JP2025103808A - Acoustic Wave Devices, Filters and Multiplexers - Google Patents

Abstract

To provide an elastic wave device that can be miniaturized.SOLUTION: An elastic wave device comprises a substrate 10, a lower electrode 12 provided on the substrate, a piezoelectric film 14 on the lower electrode, a first upper electrode 16a provided on the piezoelectric film to form a resonance region 50 where the lower electrode and the first upper electrode overlap across at least a portion of the piezoelectric film, viewed from the thickness direction of the piezoelectric film, an insulating film 20 provided on the lower electrode from the periphery 52 of the resonance region to an outer region 56 surrounding the resonance region, and a second upper electrode 16b provided in the outer region to form a region 58 where the lower electrode and the second upper electrode overlap by sandwiching at least a part of the insulating film without sandwiching the piezoelectric film, viewed from the thickness direction.SELECTED DRAWING: Figure 2

Description

The present invention relates to acoustic wave devices, filters and multiplexers.

Filters and multiplexers with piezoelectric thin film resonators are used in the high-frequency circuits of wireless terminals such as mobile phones. It is known to provide a capacitor connected in parallel to a piezoelectric thin film resonator on a substrate (for example, Patent Documents 1 and 2).

JP 2018-026735 A JP 2007-295025 A

By forming a piezoelectric thin-film resonator and a capacitor on a substrate, it is possible to reduce the number of manufacturing steps and make the device more compact than if the capacitor were provided as a separate component. However, even when forming a piezoelectric thin-film resonator and a capacitor on a substrate, there is still a demand for miniaturization.

The present invention was developed in consideration of the above problems, and aims to reduce the size.

The present invention is an acoustic wave device comprising: a substrate; a lower electrode provided on the substrate; a piezoelectric film provided on the lower electrode; a first upper electrode provided on the piezoelectric film so as to sandwich at least a portion of the piezoelectric film when viewed in the thickness direction of the piezoelectric film and form a resonance region where the lower electrode and a first upper electrode overlap; an insulating film provided on the lower electrode from the periphery of the resonance region to an external region surrounding the resonance region; and a second upper electrode provided in the external region so as to sandwich at least a portion of the insulating film without sandwiching the piezoelectric film when viewed in the thickness direction and form a region where the lower electrode and a second upper electrode overlap.

In the above configuration, the first upper electrode and the second upper electrode can be configured to be integrally provided.

In the above configuration, the overlapping region can be configured to be provided between the resonance region and an extraction region of the external region through which the lower electrode is extracted from the resonance region.

In the above configuration, the first upper electrode and the second upper electrode can be connected between the extraction region and the resonance region.

In the above configuration, the region where the first upper electrode and the second upper electrode are connected can be configured such that the overlapping region is provided in a portion of the region surrounding the resonance region, and is not provided in the remaining portion of the surrounding region.

In the above configuration, the first upper electrode and the second upper electrode may not be electrically connected.

In the above configuration, the overlapping region may be configured such that the lower electrode is provided in a portion of the region surrounding the resonance region, and is not provided in the remaining portion of the surrounding region.

In the above configuration, the insulating film may be provided between the lower electrode and the piezoelectric film in the resonance region.

In the above configuration, the insulating film may not be provided in the center of the resonance region, but may be provided to surround at least a portion of the center.

In the above configuration, a gap is provided between the substrate and the lower electrode, and the resonance region and the overlapping region can be configured to overlap the gap when viewed from the thickness direction.

The present invention is a filter including the above acoustic wave device.

The present invention is a multiplexer including the above filter.

The present invention allows for miniaturization.

