Acoustic wave device, filter, multiplexer, and method for manufacturing an acoustic wave device

Abstract

To provide an elastic wave device capable of suppressing peeling of a conductive layer.SOLUTION: An elastic wave device 100 includes: a concave-shaped conductive layer 33 in which a terminal electrode 32a that is provided to a through hole 24 penetrating through a piezoelectric layer 14 and that is electrically connected to a lower electrode is provided in contact with a side surface 40 of the piezoelectric layer 14 in the through hole 24; and a conductive layer 34 provided, on the conductive layer 33, in contact with the conductive layer 33. An absolute value of a difference in a thermal expansion coefficient between the piezoelectric layer 14 and the conductive layer 33 is smaller than an absolute value of a difference in a thermal expansion coefficient between the piezoelectric layer 14 and the conductive layer 34, and a difference between an angle θ2 formed by a lower surface 15b of the piezoelectric layer 14 and a side surface 42 of the piezoelectric layer 14 in the through hole 24 and an angle θ3 that is a maximum angle among tilt angles of the side surface 44 relative to a concave-shaped bottom surface 46 of the conductive layer 33 is larger than a difference between the angle θ2 and an angle θ1 formed by the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 in a through hole 22 that has a cavity at the inside thereof.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device, a filter, a multiplexer, and a method for manufacturing an acoustic wave device. [Background technology]

[0002] Filters and duplexers using film bulk acoustic resonators are known as filters and duplexers for use in high-frequency circuits in wireless terminals such as mobile phones. A film bulk acoustic resonator includes a piezoelectric layer and a lower electrode and an upper electrode sandwiching the piezoelectric layer. The region where the lower electrode and the upper electrode face each other across the piezoelectric layer is the resonance region where elastic waves resonate. It is known to use a lithium niobate layer or a lithium tantalate layer with a large electromechanical coupling coefficient for the piezoelectric layer (see, for example, Patent Document 1). It is also known to provide an air gap on the side of the resonance region of the piezoelectric layer to suppress unwanted spurious emissions (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-205574 [Non-patent literature]

[0004] [Non-Patent Document 1] Ting Wu and four others, "Application of Free Side Edges to Thickness Shear Bulk Acoustic Resonator on Lithium Niobate for Suppression of Transverse Resonance," Materials from the 2nd Research Meeting of the Acoustic Wave Device Technology Consortium, March 8, 2021 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to connect a conductive layer such as a pad to the lower electrode, a through-hole may be formed in the piezoelectric layer, and the conductive layer may be formed in the through-hole to connect the conductive layer to the lower electrode. In this case, in order to simplify the manufacturing process, it is desirable to form the through-hole for forming the conductive layer simultaneously with the through-hole formed on the side of the resonance region to suppress spurious emissions. However, in this case, the sidewall of the through-hole for forming the conductive layer becomes nearly vertical, which may cause peeling of the conductive layer.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to suppress peeling of the conductive layer. [Means for solving the problem]

[0007] The present invention relates to a piezoelectric layer having a lower electrode and an upper electrode, a partial region of which is sandwiched between the lower electrode and the upper electrode, a first through-hole provided along a resonance region on a side thereof, the first through-hole penetrating from a first surface on the upper electrode side to a second surface on the lower electrode side, and having a void therein, and a second through-hole penetrating from the first surface to the second surface on the lower electrode, the second through-hole being electrically connected to the lower electrode, the first conductive layer being concavely shaped and provided in contact with a side surface of the piezoelectric layer at the second through-hole, and the first conductive layer being electrically connected to the second through-hole. and a second conductive layer provided on a layer in contact with the first conductive layer, wherein the absolute value of the difference in thermal expansion coefficient between the piezoelectric layer and the first conductive layer is smaller than the absolute value of the difference in thermal expansion coefficient between the piezoelectric layer and the second conductive layer, and the difference between a first angle formed by the second surface and a side surface of the piezoelectric layer at the second through hole and a second angle which is the maximum angle among the inclination angles of the side surface of the concave shape of the first conductive layer with respect to the bottom surface of the concave shape of the first conductive layer is larger than the difference between the first angle and a third angle formed by the second surface and the side surface of the piezoelectric layer at the first through hole.

[0008] In the above configuration, the acoustic impedance of the first conductive layer may be higher than the acoustic impedance of the second conductive layer.

[0009] In the above configuration, the first conductive layer may have a lower electrical resistivity than the second conductive layer.

[0010] In the above configuration, the first angle and the third angle may be equal to or greater than 80° and equal to or less than 100°, and the second angle may be equal to or less than 60°.

[0011] In the above configuration, the piezoelectric layer may be a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer.

[0012] In the above configuration, the first conductive layer is a titanium nitride layer or a nickel layer, The second conductive layer may be a titanium layer or a chromium layer.

[0013] In the above configuration, the first through holes may be provided on both sides of the resonance region and are spaced the same distance from the resonance region.

[0014] In the above configuration, the first through hole may be provided in a region where the lower electrode and the upper electrode are not present in a plan view.

[0015] In the above configuration, the laminated conductive layer may include, on the second conductive layer, a third conductive layer having an electrical resistivity lower than that of the first conductive layer and the second conductive layer.

[0016] The present invention provides a piezoelectric layer that is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, the piezoelectric layer having a lower electrode, an upper electrode, a partial region sandwiched between the lower electrode and the upper electrode, a first through-hole provided along a resonance region that is the partial region and that penetrates from a first surface on the upper electrode side to a second surface on the lower electrode side, the first through-hole having a void therein, and a second through-hole that penetrates from the first surface to the second surface on the lower electrode, the second through-hole being provided in the second through-hole and electrically connected to the lower electrode, the second through-hole being a piezoelectric layer that is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer The acoustic wave device comprises a stacked conductive layer including: a first conductive layer which is a titanium nitride layer or nickel layer having a concave shape and provided in contact with a side surface; and a second conductive layer which is a titanium layer or chromium layer provided on the first conductive layer in contact with the first conductive layer, wherein the difference between a first angle formed by the second surface and the side surface of the piezoelectric layer at the second through hole and a second angle which is the maximum angle among the inclination angles of the side surface of the concave shape of the first conductive layer with respect to the bottom surface of the concave shape is greater than the difference between the first angle and a third angle formed by the second surface and the side surface of the piezoelectric layer at the first through hole.

[0017] The present invention is a filter including the acoustic wave device described above.

[0018] The present invention is a multiplexer including a filter as claimed in claim 11.

