11 regardless of the presence or absence of the influence of the conductor layer 5 or the like, or when it is clear that the sound velocity in the low sound velocity film 9 is lower than the sound velocity in the piezoelectric layer 11 in the same region when viewed in a plan view, it is not necessary to strictly obtain the sound velocity in such a crossover region.

[0045] Specific examples of the material of the low sound velocity film 9 include, for example, silicon dioxide (SiO2), tantalum oxide (Ta2O3), silicon oxynitride (Si2N2O), and glass. Further, a compound obtained by adding fluorine, carbon, boron, or the like to SiO2 may be used. Any combination of the various materials (for example, LT and LN) listed for the piezoelectric layer 11 and the materials listed here may be used. Note that the conditions for comparing the sound velocity in the piezoelectric layer 11 and the sound velocity in the low sound velocity film 9 have been described in detail so far. However, when the material of the low sound velocity film 9 is the material exemplified in this paragraph, some or all of the comparison conditions described so far may be ignored.

[0046] The material and thickness of the low sound velocity film 9 affect the realization of the concave inverse velocity surface. In the present embodiment, an aspect in which the material of the low sound velocity film 9 is SiO2 is taken as an example, and specific values of the thickness capable of realizing the concave inverse velocity surface are exemplified. However, as described later, even when the material of the low sound velocity film 9 is other than SiO2, the concave inverse velocity surface can be realized by appropriately setting the thickness of the low sound velocity film 9 and the conditions of other layers.

[0047] The normalized thickness b of the low-velocity film 9 may be a value that satisfies the formula (1) as described above. Also, whether the formula (1) is satisfied or not, the lower limit and the upper limit of the normalized thickness b when the concave inverse velocity surface is realized may be set as appropriate. For example, the thickness of the low-velocity film 9 may be 0.01 or more or 0.1 or more, and may also be 0.6 or less or 0.5 or less. The above lower limit and upper limit may be combined arbitrarily with each other. As shown by the simulation results and the like (Figs. 6 to 10) to be described later, the inventor of the present application has confirmed that the concave inverse velocity surface is realized at such a thickness.

[0048] (1.3. Support substrate) The material and dimensions of the support substrate 7 are arbitrary. Since the elastic wave propagating through the piezoelectric layer 11 is basically reflected by the low-velocity film 9, the influence of the material and dimensions of the support substrate 7 on the elastic wave propagating through the piezoelectric layer 11 is relatively small. The inventor of the present application has confirmed by simulation calculation that the support substrate 7 has almost no influence on whether the inverse velocity surface is concave or convex.

[0049] The material of the support substrate 7 may be one having a lower thermal expansion coefficient compared to the piezoelectric layer 11 and the like. In this case, for example, the possibility that the frequency characteristics of the elastic wave element 1 change due to temperature change can be reduced. Examples of such materials include semiconductors such as silicon (Si), single crystals such as sapphire, and ceramics such as aluminum oxide sintered bodies. Note that the support substrate 7 may be configured by laminating a plurality of layers made of different materials. The thickness of the support substrate 7 is, for example, thicker than the piezoelectric layer 11.

[0050] (2. Conductor layer) The conductor layer 5 is formed of, for example, a metal. The specific type of the metal is arbitrary. For example, the metal may be aluminum (Al) or an alloy (Al alloy) mainly composed of Al. The Al alloy may be, for example, an aluminum-copper (Cu) alloy. Note that the conductor layer 5 may be composed of a plurality of metal layers. For example, a relatively thin layer made of titanium (Ti) for strengthening the bondability between Al or the Al alloy and the piezoelectric layer 11 may be provided therebetween. The thickness of the conductor layer 5 may be appropriately set according to the characteristics required for the surface acoustic wave device 1. For example, the thickness of the conductor layer 5 may be 0.02λ or more and 0.10λ or less, and / or 50 nm or more and 600 nm or less.

[0051] As shown in FIG. 1, for example, the conductor layer 5 includes an IDT electrode 19 and a pair of reflectors 21 positioned on both sides of the IDT electrode 19.

[0052] Among the composite substrate 3 and the conductor layer 5, the region where the IDT electrode 19 and the pair of reflectors 21 are located constitutes a resonator 15. The resonator 15 is configured as a so-called one-port surface acoustic wave resonator. For example, when an electrical signal of a predetermined frequency is input from one of the terminals 17A and 17B shown conceptually and schematically, resonance occurs, and the signal that has caused the resonance can be output from the other of the terminals 17A and 17B.

[0053] Note that the resonator 15 includes not only the IDT electrode 19 and the pair of reflectors 21 but also at least a part of the upper surface side of the composite substrate 3 as described above. The at least a part includes, for example, the piezoelectric layer 11 and the low-velocity film 9. In the description of the embodiment, for convenience, it may be expressed as if only the IDT electrode 19 and the pair of reflectors 21 (the configuration excluding the composite substrate 3) are the resonator 15. Also, among the resonator 15, the region where the IDT electrode 19 is disposed (the configuration excluding the region where the reflector 21 is located) is also a resonator. This resonator may be referred to as a resonator 16.

[0054] (2.1. IDT Electrode) The IDT electrode 19 includes a pair of comb electrodes 23. Note that, in order to improve visibility, one of the comb electrodes 23 is hatched. Each comb electrode 23 includes, for example, a bus bar 25, a plurality of electrode fingers 27 extending in parallel from the bus bar 25, and dummy electrodes 29 protruding from the bus bar 25 between the plurality of electrode fingers 27. The pair of comb electrodes 23 are arranged such that the plurality of electrode fingers 27 mesh with each other (cross each other).

[0055] The bus bar 25 has, for example, a shape that generally extends linearly in the direction of propagation of the elastic wave (x direction) with a constant width. The pair of bus bars 25 face each other in a direction (y direction) crossing the direction of propagation of the elastic wave. Different from the illustrated example, the bus bar 25 may have a varying width or be inclined with respect to the direction of propagation of the elastic wave.

[0056] Each electrode finger 27 has, for example, a shape that generally extends linearly in a direction (y direction) orthogonal to the direction of propagation of the elastic wave with a constant width. In each comb electrode 23, the plurality of electrode fingers 27 are arranged in the direction of propagation of the elastic wave (x direction). Also, the plurality of electrode fingers 27 of one comb electrode 23 and the plurality of electrode fingers 27 of the other comb electrode 23 are basically arranged alternately.

[0057] The pitch p of the plurality of electrode fingers 27 (for example, the center - to - center distance between two adjacent electrode fingers 27) is basically constant within the IDT electrode 19. However, a narrow - pitch portion where the pitch p is narrower than most of the other parts, or a wide - pitch portion where the pitch p is wider than most of the other parts, may be provided in a part of the IDT electrode 19. Also, a thinning portion where the electrode fingers 27 are substantially thinned out may exist in a part of the IDT electrode 19.

[0058] In the description of the embodiments, when referring to the pitch p, unless otherwise specified, it refers to the pitch of the portion excluding the special portions such as the narrow pitch portion, the wide pitch portion, or the thinning portion as described above (the majority of the plurality of electrode fingers 27). Further, even in the case where the pitch varies among the plurality of electrode fingers 27 of the majority portion excluding the special portions (for example, 80% or more of the electrode fingers 27), the average value of the pitches of the plurality of electrode fingers 27 in the majority portion may be used as the value of the pitch p.

[0059] As can be understood from the description to be described later, the pitch p may be set according to the intended resonance frequency. For example, the pitch p may be 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 10 μm or less, 5 μm or less, or 2 μm or less. Any combination of the above lower limit and upper limit may be used.