FIG. 1 is a plan view of an acoustic wave device in accordance with a first embodiment. 2(a) to 2(c) are cross-sectional views taken along lines AA, BB, and CC in FIG. 1, respectively. 3A to 3C are cross-sectional views showing a method for manufacturing the piezoelectric thin film resonator according to the first embodiment. 4A to 4C are cross-sectional views showing a method for manufacturing the piezoelectric thin film resonator according to the first embodiment. FIG. 5 is a plan view of an acoustic wave device in accordance with a first modification of the first embodiment. 6(a) and 6(b) are cross-sectional views taken along lines AA and BB of FIG. 5, respectively. FIG. 7 is a plan view of an acoustic wave device in accordance with a second embodiment. 8(a) and 8(b) are cross-sectional views taken along lines AA and BB of FIG. 7, respectively. 9A to 9C are cross-sectional views showing a method for manufacturing a piezoelectric thin film resonator according to the second embodiment. FIG. 10 is a plan view of an acoustic wave device in accordance with a first modification of the second embodiment. 11(a) and 11(b) are cross-sectional views taken along lines AA and BB of FIG. 10, respectively. FIG. 12 is a plan view of an acoustic wave device in accordance with a second modification of the second embodiment. 13(a) and 13(b) are cross-sectional views taken along lines AA and BB in FIG. 12, respectively. FIG. 14A and FIG. 14B are cross-sectional views of acoustic wave devices according to a third embodiment and a first modified example thereof, respectively. 15A and 15B are circuit diagrams of a filter according to a fourth embodiment and a first modification thereof, respectively, and FIG. 15C is a circuit diagram of a duplexer according to a second modification of the fourth embodiment.

The following describes the examples with reference to the drawings.

Example 1 is an example in which a piezoelectric thin film resonator and a capacitor are connected in parallel as an acoustic wave device. FIG. 1 is a plan view of the acoustic wave device according to Example 1. FIGS. 2(a) to 2(c) are cross-sectional views taken along lines A-A, B-B, and C-C in FIG. 1, respectively. The thickness direction of the substrate 10 is the Z direction, the direction in which the lower electrode 12 is drawn out from the resonance region 50 is the X direction, and the direction perpendicular to the X direction within the planar direction of the substrate 10 is the Y direction.

As shown in Figs. 1 to 2(c), in the acoustic wave device 100 of the first embodiment, a lower electrode 12 is provided on a substrate 10 via a gap 30. The gap 30 has a dome-like shape. The center of the gap 30 is higher than the periphery. An insulating film 20 is provided on the lower electrode 12. A piezoelectric film 14 is provided on the lower electrode 12 and the insulating film 20. An upper electrode 16a is provided on the piezoelectric film 14. An upper electrode 16b is provided on the insulating film 20. An upper electrode 16c electrically connects the upper electrodes 16a and 16b. A protective film 24 is provided on the substrate 10 to cover the lower electrode 12, the insulating film 20, the piezoelectric film 14, and the upper electrodes 16a and 16b.

The resonance region 50 is defined by the region where the lower electrode 12 and the upper electrode 16a overlap, sandwiching at least a part of the piezoelectric film 14 when viewed from the Z direction. The capacitor region 58 is defined by the region where the lower electrode 12 and the upper electrode 16b overlap, sandwiching at least a part of the insulating film 20, but not sandwiching the piezoelectric film 14. The piezoelectric thin film resonator 70 includes the resonance region 50, and the capacitor 72 includes the capacitor region 58. Elastic waves such as thickness longitudinal vibration mode or thickness shear vibration resonate in the piezoelectric film 14 in the resonance region 50. The resonance region 50 has a central portion 54 and a peripheral portion 52 that surrounds the central portion 54 and includes the outer periphery of the resonance region 50. An external region 56 is provided to surround the resonance region 50. The insulating film 20 is provided in the peripheral portion 52 and the external region 56, but not in the central portion 54.

The region where the lower electrode 12 is drawn out from the resonance region 50 and the capacitor region 58 is the draw-out region 60. The region where the upper electrode 16a is drawn out from the resonance region 50 is the draw-out region 62. A metal layer 22a is provided on the lower electrode 12 in the draw-out region 60. A metal layer 22b is provided on the upper electrode 16a in the draw-out region 62. The metal layers 22a and 22b function as wiring or pads.

