Acoustic Wave Resonators, Filters, and Multiplexers

Abstract

To provide an acoustic wave resonator capable of suppressing a spurious.SOLUTION: An acoustic wave resonator 100 comprises: a piezoelectric substrate 10; a pair of comb type electrodes 22 which are provided on the piezoelectric substrate 10 and include a plurality of electrode fingers 23, a plurality of dummy electrode fingers 24, and a bus bar 25 to which the electrode fingers 23 and the dummy electrode fingers 24 are connected, in which a first tip end of each electrode finger 23 and a second tip of each dummy electrode finger 24 face each other, the dummy electrode finger 24 has a part 27a positioned on a second tip end side and a part 27b positioned at the side opposite to the second tip end from the part 27a, and the part 27a is narrower in width than the part 27b; and an insulation film 40 which is provided on the piezoelectric substrate 10 from an edge region 32 in a cross region 30 to a region 34a where the part 27a of the dummy electrode finger 24 of a dummy region 34 is positioned, and which is not provided in a center region 31 in the cross region 30 and a region 34b where the part 27b of the dummy electrode finger 24 of the dummy region 34 is positioned.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave resonator, a filter, and a multiplexer. [Background technology]

[0002] In high-frequency communication systems, such as mobile phones, high-frequency filters are used to remove unwanted signals outside the frequency band used for communication. High-frequency filters use acoustic wave resonators. A known acoustic wave resonator is one that includes a pair of interdigital transducers, each of which includes multiple electrode fingers, multiple dummy electrode fingers, and a bus bar connecting the multiple electrode fingers and the multiple dummy electrode fingers. Furthermore, an acoustic wave resonator using a piston mode is known as a method for reducing spurious signals without impairing the Q value (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-89069 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-178387 [Patent Document 3] Special Publication No. 2013-518455 Summary of the Invention [Problem to be solved by the invention]

[0004] The piston mode can be realized by providing an insulating film in an edge region located at the edge in the extension direction of the electrode fingers of a pair of interdigital transducers. However, with the recent trend toward higher frequencies, the edge region where the insulating film is provided has become shorter. As a result, the insulating film may be formed from the edge region to a dummy region where the dummy electrode fingers are located. In this case, the spurious suppression effect may be reduced.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress spurious signals. [Means for solving the problem]

[0006] The present invention provides an elastic wave resonator comprising: a pair of comb-shaped electrodes provided on the piezoelectric substrate, each of which includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected, wherein first tips of the plurality of electrode fingers and second tips of the plurality of dummy electrode fingers face each other, and the plurality of dummy electrode fingers have a first portion located on the second tip side and a second portion located on the opposite side of the first portion from the second tip, and the first portion has a narrower width in the short direction than the second portion; and an insulating film provided on the piezoelectric substrate from an edge region, which is a region in an intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect, to a first region, which is a region in a dummy region where the plurality of dummy electrode fingers are located, and which is a region in which the first portions of the plurality of dummy electrode fingers are located,

[0007] The present invention provides an elastic wave resonator comprising: a pair of comb electrodes provided on the piezoelectric substrate, each of which includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, wherein first tips of the plurality of electrode fingers and second tips of the plurality of dummy electrode fingers face each other, and the plurality of dummy electrode fingers have a first portion located on the second tip side and a second portion located on the opposite side of the first portion from the second tip, and the first portion is thinner than the second portion; and an insulating film provided on the piezoelectric substrate from an edge region, which is a region in an intersection region where the plurality of electrode fingers of the pair of comb electrodes intersect, to a first region, which is a region in a dummy region where the plurality of dummy electrode fingers are located, and which is a region in which the first portions of the plurality of dummy electrode fingers are located,

[0008] The present invention provides an elastic wave resonator comprising: a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each of which includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, wherein first tips of the plurality of electrode fingers face second tips of the plurality of dummy electrode fingers, and wherein the acoustic velocity of an elastic wave propagating through a first region located on the side of an intersection region where the plurality of electrode fingers intersect in a dummy region where the plurality of dummy electrode fingers are located is the same as the acoustic velocity of an elastic wave propagating through a second region of the dummy region located on the opposite side of the intersection region from the first region; and an insulating film provided on the piezoelectric substrate from an edge region located on an edge of the plurality of electrode fingers in a longitudinal direction in the intersection region to the first region of the dummy region, and which is not provided in a central region located inside the edge region in the intersection region, or in the second region of the dummy region.

[0009] The present invention provides an elastic wave resonator comprising: a piezoelectric substrate; a pair of comb electrodes provided on the piezoelectric substrate, each including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, with first tips of the plurality of electrode fingers facing second tips of the plurality of dummy electrode fingers; and an insulating film provided on the piezoelectric substrate from an edge region, which is a region where the plurality of electrode fingers of the pair of comb electrodes intersect, and which is located at an edge in a longitudinal direction of the plurality of electrode fingers in an intersection region, where the plurality of electrode fingers of the pair of comb electrodes intersect, to a first region, which is a region where the plurality of dummy electrode fingers are located, and which is located on the intersection region side, the length in the longitudinal direction in the first region differing in an arrangement direction of the plurality of electrode fingers, and which is not provided in a central region, which is a region of the intersection region located more inward than the edge region, or in a second region of the dummy region located on the opposite side of the intersection region from the first region.

[0010] In the above configuration, the insulating film may be provided on the piezoelectric substrate from the edge region to the boundary between the first region and the second region in the dummy region.

[0011] In the above configuration, the acoustic velocity of the elastic wave propagating through the first region of the dummy region may be the same as the acoustic velocity of the elastic wave propagating through the second region of the dummy region.

[0012] In the above configuration, the acoustic velocity of the elastic wave propagating through the first region of the dummy region, the acoustic velocity of the elastic wave propagating through the second region of the dummy region, and the acoustic velocity of the elastic wave propagating through the central region of the intersection region can be the same.