[0060] The number of the electrode fingers 27 may be appropriately set according to the electrical characteristics required for the resonator 15 and the like. Since FIG. 1 is a schematic diagram, the number of the electrode fingers 27 is shown to be small. Actually, more electrode fingers 27 than shown may be arranged. The same applies to the strip electrode 33 of the reflector 21 to be described later.

[0061] The lengths of the plurality of electrode fingers 27 are, for example, equal to each other. Different from the illustrated example, the IDT electrode 19 may be so-called apodized in which the lengths of the plurality of electrode fingers 27 (in another aspect, the so-called cross width) vary according to the position in the elastic wave propagation direction (x direction). The length and width of the electrode finger 27 may be appropriately set according to the required electrical characteristics and the like.

[0062] The dummy electrode 29 has, for example, a shape that projects in a direction orthogonal to the elastic wave propagation direction with a substantially constant width. Its width is, for example, equal to the width of the electrode finger 27. The plurality of dummy electrodes 29 are arranged at the same pitch as the plurality of electrode fingers 27, and the tip of the dummy electrode 29 of one comb electrode 23 faces the tip of the electrode finger 27 of the other comb electrode 23 with a gap therebetween. Note that the IDT electrode 19 may not include the dummy electrode 29.

[0063] (2.2. Reflector) A pair of reflectors 21 are located on both sides of the IDT electrode 19 in the propagation direction of the elastic wave. Each reflector 21 may be, for example, in an electrically floating state or may be given a reference potential. Each reflector 21 is formed, for example, in a lattice shape. That is, the reflector 21 includes a pair of bus bars 31 facing each other and a plurality of strip electrodes 33 extending between the pair of bus bars 31. The pitch of the plurality of strip electrodes 33 and the pitch between the adjacent electrode fingers 27 and the strip electrode 33 are, for example, equivalent to the pitch of the plurality of electrode fingers 27.

[0064] (3. Other Configurations of the Elastic Wave Element) Although not particularly shown, the upper surface of the piezoelectric layer 11 may be covered by a protective film made of SiO2 and / or Si3N4, etc. from above the conductor layer 5. The protective film may contribute, for example, to reducing the corrosion of the conductor layer 5 and / or temperature compensation for the characteristics of the elastic wave element 1. In the case where the protective film is provided, etc., an additional film made of an insulator or metal may be provided on the upper surface or the lower surface of the IDT electrode 19 and the reflector 21. The additional film contributes, for example, to improving the reflection coefficient of the elastic wave.

[0065] The configurations shown in FIGS. 1 to 3 may be appropriately packaged. The packaging may be, for example, mounting the illustrated configuration so that the upper surface of the piezoelectric layer 11 faces a substrate (not shown) with a gap therebetween and resin-sealing it from above, or may be a wafer-level package type in which a box-shaped cover is provided on the piezoelectric layer 11.

[0066] In an embodiment where a plurality of resonators 15 (or 16) are located on a single composite substrate 3, one resonator 15 may be regarded as one elastic wave element 1, or a plurality of resonators 15 (the portion corresponding to a single composite substrate 3) may be regarded as one elastic wave element 1. However, in the description of this embodiment, the term "elastic wave element 1" may, unless otherwise specified, refer to one resonator 15. Also, in an embodiment where the composite substrate 3 and the conductor layer 5 are packaged, a configuration including the package may be regarded as the elastic wave element 1, or a configuration not including the package may be regarded as the elastic wave element 1.

[0067] (4. Action and Characteristics of Elastic Wave Element) When a voltage is applied to a pair of comb electrodes 23, a voltage is applied to the piezoelectric layer 11 by a plurality of electrode fingers 27, and the piezoelectric layer 11 vibrates. That is, elastic waves are excited. Among the elastic waves of various wavelengths propagating in various directions, the elastic wave propagating in the arrangement direction of the plurality of electrode fingers 27 with the pitch p of the plurality of electrode fingers 27 being approximately a half wavelength (λ / 2) is likely to have a large amplitude because the plurality of waves excited by the plurality of electrode fingers 27 are in phase and overlap. Also, the elastic wave propagating through the piezoelectric layer 11 is converted into an electrical signal by the plurality of electrode fingers 27. At this time, similar to when the elastic wave is excited, the intensity of the electrical signal converted from the elastic wave propagating in the arrangement direction of the plurality of electrode fingers 27 with the pitch p of the plurality of electrode fingers 27 being approximately a half wavelength (λ / 2) is likely to be strong. Due to the above-described action (and other actions not described here for the sake of brevity), the elastic wave element 1 functions as a resonator having, for example, the frequency of the elastic wave with the pitch p being a half wavelength as the resonance frequency.

[0068] The pair of reflectors 21 contributes to reflecting the elastic wave and confining the energy in the arrangement region of the IDT electrode 19. However, the above-described action also occurs even if the pair of reflectors 21 is not provided (also in the resonator 16).

[0069] λ is usually the symbol indicating wavelength. The wavelength of the actual elastic wave may deviate from 2p. When the actual wavelength deviates from 2p, λ in the description of the embodiment shall mean 2p instead of the actual wavelength.

[0070] FIG. 4 is a diagram showing an example of the frequency characteristics of the elastic wave element 1 (resonator 15).

[0071] In this figure, the horizontal axis indicates the frequency (MHz). The vertical axis indicates the absolute value of impedance |Z| (Ω). The three lines in the figure show the characteristics of each of the three elastic wave elements 1 (resonators 15). Note that FIG. 4 is for explaining the general characteristics of the resonator 15 having the configuration described so far. That is, the resonator 15 having the characteristics shown by the three lines may be a comparative example, not limited to an example.

[0072] As shown in this figure, in the impedance characteristics of the resonator 15, a resonance point fr where the absolute value of impedance becomes a minimum value and an anti-resonance point fa where the absolute value of impedance becomes a maximum value appear. The former frequency is the resonance frequency, and the latter frequency is the anti-resonance frequency. Note that in the description of the embodiment, the symbols fa and fr may be used for the resonance frequency and the anti-resonance frequency.

[0073] (5. Configuration for realizing a concave inverse velocity surface) (5.1. Method for specifying the inverse velocity surface) The inverse velocity surface of the composite substrate 3 may be specified by various methods. From another perspective, the inverse velocity 1 / v (velocity v from another perspective) in various directions (various ψ) may be specified by various methods. An example of the method for specifying the inverse velocity surface is shown below.

[0074] FIG. 5 is a schematic diagram for explaining a method for specifying the velocity v in various directions. As understood from the reference signs in the figure, each of the three figures in FIG. 5 corresponds to a more schematic view of the plan view of FIG. 1.

[0075] The topmost figure in FIG. 5 schematically shows an elastic wave element (resonator) for which an inverse velocity surface is to be identified. For convenience, the reference numeral of the elastic wave element 1 in the embodiment is used for this elastic wave element. The middle figure and the bottommost figure in FIG. 5 schematically show dummy elastic wave elements 1A and 1B for identifying the inverse velocity surface of the elastic wave element 1. The elastic wave elements 1A and 1B have a configuration in which the IDT electrode 19 (and the reflector 21 as necessary) is rotated by ψ° about the z-axis with respect to the composite substrate 3 in the elastic wave element 1. In the illustrated example, the elastic wave elements 1A and 1B with ψ = 5° and ψ = 10° are schematically shown. Except for ψ, the conditions of the elastic wave elements 1, 1A, and 1B are the same as each other.

[0076] Note that the elastic wave element 1 as the object for which the inverse velocity surface is to be identified is, from another perspective, an elastic wave element according to an embodiment (or an example) or a comparative example, and from yet another perspective, is one intended for distribution or one actually in distribution. The dummy elastic wave elements 1A and 1B are, from another perspective, those fabricated for an experiment to identify the inverse velocity surface of the elastic wave element 1 or those assumed for a simulation calculation to identify the inverse velocity surface.