The capacitor region 58 is provided in a portion 65 of the external region 56 that surrounds the resonance region 50. The region 65 includes the area between the resonance region 50 and the extraction region 60. The upper electrodes 16a and 16b are electrically connected via the upper electrode 16c in a region 64 that is a portion of the region 65. The upper electrode 16c is provided on the side of the piezoelectric film 14.

The substrate 10 is an insulating substrate or a semiconductor substrate such as a silicon substrate, a sapphire substrate, a spinel substrate, an alumina substrate, a quartz substrate, a glass substrate, a ceramic substrate, or a GaAs substrate. The lower electrode 12 and the upper electrodes 16a to 16c are single layer films or laminated films mainly composed of, for example, ruthenium (Ru), chromium (Cr), aluminum (Al), titanium (Ti), copper (Cu), silver (Ag), gold (Au), molybdenum (Mo), tungsten (W), tantalum (Ta), platinum (Pt), rhodium (Rh), or iridium (Ir).

The piezoelectric film 14 is aluminum nitride (AlN), zinc oxide (ZnO), zirconium titanate (PZT), lead titanate (PbTiO ₃ ), lithium tantalate (TaLiO ₃ ), lithium niobate (NbLiO ₃ ), or quartz. The piezoelectric film 14 may be mainly composed of aluminum nitride, and may contain other elements to improve resonance characteristics or piezoelectricity. For example, the piezoelectricity of the piezoelectric film 14 is improved by using scandium (Sc), two elements of a group 2 element and a group 4 element, or two elements of a group 2 element and a group 5 element as an additive element. Therefore, the effective electromechanical coupling coefficient of the piezoelectric thin film resonator can be improved. The group 2 element is, for example, calcium (Ca), magnesium (Mg), strontium (Sr), or zinc (Zn). The group 4 element is, for example, titanium, zirconium (Zr), or hafnium (Hf). The Group 5 element is, for example, tantalum, niobium (Nb) or vanadium (V). Furthermore, the piezoelectric film 14 may be mainly composed of aluminum nitride and may also contain boron (B).

The insulating film 20 is an inorganic insulating film such as silicon oxide, silicon nitride, or aluminum oxide, which may or may not contain impurities such as fluorine. The Young's modulus of the insulating film 20 is smaller than that of the piezoelectric film 14, for example. The sign of the temperature coefficient of the elastic constant of the insulating film 20 is opposite to that of the temperature coefficient of the elastic constant of the piezoelectric film 14, for example. The metal layer 22a is a metal with low resistivity, such as gold or copper. The protective film 24 is an inorganic insulating film such as silicon oxide, silicon nitride, or aluminum oxide, for example.

In the case of a piezoelectric thin film resonator having a resonant frequency of 2 GHz, the lower electrode 12 is, for example, a chromium film with a thickness of 100 nm and a ruthenium film with a thickness of 250 nm from the substrate 10 side. The piezoelectric film 14 is, for example, aluminum nitride with a thickness of 11,000 nm. The upper electrodes 16a and 16b are, from the piezoelectric film 14 side, a ruthenium film with a thickness of 250 nm and a chromium film with a thickness of 50 nm. The insulating film 20 is a silicon oxide film with a thickness of 100 nm. The film thickness of each layer can be set appropriately to obtain the desired resonance characteristics.

[Production method of Example 1]
3(a) to 4(c) are cross-sectional views showing a method for manufacturing a piezoelectric thin film resonator according to the first embodiment. As shown in FIG. 3(a), a sacrificial layer 32 is formed on a substrate 10. The sacrificial layer 32 is, for example, magnesium oxide (MgO), zinc oxide (ZnO), germanium (Ge), silicon oxide (SiO ₂ ), or the like. The thickness of the sacrificial layer 32 is, for example, 10 nm to 100 nm. The sacrificial layer 32 is patterned into a desired shape. A lower electrode 12 is formed on the substrate 10 and the sacrificial layer 32. The lower electrode 12 is patterned into a desired shape.