[0019] The present invention provides a piezoelectric element comprising the steps of: forming a piezoelectric layer on a lower electrode; forming an upper electrode on the piezoelectric layer so as to sandwich a partial region of the piezoelectric layer between the upper electrode and the lower electrode; simultaneously forming a first through-hole in the piezoelectric layer, which is located to the side of a resonance region that is the partial region and which penetrates from a first surface of the piezoelectric layer on the upper electrode side to a second surface of the piezoelectric layer on the lower electrode side, and a second through-hole on the lower electrode that penetrates from the first surface to the second surface; and forming a first conductive layer having a concave shape in contact with a side surface of the piezoelectric layer at the second through-hole. a step of processing the first conductive layer so that the maximum angle of inclination of the side surface of the concave shape of the first conductive layer relative to the bottom surface of the concave shape is smaller than the angle formed by the second surface of the piezoelectric layer and the side surface of the piezoelectric layer at the second through hole; and a step of forming, after processing the first conductive layer, a second conductive layer on and in contact with the first conductive layer, the second conductive layer having a thermal expansion coefficient whose difference with the thermal expansion coefficient of the piezoelectric layer is larger than the difference between the thermal expansion coefficients of the piezoelectric layer and the first conductive layer.

[0020] In the above configuration, the step of processing the first conductive layer may be configured to process the first conductive layer using an ion milling method or a reverse sputtering method. [Effects of the Invention]

[0021] According to the present invention, peeling of the conductive layer can be suppressed. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a plan view of an acoustic wave device in accordance with a first embodiment. [Figure 2] 2(a) is a cross-sectional view taken along line AA in FIG. 1, and FIG. 2(b) is a cross-sectional view taken along line BB in FIG. [Figure 3] 3(a) is an enlarged cross-sectional view of the vicinity of the through-hole in FIG. 2(b), and FIG. 3(b) is an enlarged cross-sectional view of the vicinity of the terminal electrode in FIG. 2(a). [Figure 4] 4(a) and 4(b) are diagrams showing the crystal orientation of the piezoelectric layer in Example 1. FIG. [Figure 5] 5(a) to 5(d) are cross-sectional views (part 1) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 6] 6(a) to 6(d) are cross-sectional views (part 2) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 7] 7(a) to 7(d) are cross-sectional views (part 3) illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 8] 8(a) to 8(f) are cross-sectional views (part 1) showing a method for forming through holes and terminal electrodes. [Figure 9] 9(a) to 9(f) are cross-sectional views (part 2) showing a method for forming through-holes and terminal electrodes. [Figure 10] 10(a) is a cross-sectional view of the vicinity of a through hole in a modified example of the first embodiment, and FIG. 10(b) is a cross-sectional view of the vicinity of a terminal electrode in the modified example of the first embodiment. [Figure 11] 11(a) to 11(e) are cross-sectional views showing a method for forming a terminal electrode in a modified example of the first embodiment. [Figure 12] 12(a) and 12(b) are cross-sectional views of an acoustic wave device according to a comparative example. [Figure 13] 13(a) is an enlarged cross-sectional view of the vicinity of the through-hole in FIG. 12(b), and FIG. 13(b) is an enlarged cross-sectional view of the vicinity of the terminal electrode in FIG. 12(a). [Figure 14] 14(a) to 14(c) are cross-sectional views showing a method for forming a terminal electrode in a comparative example. [Figure 15] 15(a) and 15(b) are cross-sectional views of an acoustic wave device in accordance with the second embodiment. [Figure 16] FIG. 16 is a plan view of a filter according to a third embodiment. [Figure 17] FIG. 17 is a circuit diagram of a duplexer according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0024] FIG. 1 is a plan view of an acoustic wave device 100 in accordance with a first embodiment. FIG. 2(a) is a cross-sectional view taken along line AA in FIG. 1, and FIG. 2(b) is a cross-sectional view taken along line BB in FIG. 1. In FIG. 1, for clarity, the resonance region 50 is hatched, and the through-holes 22 are depicted with thicker lines than the other portions. The normal direction of the piezoelectric layer 14 is the Z direction, the extension direction of the upper electrode 16 within the planar direction of the piezoelectric layer 14 is the +Y direction, the extension direction of the lower electrode 12 is the −Y direction, and the direction perpendicular to the ±Y directions is the X direction. Note that the X direction, Y direction, and Z direction do not necessarily correspond to the X axis, Y axis, and Z axis of the crystal orientation of the piezoelectric layer 14.

[0025] As shown in FIGS. 1, 2(a), and 2(b), the acoustic wave device 100 is a piezoelectric thin film resonator including a lower electrode 12, a piezoelectric layer 14, and an upper electrode 16. An acoustic reflection film 31 is provided on a substrate 10, and the piezoelectric layer 14 is provided on the acoustic reflection film 31. An upper surface 15a and a lower surface 15b of the piezoelectric layer 14 are flat. An upper electrode 16 and a lower electrode 12 are provided above and below the piezoelectric layer 14. A region where the lower electrode 12 and the upper electrode 16 overlap in a planar view, sandwiching at least a portion of the piezoelectric layer 14 therebetween, is a resonance region 50.

[0026] The substrate 10 is, for example, a silicon substrate, sapphire substrate, alumina substrate, spinel substrate, quartz substrate, quartz crystal substrate, glass substrate, ceramic substrate, or GaAs substrate. The piezoelectric layer 14 is, for example, a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer. The thickness of the piezoelectric layer 14 is, for example, approximately 200 nm to 1000 nm. The lower electrode 12 and the upper electrode 16 are, for example, single-layer films of ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), iridium (Ir), or the like, or stacked films thereof. The thickness of the lower electrode 12 and the upper electrode 16 is, for example, approximately 20 nm to 150 nm.

[0027] A through-hole 24 is provided on the lower electrode 12, penetrating the piezoelectric layer 14 from the upper surface 15a to the lower surface 15b, and a terminal electrode 32a is provided to fill the through-hole 24 and electrically connect to the lower electrode 12. The electrical connection may be a connection that provides conduction for either direct current or alternating current. A terminal electrode 32b is provided on the upper electrode 16 and electrically connects to the upper electrode 16. The terminal electrodes 32a and 32b are laminated conductive layers of a conductive layer 33, a conductive layer 34, and a conductive layer 35. The conductive layer 34 functions as an adhesive layer for adhering the conductive layer 35.

[0028] A metal film 20 is provided under the lower electrode 12 so as to overlap the terminal electrode 32a in a plan view. The metal film 20 is provided to electrically connect the terminal electrode 32a and the lower electrode 12 even if the lower electrode 12 is also removed when forming the through-hole 24 in the piezoelectric layer 14. The metal film 20 is, for example, a titanium film.

[0029] When high-frequency power is applied between the terminal electrodes 32a and 32b (i.e., between the lower electrode 12 and the upper electrode 16), an elastic wave is excited in the piezoelectric layer 14 in the resonance region 50. The wavelength of the elastic wave is approximately twice the total thickness of the lower electrode 12, the piezoelectric layer 14, and the upper electrode 16. When the piezoelectric layer 14 is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, an elastic wave is excited in the piezoelectric layer 14, in which the displacement of the elastic wave vibrates in a direction approximately perpendicular to the Z direction (i.e., the strain direction relative to the thickness). This vibration is called thickness-shear vibration. The direction in which the displacement of the thickness-shear vibration is greatest (the displacement direction of the thickness-shear vibration) is defined as the vibration direction 80 of the thickness-shear vibration. Here, the vibration direction 80 of the thickness-shear vibration is the Y direction. The planar shape of the resonance region 50 is rectangular. The rectangle has four approximately straight sides. Of the four sides, one pair extends approximately along the Y direction (i.e., the vibration direction 80 of the thickness-shear vibration), and another pair extends approximately along the X direction (i.e., the direction perpendicular to the vibration direction 80 of the thickness-shear vibration).