[0077] In FIGS. 1 to 3 and FIG. 5, for convenience, an orthogonal coordinate system D1D2D3 fixed to the IDT electrode 19 is attached. The D3 direction is the normal direction of the IDT electrode 19 (the upper surface of the composite substrate 3) and is the same as the z direction. The D1 direction is the arrangement direction of the plurality of electrode fingers 27. The D2 direction is a direction orthogonal to the D1 direction and the D3 direction.

[0078] Returning to FIG. 5, the orthogonal coordinate system xyz is defined in the elastic wave element 1 and is common to the elastic wave elements 1, 1A, and 1B in which the orientations of the IDT electrodes 19 are different from each other. From another perspective, the orthogonal coordinate system xyx is fixed to the composite substrate 3. On the other hand, since the orthogonal coordinate system D1D2D3 is fixed to the IDT electrode 19, it is different for the elastic wave elements 1, 1A, and 1B.

[0079] As described above, among the elastic waves of various directions and various wavelengths excited by the IDT electrode 19, the pitch p of the plurality of electrode fingers 27 is approximately a half wavelength, and the elastic wave propagating in the arrangement direction (D1 direction) of the plurality of electrode fingers 27 is likely to resonate. Therefore, the D1 direction can be regarded as the propagation direction of the elastic wave that resonates in the elastic wave elements 1, 1A, and 1B.

[0080] The x direction is the propagation direction of the elastic wave intended to be used in the elastic wave element 1, and from another perspective, it is the propagation direction of the elastic wave that resonates in the elastic wave element 1. Therefore, in the elastic wave element 1, the D1 direction and the x direction coincide. On the other hand, in the elastic wave elements 1A and 1B, the D1 direction is inclined by ψ with respect to the x direction.

[0081] The three aforementioned lines shown in FIG. 4 show examples of the characteristics of the elastic wave elements 1, 1A, and 1B. The elastic wave elements 1, 1A, and 1B have different resonance frequencies fr (and anti-resonance frequencies fa) from each other. Here, theoretically, the velocity v of the elastic wave is the product of the resonance frequency fr and the wavelength λ (= 2p). Also, in the elastic wave elements 1, 1A, and 1B, the pitch p of the electrode fingers is the same for each other. Therefore, the difference in the resonance frequency fr is due to the fact that the velocities v of the elastic waves propagating in the D1 direction in the elastic wave elements 1, 1A, and 1B are different from each other.

[0082] From another perspective, for a plurality of elastic wave elements 1, 1A, and 1B with different D1 directions (in other words, different ψ), by obtaining the resonance frequency fr and calculating v = fr × 2p, the velocities v of the elastic waves in various directions (various ψ) can be obtained. Consequently, for the elastic wave element 1, the inverse velocity surface can be specified. The specification of the velocities v of a plurality of elastic wave elements with different D1 directions (in other words, the specification of the inverse velocity surface) may be done by simulation calculation, may be done by experiment, or may be done by a combination of both (for example, correction or interpolation of the other result based on one result).

[0083] (5.2. Example of Simulation Calculation) Based on the above method for specifying the inverse velocity surface, the inventor of the present application performed simulation calculations under various conditions. As a result, it was confirmed that a concave inverse velocity surface is realized in the composite substrate 3 having the piezoelectric layer 11 and the low acoustic velocity film 9. An example of the simulation executed is shown below.

[0084] The conditions common to various simulations described below (hereinafter sometimes referred to as "common conditions") are as follows. · Composite substrate 3 ·· Piezoelectric layer 11 ··· Material: Rotated Y-cut X-propagating LT ·· Low acoustic velocity film 9 ··· Material: SiO2 ·· Support substrate 7 ··· Material: Si ··· Thickness: Infinite · Conductor layer 5 ·· Two-layer structure of a Ti layer on the piezoelectric layer 11 and an Al-Cu alloy layer on the Ti layer ·· Thickness of the Ti layer: 60 Å (0.003λ) ·· Thickness of the Al-Cu alloy layer: 1400 Å (0.07λ) ·· IDT electrode 19 ··· Pitch p: 1 μm ··· Duty: 0.5 ··· Number: Infinite In the above, Duty is the value obtained by dividing the width of the electrode finger 27 (length in the D1 direction) by the pitch p. In the simulation calculation, the impedance for each frequency as shown in FIG. 4 was calculated by the FEM (Finite Element Method). From the calculation results, the resonance frequency fr was specified and the inverse velocity 1 / v was calculated.

[0085] Figs. 6 to 8 are diagrams showing examples of simulation results. Regarding the horizontal axis and vertical axis of these drawings, it is as described in the above-mentioned explanation regarding FIG. 6.

[0086] FIG. 6 shows examples of inverse velocity surfaces for three cases where the normalized thickness a of the piezoelectric layer 11 is different from each other, as shown in the legend in the figure. Regarding the simulation results shown in FIG. 6, the simulation conditions other than the common conditions described above are as follows. · Normalized thickness a of the piezoelectric layer 11: 0.20, 0.30, or 0.40 · Normalized thickness b of the low sound velocity film 9: 0.01 · Cut angle c of the piezoelectric layer 11: 26° It was confirmed that a concave inverse velocity surface can be realized by the composite substrate 3 having the piezoelectric layer 11 and the low sound velocity film 9 in the cases where the normalized thickness a is 0.30 and 0.40 (lines L2 and L3).

[0087] FIG. 7 shows examples of inverse velocity surfaces for two cases where the normalized thickness b of the low sound velocity film 9 is different from each other, as shown in the legend in the figure. Regarding the simulation results shown in FIG. 7, the simulation conditions other than the common conditions described above are as follows. · Normalized thickness a of the piezoelectric layer 11: 0.30 · Normalized thickness b of the low sound velocity film 9: 0.01 or 0.02 · Cut angle c of the piezoelectric layer 11: 26° Note that, as understood from the comparison with the previous paragraph, the case of b = 0.01 in FIG. 7 is the same as the case of a = 0.30 in FIG. 6. It was confirmed from FIG. 7 that a concave inverse velocity surface can be realized by the composite substrate 3 having the piezoelectric layer 11 and the low sound velocity film 9.

[0088] FIG. 8 shows examples of inverse velocity surfaces for four cases where the cut angle c (°) of the piezoelectric layer 11 is different from each other, as shown in the legend in the figure. Regarding the simulation results shown in FIG. 8, the simulation conditions other than the common conditions described above are as follows. · Normalized thickness a of the piezoelectric layer 11: 0.30 · Normalized thickness b of the low sound velocity film 9: 0.01 · Cut angle c of the piezoelectric layer 11: 20°, 26°, 30°, or 40° As can be understood from the comparison with the previous paragraph, the case of c = 26° in FIG. 8 is the same as the case of a = 0.30 in FIG. 6. From FIG. 8, it was confirmed that the concave inverse velocity surface can be realized by the composite substrate 3 having the piezoelectric layer 11 and the low sound velocity film 9.

[0089] (5.3. Expression showing the condition for realizing the inverse velocity surface) The inventor of the present application obtained the above-mentioned formula (1) by setting various values for the normalized thicknesses a and b and the cut angle c and performing a large number of simulation calculations. The process until the formula (1) is obtained will be described below. Regarding whether the inverse velocity surface is concave or convex, the influence of conditions other than a, b, and c (for example, the thickness of the electrode finger 27 and the thickness of the support substrate 7) is relatively small unless these conditions are special conditions.