As shown in FIG. 3(b), an insulating film 20 is formed on the substrate 10 and the lower electrode 12. The insulating film 20 is patterned into a desired shape. A piezoelectric film 14 is formed on the substrate 10, the lower electrode 12, and the insulating film 20. The insulating film 20 is patterned into a desired shape. The sacrificial layer 32, the lower electrode 12, the insulating film 20, and the piezoelectric film 14 are formed, for example, by sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition). The sacrificial layer 32, the lower electrode 12, the insulating film 20, and the piezoelectric film 14 are patterned, for example, by photolithography and etching.

As shown in FIG. 3(c), the upper electrode 16 is formed on the substrate 10, the lower electrode 12, the insulating film 20, and the piezoelectric film 14. The upper electrode 16 is formed on the entire surface of the substrate 10 by, for example, a sputtering method.

Figure 4(a) includes the B-B cross section of Figure 1, and Figure 4(b) shows the C-C cross section of Figure 1. As shown in Figures 4(a) and 4(b), the upper electrode 16 is patterned using, for example, photolithography and etching. As a result, an upper electrode 16a is formed on the piezoelectric film 14 in the resonance region 50, and an upper electrode 16b is formed on the insulating film 20 in the capacitor region 58. In Figure 4(a), the upper electrode 16c is left on the side of the piezoelectric film 14. In Figure 4(b), the upper electrode 16 is not left on the side of the piezoelectric film 14.

Figure 4(c) includes the cross section B-B of Figure 1. As shown in Figure 4(c), a protective film 24 is formed on the substrate 10, the lower electrode 12, the insulating film 20, the piezoelectric film 14, and the upper electrode 16. The protective film 24 is formed, for example, by using a CVD method. A part of the protective film 24 on the lower electrode 12 and a part on the upper electrode 16a are removed to form an opening. The opening in the protective film 24 is formed, for example, by using a photolithography method and an etching method. Metal layers 22a and 22b are formed on the lower electrode 12 and the upper electrode 16a, and are in electrical contact with the lower electrode 12 and the upper electrode 16a through the opening in the protective film 24.

Then, the sacrificial layer 32 is removed using a medium (etchant) that etches the sacrificial layer 32. When the sacrificial layer 32 is removed, a gap 30 is formed between the lower electrode 12 and the substrate 10. The gap 30 has a dome shape. In this manner, the acoustic wave device 100 shown in Figures 1 to 2(c) is manufactured.

According to the first embodiment, the insulating film 20 is provided on the lower electrode 12 from the peripheral portion 52 of the resonance region 50 to the external region 56 outside the resonance region 50. The resonance region 50 is a region where the lower electrode 12 and the upper electrode 16a (first upper electrode) overlap, sandwiching at least a portion of the piezoelectric film 14, as viewed from the Z direction. The capacitor region 58 (overlapping region) is a region in the external region 56 where the lower electrode 12 and the upper electrode 16b (second upper electrode) overlap, sandwiching at least a portion of the insulating film 20, without sandwiching the piezoelectric film 14, as viewed from the Z direction.

In this way, the insulating film 20 provided in the resonance region 50 of the piezoelectric thin film resonator 70 is extended to the outer region 56, and the upper electrode 16a is formed on the insulating film 20 to form the capacitor 72. This allows the piezoelectric thin film resonator 70 and the capacitor 72, which are electrically connected via the lower electrode 12, to be formed in close proximity. This allows the acoustic wave device 100 to be miniaturized. In addition, the insulating film 20 used in the piezoelectric thin film resonator 70 is used as the dielectric layer of the capacitor 72. This eliminates the need to form a separate dielectric layer for the capacitor 72, reducing the number of manufacturing steps.

The upper electrodes 16a and 16b are provided as a continuous, integrated unit via the upper electrode 16c. This electrically connects the upper electrodes 16a and 16b. Therefore, the capacitor 72 can be connected in parallel to the piezoelectric thin film resonator 70 between the metal layers 22a and 22b.