[0030] The acoustic reflection film 31 is formed by alternating low-acoustic-impedance films 31a and high-acoustic-impedance films 31b. The thickness of each of the films 31a and 31b is, for example, approximately λ / 4 (λ is the wavelength of the acoustic wave). This allows the acoustic reflection film 31 to reflect acoustic waves. The number of layers of the films 31a and 31b can be set arbitrarily. The acoustic reflection film 31 may be formed by stacking at least two types of layers with different acoustic properties at an interval. The substrate 10 may also be one of the at least two types of layers with different acoustic properties of the acoustic reflection film 31. For example, the acoustic reflection film 31 may be formed by providing one layer of a film with a different acoustic impedance within the substrate 10. In a plan view, the acoustic reflection film 31 overlaps the resonance region 50, and is the same size as or larger than the resonance region 50. The low-acoustic-impedance film 31a of the acoustic reflection film 31 is, for example, a silicon oxide film, and the high-acoustic-impedance film 31b is, for example, a tungsten film.

[0031] The resonance region 50 has a central region 52 and edge regions 54a and 54b located on both sides of the central region 52 in the Y direction. The edge regions 54a and 54b extend substantially along the X direction. The widths of the edge regions 54a and 54b in the Y direction are substantially constant in the X direction.

[0032] An additional film 18a is provided on the upper electrode 16, extending from the edge region 54a to a region 56a outside the resonance region 50. An additional film 18b is provided on the upper electrode 16 and the piezoelectric layer 14, extending from the edge region 54b to a region 56b outside the resonance region 50. The additional films 18a and 18b are not provided in the central region 52. The additional films 18a and 18b are formed substantially along the X direction, and their width in the Y direction is substantially constant in the X direction. The additional films 18a and 18b are either metal films such as those exemplified for the lower electrode 12 and the upper electrode 16, or insulating films such as silicon oxide films, silicon nitride films, aluminum oxide films, tantalum oxide films, or niobium oxide films. The provision of the additional films 18a and 18b realizes a piston mode, thereby suppressing spurious responses.

[0033] A pair of through holes 22 are formed in the piezoelectric layer 14, sandwiching the resonance region 50 in the X direction and extending along the resonance region 50 in the Y direction. The through holes 22 are provided, for example, in a region where the lower electrode 12 and the upper electrode 16 are not present in a plan view. For example, in a plan view, the through holes 22 contact the resonance region 50 on both sides of the resonance region 50 in the X direction. That is, in a plan view, the through holes 22 define opposing sides of the rectangular resonance region 50 in the X direction. Note that the through holes 22 may not contact the resonance region 50 but may be located away from the resonance region 50. Preferably, the through holes 22 are formed on both sides of the resonance region 50 at the same distance from the resonance region 50. The through holes 22 have, for example, a rectangular shape in a plan view. The additional films 18a, 18b and the pair of through holes 22 are provided to surround the resonance region 50 in a plan view. The width of the additional films 18a, 18b in the Y direction is, for example, about 20 μm to 100 μm. The width of the through-holes 22 in the X direction is, for example, about 20 μm to 100 μm. By providing the through-holes 22, the acoustic waves excited in the resonance region 50 are confined within the resonance region 50. Note that such an effect of confining acoustic waves by the through-holes 22 can also be obtained in an acoustic wave device having a comb-shaped electrode, or an acoustic wave device using surface acoustic waves such as Love waves or Lamb waves.

[0034] Fig. 3(a) is an enlarged cross-sectional view of the vicinity of through-hole 22 in Fig. 2(b), and Fig. 3(b) is an enlarged cross-sectional view of the vicinity of terminal electrode 32a in Fig. 2(a). As shown in Fig. 3(a), it is desirable that side surface 40 of piezoelectric layer 14 at through-hole 22 be vertical in order to suppress spurious emissions. An angle θ1 formed between lower surface 15b of piezoelectric layer 14 and side surface 40 of piezoelectric layer 14 at through-hole 22 is, for example, 80° or more and 100° or less.

[0035] 3(b), since the through-holes 24 are formed at the same time as the through-holes 22, the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 is the same as the angle θ1 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 at the through-hole 22. In other words, the angle θ2 is, for example, between 80° and 100°. The same angle allows for a difference equivalent to a manufacturing error.

[0036] The conductive layer 33 included in the terminal electrode 32a is provided in contact with the side surface 42 of the piezoelectric layer at the through-hole 24 and has a concave shape. The maximum inclination angle θ3 of the side surface 44 of the concave shape relative to the bottom surface 46 of the concave shape of the conductive layer 33 is smaller than the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24. The angle θ3 is, for example, not less than 20° and not more than 60°.

[0037] Therefore, the difference between the angle θ2 and the angle θ3 (θ2−θ3) is greater than the difference between the angle θ2 and the angle θ1 (θ2−θ1).

[0038] Comparing the thermal expansion coefficients of the conductive layer 33 and the conductive layer 34, the thermal expansion coefficient of the conductive layer 33 is closer to the thermal expansion coefficient of the piezoelectric layer 14 than the thermal expansion coefficient of the conductive layer 34. For example, the thermal expansion coefficient of the conductive layer 33 is a value between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 34. Therefore, the absolute value of the difference between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 33 is smaller than the absolute value of the difference between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 34. Furthermore, the acoustic impedance of the conductive layer 33 is higher than the acoustic impedance of the conductive layer 34. For example, the conductive layer 33 is a titanium nitride layer or a nickel layer, and the conductive layer 34 is a titanium layer or a chromium layer. Furthermore, the conductive layer 35 has a lower electrical resistivity than the conductive layers 33 and 34. For example, the conductive layer 35 is a gold layer or an aluminum layer.