[0090] The inverse velocity surface can be approximated by a parabola (quadratic curve) (not shown). This parabola is represented by the function 1 / v(ψ) with ψ as a variable. And v(ψ) can be represented by the following formula in the range where ψ is relatively small. v(ψ)=v0×(1 + γ / 2×ψ 2 ) (3)

[0091] The velocity v0 is the velocity v of the elastic wave when ψ = 0°. Therefore, the formula (3) can be rewritten as the following formula regarding the normalized velocity 1 / v n . 1 / v n (ψ)=1 / (1 + γ / 2×ψ 2 ) (4)

[0092] Although not particularly shown, when γ < -1, the line (inverse velocity surface) represented by the formula (4) is a concave curve passing through the points of 1 / v x = 1 and 1 / v y = 0 (referred to as the first point in this paragraph). When γ = -1, the line represented by the formula (4) passes through the first point and becomes a straight line parallel to the vertical axis 1 / v y . When γ > -1, the line represented by the formula (4) is a convex curve passing through the first point.

[0093] When the values of a, b, and c change, the shape of the inverse velocity surface changes. From another perspective, γ when the inverse velocity surface is approximated by a parabola has a correlation with a, b, and c. Therefore, if the value of γ is obtained from the values of a, b, and c and the obtained value of γ is less than -1, it can be said that the inverse velocity surface is concave. From another perspective, a, b, and c may be set so that the value of γ specified based on the values of a, b, and c is less than -1 in order to realize a concave inverse velocity surface.

[0094] The method for specifying the value of γ based on the values of a, b, and c may be various methods. For example, as described later, an equation for calculating the value of γ based on the values of a, b, and c may be used. In the aforementioned equation (1), the left side corresponds to an equation for calculating the value of γ from the values of a, b, and c. Also, a map associating the values of a, b, c, and γ with each other may be referred to to specify the value of γ corresponding to the values of a, b, and c. Furthermore, the value of γ corresponding to the values of a, b, and c may be specified by AI (Artificial Intelligence) technology. In these various specifying methods, other conditions other than a, b, and c may be incorporated as factors for specifying the value of γ.

[0095] As mentioned above, the left side of equation (1) corresponds to an equation for calculating the value of γ from the values of a, b, and c. This equation was obtained by the following procedure. First, for each of a plurality of cases where the values of a, b, and c were variously changed, the inverse velocity surface was specified by simulation calculation (described above) for obtaining the inverse velocity surface. For each inverse velocity surface, the one that most closely approximated the parabola represented by equation (4) was obtained by the least squares method. That is, the value of γ was obtained for each combination of the values of a, b, and c. The specification of this closest parabola was performed for the inverse velocity surface where ψ is 0° or more and 15° or less. Thereafter, based on the various values of a, b, and c used in the simulation and the various corresponding values of γ, non-linear regression analysis using the least squares method was performed to obtain an equation for calculating γ from a, b, and c.

[0096] In the simulation for obtaining the left side of the aforementioned formula (1), the conditions other than the aforementioned common conditions are as follows. · Normalized thickness a: It varies in the range of 0.1 or more and 0.6 or less in steps of 0.1. · Normalized thickness b: It varies in the range of 0.1 or more and 0.6 or less in steps of 0.1. · Cutting angle c: It varies in the range of 10° or more and 80° or less in steps of 10°.

[0097] Figures 9 and 10 are diagrams illustrating the value of γ calculated by the left side of formula (1). In these diagrams, the horizontal axis represents the normalized thickness a, and the vertical axis represents γ.

[0098] In Figure 9, as shown in the legend in the figure, three lines with different normalized thicknesses b of the low-velocity film 9 are shown. Specifically, b for the three lines is 0.1, 0.3, or 0.6. Also, the cutting angle c for the three lines is 50°.

[0099] In Figure 10, as shown in the legend in the figure, three lines with different cutting angles c of the piezoelectric layer 11 are shown. Specifically, c for the three lines is 20°, 50°, or 70°. Also, the normalized thickness b for the three lines is 0.1.

[0100] (5.4. Examination of the conditions for realizing the inverse velocity surface) The tendency of the conditions for realizing the concave inverse velocity surface can be read from Figures 6 to 10.

[0101] For example, as shown in Figures 9 and 10, the larger the value of the normalized thickness a of the piezoelectric layer 11, the smaller the value of γ. That is, the larger the value of the normalized thickness a, the easier it is to realize the concave inverse velocity surface. This is also consistent with the fact that in Figure 6, as the normalized thickness a increases, the inverse velocity surface transitions from convex to concave.

[0102] Also, for example, as shown in FIG. 9, the value of the normalized thickness b of the low sound velocity film 9 is closer to a value between the lower limit value (0.1) and the upper limit value (0.6) of the conditions of this simulation (the value illustrated in FIG. 9 is 0.3), the value of γ becomes smaller. That is, the closer the value of the normalized thickness b is to a specific value (not limited to 0.3), the easier it is to realize a concave inverse velocity surface.

[0103] Also, for example, as shown in FIG. 10, the value of the cut angle c is closer to a value between a value close to the lower limit value of the conditions of this simulation (20°) and a value close to the upper limit value (70°) (the value illustrated in FIG. 10 is 50°), the value of γ becomes smaller. That is, the closer the value of the cut angle c is to a specific value (not limited to 50°), the easier it is to realize a concave inverse velocity surface.

[0104] FIGS. 6 to 10 take, as an example, an embodiment in which the material of the piezoelectric layer 11 and the material of the low sound velocity film 9 are specific materials (rotated Y-cut X-propagation LT and SiO2). However, considering the above-described tendency and common technical knowledge, it can be understood that a concave inverse velocity surface can be realized even with other materials. For example, it is as follows.

[0105] As described with reference to FIGS. 6 and 9, when the normalized thickness a of the piezoelectric layer 11 becomes relatively thick, γ is likely to be less than -1. As a reason for such a tendency, for example, among the influences of the piezoelectric layer 11 and the low sound velocity film 9 on the inverse velocity surface, the influence of the piezoelectric layer 11 on the inverse velocity surface becomes large, and the shape of the inverse velocity surface in the piezoelectric layer 11 alone is likely to appear.

[0106] On the other hand, for example, even when the piezoelectric layer 11 is LT that is not rotated Y-cut X-propagation and when the piezoelectric layer 11 is LN with an arbitrary cut angle, the sound velocities in directions where the angles around the normal of the piezoelectric layer 11 (refer to ψ) are different from each other are different from each other. Therefore, among the above-described different directions, if the direction in which the sound velocity is fast is set as the x direction (the propagation direction of the elastic wave for which utilization is intended) and the normalized thickness a of the piezoelectric layer 11 is made relatively thick, a concave inverse velocity surface is realized.

[0107] Also, as described with reference to FIG. 10, there exists a size at which γ tends to be small with respect to the normalized thickness b of the low acoustic velocity film 9. Therefore, by searching for the normalized thickness b of a size at which γ tends to be small, it is possible to realize a concave inverse velocity surface while reducing the normalized thickness a of the piezoelectric layer 11. It is considered that the tendency remains the same even if the material of the low acoustic velocity film 9 is other than SiO2.

[0108] (6. Summary of the First Embodiment) As described above, the composite substrate 3 according to the present embodiment has a piezoelectric layer 11 and a low acoustic velocity film 9 that spreads along the lower surface of the piezoelectric layer 11 and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer 11. Further, the inverse velocity surface of the elastic wave propagating through the piezoelectric layer 11 is concave.

[0109] From another perspective, the elastic wave element 1 according to the present embodiment has the composite substrate 3 as described above and a first IDT electrode (IDT electrode 19). The IDT electrode 19 has a plurality of electrode fingers 27 arranged along the upper surface of the piezoelectric layer 11.