[0013] In the above configuration, the length of the gap region, which is the region located between the tips of the electrode fingers and the tips of the dummy electrode fingers, in the longitudinal direction of the electrode fingers can be configured to be less than or equal to twice the average pitch of the electrode fingers of the pair of comb electrodes.

[0014] The present invention is a filter including the acoustic wave resonator described above.

[0015] The present invention is a multiplexer including the filter described above. [Effects of the Invention]

[0016] According to the present invention, spurious signals can be suppressed. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave resonator in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Figure 2] 2(a) and 2(b) are diagrams showing the acoustic velocity of elastic waves in Example 1. FIG. [Figure 3] FIG. 3(a) is a plan view of an acoustic wave resonator according to a comparative example, and FIG. 3(b) is a cross-sectional view taken along line AA of FIG. 3(a). [Figure 4] 4(a) and 4(b) are diagrams showing the acoustic velocity of elastic waves in the comparative example. [Figure 5] FIG. 5(a) shows the simulation results of the absolute value |Y| of admittance versus frequency for the acoustic wave resonators according to Example 1 and the comparative example, and FIG. 5(b) shows the simulation results of the real part Real(Y) of admittance versus frequency. [Figure 6] FIG. 6(a) shows experimental results of the absolute value |Y| of admittance versus frequency for the acoustic wave resonators according to Example 1 and the comparative example, and FIG. 6(b) shows experimental results of the real part Real(Y) of admittance versus frequency. [Figure 7] FIG. 7(a) is a plan view of an acoustic wave resonator according to a first modification of the first embodiment, and FIG. 7(b) is a cross-sectional view taken along line AA of FIG. 7(a). [Figure 8] FIG. 8(a) is a plan view of an acoustic wave resonator according to a second modification of the first embodiment, and FIG. 8(b) is a cross-sectional view taken along the line AA of FIG. 8(a). [Figure 9]FIG. 9(a) is a plan view of an acoustic wave resonator in accordance with a second embodiment, and FIG. 9(b) is a cross-sectional view taken along line AA of FIG. 9(a). [Figure 10] 10(a) and 10(b) are diagrams showing the acoustic velocity of the elastic wave in Example 2. FIG. [Figure 11] FIG. 11(a) is a plan view of an acoustic wave resonator in accordance with Example 3, and FIG. 11(b) is a cross-sectional view taken along line AA of FIG. 11(a). [Figure 12] 12(a) and 12(b) are diagrams showing the acoustic velocity of the elastic wave in Example 3. FIG. [Figure 13] 13(a) to 13(d) are cross-sectional views of the samples used in the simulation. [Figure 14] FIG. 14 is a circuit diagram of a filter according to a fourth embodiment. [Figure 15] FIG. 15 is a circuit diagram of a duplexer according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0019] 1(a) is a plan view of an acoustic wave resonator 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). The arrangement direction of electrode fingers 23 is defined as the X direction, the longitudinal direction of electrode fingers 23 as the Y direction, and the thickness direction of piezoelectric substrate 10 as the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X axis direction and Y axis direction of the crystal orientation of piezoelectric substrate 10. When piezoelectric substrate 10 is a rotated Y-cut X-propagation piezoelectric substrate, the X direction corresponds to the X axis direction of the crystal orientation.

[0020] 1(a) and 1(b), acoustic wave resonator 100 includes an interdigital transducer (IDT) 20 and a reflector 21 provided on a piezoelectric substrate 10. IDT 20 and reflector 21 are formed of a metal film 26 on piezoelectric substrate 10.

[0021] The IDT 20 includes a pair of comb electrodes 22. The comb electrode 22 includes a plurality of electrode fingers 23, a plurality of dummy electrode fingers 24, and a bus bar 25 to which the plurality of electrode fingers 23 and the plurality of dummy electrode fingers 24 are connected. The thickness of the electrode fingers 23 and the thickness of the dummy electrode fingers 24 are the same. The "same thickness" allows for a difference of about the manufacturing error, for example, 0.95 times or more and 1.05 times or less. Tips 23a of the plurality of electrode fingers 23 of one comb electrode 22 face tips 24a of the plurality of dummy electrode fingers 24 of the other comb electrode 22. The region where the electrode fingers 23 of the pair of comb electrodes 22 intersect is an intersection region 30. The length of the intersection region 30 in the Y direction is the aperture length. The pair of comb electrodes 22 face each other such that the electrode fingers 23 are substantially staggered in at least a portion of the intersection region 30. The main mode acoustic waves (surface acoustic waves) excited by the electrode fingers 23 in the intersection region 30 propagate mainly in the X direction. The pitch of the electrode fingers 23 of one of the interdigital transducers 22 is approximately equal to the wavelength λ of the surface acoustic waves. The pitch D of the electrode fingers 23 is approximately twice the pitch of the electrode fingers 23 of one of the interdigital transducers 22. The reflector 21 reflects the surface acoustic waves excited by the electrode fingers 23 of the IDT 20. As a result, the surface acoustic waves are confined within the intersection region 30 of the IDT 20.

[0022] Intersection region 30 has edge region 32, which is a region located at the edge in the Y direction, and central region 31, which is a region located more inward than edge region 32 in the Y direction. Edge region 32 can also be said to be the region of intersection region 30 where the tips of electrode fingers 23 are located. Gap region 33 is the region located between the tips of electrode fingers 23 of one comb electrode 22 and the tips of dummy electrode fingers 24 of the other comb electrode 22. Dummy region 34 is the region where dummy electrode fingers 24 are located. Busbar region 35 is the region where busbar 25 is located. The region of dummy region 34 located on the gap region 33 side is region 34a, and the region on the busbar region 35 side is region 34b.