[0039] Table 1 shows the thermal expansion coefficient (ppm / K), electrical resistivity (μΩ·cm), and density (kg / m) of titanium nitride, nickel, titanium, chromium, lithium niobate, lithium tantalate, gold, and aluminum. 3), bulk modulus (GPa), sound velocity (m / s), acoustic impedance, and reflectivity of elastic waves for lithium niobate. The reflectivity was calculated using the formula (Zb-Za) / (Zb+Za), where Za is the acoustic impedance of lithium niobate and Zb is the acoustic impedance of each material. [Table 1]

[0040] As shown in Table 1, the thermal expansion coefficient of titanium nitride is 9.4 ppm / K, the thermal expansion coefficient of nickel is 15 ppm / K, the thermal expansion coefficient of titanium is 8.4 ppm / K, the thermal expansion coefficient of chromium is 8.4 ppm / K, the thermal expansion coefficient of lithium niobate is 14 ppm / K, and the thermal expansion coefficient of lithium tantalate is 16 ppm / K. Therefore, when piezoelectric layer 14 is a lithium niobate layer or a lithium tantalate layer, conductive layer 33 is a titanium nitride layer or a nickel layer, and conductive layer 34 is a titanium layer or a chromium layer, the absolute value of the difference between the thermal expansion coefficient of piezoelectric layer 14 and the thermal expansion coefficient of conductive layer 33 is smaller than the absolute value of the difference between the thermal expansion coefficient of piezoelectric layer 14 and the thermal expansion coefficient of conductive layer 34. In addition, the acoustic impedance of titanium nitride is 3.62×10 7 , the acoustic impedance of nickel is 4.00×10 7 , the acoustic impedance of titanium is 2.23 × 10 7 , the acoustic impedance of chromium is 3.39×10 7 Therefore, when conductive layer 33 is a titanium nitride layer or a nickel layer and conductive layer 34 is a titanium layer or a chromium layer, the acoustic impedance of conductive layer 33 is higher than the acoustic impedance of conductive layer 34. Furthermore, the electrical resistivity of titanium nitride is 25 μΩ·cm, the electrical resistivity of nickel is 6.84 μΩ·cm, the electrical resistivity of titanium is 42 μΩ·cm, the electrical resistivity of chromium is 12.9 μΩ·cm, the electrical resistivity of gold is 2.35 μΩ·cm, and the electrical resistivity of aluminum is 2.65 μΩ·cm. Therefore, when conductive layer 33 is a titanium nitride layer or a nickel layer, conductive layer 34 is a titanium layer, and conductive layer 35 is a gold layer or an aluminum layer, conductive layer 35 has a lower electrical resistivity than conductive layers 33 and 34.

[0041] 4(a) and 4(b) are perspective views showing the crystal orientation of the piezoelectric layer 14 in Example 1. FIG. 4(a) shows the case where the piezoelectric layer 14 is made of lithium niobate, and FIG. 4(b) shows the case where the piezoelectric layer 14 is made of lithium tantalate. The dashed arrows on the left side of FIGS. 4(a) and 4(b) correspond to the X, Y, and Z directions in FIGS. 1, 2(a), and 2(b). The solid lines in the right-hand diagrams show the orientations of the crystal axes of the piezoelectric layer 14. Here, the Euler angles (α, β, γ) are defined as follows: In a right-handed XYZ coordinate system, the normal direction to the top surface of the piezoelectric layer 14 is defined as the Z direction, and the directions perpendicular to the Z direction and perpendicular to each other in the planar direction of the top surface of the piezoelectric layer 14 are defined as the X and Y directions. First, the X, Y, and Z directions are defined as the X-axis, Y-axis, and Z-axis directions of the crystal orientation, respectively. Next, a rotation α is performed around the Z axis from the +X axis to the +Y axis. After the α rotation, the crystal is rotated β from the +Y axis to the +Z axis around the X axis direction. After the β rotation, the crystal is rotated γ from the +X axis to the +Y axis around the Z axis direction. The Euler angles of the crystal whose crystal orientation has been rotated in this way are (α, β, γ). In this embodiment, α, β, and γ are expressed using 0° to 180°, but the Euler angles expressed using (α, β, γ) include equivalent Euler angles.

[0042] First, we will explain the case where the piezoelectric layer 14 is made of lithium niobate. As shown in the upper diagram of FIG. 4(a), the +X direction, +Y direction, and +Z direction are the +X-axis direction, +Y-axis direction, and +Z-axis direction of the crystal orientation of the piezoelectric layer 14, respectively. From this state, the +Y-axis direction and +Z-axis direction are rotated 105° from the +Y-axis direction toward the +Z-axis direction on the Y-axis / Z-axis plane around the X-axis direction. By rotating in this way, as shown in the lower diagram of FIG. 4(a), the +Z direction becomes the direction obtained by rotating the +Z-axis direction 105° toward the +Y-axis direction. At this time, the Y direction becomes the vibration direction 80 of the thickness-shear vibration. The Euler angles are (0°, 105°, 0°).

[0043] The normal direction (Z direction) of the top surface of the piezoelectric layer 14 is a direction within the Y-axis / Z-axis plane. This generates thickness-shear vibration in the planar direction of the piezoelectric layer 14. The X-axis direction is preferably within a range of ±5° from the planar direction of the piezoelectric layer 14, more preferably within a range of ±1°. The normal direction (Z direction) of the top surface of the piezoelectric layer 14 is set to a direction rotated 105° from the +Z-axis direction of the crystal orientation toward the +Y-axis direction. This causes the vibration direction 80 of the thickness-shear vibration and its perpendicular direction to become the planar direction of the piezoelectric layer 14. The +Z direction is preferably within a range of ±5° from the direction rotated 105° from the +Z-axis direction toward the +Y-axis direction, more preferably within a range of ±1°. The Euler angles are preferably (0°±5°, 105°±5°, 0°±5).

[0044] Next, we will explain the case where the piezoelectric layer 14 is made of lithium tantalate. As shown in the upper diagram of FIG. 4(b), the +X, +Y, and +Z directions are the +X, +Y, and +Z directions of the crystal orientation of the piezoelectric layer 14, respectively. From this state, the +X and +Y axes are rotated 138° from the +X axis toward the +Y axis on the X-Y plane around the Z axis. Next, the +Y and +Z axes are rotated 90° from the +Y axis toward the +Z axis around the X axis, and then the +X and +Y axes are rotated 90° from the +X axis toward the +Y axis around the Z axis. After this rotation, as shown in the lower diagram of FIG. 4(b), the +Z direction becomes the +X axis, and the -Y direction becomes the direction obtained by rotating the +Y axis toward the -Z axis by 42°. At this time, the Y direction becomes the vibration direction 80° of the thickness-shear vibration. The Euler angles are (138°, 90°, 90°).

[0045] The normal direction (Z direction) of the top surface of the piezoelectric layer 14 is the X-axis direction. As a result, thickness-shear vibration occurs in the planar direction of the piezoelectric layer 14. The X-axis direction is preferably within a range of ±5° from the normal direction of the piezoelectric layer 14, and more preferably within a range of ±1°. The Y-direction is the direction rotated 42° from the +Y-axis direction of the crystal orientation to the -Z-axis direction. As a result, the direction rotated 42° from the +Y-axis direction to the -Z-axis direction in the planar direction of the piezoelectric layer 14 becomes the vibration direction 80 of thickness-shear vibration. The Euler angles are preferably (138°±5°, 90°±5°, 90°±5).