[0110] Therefore, for example, while obtaining the effects of the composite substrate 3, it is possible to obtain the effects due to the concave inverse velocity surface. Examples of the effects of the composite substrate 3 include an effect of confining energy related to elastic waves and an effect of increasing the frequency by using plate waves. Examples of the effects due to the concave inverse velocity surface include that spurious of the transverse mode between the resonance frequency fr and the anti-resonance frequency fa is likely to be reduced as compared with a mode in which the inverse velocity surface is convex. Here, as described above, the fact that a concave inverse velocity surface can be realized in the composite substrate 3 was first discovered by the inventor of the present application.

[0111] The piezoelectric layer 11 and the low acoustic velocity film 9 may acoustically directly overlap. The piezoelectric layer 11 may be composed of a lithium tantalate single crystal with a rotation Y-cut X-propagation. The low acoustic velocity film may be composed of SiO2. Here, let twice the pitch p of the plurality of electrode fingers 27 be λ (μm). Let the normalized thickness obtained by dividing the thickness a′ (μm) of the piezoelectric layer 11 by λ be a. Let the normalized thickness obtained by dividing the thickness b′ (μm) of the low acoustic velocity film 9 by λ be b. Let the inclination angle of the Y-axis with respect to the normal (z-axis) of the piezoelectric layer 11 be c (°). At this time, a, b, and c may be values that satisfy the above-mentioned formula (1).

[0112] In this case, for example, a, b, and c take values within a range where it is confirmed by simulation calculation that a concave inverse velocity surface is realized. Therefore, a concave inverse velocity surface is stably realized.

[0113] The normalized thickness a of the piezoelectric layer 11 may be 1.0 or less. In this case, for example, since the normalized thickness a is sufficiently thin, the effect of the composite substrate 3 is easily obtained.

[0114] The normalized thickness b of the low acoustic velocity film may be 0.5 or less. Here, as shown in FIG. 9, when the normalized thickness b is 0.1 or 0.3 as compared with the case where the normalized thickness b is 0.6, γ is likely to be less than -1. Therefore, when the normalized thickness b is 0.5 or less, for example, it becomes easier to realize a concave inverse velocity surface.

[0115] <Second Embodiment> FIG. 11 is a cross-sectional view showing the configuration of the elastic wave element 201 according to the second embodiment. This figure corresponds to FIG. 2 of the first embodiment.

[0116] The composite substrate 203 of the elastic wave device 201 has a high sound velocity film 13 between the piezoelectric layer 11 and the low sound velocity film 9. The sound velocity in the high sound velocity film 13 is higher than the sound velocity in the piezoelectric layer 11. The high sound velocity film 13 directly overlaps the piezoelectric layer 11 and the low sound velocity film 9 acoustically. And also in the second embodiment, a concave inverse velocity surface is realized as in the first embodiment. Note that the conditions for comparing the sound velocities (such as comparing the phase velocities of bulk waves) and the meaning of directly overlapping acoustically are as described in the description of the piezoelectric layer 11 and the low sound velocity film 9 in the first embodiment.

[0117] The material of the high sound velocity film 13 is arbitrary as long as the sound velocity in the high sound velocity film 13 is higher than the sound velocity in the piezoelectric layer 11. Physical property values (such as density, Young's modulus, and acoustic impedance) that interact with the sound velocity may also be arbitrarily set. Specific materials for the high sound velocity film 13 include, for example, aluminum oxide (Al2O3), silicon nitride (Si3N4), and aluminum nitride (AlN). Note that when the material of the high sound velocity film 13 is the material exemplified in this paragraph, some or all of the conditions for comparing the sound velocities described in the description of the first embodiment may be ignored.

[0118] Let the normalized thickness d be the value obtained by dividing the thickness d′ (μm) of the high sound velocity film 13 by the wavelength λ (μm). The normalized thickness d of the low sound velocity film 9 may be, for example, a value that satisfies the following formula (2) described later. Also, when formula (2) is satisfied or not satisfied, the lower limit and the upper limit of the normalized thickness d when a concave inverse velocity surface is realized may be appropriately set. For example, the normalized thickness d may be 0.01 or more and 0.2 or less. As shown by the value of γ (FIG. 12) based on the simulation results described later, the inventor of the present application has confirmed that a concave inverse velocity surface is realized at such a thickness.

[0119] The material and thickness of the high - supersonic film 13 affect the realization of the concave - shaped reverse - velocity surface. In this embodiment, taking the aspect where the material of the high - supersonic film 13 is Al2O3 as an example, specific values of the thickness capable of realizing the concave - shaped reverse - velocity surface are exemplified. However, as will be described later, even when the material of the high - supersonic film is other than Al2O3, if the thickness of the high - supersonic film 13 and the conditions of other layers are appropriately set, the concave - shaped reverse - velocity surface can be realized.

[0120] In the elastic - wave element 201, the normalized thickness a of the piezoelectric layer 11, the normalized thickness b of the low - supersonic film 9, the cut - angle c (°) of the piezoelectric layer 11 (rotated Y - cut X - propagation LT), and the normalized thickness d of the high - supersonic film 13 may be set so that the following formula (2) is satisfied. -3.26163a - 0.30469b - 0.02132c + 3.843127d + 2.196667a 2 +0.960417b 2 +0.00026c 2 -7.75985d 2 -0.01579ab + 0.001339ac - 1.26908ad - 0.00246bc - 0.8485bd - 0.01067cd + 0.151192 < - 1 (2)

[0121] The method for obtaining the above formula (2) is the same as the method for obtaining formula (1) in the first embodiment. In the simulation of the second embodiment, the conditions different from those in the simulation of the first embodiment are as follows. · High - supersonic film 13 ·· Material: Al2O3 ·· Normalized thickness: 0.01, 0.03, 0.05, 0.1 or 0.2

[0122] FIG. 12 is a diagram illustrating the value of γ calculated by the left side of equation (2). In these diagrams, the horizontal axis represents the normalized thickness d, and the vertical axis represents γ. In FIG. 12, as shown in the legend in the figure, three lines with different normalized thicknesses a of the piezoelectric layer 11 are shown. Specifically, a for the three lines is 0.1, 0.4, or 0.6. Also, for the three lines, the normalized thickness b of the low acoustic velocity film 9 is 0.2, and the cut angle c is 40°.

[0123] As shown in FIG. 12, the smaller the value of the normalized thickness d of the high acoustic velocity film 13, the smaller the value of γ. Also, similar to the first embodiment, the larger the normalized thickness a of the piezoelectric layer 11, the smaller the value of γ. From the tendency shown in FIG. 12, it can be understood that even for materials other than the materials used in the simulation, if the normalized thickness a is increased and the normalized thickness d is decreased, a concave inverse velocity surface can be realized.

[0124] As described above, also in the second embodiment, the composite substrate 203 has the piezoelectric layer 11 and the low acoustic velocity film 9 that spreads along the lower surface of the piezoelectric layer 11 and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer 11. Also, the inverse velocity surface of the elastic wave propagating through the piezoelectric layer 11 is concave. Therefore, the same effects as those of the first embodiment are achieved.

[0125] The composite substrate 203 may further include a high acoustic velocity film 13 that directly overlaps the piezoelectric layer 11 and the low acoustic velocity film 9 acoustically between the piezoelectric layer 11 and the low acoustic velocity film 9. The piezoelectric layer 11 may be composed of a lithium tantalate single crystal with a rotation Y-cut X-propagation. The low acoustic velocity film 9 may be composed of silicon dioxide. The high acoustic velocity film 13 may be composed of aluminum oxide. Here, let 2 times the pitch p of the plurality of electrode fingers 27 be λ (μm). Let the normalized thickness obtained by dividing the thickness a′ (μm) of the piezoelectric layer 11 by λ be a. Let the normalized thickness obtained by dividing the thickness b′ (μm) of the low acoustic velocity film 9 by λ be b. Let the inclination angle of the Y-axis with respect to the normal of the piezoelectric layer 11 be c°. Let the normalized thickness obtained by dividing the thickness d′ (μm) of the high acoustic velocity film 13 by λ be d. At this time, a, b, c, and d may be values that satisfy the aforementioned formula (2).