[0023] Dummy electrode finger 24 has portion 27a located on the tip 24a side in region 34a, and portion 27b located on the opposite side of portion 27a from tip 24a in region 34b. In dummy electrode finger 24, width W1 of portion 27a in the X direction is narrower than width W2 of portion 27b in the X direction. Width W2 of portion 27b is, for example, the same as the width of electrode finger 23 in the X direction. The term "same width" allows for a difference equivalent to a manufacturing error, and is, for example, 0.95 to 1.05 times the width W2 of portion 27a. Width W1 of portion 27a is, for example, 0.8 times or less, or may be 0.7 times or less, or 0.6 times or less, of width W2 of portion 27b. In dummy electrode finger 24, length L1 of portion 27a in the Y direction is longer than length L2 of portion 27b in the Y direction, but may be the same or shorter.

[0024] An insulating film 40 is provided on the piezoelectric substrate 10, extending from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34. The insulating film 40 covers the electrode fingers 23 located in the edge region 32 and the gap region 33, and the electrode fingers 23 and dummy electrode fingers 24 located in the region 34a of the dummy region 34. The insulating film 40 is also provided in portions of the edge region 32, the gap region 33, and the region 34a of the dummy region 34 where the electrode fingers 23 and the dummy electrode fingers 24 are not provided. The insulating film 40 is not provided in the central region 31, the region 34b of the dummy region 34, or the busbar region 35.

[0025] The piezoelectric substrate 10 is, for example, a single-crystal lithium tantalate (LiTaO) substrate or a single-crystal lithium niobate (LiNbO) substrate, such as a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut X-propagation lithium niobate substrate. As an example, the piezoelectric substrate 10 is a 36° to 48° Y-cut X-propagation lithium tantalate substrate.

[0026] The metal film 26 is a film whose main component is, for example, aluminum (Al), copper (Cu), molybdenum (Mo), iridium (Ir), platinum (Pt), rhenium (Re), rhodium (Rh), ruthenium (Ru), tantalum (Ta), or tungsten (W). An adhesive film such as a titanium (Ti) film or a chromium (Cr) film may be provided between the electrode fingers 23, dummy electrode fingers 24, and bus bars 25 and the piezoelectric substrate 10. The adhesive film is thinner than the electrode fingers 23, dummy electrode fingers 24, and bus bars 25. An insulating film may be provided to cover the electrode fingers 23 and dummy electrode fingers 24. In this case, the insulating film 40 may be provided on the insulating film. The insulating film may function as a protective film.

[0027] The insulating film 40 is a film whose main component is, for example, silicon oxide (SiO2), tantalum oxide (Ta2O5), or niobium oxide (Nb2O5), but may be a film whose main component is another material as long as it is possible to adjust the acoustic velocity of the elastic waves propagating through the edge region 32, the gap region 33, and the region 34a of the dummy region 34.

[0028] Here, for a film to have a certain element as its main component, it is acceptable for the film to contain intentional or unintentional impurities other than the main component. When a certain element is the main component of a film, the concentration of the element is, for example, 50 atomic % or more, for example, 80 atomic % or more. When two elements are the main components, such as silicon oxide, the sum of the silicon concentration and the oxygen concentration is, for example, 50 atomic % or more, for example, 80 atomic % or more, and the silicon concentration and the oxygen concentration are each, for example, 10 atomic % or more.

[0029] 2(a) and 2(b) are diagrams showing the acoustic velocity of an acoustic wave in Example 1. Fig. 2(a) shows the state before the insulating film 40 is provided, and Fig. 2(b) shows the state after the insulating film 40 is provided. As shown in Fig. 2(a), in the dummy electrode finger 24, the width W1 of the portion 27a is narrower than the width W2 of the portion 27b, and therefore the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is faster than the acoustic velocity of the surface acoustic wave propagating through the region 34b.

[0030] 2(b), by providing the insulating film 40 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic waves propagating through the edge region 32, the gap region 33, and the region 34a of the dummy region 34 becomes slower than before the insulating film 40 is provided. As a result, the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 approaches, and preferably becomes the same as, the acoustic velocity of the surface acoustic waves propagating through the region 34b. In this way, after the insulating film 40 is provided, the width W1 of the portion 27a of the dummy electrode finger 24 is narrowed so that the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 approaches, and preferably becomes the same as, the acoustic velocity of the surface acoustic waves propagating through the region 34b.

[0031] By making the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 closer to that of the surface acoustic waves propagating through the region 34b, the difference between the acoustic velocity of the surface acoustic waves propagating through the regions 34a and 34b of the dummy region 34 and the acoustic velocity of the surface acoustic waves propagating through the central region 31 can be reduced, preferably made equal. Furthermore, by providing the insulating film 40, the acoustic velocity of the surface acoustic waves propagating through the edge region 32 becomes slower than that of the surface acoustic waves propagating through the central region 31. For example, the acoustic velocity of the surface acoustic waves propagating through the central region 31 is greater than 1.01 times but less than 1.035 times the acoustic velocity of the surface acoustic waves propagating through the edge region 32. The acoustic velocity of the surface acoustic waves propagating through the gap region 33 remains faster than that of the surface acoustic waves propagating through the central region 31, even after the insulating film 40 is provided. For example, the sound velocity of the surface acoustic wave propagating through the gap region 33 is greater than 1.01 times and less than 1.035 times the sound velocity of the surface acoustic wave propagating through the central region 31 .

[0032] [Manufacturing method] A method for manufacturing the acoustic wave resonator 100 according to the first embodiment will be described. First, a metal film 26 is formed on a piezoelectric substrate 10, and then the metal film 26 is patterned into a desired shape. As a result, an IDT 20 including a pair of interdigital transducers 22, each of which includes a plurality of electrode fingers 23, a plurality of dummy electrode fingers 24, and a bus bar 25, and a reflector 21 are formed on the piezoelectric substrate 10. The dummy electrode finger 24 has a narrow portion 27a and a portion 27b that is wider than the portion 27a and has the same width as the electrode finger 23. A gap is formed between the tip of the electrode finger 23 and the tip of the dummy electrode finger 24. The metal film 26 is formed by, for example, sputtering, vacuum deposition, or CVD (Chemical Vapor Deposition). The metal film 26 is patterned by, for example, photolithography and etching.