[0046] [Manufacturing method of Example 1] FIGS. 5(a) to 8(d) are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. FIGS. 5(a), 5(c), 6(a), 6(c), 7(a), and 7(c) are cross-sectional views of a portion corresponding to the line AA in FIG. 1, and FIGS. 5(b), 5(d), 6(b), 6(d), 7(b), and 7(d) are cross-sectional views of a portion corresponding to the line BB in FIG. 1. As shown in FIGS. 5(a) and 5(b), a piezoelectric substrate is prepared as the piezoelectric layer 14. A bottom electrode 12 is formed on the piezoelectric layer 14. A metal film 20 is formed on the bottom electrode 12. The bottom electrode 12 and the metal film 20 are formed by depositing a metal film using, for example, sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition), and then patterning the metal film into a desired shape using, for example, photolithography and etching. The lower electrode 12 and the metal film 20 may be formed using a lift-off method.

[0047] As shown in Figures 5(c) and 5(d), an acoustic reflection film 31 is formed on the piezoelectric layer 14 to cover the lower electrode 12 and the metal film 20. The acoustic reflection film 31 is formed by alternately depositing films 31a with low acoustic impedance and films 31b with high acoustic impedance, and patterning the film 31b with high acoustic impedance into a desired shape. The films 31a and 31b are deposited using, for example, sputtering or CVD, and patterned using, for example, photolithography and etching. The top surface of the acoustic reflection film 31 is planarized using, for example, CMP (Chemical Mechanical Polishing).

[0048] As shown in Figures 6(a) and 6(b), the laminate of the piezoelectric layer 14 and the acoustic reflection film 31 is turned upside down, and the lower surface of the acoustic reflection film 31 is bonded to the upper surface of the substrate 10. For example, a surface activation method is used for bonding. A bonding layer such as a silicon film may be provided between the substrate 10 and the acoustic reflection film 31. Next, the piezoelectric layer 14 is thinned to a desired thickness. For example, a grinding method and / or a CMP method is used for thinning. For example, the piezoelectric layer 14 is made to approximately the desired thickness using a grinding method, and the upper surface is flattened using a CMP method. As a result, the upper surface 15a of the piezoelectric layer 14 becomes flat within the manufacturing tolerances.

[0049] As shown in Figures 6(c) and 6(d), an upper electrode 16 is formed on the piezoelectric layer 14. The upper electrode 16 is formed by depositing a metal film using, for example, sputtering, vacuum deposition, or CVD, and then patterning the metal film into a desired shape using, for example, photolithography and etching. The upper electrode 16 may also be formed using a lift-off method. Additional films 18a and 18b are formed on the upper electrode 16. The additional films 18a and 18b are formed by depositing a film using, for example, sputtering, vacuum deposition, or CVD, and then patterning the film into a desired shape using, for example, photolithography and etching. The additional films 18a and 18b may also be formed using a lift-off method.

[0050] As shown in Figures 7(a) and 7(b), through-holes 22 and 24 are formed in the piezoelectric layer 14, penetrating from the upper surface 15a to the lower surface 15b. The through-holes 22 and 24 are formed by, for example, photolithography and etching. The through-holes 22 and 24 are formed simultaneously and have widths 10 times or more greater than their depths, so that the sidewalls are formed at similar angles.

[0051] As shown in Figures 7(c) and 7(d), a terminal electrode 32a is formed in the through hole 24 so as to be electrically connected to the lower electrode 12, and a terminal electrode 32b is formed on the upper electrode 16 so as to be electrically connected to the upper electrode 16.

[0052] Here, a method for forming the through holes 22, 24 and the terminal electrode 32a will be described in detail with reference to Figures 8(a) to 9(f). Figures 8(a), 8(c), 8(e), 9(a), 9(c), and 9(e) are cross-sectional views of the area where the through hole 24 and the terminal electrode 32a are formed, and Figures 8(b), 8(d), 8(f), 9(b), 9(d), and 9(f) are cross-sectional views of the area where the through hole 22 is formed.

[0053] As shown in FIGS. 8(a) and 8(b), a resist film 60 is formed on the piezoelectric layer 14. Openings corresponding to the locations where the through holes 22 and 24 will be formed are formed in the resist film 60. Using the resist film 60 as a mask, the piezoelectric layer 14 is etched by ion milling. This forms the through holes 22 and 24 in the piezoelectric layer 14. Because the through holes 22 and 24 are formed simultaneously and have widths at least 10 times their depths (this is not shown in FIGS. 8(a) and 8(b) due to drawing limitations), the sidewalls are formed at similar angles. Therefore, as described with reference to FIGS. 3(a) and 3(b), the angle θ1 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 at the through hole 22 is the same as the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through hole 24. In order to suppress spurious responses, the side surface 40 of the piezoelectric layer 14 in the through-hole 22 is made nearly vertical, and therefore the angle θ1 and the angle θ2 are set to be 80° or more and 100° or less.

[0054] As shown in FIGS. 8(c) and 8(d), after removing the resist film 60, a resist film 62 having openings corresponding to the positions where the terminal electrodes 32a are to be formed is formed on the piezoelectric layer 14.

[0055] 8(e) and 8(f), the conductive layer 33 is formed by sputtering using the resist film 62 as a mask. The conductive layer 33 is formed in contact with the side surface 42 of the piezoelectric layer 14 in the through-hole 24.

[0056] As shown in FIGS. 9(a) and 9(b), the conductive layer 33 is etched using an ion milling method. During this process, the substrate 10 is tilted so that an ion beam is incident on the conductive layer 33 from an oblique direction. As a result, the bottom surface 46 of the concave-shaped conductive layer 33 becomes thinner, and the side surface 44 becomes inclined relative to the bottom surface 46. Therefore, as described with reference to FIG. 3(b), the maximum angle θ3 of the inclination angle of the side surface 44 of the concave shape relative to the bottom surface 46 of the concave shape of the conductive layer 33 is smaller than the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24, and is, for example, between 20° and 60°.

[0057] 9(c) and 9(d), a conductive layer 34 is formed on the conductive layer 33 by vacuum deposition. A conductive layer 35 is formed on the conductive layer 34 by vacuum deposition. For example, when the conductive layer 33 is formed by sputtering and then the conductive layer 35 is formed by vacuum deposition, the conductive layer 34 is formed to ensure adhesion of the conductive layer 35.

[0058] 9(e) and 9(f), the conductive layers 33, 34, and 35 on the resist film 62 are removed using photolithography and etching, and then the resist film 62 is removed. As a result, the terminal electrode 32a, which is a laminated film of the conductive layers 33, 34, and 35, is formed, and is embedded in the through-hole 24 formed in the piezoelectric layer 14 and electrically connected to the lower electrode 12.