[0126] In this case, the same effects as those when formula (1) is satisfied in the first embodiment are achieved. For example, a, b, c, and d take values within a range in which it has been confirmed by simulation calculation that a concave inverse velocity surface is realized. Therefore, a concave inverse velocity surface is stably realized.

[0127] <Other Embodiments> Although not particularly illustrated, the composite substrate may have a configuration other than the first and second embodiments.

[0128] For example, the composite substrate may have, in order from above, a piezoelectric layer 11, a low acoustic velocity film 9, a high acoustic velocity film 13, and a support substrate 7. That is, in the second embodiment, the positional relationship between the low acoustic velocity film 9 and the high acoustic velocity film 13 may be reversed. The inventor of the present application has confirmed by simulation calculation that the high acoustic velocity film 13 in this case has almost no influence on whether the inverse velocity surface is concave or convex. Therefore, for example, when realizing a concave inverse velocity surface, the values of a, b, and c may be set so that formula (1) of the first embodiment is satisfied.

[0129] Further, for example, the composite substrate may have a multilayer film composed of a total of three or more low-velocity films 9 and high-velocity films 13 between the piezoelectric layer 11 and the support substrate 7. In the multilayer film, the low-velocity films 9 and the high-velocity films 13 are alternately laminated. When the uppermost layer of the multilayer film (the layer in contact with the piezoelectric layer 11) is the low-velocity film 9, for example, a concave inverse velocity surface may be realized by satisfying the formula (1). When the uppermost layer of the multilayer film is the high-velocity film 13, for example, a concave inverse velocity surface may be realized by satisfying the formula (2).

[0130] <Modification example> Hereinafter, a modification example related to the IDT electrode will be shown. In the description of the modification example, for convenience, the reference numerals of the first embodiment may be used. However, the modification example may be applied to embodiments other than the first embodiment.

[0131] (First modification example) FIG. 13 is a plan view showing the configuration of the elastic wave element 1C (resonator 15C) according to the first modification example. This figure corresponds to FIG. 1.

[0132] Briefly speaking, the elastic wave element 1C is configured such that the IDT electrode 19C is inclined obliquely with respect to the x direction (the propagation direction of the elastic wave intended to be utilized). Thereby, the spurious of the transverse mode can be further reduced. Specifically, it is as follows.

[0133] Let the virtual line connecting the tips of the plurality of electrode fingers 27 of one of the comb electrodes 23C be line VL1. Also, let the virtual line connecting the tips of the plurality of electrode fingers 27 of the other comb electrode 23C be line VL2. At this time, lines VL1 and VL2 are inclined with respect to the x direction. Note that the x direction is, for example, the direction in which the plurality of electrode fingers 27 are arranged and is a direction orthogonal to the direction in which the plurality of electrode fingers 27 extend. The region sandwiched between line VL1 and line VL2 is the intersection region CR where the plurality of electrode fingers 27 of the pair of comb electrodes 23C intersect.

[0134] Let the inclination angles of lines VL1 and VL2 with respect to the x - direction be angle α. Angle α may be the same for line VL1 and line VL2 (in the illustrated example), or may be different. The specific value of angle α is arbitrary. For example, it may be 0° or more, 5° or more, 10° or more, or 15° or more, and may also be 45° or less, 30° or less, 15° or less, or 10° or less. The above - mentioned lower limit and upper limit may be combined with any arbitrary ones so as not to cause contradictions. Also, line VL1 and / or line VL2 may be in a single straight - line form over its entire length, or may have a bent portion (angular or R - shaped).

[0135] In the illustrated example, the reflector 21 has the same configuration as the reflector 21 of the embodiment. However, the reflector 21 may be inclined with respect to the x - direction, similar to the IDT electrode 19C. Specifically, for example, the bus bar 31 of the reflector 21 may extend parallel to the virtual lines VL1 and VL2.

[0136] As described above, the first IDT electrode (IDT electrode 19C) has a first bus bar (bus bar 25 of one of the comb - shaped electrodes 23C) and a second bus bar (bus bar 25 of the other comb - shaped electrode 23C), and a plurality of first electrode fingers (a plurality of electrode fingers 27 of the above - mentioned one comb - shaped electrode 23C) and a plurality of second electrode fingers (a plurality of electrode fingers 27 of the above - mentioned other comb - shaped electrode 23C). The two bus bars 25 face each other in a direction intersecting the x - direction (the elastic - wave propagation direction) when the piezoelectric layer 11 is viewed in plan. The plurality of first electrode fingers extend in the y - direction orthogonal to the x - direction from the first bus bar toward the second bus bar. The plurality of second electrode fingers extend in the y - direction from the second bus bar toward the first bus bar and are alternately arranged with the plurality of first electrode fingers in the x - direction. The virtual line VL1 connecting the tips of the plurality of first electrode fingers and the virtual line VL2 connecting the tips of the plurality of second electrode fingers are inclined with respect to the x - direction.

[0137] In this case, for example, since the inverse - velocity surface is concave, the spurious of the transverse mode can be reduced, and also, since the intersection region CR is inclined, the spurious of the transverse mode can be reduced.

[0138] (Second Modified Example) FIG. 14 is a schematic diagram for explaining the elastic wave element 1D according to the second modified example. In the description of this modified example, unless otherwise specified, the sound velocity is assumed to be the sound velocity considering the influence of the conductor layer 5 (reference numeral omitted in FIG. 14).

[0139] The left side portion of FIG. 14 is a plan view showing a part of the configuration of the elastic wave element 1D and corresponds to a part of FIG. 1. The right side portion of FIG. 14 is a graph showing the sound velocity profile in the elastic wave element 1D.

[0140] The axis parallel to the y direction in the graph on the right side of FIG. 14 indicates the position of the IDT electrode 19D in the y direction, and the corresponding positions of both are connected by a dotted line. The axis parallel to the x direction indicates the sound velocity V. On this axis, the right side (+x side) of FIG. 14 corresponds to the side where the sound velocity is high.

[0141] Note that the graph on the right side of FIG. 1 only shows the ranking of the sound velocity in a plurality of regions. That is, the actual values are not necessarily reflected in the absolute value of the sound velocity in each region, the difference in the sound velocity between a plurality of regions, and the ratio of the sound velocity between a plurality of regions.

[0142] The reference numerals (CR, RM, RE, RG, and RB) attached to the right side of FIG. 14 are the reference numerals attached to different regions within the IDT electrode 19D. Specifically, in the illustrated example, the IDT electrode 19 has the crossing region CR mentioned in the description of the first modified example, the bus bar region RB where the bus bar 25 is located, and the gap region RG located between the crossing region CR and the bus bar region RB.

[0143] Briefly speaking, the shape of the IDT electrode 19D of the elastic wave element 1D is for utilizing the piston mode. The piston mode can be said to be a mode in which, for example, when looking at the yz cross section, the amplitude is generally constant in at least the central side region of the crossing region CR and the amplitude is rapidly reduced outside thereof.

[0144] To utilize the piston mode, for example, the IDT electrode 19D has three or more regions within the intersection region CR where the sound velocity of the elastic wave is different from each other. In the illustrated example, the intersection region CR has a central region RM located at the center of the intersection region CR and two edge regions RE located at both side edges of the intersection region CR. The shape of the IDT electrode 19D is set such that the sound velocity in the central region RM is different from the sound velocity in the edge region RE.