[0033] Next, an insulating film 40 is formed so as to cover the electrode fingers 23 and the dummy electrode fingers 24 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34. The insulating film 40 is formed, for example, by forming a mask layer having an opening on the piezoelectric substrate 10 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34, depositing the insulating film 40 using the mask layer as a mask, and then removing the mask layer. The mask layer is made of, for example, photoresist. The insulating film 40 is deposited by, for example, sputtering, vacuum deposition, or CVD. In this way, the acoustic wave resonator 100 according to the first embodiment is formed.

[0034] [Comparative Example] 3(a) is a plan view of acoustic wave resonator 1000 according to the comparative example, and FIG. 3(b) is a cross-sectional view taken along line AA of FIG. 3(a). As shown in FIGS. 3(a) and 3(b), in acoustic wave resonator 1000 according to the comparative example, the width of dummy electrode fingers 24 in the X direction is substantially constant in the Y direction. Therefore, the width of dummy electrode fingers 24 in the X direction is the same whether or not insulating film 40 is provided. The other configurations are the same as those of Example 1, and therefore will not be described again.

[0035] 4(a) and 4(b) are diagrams showing the acoustic velocity of an acoustic wave in a comparative example. Fig. 4(a) shows the state before the insulating film 40 is provided, and Fig. 4(b) shows the state after the insulating film 40 is provided. As shown in Fig. 4(a), the width of the dummy electrode fingers 24 in the X direction is approximately constant in the Y direction, so the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is the same as the acoustic velocity of the surface acoustic wave propagating through the region 34b.

[0036] 4(b), by providing the insulating film 40 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 becomes slower than the acoustic velocity of the surface acoustic wave propagating through the region 34b. The acoustic velocity of the surface acoustic wave propagating through the edge region 32 becomes slower than the acoustic velocity of the surface acoustic wave propagating through the central region 31. The acoustic velocity of the surface acoustic wave propagating through the gap region 33 remains faster than the acoustic velocity of the surface acoustic wave propagating through the central region 31, even after the insulating film 40 is provided.

[0037] By providing an insulating film 40 in the edge region 32, the acoustic velocity of the surface acoustic wave propagating through the edge region 32 is slower than that of the surface acoustic wave propagating through the central region 31, thereby achieving a piston mode. However, the length of the edge region 32 in the Y direction is shortened as the frequency increases, and the length of the gap region 33 in the Y direction is set to be equal to or less than the wavelength λ to obtain good characteristics. For this reason, when providing the insulating film 40 in the edge region 32 from the viewpoint of the minimum manufacturable dimensions of the insulating film 40, the insulating film 40 may be formed from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34. When the insulating film 40 is formed in the region 34a, the acoustic velocity of the surface acoustic wave propagating through the region 34a becomes slower than that of the surface acoustic wave propagating through the region 34b and the central region 31, as shown in FIG. 4(b).

[0038] In order to suppress transverse-mode spurious emissions, it is preferable that the acoustic velocity of the surface acoustic waves propagating through the dummy region 34 be the same as the acoustic velocity of the surface acoustic waves propagating through the central region 31. However, if the insulating film 40 for realizing the piston mode is provided in the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic waves propagating through the region 34a will be slower than the acoustic velocity of the surface acoustic waves propagating through the region 34b and the central region 31, and the effect of suppressing transverse-mode spurious emissions will be reduced.

[0039] [simulation] Simulations were performed to evaluate spurious responses of the acoustic wave resonators according to Example 1 and the comparative example. The simulation for the acoustic wave resonator according to the comparative example was performed on samples 1 and 2 in which the length over which insulating film 40 covers dummy region 34 was changed. The simulation conditions were as follows: Common conditions Piezoelectric substrate 10:42° Y-cut X-propagation lithium tantalate substrate IDT 20 and reflector 21: 220 nm thick aluminum film Insulating film 40: 16 nm thick niobium oxide film Anisotropy coefficient of piezoelectric substrate 10: 0.3 Elastic wave wavelength λ: 2.2 μm Duty ratio of electrode finger 23: 50% Length of edge region 32 in the Y direction: 0.3λ Length of gap region 33 in the Y direction: 500 nm Length of dummy electrode finger 24 in the Y direction: 1.5λ Conditions of Example 1 Length of portion 27a of dummy electrode finger 24 in the Y direction: 1.3λ Duty ratio of portion 27a of dummy electrode finger 24: 35% Length of portion 27b of dummy electrode finger 24 in the Y direction: 0.2λ Duty ratio of portion 27b of dummy electrode finger 24: 50% Difference in sound speed between area 34a and area 34b of dummy area 34: 0% Conditions for Comparative Example Sample 1 Duty ratio of dummy electrode finger 24: 50% Length in the Y direction of the region 34a of the dummy region 34 where the insulating film 40 covers the dummy electrode finger 24: 500 nm Difference in sound speed between area 34a and area 34b of dummy area 34: 1.47% Conditions for Comparative Example Sample 2 Duty ratio of dummy electrode finger 24: 50% Length in the Y direction of the region 34a of the dummy region 34 where the insulating film 40 covers the dummy electrode finger 24: 700 nm Difference in sound speed between area 34a and area 34b of dummy area 34: 1.47%

[0040] 5(a) shows the simulation results of the absolute value |Y| of admittance versus frequency for the acoustic wave resonators according to Example 1 and the comparative example, and FIG. 5(b) shows the simulation results of the real part of admittance Real(Y) versus frequency. Peaks at the resonant frequency fr and the antiresonant frequency fa are observed for the absolute value |Y| of admittance. Larger spurious responses are observed for the real part of admittance Real(Y) compared to the absolute value |Y|.