[0059] [Variations] Fig. 10(a) is a cross-sectional view of the vicinity of the through hole 22 in a modified example of Example 1, and Fig. 10(b) is a cross-sectional view of the vicinity of the terminal electrode 32a in a modified example of Example 1. In Example 1, as shown in Fig. 3(b), the bottom surface 46 of the conductive layer 33 is located below the top surface 15a of the piezoelectric layer 14. In contrast, in the modified example of Example 1, as shown in Fig. 10(b), the bottom surface 46 of the conductive layer 33 is located above the top surface 15a of the piezoelectric layer 14.

[0060] In the modification of Example 1, as in Example 1, the angle θ1 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 at the through-hole 22 and the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 are the same angle, e.g., not less than 80° and not more than 100°. The maximum angle θ3 among the inclination angles of the side surface 44 of the concave shape with respect to the bottom surface 46 of the concave shape of the conductive layer 33 is smaller than the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 and is not less than 20° and not more than 60°. Therefore, the difference between the angle θ2 and the angle θ3 (θ2 - θ3) is greater than the difference between the angle θ2 and the angle θ1 (θ2 - θ1).

[0061] [Manufacturing method of modified example of Example 1] 11(a) to 11(e) are cross-sectional views showing a method for forming terminal electrodes 32a in a modified example of Example 1. As shown in Fig. 11(a), first, the same steps as those described in Figs. 8(a) and 8(c) of Example 1 are performed to form through holes 24 in the piezoelectric layer 14, and then a resist film 62 having openings corresponding to the locations where the terminal electrodes 32a will be formed is formed on the piezoelectric layer 14. The through holes 24 are formed simultaneously with the through holes 22, as described in Example 1.

[0062] 11(b), the conductive layer 33 is formed by sputtering using the resist film 62 as a mask. The conductive layer 33 is formed in contact with the side surface 42 of the piezoelectric layer 14 in the through-hole 24.

[0063] As shown in FIG. 11(c), the conductive layer 33 is etched using a reverse sputtering method. When the conductive layer 33 is etched using a reverse sputtering method, the etched atoms tend to reattach to the conductive layer 33. As a result, the side surface 44 of the concave shape of the conductive layer 33 is etched and tilted, and the etched atoms attach to the bottom surface 46, so that the bottom surface 46 is positioned higher than the upper surface 15a of the piezoelectric layer 14. As a result, as described with reference to FIG. 10(b), the maximum tilt angle θ3 of the side surface 44 of the concave shape of the conductive layer 33 relative to the bottom surface 46 of the concave shape of the conductive layer 33 is smaller than the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24, and is, for example, 20° to 60°.

[0064] 11(d), a conductive layer is formed by vacuum deposition on the conductive layer 33. A conductive layer 35 is formed by vacuum deposition on the conductive layer 34.

[0065] 11(e), the conductive layers 33, 34, and 35 on the resist film 62 are removed using photolithography and etching, and then the resist film 62 is removed. As a result, the terminal electrode 32a, which is a laminated film of the conductive layers 33, 34, and 35, is formed, and is embedded in the through-hole 24 formed in the piezoelectric layer 14 and electrically connected to the lower electrode 12.

[0066] [Comparative Example] 12(a) and 12(b) are cross-sectional views of an acoustic wave device 500 according to a comparative example. FIG. 13(a) is an enlarged cross-sectional view of the vicinity of the through hole 22 in FIG. 12(b), and FIG. 13(b) is an enlarged cross-sectional view of the vicinity of the terminal electrode 32a in FIG. 12(a). As shown in FIGS. 12(a), 12(b), 13(a), and 13(b), in the acoustic wave device 500 according to the comparative example, the terminal electrodes 32a and 32b are laminated films of a conductive layer 34 and a conductive layer 35. In the terminal electrode 32a, the conductive layer 34 is provided in contact with the side surface 42 of the piezoelectric layer 14 in the through hole 24, and the conductive layer 35 is provided on the conductive layer 34. The angle θ1 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 at the through-hole 22 and the angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 are the same angle, for example, between 80° and 100°, as in Example 1. The other configurations are the same as in Example 1, and therefore description thereof will be omitted.

[0067] [Manufacturing method for comparative example] 14(a) to 14(c) are cross-sectional views showing a method for forming terminal electrodes 32a in a comparative example. As shown in Fig. 14(a), first, the same steps as those described in Fig. 8(a) and Fig. 8(c) of Example 1 are performed to form through-holes 24 in the piezoelectric layer 14, and then a resist film 62 having openings corresponding to the locations where the terminal electrodes 32a will be formed is formed on the piezoelectric layer 14. The through-holes 24 are formed simultaneously with the through-holes 22, as described in Example 1.

[0068] 14(b), using the resist film 62 as a mask, the conductive layer 34 is formed by vacuum deposition. The conductive layer 34 is formed in contact with the side surface 42 of the piezoelectric layer 14 in the through-hole 24. The conductive layer 35 is formed on the conductive layer 34 by vacuum deposition.

[0069] 14(c), the conductive layers 34 and 35 on the resist film 62 are removed by photolithography and etching, and then the resist film 62 is removed. As a result, the terminal electrode 32a, which is a laminated film of the conductive layers 34 and 35, is formed, and is embedded in the through-hole 24 formed in the piezoelectric layer 14 and electrically connected to the lower electrode 12.

[0070] 13(b), in the acoustic wave device 500 according to the comparative example, the conductive layer 34 included in the terminal electrode 32a is formed in contact with the side surface 42 of the piezoelectric layer 14 at the through-hole 24. The angle θ2 formed between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 is approximately perpendicular, at 80° to 100°. This results in poor adhesion between the side surface 42 of the piezoelectric layer 14 and the conductive layer 34. For this reason, thermal expansion and contraction of the piezoelectric layer 14 and the conductive layer 34 due to temperature changes, for example, can apply thermal stress to the conductive layer 34, which can cause the conductive layer 34 to peel off from the side surface 42 of the piezoelectric layer 14 in region A. In this case, cracks can occur in the conductive layer 34 and / or the conductive layer 35, resulting in an increase in the electrical resistance of the terminal electrode 32a.

[0071] 3(b) and 10(b), the conductive layer 33 is provided in contact with the side surface 42 of the piezoelectric layer 14 in the through hole 24, and the conductive layer 34 is provided on the concave conductive layer 33 in contact with the conductive layer 33. The concave side surface 44 of the conductive layer 33 is inclined relative to the side surface 42 of the piezoelectric layer 14 in the through hole 24. Therefore, the difference between the angle θ2 formed by the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 in the through hole 24 and the maximum angle θ3 of the inclination angle of the concave side surface 44 with respect to the bottom surface 46 of the concave shape of the conductive layer 33 is greater than the difference between the angle θ2 formed by the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 in the through hole 24 and the angle θ1 formed by the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 in the through hole 22. In this way, the conductive layer 34 is formed in contact with the concave side surface 44 of the conductive layer 33, which is inclined relative to the side surface 42 of the piezoelectric layer 14 in the through hole 24. This improves adhesion between the conductive layer 34 and the conductive layer 33, preventing the conductive layer 34 from peeling off from the conductive layer 33. Furthermore, the conductive layer 33 has a thermal expansion coefficient closer to that of the piezoelectric layer 14 than the conductive layer 34. That is, the absolute value of the difference between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 33 is smaller than the absolute value of the difference between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 34. Therefore, even if the piezoelectric layer 14 and the conductive layer 33 thermally expand and contract with temperature changes, the thermal stress applied to the conductive layer 33 is reduced because the thermal expansion coefficient of the conductive layer 33 is closer to that of the piezoelectric layer 14 than that of the conductive layer 34. This prevents the conductive layer 33 from peeling off from the side surface 42 of the piezoelectric layer 14.