The capacitor region 58 is provided in the external region 56 between the extension region 60 and the resonance region 50. This reduces the electrical resistance between the capacitor 72 and the lower electrode 12 of the extension region 60.

When the capacitor region 58 is provided so as to surround the resonance region 50, the elastic waves of the piezoelectric film 14 leak through the upper electrode 16b of the capacitor region 58. This reduces the Q value of the piezoelectric thin film resonator 70 and increases the loss. Therefore, it is preferable that the capacitor region 58 is provided in a portion 65 of the region where the lower electrode 12 surrounds the resonance region 50, and is not provided in the remaining region 66 of the surrounding region. The length of the region 65 is preferably 80% or less of the length of the region where the lower electrode 12 surrounds the resonance region 50, and more preferably 50% or less.

The upper electrodes 16a and 16b are connected between the lead-out region 60 and the resonance region 50. This reduces the electrical resistance between the capacitor 72 and the piezoelectric thin film resonator 70.

If an upper electrode 16c is provided on the side of the piezoelectric film 14, the elastic waves of the piezoelectric film 14 leak through the upper electrode 16c. This reduces the Q value of the piezoelectric thin film resonator 70 and increases the loss. Therefore, it is preferable that the region 64 where the upper electrodes 16a and 16b are connected is provided in a part of the region 65 that surrounds the resonance region 50 of the capacitor region 58, and is not provided in the remaining part of the surrounding region 65. The length of region 64 is preferably 80% or less of the length of region 65, and more preferably 50% or less.

The insulating film 20 may be provided on the lower electrode 12. For example, the piezoelectric film 14 may have two stacked piezoelectric films, and the insulating film 20 may be provided between the two piezoelectric films in the resonance region 50. In the resonance region 50, the insulating film 20 may be provided between the piezoelectric film 14 and the upper electrode 16a. If the insulating film 20 covers at least a portion of the side surface of the piezoelectric film 14, elastic waves are likely to leak from the resonance region 50 through the insulating film 20. Therefore, as in Example 1, in the resonance region 50, it is preferable that the insulating film 20 is provided between the lower electrode 12 and the piezoelectric film 14.

The insulating film 20 may be provided in at least a portion of the resonance region 50. In the first embodiment, the insulating film 20 is not provided in the central portion 54 of the resonance region 50, but is provided so as to surround at least a portion of the central portion 54. This makes it possible to suppress leakage of elastic waves outside the resonance region 50, thereby suppressing losses.

The Young's modulus of the insulating film 20 is lower than that of the piezoelectric film 14. This can further prevent the elastic wave from leaking outside the resonance region 50, thereby further reducing loss. For example, the piezoelectric film 14 is mainly composed of aluminum nitride, and the insulating film 20 is mainly composed of silicon oxide. This can make the Young's modulus of the insulating film 20 lower than that of the piezoelectric film 14.

When the insulating film 20 is used as a temperature compensation film, the sign of the temperature coefficient of the elastic constant of the insulating film 20 is made opposite to the sign of the temperature coefficient of the elastic constant of the piezoelectric film 14. The insulating film 20 is also provided in the central portion 54. This makes it possible to reduce the frequency temperature coefficient of the piezoelectric thin film resonator 70. For example, the piezoelectric film 14 is mainly composed of aluminum nitride, and the insulating film 20 is mainly composed of silicon oxide. This makes it possible to make the signs of the temperature coefficients of the elastic constant of the insulating film 20 and the piezoelectric film 14 opposite.

A gap 30 is provided between the substrate 10 and the lower electrode 12, and the resonance region 50 and the capacitor region 58 overlap the gap 30. This allows the acoustic wave device to be miniaturized.

[Modification 1 of Example 1]
Fig. 5 is a plan view of an acoustic wave device in accordance with a first modified example of the first embodiment, Fig. 6(a) and Fig. 6(b) are cross-sectional views taken along lines AA and BB in Fig. 5, respectively.