[0041] As shown in FIG. 5( a), there was almost no difference in the resonant frequency fr and the antiresonant frequency fa between Example 1 and Comparative Samples 1 and 2. As shown in FIG. 5( b), Comparative Sample 2 had larger spurious responses than Comparative Sample 1. This indicates that the larger the area of ​​dummy region 34 covered by insulating film 40 and the larger the region 34a in dummy region 34 where the acoustic velocity is slower than that of the surface acoustic wave propagating through central region 31, the larger the spurious responses. In contrast, Example 1 had more suppressed spurious responses than Comparative Samples 1 and 2. This is thought to be because, when insulating film 40 is formed to cover portion 27a of dummy electrode finger 24 by narrowing width W1, the acoustic velocity of the surface acoustic wave propagating through region 34a of dummy region 34 becomes the same as the acoustic velocity of the surface acoustic wave propagating through region 34b and central region 31.

[0042] [experiment] The acoustic wave resonators according to Example 1 and Comparative Example were fabricated and an experiment was conducted to evaluate spurious emissions under the following conditions. Common conditions Piezoelectric substrate 10:42° Y-cut X-propagation lithium tantalate substrate IDT 20 and reflector 21: a stack of a 10 nm thick titanium film and a 135 nm thick aluminum film Insulating film 40: niobium oxide film with a thickness of 22 nm Anisotropy coefficient of piezoelectric substrate 10: 0.1 Elastic wave wavelength λ: 2.2 μm Duty ratio of electrode finger 23: 50% Length of edge region 32 in the Y direction: 0.3λ Length of gap region 33 in the Y direction: 500 nm Length of dummy electrode finger 24 in the Y direction: 1.5λ Conditions of Example 1 Length of portion 27a of dummy electrode finger 24 in the Y direction: 1.3λ Duty ratio of portion 27a of dummy electrode finger 24: 35% Length of portion 27b of dummy electrode finger 24 in the Y direction: 0.2λ Duty ratio of portion 27b of dummy electrode finger 24: 50% Difference in sound speed between area 34a and area 34b of dummy area 34: 0% Conditions for the comparative example Duty ratio of dummy electrode finger 24: 50% The length in the Y direction of the region 34a of the dummy region 34 where the insulating film 40 covers the dummy electrode finger 24: 1.3λ Difference in sound speed between area 34a and area 34b of dummy area 34: 1.47%

[0043] Fig. 6(a) shows experimental results of the absolute value |Y| of admittance versus frequency for the acoustic wave resonators according to Example 1 and the comparative example, and Fig. 5(b) shows experimental results of the real part Real(Y) of admittance versus frequency. As shown in Fig. 6(a), there is almost no difference between Example 1 and the comparative example in terms of the resonant frequency fr and the antiresonant frequency fa. As shown in Fig. 6(b), Example 1 exhibited more suppressed spurious responses than the comparative example.

[0044] [Modification of Example 1] FIG. 7(a) is a plan view of acoustic wave resonator 110 according to Modification 1 of Example 1, and FIG. 7(b) is a cross-sectional view taken along line AA of FIG. 7(a). As shown in FIGS. 7(a) and 7(b), acoustic wave resonator 110 according to Modification 1 of Example 1 has a configuration in which, in addition to the narrowing of dummy electrode fingers 24, the width of electrode fingers 23 is also narrowed in region 34a of dummy region 34. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted. In this manner, the width of electrode fingers 23 may also be narrowed in addition to the narrowing of dummy electrode fingers 24.

[0045] Fig. 8(a) is a plan view of an acoustic wave resonator 120 according to a second modification of the first embodiment, and Fig. 8(b) is a cross-sectional view taken along line AA of Fig. 8(a). In the acoustic wave resonator 100 according to the first embodiment, as shown in Figs. 1(a) and 1(b), the insulating film 40 is provided to cover the entire region 34a of the dummy region 34. In contrast, in the acoustic wave resonator 120 according to the second modification of the first embodiment, as shown in Figs. 8(a) and 8(b), the insulating film 40 is provided to cover only a portion of the region 34a of the dummy region 34.

[0046] As described above, according to the first embodiment and its modifications, dummy electrode finger 24 has portion 27a located on the tip 24a side and portion 27b located on the opposite side of portion 27a from tip 24a, and portion 27a is narrower in width in the X direction (short side direction) than portion 27b. Insulating film 40 is provided on piezoelectric substrate 10 from edge region 32 to region 34a of dummy region 34 where portion 27a of dummy electrode finger 24 is located, but is not provided in central region 31 or region 34b of dummy region 34 where portion 27b of dummy electrode finger 24 is located. This reduces the difference in acoustic velocity between surface acoustic waves propagating through region 34a of dummy region 34 and those propagating through region 34b, as shown in FIG. 2B , thereby reducing the difference in acoustic velocity between surface acoustic waves propagating through regions 34a and 34b of dummy region 34 and those propagating through central region 31. Therefore, transverse mode spurious emissions can be suppressed.

[0047] To achieve the piston mode, it is preferable that the Y-direction length of the central region 31 and the Y-direction length of the edge region 32 satisfy a certain relationship. For example, it is preferable that the Y-direction length of the central region 31 is longer than the total Y-direction length of the edge regions 32. The Y-direction length of each of the edge regions 32 is preferably 1λ or less (e.g., 1 / 20 or less of the aperture length), more preferably 0.5λ or less (e.g., 1 / 40 or less of the aperture length). The Y-direction length of each of the edge regions 32 is preferably 0.05λ or more (e.g., 1 / 400 or more of the aperture length), more preferably 0.1λ or more (e.g., 1 / 200 or more of the aperture length). The edge region 32 may be provided only on one side of the central region 31. The Y-direction length of the gap region 33 is preferably 2λ or less (e.g., 1 / 10 or less of the aperture length), more preferably 1λ or less (e.g., 1 / 20 or less of the aperture length). The length of each gap region 33 in the Y direction is preferably 0.1λ or more (for example, 1 / 200 or more of the opening length), and more preferably 0.2λ or more (for example, 1 / 100 or more of the opening length).