[0072] 8(a) and 8(b), through-holes 22 that penetrate from the upper surface 15a to the lower surface 15b of the piezoelectric layer 14 along the resonance region 50 on the side of the resonance region 50, and through-holes 24 that penetrate from the upper surface 15a to the lower surface 15b of the piezoelectric layer 14 on the lower electrode 12 are simultaneously formed in the piezoelectric layer 14. Then, as shown in FIG. 8(e) and FIG. 11(b), a conductive layer 33 having a concave shape is formed in contact with the side surface 42 of the piezoelectric layer 14 at the through-hole 24. As shown in FIGS. 9( a) and 11(c), the conductive layer 33 is processed so that the maximum angle θ3 (see FIGS. 3(b) and 10(b)) of the inclination angles of the side surfaces 44 of the concave shape relative to the bottom surface 46 of the concave shape of the conductive layer 33 is smaller than the angle θ2 (see FIGS. 3(b) and 10(b)) formed between the lower surface 15b of the piezoelectric layer 14 and the side surfaces 42 of the piezoelectric layer 14 at the through holes 24. As shown in FIGS. 9(c) and 11(d), after the conductive layer 33 is processed, a conductive layer 34 having a thermal expansion coefficient that is greater than the difference between the thermal expansion coefficients of the piezoelectric layer 14 and the conductive layer 33 is formed on and in contact with the conductive layer 33. This prevents the conductive layer 34 from peeling off from the conductive layer 33, and also prevents the conductive layer 33 from peeling off from the side surfaces 42 of the piezoelectric layer 14.

[0073] In addition, in Example 1 and its modified examples, the conductive layer 33 is processed using ion milling or reverse sputtering so that the angle θ3 is smaller than the angle θ2. This makes it easy to make the angle θ3 smaller than the angle θ2.

[0074] Furthermore, in Example 1 and its modified examples, the acoustic impedance of the conductive layer 33 is higher than the acoustic impedance of the conductive layer 34. In this way, by providing the conductive layer 33, which has a high acoustic impedance, in contact with the side surface 42 of the piezoelectric layer 14, the reflectance of the elastic wave increases, as shown in Table 1. Therefore, the elastic wave is more easily confined within the resonance region 50, and the elastic wave can be prevented from leaking out of the resonance region 50.

[0075] Furthermore, in Example 1 and its modified examples, the electrical resistivity of conductive layer 33 is smaller than the electrical resistivity of conductive layer 34. This makes it possible to suppress heat generation in conductive layer 33 even when conductive layer 33 is provided.

[0076] In Example 1 and its modified examples, the angle θ1 between the lower surface 15b of the piezoelectric layer 14 and the side surface 40 of the piezoelectric layer 14 at the through-hole 22, and the angle θ2 between the lower surface 15b of the piezoelectric layer 14 and the side surface 42 of the piezoelectric layer 14 at the through-hole 24 are 80° or more and 100° or less. The angle θ1 at the through-hole 22 being 80° or more and 100° or less can effectively suppress spurious emissions. The maximum inclination angle θ3 of the side surface 44 of the concave shape relative to the bottom surface 46 of the concave shape of the conductive layer 33 is 60° or less. This can effectively suppress peeling of the conductive layer 34 from the conductive layer 33. From the viewpoint of suppressing spurious emissions, the angle θ1 is preferably 82° or more and 98° or less, more preferably 85° or more and 95° or less, and even more preferably 88° or more and 92° or less. In order to prevent peeling of the conductive layer 34, the angle θ3 is preferably 55° or less, more preferably 50° or less, and even more preferably 45° or less. In order to prevent the device from becoming large, the angle θ3 is preferably 20° or more, more preferably 30° or more, and even more preferably 40° or more.

[0077] In Example 1 and its modified examples, the piezoelectric layer 14 is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, the conductive layer 33 is a titanium nitride layer or a nickel layer, and the conductive layer 34 is a titanium layer or a chromium layer. When using such materials, if the conductive layer 34 is provided in contact with the side surface 42 of the piezoelectric layer 14, as in the comparative example, peeling of the conductive layer 34 may occur. However, by providing the conductive layer 33 between the piezoelectric layer 14 and the conductive layer 34, peeling of the conductive layers 33 and 34 can be suppressed. Note that each layer may contain impurities of about several atomic percent as long as it is mainly composed of atoms of the above materials.

[0078] Furthermore, in the first embodiment and its modified example, the through holes 22 are provided on both sides of the resonance region 50 and are at the same distance from the resonance region 50. This makes it possible to effectively suppress spurious emissions.

[0079] Furthermore, in the first embodiment and its modified example, a conductive layer 35 having a lower electrical resistivity than the conductive layers 33 and 34 is provided on the conductive layer 34. This allows the electrical resistance of the terminal electrode 32a to be reduced. [Example]

[0080] 15(a) and 15(b) are cross-sectional views of an acoustic wave device 200 in accordance with Example 2. As shown in Fig. 15(a) and 15(b), the acoustic wave device 200 in accordance with Example 2 has a void 36 instead of the acoustic reflection film 31. The void 36 is provided continuous with the through-hole 22. The other configurations are the same as those in Example 1, and therefore description thereof will be omitted.

[0081] The acoustic wave device may be an SMR (Solidly Mounted Resonator) in which an acoustic reflection film 31 that reflects acoustic waves is provided below the lower electrode 12, as in Example 1 and its modified examples, or an FBAR (Film Bulk Acoustic Resonator) in which an air gap 36 is provided below the lower electrode 12, as in Example 2. [Example]

[0082] Fig. 16 is a plan view of a filter 300 according to a third embodiment. In Fig. 16, the lower electrode 12 is indicated by a dashed line, and the upper electrode 16 is indicated by a solid line. The resonance regions of the series resonators S1 to S5 and the parallel resonators P1 to P4 are hatched. As shown in Fig. 16, the filter 300 according to the third embodiment has one or more series resonators S1 to S5 and one or more parallel resonators P1 to P4 provided on a single piezoelectric layer 14.