[0145] More specifically, in the illustrated example, each electrode finger 27 has, in order from the root side to the tip side, a first part 27Da located in the first gap region RG, a second part 27Db located in the first edge region RE, a third part 27Dc located in the central region RM, and a fourth part 27Dd located in the second edge region RE. The widths of the second part 27Db and the fourth part 27Dd located in the edge region RE are different from the widths of the other parts. Thereby, the sound velocity in the central region RM and the sound velocity in the edge region RE are different.

[0146] The sound velocity considering the influence of the IDT electrode 19D is slower in a region where the ratio of the area of the conductor layer 5 is larger, although it also depends on, for example, the thickness of the conductor layer 5. Therefore, in the illustrated example, listing the regions in order from the one with the slowest sound velocity, they are the bus bar region RB, the central region RM, and the gap region RG. The sound velocity in the edge region RE may be made higher (in the illustrated example) or lower than the sound velocity in the central region RM. In the illustrated example, by making the widths of the second part 27Db and the fourth part 27Dd thinner than the width of the third part 27Dc, the sound velocity in the edge region RE is made higher than the sound velocity in the central region RM.

[0147] In the width direction (y direction) of the intersection region CR, the ratio occupied by the central region RM may be arbitrarily set. Usually, the central region RM is set to be relatively wide. For example, the central region RM has a width of 1 / 2 or more or 2 / 3 or more of the width of the intersection region CR. Also, the intersection region CR and the two edge regions RE are, for example, located symmetrically with respect to the center line of the intersection region CR.

[0148] Elastic wave elements that utilize the piston mode can be various other than the illustrated examples. For example, the central region RM and / or the edge region RE may be further divided into regions with different sound velocities from each other. From another perspective, for example, the intersection region CR may have five or more and an odd number of regions with different sound velocities symmetrically with respect to the center line of the intersection region CR. In the illustrated example, the IDT electrode 19D does not have the dummy electrode 29, but may have the dummy electrode 29. The specific region (the edge region RE in the illustrated example) for utilizing the piston mode may be formed in the gap region RG and / or the bus bar region RB in addition to, or instead of, the intersection region CR. Also, for example, the difference in sound velocity may be realized by the difference in the thickness of the conductor layer 5, or by the presence or absence and / or the difference in the thickness of other layers overlapping the conductor layer 5. Further, the elastic wave element that utilizes the piston mode may be such that the intersection region CR is inclined with respect to the x direction as shown in the first modification example.

[0149] As described above, the first IDT electrode (IDT electrode 19D) includes a first bus bar (bus bar 25 of one comb-shaped electrode 23D) and a second bus bar (bus bar 25 of the other comb-shaped electrode 23D), a plurality of first electrode fingers (a plurality of electrode fingers 27D of the one comb-shaped electrode 23D), and a plurality of second electrode fingers (a plurality of electrode fingers 27D of the other comb-shaped electrode 23D). The two bus bars 25 face each other in a direction intersecting the x direction (the elastic wave propagation direction) when the piezoelectric layer 11 is viewed in plan view. The plurality of first electrode fingers extend in the y direction orthogonal to the x direction from the first bus bar toward the second bus bar. The plurality of second electrode fingers extend in the y direction from the second bus bar toward the first bus bar, and are alternately arranged with the plurality of first electrode fingers in the x direction. An intersection region CR sandwiched between a virtual line VL1 connecting the tips of the plurality of first electrode fingers (see the reference numeral in FIG. 13) and a virtual line VL2 connecting the tips of the plurality of second electrode fingers (see the reference numeral in FIG. 13) may have two edge regions RE and a central region RM. The two edge regions RE may be adjacent to the two virtual lines VL1 and VL2. The central region RM may be located closer to the center of the intersection region CR than the two edge regions RE. The velocity of the elastic wave excited by the IDT electrode 19D and propagating through the piezoelectric layer 11 may be different between the central region RM and the two edge regions RE.

[0150] In this case, for example, by virtue of the inverse velocity surface being concave, spurious signals in the transverse mode can be reduced while utilizing the piston mode to reduce spurious signals in the transverse mode.

[0151] (Filter and demultiplexer) In the previous description, the elastic wave element 1 has been described as being the resonator 15. However, as described below, the elastic wave element 1 may be a filter or a demultiplexer. In the description here, for convenience, the reference numerals of the first embodiment are used, but the elastic wave element according to the second embodiment or a modification may also be a filter or a demultiplexer.

[0152] FIG. 15 is a circuit diagram schematically showing the configuration of the demultiplexer 101. The demultiplexer 101 may be an example of an elastic wave element. As understood from the reference numerals shown in the upper left of the drawing of this figure, in this figure, the comb electrode 23 is schematically shown in a bifurcated fork shape, and the reflector 21 is represented by a single line with both ends bent.

[0153] The demultiplexer 101 has, for example, a transmission filter 109 that filters a transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and a reception filter 111 that filters a reception signal from the antenna terminal 103 and outputs it to a pair of reception terminals 107. Each of the transmission filter 109 and the reception filter 111 may be an example of an elastic wave element.

[0154] The transmission filter 109 is constituted by, for example, a ladder-type filter in which a plurality of resonators 15 are connected in a ladder type. That is, the transmission filter 109 has a plurality (one or more) of resonators 15 (series resonators) connected in series between the transmission terminal 105 and the antenna terminal 103, and a plurality (one or more) of resonators 15 (parallel arms, parallel resonators) that connect the series line (series arm) and the reference potential. The plurality of resonators 15 constituting the transmission filter 109 are provided, for example, on the same composite substrate 3.

[0155] The reception filter 111 is constituted by including, for example, a resonator 15 and a multi-mode filter (including a double-mode filter) 113. The multi-mode filter 113 may be an example of an elastic wave element. The multi-mode filter 113 has a plurality (three in the illustrated example) of IDT electrodes 19 (resonators 16 from another viewpoint, reference numerals are omitted here) arranged in the propagation direction of the elastic wave, and a pair of reflectors 21 arranged on both sides thereof. The resonator 15 and the multi-mode filter 113 constituting the reception filter 111 are provided, for example, on the same composite substrate 3.

[0156] Note that the transmission filter 109 and the reception filter 111 may be provided on the same composite substrate 3, or may be provided on different composite substrates 3. FIG. 15 is merely an example of the configuration of the demultiplexer 101. For example, the reception filter 111 may be configured by a ladder filter in the same manner as the transmission filter 109. Further, the series resonators and parallel resonators constituting one ladder filter may be provided on separate composite substrates 3. Also, the demultiplexer 101 (multiplexer) is not limited to a duplexer including the transmission filter 109 and the reception filter 111. For example, the demultiplexer may be a diplexer, or may include three or more filters (e.g., a triplexer or a quadplexer).

[0157] (Module and Communication Device) The surface acoustic wave device may be used, for example, in a module for communication and / or a communication device. An example is shown below.

[0158] FIG. 16 is a block diagram showing a main part of a communication device 151 as an example of the use of the demultiplexer 101 (an example of a surface acoustic wave device or a configuration including a surface acoustic wave device). The communication device 151 has a module 171 and a housing 173 that houses the module 171. The module 171 performs wireless communication using radio waves and includes the demultiplexer 101.

[0159] In module 171, a transmission information signal TIS containing information to be transmitted is modulated and frequency-upconverted (converted into a high-frequency signal of a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153 (an example of an integrated circuit element) to obtain a transmission signal TS. The transmission signal TS has unnecessary components outside the transmission passband removed by a band-pass filter 155, is amplified by an amplifier 157, and is input to a diplexer 101 (transmission terminal 105). Then, the diplexer 101 (transmission filter 109) removes unnecessary components outside the transmission passband from the input transmission signal TS, and outputs the transmission signal TS after the removal to an antenna 159 from an antenna terminal 103. The antenna 159 converts the input electrical signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

[0160] Also, in module 171, a radio signal (radio wave) received by the antenna 159 is converted into an electrical signal (received signal RS) by the antenna 159 and input to the diplexer 101 (antenna terminal 103). The diplexer 101 (reception filter 111) removes unnecessary components outside the reception passband from the input received signal RS and outputs it from a reception terminal 107 to an amplifier 161. The output received signal RS is amplified by the amplifier 161, and unnecessary components outside the reception passband are removed by a band-pass filter 163. Then, the received signal RS is frequency-downconverted and demodulated by the RF-IC 153 to obtain a received information signal RIS.