[0048] 1(a) and 7(a), in the first embodiment and the first modification, the insulating film 40 is provided on the piezoelectric substrate 10 from the edge region 32 to the boundary between the regions 34a and 34b of the dummy region 34. In other words, the insulating film 40 is provided to cover the entire region 34a of the dummy region 34 in the Y direction. This tends to make the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 the same as that of the surface acoustic wave propagating through the region 34b. As a result, the acoustic velocity of the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 tends to be the same as that of the surface acoustic wave propagating through the central region 31. This makes it possible to suppress transverse-mode spurious responses.

[0049] 8(a), the insulating film 40 may not be provided in part of the region 34a of the dummy region 34. In this case, the insulating film 40 preferably covers 70% or more of the region 34a in the Y direction, more preferably 80% or more, and even more preferably 90% or more, of the region 34a, so that the region in the dummy region 34 where surface acoustic waves propagate at the same acoustic velocity as the surface acoustic waves propagating through the central region 31 becomes larger.

[0050] Furthermore, in the first embodiment and its modified examples, the width W2 in the X direction of the portion 27b of the dummy electrode finger 24 is the same as the width in the X direction of the electrode finger 23. This allows the acoustic velocity of the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 to be the same as the acoustic velocity of the surface acoustic wave propagating through the central region 31. The widths of the electrode fingers being the same means that a manufacturing error is tolerated, and may be, for example, 0.95 to 1.05 times the width of the electrode finger 24, or 0.98 to 1.02 times the width of the electrode finger 24.

[0051] In Example 1 and its modified examples, the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 is the same as the acoustic velocity of the surface acoustic waves propagating through the region 34b. This tends to make the acoustic velocity of the surface acoustic waves propagating through the regions 34a and 34b of the dummy region 34 the same as the acoustic velocity of the surface acoustic waves propagating through the central region 31, thereby suppressing transverse-mode spurious emissions. The acoustic velocity being the same means that a difference in acoustic velocity due to manufacturing errors is tolerated. For example, the acoustic velocity of the surface acoustic waves is 0.98 to 1.02 times, 0.985 to 1.015 times, or 0.99 to 1.01 times. For example, when a 42° rotated Y-cut X-propagation lithium tantalate substrate is used as the piezoelectric substrate 10, if the acoustic velocity difference between the dummy region 34 and the central region 31 is within 160 m / s, the acoustic velocity in the dummy region 34 and the central region 31 can be said to be the same.

[0052] In the first embodiment and its modifications, the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic waves propagating through the region 34b, and the acoustic velocity of the surface acoustic waves propagating through the central region 31 are the same. This makes it possible to suppress transverse mode spurious. The acoustic velocities being the same means, for example, that the acoustic velocity of the surface acoustic waves is 0.98 to 1.02 times, or may be 0.985 to 1.015 times, or may be 0.99 to 1.01 times.

[0053] In Example 1 and its modified examples, the length of gap region 33 in the Y direction is equal to or less than twice (1λ) the average pitch D of electrode fingers 23 of a pair of comb-shaped electrodes 22. In this case, for manufacturing reasons, insulating film 40 is likely to be formed from edge region 32 to dummy region 34, so it is preferable to narrow width W1 of portion 27a of dummy electrode fingers 24. For this reason, it is preferable to narrow width W1 of portion 27a of dummy electrode fingers 24 when the length of gap region 33 in the Y direction is equal to or less than 1.5 times (0.75λ) the average pitch D of electrode fingers 23, and it is more preferable to narrow width W1 of portion 27a of dummy electrode fingers 24 when the length is equal to or less than 1 time (0.5λ). The average pitch D of multiple electrode fingers 23 can be calculated by dividing the width of IDT 20 in the X direction by the number of electrode fingers 23. [Example]

[0054] FIG. 9(a) is a plan view of acoustic wave resonator 200 according to Example 2, and FIG. 9(b) is a cross-sectional view taken along line AA of FIG. 9(a). As shown in FIGS. 9(a) and 9(b), in acoustic wave resonator 200 according to Example 2, dummy electrode finger 24 has a width W in the X direction that is substantially constant in the Y direction and is the same as the width of electrode finger 23 in the X direction. However, thickness T1 of portion 27a located in region 34a is thinner than thickness T2 of portion 27b located in region 34b. Thickness T1 of portion 27a of dummy electrode finger 24 is, for example, 0.8 times or less, or may be 0.7 times or less, or may be 0.6 times or less, of thickness T2 of portion 27b. Thickness T2 of portion 27b of dummy electrode finger 24 is the same as the thickness of electrode finger 23. The other configurations are the same as those of Example 1, and therefore description thereof will be omitted.

[0055] 10(a) and 10(b) are diagrams showing the acoustic velocity of an acoustic wave in Example 2. Fig. 10(a) shows the state before the insulating film 40 is provided, and Fig. 10(b) shows the state after the insulating film 40 is provided. As shown in Fig. 10(a), in dummy electrode finger 24, thickness T1 of portion 27a is thinner than thickness T2 of portion 27b, and therefore the acoustic velocity of surface acoustic waves propagating through region 34a of dummy region 34 is faster than the acoustic velocity of surface acoustic waves propagating through region 34b.