As shown in Figures 5 to 6(b), in the acoustic wave device 102 of the first modified example of the first embodiment, the capacitor region 58 is provided in the entire region 65 of the region where the lower electrode 12 surrounds the resonance region 50. The region 64 where the upper electrodes 16a and 16b are connected is provided in the entire region 65 of the capacitor region 58 surrounding the resonance region 50. The other configurations are the same as those of the first embodiment, and the description will be omitted.

In the first variation of the first embodiment, although there is a large leakage of elastic waves from the resonance region 50, the area of the capacitor region 58 can be increased, so the capacitance of the capacitor 72 can be increased.

The second embodiment is an example of an acoustic wave device in which a piezoelectric thin film resonator and a capacitor are connected in series. FIG. 7 is a plan view of the acoustic wave device according to the second embodiment. FIG. 8(a) and FIG. 8(b) are cross-sectional views taken along lines A-A and B-B of FIG. 7, respectively.

As shown in Figures 7 to 8(b), in the acoustic wave device 104 of Example 2, the upper electrodes 16a and 16b are not electrically connected. The metal layer 22a is not provided on the lower electrode 12, and the upper electrode 16b is provided in the extension region 60. The metal layer 22a is provided on the upper electrode 16b in the extension region 60. In the region where the lower electrode 12 surrounds the resonance region 50, the insulating film 20 is provided up to the outside of the lower electrode 12. The upper electrode 16b is provided outside the lower electrode 12. The lower electrode 12 and the upper electrode 16b are not electrically connected.

The capacitor region 58 is provided in the external region 56 between the resonance region 50 and the extraction region 60. In the region 65 where the capacitor region 58 is provided among the regions where the lower electrode 12 surrounds the resonance region 50, the upper electrode 16b is provided from the outside of the insulating film 20 to the insulating film 20 in the region where the lower electrode 12 is provided. In the capacitor region 58, the lower electrode 12 and the upper electrode 16b overlap with the insulating film 20 sandwiched between them. In the region 66 other than the region 65 where the lower electrode 12 surrounds the resonance region 50, the upper electrode 16b is provided up to the insulating film 20 in the region where the lower electrode 12 is not provided, and is not provided on the insulating film 20 in the region where the lower electrode 12 is provided. As a result, the capacitor region 58 is not formed in the region 66. The other configurations are the same as those in the first embodiment, and will not be described.

[Production method of Example 2]
9(a) to 9(c) are cross-sectional views showing a method for manufacturing a piezoelectric thin-film resonator according to Example 2. Fig. 9(a) and Fig. 9(b) are cross-sectional views including a cross section A-A in Fig. 7, and Fig. 9(c) is a cross-sectional view including a cross section B-B in Fig. 7.

As shown in FIG. 9(a), the upper electrode 16 is formed in the same manner as in FIG. 3(a) to FIG. 3(c) of the first embodiment. As shown in FIG. 9(b) and FIG. 9(c), the upper electrode 16 is patterned, for example, by photolithography and etching. As a result, the upper electrode 16a is formed on the piezoelectric film 14 in the resonance region 50, and the upper electrode 16b is formed on the insulating film 20 in the capacitor region 58. In FIG. 9(b), the upper electrode 16b is formed on the insulating film 20 on the lower electrode 12. In FIG. 9(c), the upper electrode 16b is not formed on the insulating film 20 on the lower electrode 12. Thereafter, the steps from FIG. 4(c) onward in the first embodiment are performed to manufacture the acoustic wave device according to the second embodiment.

In the second embodiment, the upper electrodes 16a and 16b are not electrically connected. This allows the capacitor 72 to be connected in series with the piezoelectric thin film resonator 70 between the metal layers 22a and 22b.

The capacitor region 58 is provided in a portion 65 of the region in which the lower electrode 12 surrounds the resonance region 50, and is not provided in the remaining region 66. This prevents the elastic waves of the piezoelectric film 14 from leaking through the upper electrode 16b of the capacitor region 58, thereby suppressing losses in the piezoelectric thin film resonator 70.