[0083] The series resonators S1 to S5 are connected in series between the input terminal Tin and the output terminal Tout. The parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. One end of each of the parallel resonators P1 to P4 is connected to a path between the input terminal Tin and the output terminal Tout, and the other end is connected to ground terminals Tg1 and Tg2. At least one of the series resonators S1 to S5 and the parallel resonators P1 to P4 can be the piezoelectric thin film resonator of Example 1, the modified example of Example 1, or Example 2. The input terminal Tin and the ground terminal Tg1 correspond to the terminal electrode 32a, and the output terminal Tout and the ground terminal Tg2 correspond to the terminal electrode 32b. The number of resonators in the ladder filter can be set appropriately. [Example]

[0084] FIG. 17 is a circuit diagram of a duplexer 400 according to a fourth embodiment. As shown in FIG. 17, in the duplexer 400 according to the fourth embodiment, a transmit filter 70 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 70 passes signals in the transmit band, among signals input from the transmit terminal Tx, to the common terminal Ant as transmit signals and suppresses signals of other frequencies. The receive filter 72 passes signals in the receive band, among signals input from the common terminal Ant, to the receive terminal Rx as receive signals and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of the third embodiment. Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0085] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as defined in the claims. [Explanation of symbols]

[0086] 10 Substrate 12 Lower electrode 14 Piezoelectric layer 15a Upper surface of the piezoelectric layer 15b Lower surface of piezoelectric layer 16 Upper electrode 18a, 18b Additional membrane 20 Metal Film 22 Through hole 24 through holes 31 Acoustic reflective film 31a Low acoustic impedance membrane 31b High acoustic impedance membrane 32a, 32b terminal electrode 33, 34, 35 Conductive layer 36 void 40, 42 Side of the piezoelectric layer 44 Concave side 46 Concave bottom 50 resonance area 60, 62 Resist film 70 Transmission Filter 72 Receive Filter 100, 200, 500 Acoustic Wave Devices 300 filters 400 Duplexer

Claims

1. a bottom electrode and a top electrode; a piezoelectric layer having a partial region sandwiched between the lower electrode and the upper electrode, the piezoelectric layer having a first through-hole provided along a resonance region on a side of the resonance region, the first through-hole penetrating from a first surface on the upper electrode side to a second surface on the lower electrode side and having a void therein, and a second through-hole penetrating from the first surface on the lower electrode to the second surface; an elastic wave device comprising: a stacked conductive layer that is provided in the second through hole and electrically connected to the lower electrode, the stacked conductive layer including: a first conductive layer that is provided in contact with a side surface of the piezoelectric layer in the second through hole and has a concave shape; and a second conductive layer that is provided on the first conductive layer and in contact with the first conductive layer, wherein the absolute value of the difference in thermal expansion coefficients between the piezoelectric layer and the first conductive layer is smaller than the absolute value of the difference in thermal expansion coefficients between the piezoelectric layer and the second conductive layer, and a difference between a first angle formed by the second surface and the side surface of the piezoelectric layer in the second through hole and a second angle that is the maximum angle among the inclination angles of the side surface of the concave shape of the first conductive layer with respect to a bottom surface of the concave shape of the first conductive layer is larger than the difference between the first angle and a third angle formed by the second surface and the side surface of the piezoelectric layer in the first through hole.

2. The acoustic wave device of claim 1 , wherein the acoustic impedance of the first conductive layer is higher than the acoustic impedance of the second conductive layer.

3. The acoustic wave device according to claim 1 , wherein the first conductive layer has a lower electrical resistivity than the second conductive layer.

4. The acoustic wave device according to claim 1 , wherein the first angle and the third angle are equal to or greater than 80° and equal to or less than 100°, and the second angle is equal to or less than 60°.

5. 3. The acoustic wave device according to claim 1, wherein the piezoelectric layer is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer.

6. the first conductive layer is a titanium nitride layer or a nickel layer; 3. The acoustic wave device according to claim 1, wherein the second conductive layer is a titanium layer or a chromium layer.

7. The acoustic wave device according to claim 1 , wherein the first through holes are provided on both sides of the resonance region and are spaced the same distance from the resonance region.

8. The acoustic wave device according to claim 1 , wherein the first through hole is provided in a region where the lower electrode and the upper electrode are not present in a plan view.

9. The acoustic wave device according to claim 1 , wherein the laminated conductive layer includes a third conductive layer disposed on the second conductive layer and having an electrical resistivity lower than that of the first conductive layer and the second conductive layer.

10. a bottom electrode and a top electrode; a piezoelectric layer that is a single-crystal lithium niobate layer or a single-crystal lithium tantalate layer, a partial region of which is sandwiched between the lower electrode and the upper electrode, the piezoelectric layer having: a first through-hole that is provided along a resonance region on a side of the resonance region, the first through-hole penetrating from a first surface on the upper electrode side to a second surface on the lower electrode side, the first through-hole having a void therein; and a second through-hole that is on the lower electrode and penetrating from the first surface to the second surface; an elastic wave device comprising: a stacked conductive layer that is provided in the second through hole and electrically connected to the lower electrode, the stacked conductive layer including: a first conductive layer that is a titanium nitride layer or a nickel layer that is provided in contact with a side surface of the piezoelectric layer in the second through hole and has a concave shape; and a second conductive layer that is a titanium layer or a chromium layer that is provided on the first conductive layer and in contact with the first conductive layer, wherein a difference between a first angle formed by the second surface and the side surface of the piezoelectric layer in the second through hole and a second angle that is the maximum angle among the inclination angles of the side surface of the concave shape of the first conductive layer with respect to a bottom surface of the concave shape of the first conductive layer is greater than a difference between the first angle and a third angle formed by the second surface and the side surface of the piezoelectric layer in the first through hole.

11. A filter comprising the acoustic wave device according to claim 1 or 10.

12. A multiplexer including the filter of claim 11.

13. forming a piezoelectric layer on the bottom electrode; forming an upper electrode on the piezoelectric layer so as to sandwich a partial region of the piezoelectric layer between the upper electrode and the lower electrode; a step of simultaneously forming a first through-hole penetrating from a first surface of the piezoelectric layer on the upper electrode side to a second surface of the piezoelectric layer on the lower electrode side along the resonance region, the first through-hole being located to a side of the resonance region, which is the partial region, and a second through-hole penetrating from the first surface to the second surface on the lower electrode; forming a first conductive layer having a concave shape in contact with a side surface of the piezoelectric layer in the second through hole; processing the first conductive layer so that a maximum angle of inclination of a side surface of the concave shape of the first conductive layer relative to a bottom surface of the concave shape is smaller than an angle formed between the second surface of the piezoelectric layer and a side surface of the piezoelectric layer at the second through hole; and after processing the first conductive layer, forming a second conductive layer on and in contact with the first conductive layer, the second conductive layer having a thermal expansion coefficient that is greater than the difference in thermal expansion coefficient between the piezoelectric layer and the first conductive layer.

14. The method for manufacturing an acoustic wave device according to claim 13 , wherein the step of processing the first conductive layer processes the first conductive layer using an ion milling method or a reverse sputtering method.

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