[0056] 10(b), by providing the insulating film 40 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 approaches, and preferably becomes the same as, the acoustic velocity of the surface acoustic waves propagating through the region 34b of the dummy region 34. In this way, the thickness T1 of the portion 27a of the dummy electrode finger 24 is thin so that the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 approaches (preferably becomes the same as) the acoustic velocity of the surface acoustic waves propagating through the region 34b of the dummy region 34 after the insulating film 40 is provided. By making the acoustic velocity of the surface acoustic waves propagating through the region 34a of the dummy region 34 approach the acoustic velocity of the surface acoustic waves propagating through the region 34b, the difference between the acoustic velocity of the surface acoustic waves propagating through the regions 34a and 34b of the dummy region 34 and the acoustic velocity of the surface acoustic waves propagating through the central region 31 can be reduced, and preferably made the same. Furthermore, by providing the insulating film 40, the acoustic velocity of the surface acoustic wave propagating through the edge region 32 becomes slower than the acoustic velocity of the surface acoustic wave propagating through the central region 31. The acoustic velocity of the surface acoustic wave propagating through the gap region 33 remains faster than the acoustic velocity of the surface acoustic wave propagating through the central region 31, even after the insulating film 40 is provided.

[0057] According to the second embodiment, dummy electrode finger 24 has portion 27a located on the tip 24a side and portion 27b located on the opposite side of portion 27a from tip 24a, with portion 27a being thinner than portion 27b. Insulating film 40 is provided on piezoelectric substrate 10 from edge region 32 to region 34a of dummy region 34 where portion 27a of dummy electrode finger 24 is located, but is not provided in central region 31 or region 34b of dummy region 34 where portion 27b of dummy electrode finger 24 is located. This reduces the difference in acoustic velocity between surface acoustic waves propagating through region 34a of dummy region 34 and those propagating through region 34b, as shown in FIG. 10( b). This reduces the difference in acoustic velocity between surface acoustic waves propagating through regions 34a and 34b of dummy region 34 and those propagating through central region 31. This suppresses transverse-mode spurious emissions.

[0058] In Example 2 as well, it is preferable that the insulating film 40 is provided from the edge region 32 to the boundary between regions 34a and 34b of the dummy region 34, but as in Variation 2 of Example 1, it may not be provided in part of region 34a of the dummy region 34.

[0059] In the second embodiment, thickness T2 of portion 27b of dummy electrode finger 24 is the same as the thickness of electrode finger 23. This allows the acoustic velocity of surface acoustic waves propagating through regions 34a and 34b of dummy region 34 to be the same as the acoustic velocity of surface acoustic waves propagating through central region 31. Having the same thickness of the electrode fingers means that manufacturing errors are tolerated, and this means, for example, between 0.95 and 1.05 times, or between 0.98 and 1.02 times.

[0060] In the second embodiment, similar to the first embodiment, the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is the same as the acoustic velocity of the surface acoustic wave propagating through the region 34b. This tends to make the acoustic velocity of the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 the same as the acoustic velocity of the surface acoustic wave propagating through the central region 31, thereby suppressing transverse-mode spurious. Similarly to the first embodiment, the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is the same as the acoustic velocity of the surface acoustic wave propagating through the region 34b of the dummy region 34, and the acoustic velocity of the surface acoustic wave propagating through the central region 31. This allows suppression of transverse-mode spurious. Similarly to the first embodiment, the length of the gap region 33 in the Y direction is equal to or less than twice (1λ) the average pitch D of the electrode fingers 23 of the pair of comb-shaped electrodes 22. In this case, for manufacturing reasons, insulating film 40 is likely to be formed from edge region 32 to dummy region 34, so it is preferable to reduce thickness T1 of portion 27a of dummy electrode finger 24.

[0061] In the second embodiment, the thickness of electrode fingers 23 may be reduced in addition to reducing the thickness of dummy electrode fingers 24 in region 34a of dummy region 34. By combining the first and second embodiments, the width and thickness of dummy electrode fingers 24 and / or electrode fingers 23 in region 34a of dummy region 34 may be reduced.

[0062] As described above, according to Examples 1 and 2, the insulating film 40 is provided from the edge region 32 to the region 34a of the dummy region 34 that is located on the intersection region 30 side, but is not provided in the central region 31 or the region 34b of the dummy region 34 that is located on the busbar region 35 side. The pair of comb electrodes 22 are configured so that the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is the same as the acoustic velocity of the surface acoustic wave propagating through the region 34b. This makes it easier for the acoustic velocity of the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 to be the same as the acoustic velocity of the surface acoustic wave propagating through the central region 31, thereby suppressing transverse mode spurious emissions. [Example]

[0063] FIG. 11(a) is a plan view of an acoustic wave resonator 300 according to the third embodiment, and FIG. 11(b) is a cross-sectional view taken along line AA of FIG. 11(a). As shown in FIGS. 11(a) and 11(b), in the acoustic wave resonator 300 according to the third embodiment, the width W of the dummy electrode fingers 24 in the X direction is substantially constant in the Y direction and is the same as the width of the electrode fingers 23 in the X direction. The thickness T of the dummy electrode fingers 24 is substantially constant in the Y direction and is the same as the thickness of the electrode fingers 23. The insulating film 40 has a portion that extends from the edge region 32 to the region 34a of the dummy region 34 via the gap region 33, and a portion that extends from the edge region 32 to the gap region 33 and is not provided in the dummy region 34. That is, the side surface of the insulating film 40 facing the bus bar 25 has an uneven shape. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0064] 12(a) and 12(b) are diagrams showing the acoustic velocity of an acoustic wave in Example 3. Fig. 12(a) shows the state before the insulating film 40 is provided, and Fig. 12(b) shows the state after the insulating film 40 is provided. As shown in Fig. 12(a), the dummy electrode fingers 24 have a substantially constant thickness and a substantially constant width in the X direction. Therefore, the acoustic velocity of the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 is the same as that of the surface acoustic wave propagating through the central region 31.