In region 66, the insulating film 20 and the upper electrode 16b are overlapped on the outside of the lower electrode 12. This allows the piezoelectric thin film resonator 70 and the capacitor 72 to be supported above the gap 30.

[Modification 1 of Example 2]
Fig. 10 is a plan view of an acoustic wave device in accordance with a first modified example of the second embodiment, Fig. 11A and Fig. 11B are cross-sectional views taken along lines AA and BB in Fig. 10, respectively.

As shown in Figs. 10 to 11(b), in the acoustic wave device 106 of the first modified example of the second embodiment, the capacitor region 58 is provided in the entire region 65 of the region in which the lower electrode 12 surrounds the resonance region 50. The rest of the configuration is the same as in the second embodiment, and the description is omitted.

In the first modification of the second embodiment, although there is a large leakage of the elastic wave from the resonance region 50, the area of the capacitor region 58 can be increased, so that the capacitance of the capacitor 72 can be increased.

[Modification 2 of Example 2]
Fig. 12 is a plan view of an acoustic wave device in accordance with a second modification of the second embodiment, Fig. 13A and Fig. 13B are cross-sectional views taken along lines AA and BB in Fig. 12, respectively.

As shown in Figs. 12 to 13(b), in an acoustic wave device 108 according to the second modification of the second embodiment, the insulating film 20 is formed to be larger than the gap 30. As shown in Fig. 13(b), in a region 56 where a capacitor region 58 is not provided, the upper electrode 16b is not provided on the gap 30. The other configurations are the same as those of the second embodiment, and therefore will not be described.

In the region 66 of the second modified example of the second embodiment, the piezoelectric thin film resonator 70 and the capacitor 72 can be supported above the gap 30 by the insulating film 20 on the outside of the lower electrode 12.

Example 3 and its modified example 1 are examples in which the configuration of the void is changed. FIG. 14(a) is a cross-sectional view of an acoustic wave device according to Example 3. As shown in FIG. 14(a), in the acoustic wave device 110 of Example 3, a recess is formed on the upper surface of the substrate 10. The lower electrode 12 is formed flat on the substrate 10. As a result, the void 30 is formed in the recess of the substrate 10. In a plan view, the void 30 is formed to include the resonance region 50 and the capacitor region 58. The other configurations are the same as those of Example 1, and a description thereof will be omitted. The void 30 may be formed to penetrate the substrate 10.

[Modification 1 of Example 3]
14B is a cross-sectional view of an acoustic wave device according to the first modification of the third embodiment. As shown in FIG. 14B, in an acoustic wave device 112 according to the first modification of the third embodiment, an acoustic reflection film 31 is formed under a lower electrode 12 in a resonance region 50. The acoustic reflection film 31 is formed by alternately providing a film 31a having a low acoustic impedance and a film 31b having a high acoustic impedance. The film thicknesses of the films 31a and 31b are, for example, approximately λ/4 (λ is the wavelength of the acoustic wave). The number of layers of the films 31a and 31b can be set arbitrarily. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

In Examples 1 and 2 and their modified examples, a gap 30 may be formed similarly to Example 3, or an acoustic reflection film 31 may be formed instead of the gap 30 similarly to Modification 1 of Example 3.

Although an elliptical shape has been described as an example of the planar shape of the resonance region 50, the planar shape of the resonance region 50 may be any shape, such as a polygonal shape such as a square or a pentagon.

Example 4 is an example of a filter and a duplexer using the acoustic wave devices of Examples 1 to 3 and their modified examples. FIG. 15(a) is a circuit diagram of a filter according to Example 4. As shown in FIG. 15(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P4 are connected in parallel between the input terminal Tin and the output terminal Tout. One end of the parallel resonators P1 to P4 is electrically connected to the ground terminal Tgnd. A capacitor C1 is connected in parallel to the series resonator S1. The series resonator S1 and the capacitor C1 are the acoustic wave devices according to Examples 1, 3 and their modified examples. By connecting the capacitor C1 in parallel to the series resonator S1, the electromechanical coupling coefficient of the series resonator S1 can be reduced. This allows the skirt characteristics on the high frequency side of the pass band to be steep.