[0161] Note that the transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, they may be analog audio signals or digitized audio signals. The passband of the radio signal may be set as appropriate. In this embodiment, a relatively high-frequency passband (for example, 5 GHz or higher) is also possible. The modulation method may be phase modulation, amplitude modulation, frequency modulation, or any combination of two or more of these. In FIG. 16, the circuit method is exemplified by the direct conversion method, but it may be any other appropriate method. For example, it may be a double superheterodyne method. Further, FIG. 22 schematically shows only the main part, and a low-pass filter, an isolator, etc. may be added at appropriate positions, or the positions of amplifiers, etc. may be changed.

[0162] Module 171 has, for example, components from the RF-IC 153 to the antenna 159 on the same circuit board. That is, the surface acoustic wave element (part or all of the diplexer 101) is modularized in combination with other components. Note that the surface acoustic wave element may be included in the communication device 151 without being modularized. Also, the components exemplified as the components of module 171 may be located outside the module or may not be housed in the housing 173. For example, the antenna 159 may be exposed outside the housing 173.

[0163] The technology according to the present disclosure is not limited to the above embodiments and modified examples, and may be implemented in various aspects.

[0164] As a composite substrate, a composite substrate 3 that forms part of the surface acoustic wave device 1 was shown. However, the composite substrate may be in a wafer state (not diced) or may be in a state where the conductor layer 5 is not disposed. As understood from the description of the embodiment, in the surface acoustic wave device 1, the x direction (the propagation direction of the surface acoustic wave for which utilization is intended. From another perspective, the direction in which it is determined whether it is concave or not) may be specified based on the arrangement direction and / or the extending direction of the plurality of electrode fingers 27. On the other hand, in the composite substrate (wafer) before the conductor layer 5 is formed, for example, the x direction may be specified based on an orifice or a specification sheet or the like.

Explanation of Signs

[0165] 1…Surface acoustic wave device, 3…Composite substrate, 5…Conductor layer, 7…Support substrate, 9…Low-velocity film, 11…Piezoelectric layer, 13…High-velocity film, 19…IDT electrode.

Claims

1. A composite substrate having a piezoelectric layer and a low acoustic velocity film that spreads along the lower surface of the piezoelectric layer and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer, a first IDT electrode having a plurality of electrode fingers arranged along the upper surface of the piezoelectric layer, and having, the piezoelectric layer and the low acoustic velocity film directly overlap acoustically, the piezoelectric layer is made of a lithium tantalate single crystal with a rotated Y-cut X propagation, the low acoustic velocity film is made of silicon dioxide, when twice the pitch of the plurality of electrode fingers is λ (μm), the normalized thickness obtained by dividing the thickness (μm) of the piezoelectric layer by λ is a, the normalized thickness obtained by dividing the thickness (μm) of the low acoustic velocity film by λ is b, and the inclination angle of the Y-axis with respect to the normal of the piezoelectric layer is c°, a, b, and c satisfy the following formula (1), an elastic wave element. -3.36797a + 2.582139a 2 -1.02894b + 1.487276b 2 -0.02411c + 0.000309c 2 +0.432673ab - 0.00517ac + 0.000873bc + 0.272652 < -1 (1)

2. A composite substrate having a piezoelectric layer and a low acoustic velocity film that spreads along the lower surface of the piezoelectric layer and has a lower acoustic velocity than the acoustic velocity in the piezoelectric layer, a first IDT electrode having a plurality of electrode fingers arranged along the upper surface of the piezoelectric layer, and having, the composite substrate further has a high acoustic velocity film that directly overlaps the piezoelectric layer and the low acoustic velocity film acoustically between the piezoelectric layer and the low acoustic velocity film, the piezoelectric layer is made of a lithium tantalate single crystal with a rotated Y-cut X propagation, the low acoustic velocity film is made of silicon dioxide, the high acoustic velocity film is made of aluminum oxide, when twice the pitch of the plurality of electrode fingers is λ (μm), the normalized thickness obtained by dividing the thickness (μm) of the piezoelectric layer by λ is a, the normalized thickness obtained by dividing the thickness (μm) of the low acoustic velocity film by λ is b, the inclination angle of the Y-axis with respect to the normal of the piezoelectric layer is c°, and the normalized thickness obtained by dividing the thickness (μm) of the high acoustic velocity film by λ is d, a, b, c, and d satisfy the following formula (2), an elastic wave element. -3.26163a - 0.30469b - 0.02132c + 3.843127d + 2.196667a 2 + 0.960417b 2 + 0.00026c 2 - 7.75985d 2 - 0.01579ab + 0.001339ac - 1.26908ad - 0.00246bc - 0.8485bd - 0.01067cd + 0.151192 < -1 (2)

3. the normalized thickness a of the piezoelectric layer is 1.0 or less The elastic wave element according to claim 1 or 2.

4. the normalized thickness b of the low acoustic velocity film is 0.5 or less The elastic wave element according to claim 1 or 2.

5. The first IDT electrode, a first bus bar and a second bus bar that face each other in a direction intersecting the x direction when the piezoelectric layer is viewed in plan, a plurality of first electrode fingers extending in the y direction perpendicular to the x direction from the first bus bar toward the second bus bar, It extends in the y direction from the second bus bar toward the first bus bar, and has a plurality of first electrode fingers and a plurality of second electrode fingers alternately arranged in the x direction. The virtual lines connecting the tips of the plurality of first electrode fingers and the virtual lines connecting the tips of the plurality of second electrode fingers are inclined with respect to the x direction. The elastic wave element according to claim 1 or 2.

6. The first IDT electrode A first bus bar and a second bus bar that face each other in a direction intersecting the x direction when the piezoelectric layer is viewed in plan, A plurality of first electrode fingers extending in the y direction orthogonal to the x direction from the first bus bar toward the second bus bar, It extends in the y direction from the second bus bar toward the first bus bar, and has a plurality of first electrode fingers and a plurality of second electrode fingers alternately arranged in the x direction. The intersection region sandwiched between the virtual lines connecting the tips of the plurality of first electrode fingers and the virtual lines connecting the tips of the plurality of second electrode fingers Two edge regions adjacent to the two virtual lines, A central region located closer to the center of the intersection region than the two edge regions. The velocity of the elastic wave excited by the first IDT electrode and propagating in the x direction through the piezoelectric layer is different between the central region and the two edge regions. The elastic wave element according to claim 1 or 2.

7. It has a ladder-type filter including a plurality of IDT electrodes located on the upper surface of the piezoelectric layer and connected to each other in a ladder type. The elastic wave element according to claim 1 or 2.

8. It has a multi-mode filter including a plurality of IDT electrodes located on the upper surface of the piezoelectric layer and arranged in the arrangement direction of the plurality of electrode fingers. The elastic wave element according to claim 1 or 2.

9. The elastic wave element according to claim 1 or 2, An antenna connected to the elastic wave element, An integrated circuit element connected to the antenna via the elastic wave element, A module having the above.

10. The elastic wave element according to claim 1 or 2, An antenna connected to the elastic wave element, An integrated circuit element connected to the antenna via the elastic wave element, A housing containing the elastic wave element and the integrated circuit element, A communication device having the above.

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