[Modification 1 of Example 4]
Fig. 15(b) is a circuit diagram of a filter according to a first modification of the fourth embodiment. As shown in Fig. 15(b), a capacitor C2 is connected in series to a series resonator S1. The series resonator S1 and the capacitor C2 are acoustic wave devices according to the second embodiment and its modification. By providing the capacitor C2, it is possible to improve the attenuation characteristics in a band lower than the pass band. The other configurations are the same as those of the fourth embodiment, and therefore description thereof will be omitted.

In the fourth embodiment and its first modified example, a capacitor can be connected in parallel or series to at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P4. The number of resonators in the ladder filter can be set as appropriate.

[Modification 2 of Example 4]
FIG. 15C is a circuit diagram of a duplexer according to a second modification of the fourth embodiment. As shown in FIG. 15C, a transmission filter 40 is connected between a common terminal Ant and a transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 40 passes a signal in a transmission band among signals input from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in a reception band among signals input from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals of other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the fourth embodiment and its first modification.

Although a duplexer has been used as an example of a multiplexer, a triplexer or quadplexer may also be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 10 Substrate 12 Lower electrode 14 Piezoelectric film 16 Upper electrode 20 Insulating film 22a, 22b Metal layer 30 Gap 31 Acoustic reflection film 40 Transmitting filter 42 Receiving filter 50 Resonating region 52 Periphery 54 Central portion 56 Outer region 58 Region 60, 62 Lead-out region 64, 65, 66 Region

Claims (12)

A substrate;
a lower electrode provided on the substrate;
a piezoelectric film provided on the lower electrode;
a first upper electrode provided on the piezoelectric film so as to sandwich at least a portion of the piezoelectric film when viewed in a thickness direction of the piezoelectric film, and to form a resonance region where the lower electrode and the first upper electrode overlap;
an insulating film provided on the lower electrode from a periphery of the resonance region to an outer region surrounding the resonance region;
a second upper electrode provided in the external region so as to sandwich at least a portion of the insulating film without sandwiching the piezoelectric film when viewed in the thickness direction, forming a region where the lower electrode and a second upper electrode overlap;
1. An acoustic wave device comprising: The acoustic wave device according to claim 1, wherein the first upper electrode and the second upper electrode are integrally formed. The acoustic wave device according to claim 2, wherein the overlapping region is provided between the resonance region and an extraction region of the external region through which the lower electrode is extracted from the resonance region. The acoustic wave device according to claim 3, wherein the first upper electrode and the second upper electrode are connected between the extraction region and the resonance region. The acoustic wave device according to any one of claims 2 to 4, wherein the region where the first upper electrode and the second upper electrode are connected is provided in a part of the region surrounding the resonance region, and is not provided in the remaining part of the surrounding region. The acoustic wave device of claim 1, wherein the first upper electrode and the second upper electrode are not electrically connected. The acoustic wave device according to claim 6, wherein the overlapping region is provided in a portion of the region surrounding the resonance region, and is not provided in the remaining portion of the surrounding region. The acoustic wave device according to any one of claims 1 to 4, 6 and 7, wherein in the resonance region, the insulating film is provided between the lower electrode and the piezoelectric film. The acoustic wave device according to any one of claims 1 to 4, 6 and 7, wherein the insulating film is not provided in the center of the resonance region, but is provided so as to surround at least a portion of the center. The acoustic wave device according to any one of claims 1 to 4, 6 and 7, wherein a gap is provided between the substrate and the lower electrode, and the resonance region and the overlapping region overlap the gap when viewed in the thickness direction. A filter including an acoustic wave device according to any one of claims 1 to 4, 6 and 7. A multiplexer including the filter according to claim 11.

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