[0065] As shown in FIG. 12( b), by providing the insulating film 40 from the edge region 32 through the gap region 33 to the region 34a of the dummy region 34, the acoustic velocity of the surface acoustic wave propagating in the region 34a becomes slower than the acoustic velocity of the surface acoustic wave propagating in the region 34b and the central region 31. However, since the insulating film 40 is not provided over the entire region 34a in the X direction and there are portions of the region 34a where the insulating film 40 is not provided, the decrease in the acoustic velocity of the surface acoustic wave propagating in the region 34a is kept small. By providing the insulating film 40, the acoustic velocity of the surface acoustic wave propagating in the edge region 32 becomes slower than the acoustic velocity of the surface acoustic wave propagating in the central region 31. The acoustic velocity of the surface acoustic wave propagating in the gap region 33 remains faster than the acoustic velocity of the surface acoustic wave propagating in the central region 31 even after the insulating film 40 is provided.

[0066] [simulation] A simulation was performed to see how the difference in sound velocity between the surface acoustic wave propagating in the central region 31 and the surface acoustic wave propagating in the region 34a changes when the size of the insulating film 40 provided in the region 34a of the dummy region 34 is changed. Figures 13(a) to 13(d) are cross-sectional views of samples A to D used in the simulation. Figures 13(a) to 13(d) show cross sections of the region 34a of the dummy region 34.

[0067] As shown in FIG. 13(a), in sample A, a piezoelectric substrate 10 is provided on a support substrate 60 with an insulating film 62 interposed therebetween. An IDT 20 (only the electrode fingers 23 and dummy electrode fingers 24 are shown) and a reflector 21 (not shown) are provided on the piezoelectric substrate 10. A protective film 64 is provided to cover the IDT 20 and the reflector 21. The insulating film 40 is not provided in the region 34a of the dummy region 34. As shown in FIG. 13(b), in sample B, the insulating film 40 is provided over the entire region 34a of the dummy region 34. The other configurations are the same as those of sample A.

[0068] As shown in FIG. 13(c), in sample C, the insulating film 40 is provided only on the dummy electrode fingers 24 in the region 34a of the dummy region 34. Therefore, in sample B, the insulating film 40 is provided over 100% of the region 34a of the dummy region 34, whereas in sample C, the insulating film 40 is provided over 25% of the region 34a. The other configurations are the same as those of sample A. As shown in FIG. 13(d), in sample D, the insulating film 40 is provided in the region 34a of the dummy region 34, covering the dummy electrode fingers 24 between the centers of the dummy electrode fingers 24 and the electrode fingers 23 adjacent to them on both sides. Therefore, in sample D, the insulating film 40 is provided over 50% of the region 34a. The other configurations are the same as those of sample A.

[0069] A simulation was performed for samples A to D to evaluate the difference in sound velocity between the surface acoustic wave propagating through the central region 31 and the surface acoustic wave propagating through the region 34a of the dummy region 34. The simulation conditions were as follows. Support substrate 60: sapphire substrate Insulating film 62: silicon oxide (SiO2) layer with a thickness of 0.2λ Piezoelectric substrate 10: 42° Y-cut X-propagation lithium tantalate substrate with a thickness of 0.3λ IDT 20 and reflector 21: Aluminum film with a thickness of 0.096λ Insulating film 40: niobium oxide film with a thickness of 0.01λ Elastic wave wavelength λ: 2.2 μm Duty ratio of the electrode fingers 23 and the dummy electrode fingers 24: 50%

[0070] The simulation results are shown in Table 1. As shown in Table 1, samples B to D, in which the insulating film 40 was provided in the region 34a of the dummy region 34, had lower resonance frequencies than sample A, in which the insulating film 40 was not provided. This is thought to be due to the mass loading effect of the insulating film 40. For sample B, in which the insulating film 40 was provided over 100% of the region 34a of the dummy region 34, the ratio ((Vc-Va) / Va)×100) of the difference in sound velocity between the velocities Va of the surface acoustic waves propagating through the region 34a of the dummy region 34 and Vc, to the velocity Vc of the surface acoustic waves propagating through the central region 31, was 1.9%. On the other hand, for sample C, in which the insulating film 40 was provided only on the dummy electrode fingers 24 in the region 34a of the dummy region 34, covering 25% of the region 34a, the ratio of the difference in sound velocity between the velocities Va and Vc, to the velocity Vc, was 1.4%. Thus, it was found that by reducing the area where the insulating film 40 is provided in the area 34a of the dummy area 34, the difference between the acoustic velocity Vc of the surface acoustic wave propagating in the central area 31 and the acoustic velocity Va of the surface acoustic wave propagating in the area 34a of the dummy area 34 becomes smaller. Furthermore, in sample D, in which the insulating film 40 is provided from the dummy electrode finger 24 to the space where there are no electrode fingers on both sides, covering 50% of the area 34a of the dummy area 34, the ratio of the difference between the acoustic velocity Va and the acoustic velocity Vc to the acoustic velocity Vc was 1.1%. [Table 1]

[0071] According to the third embodiment, the insulating film 40 is provided on the piezoelectric substrate 10 from the edge region 32 to the region 34a of the dummy region 34 located on the intersection region 30 side, and the length in the Y direction of the region 34a varies in the X direction. The insulating film 40 is not provided in the central region 31 or the region 34b of the dummy region 34 located on the busbar region 35 side. As a result, as shown in FIG. 12(b), after the insulating film 40 is provided, the decrease in the acoustic velocity of the surface acoustic wave propagating through the region 34a of the dummy region 34 is minimized, and the difference in acoustic velocity between the surface acoustic wave propagating through the region 34a and the region 34b can be reduced. As a result, the difference in acoustic velocity between the surface acoustic wave propagating through the regions 34a and 34b of the dummy region 34 and the surface acoustic wave propagating through the central region 31 can be reduced, thereby suppressing transverse-mode spurious emissions.

[0072] In the third embodiment, the minimum manufacturable width of the insulating film 40 in the X and Y directions is the same. As the wavelength λ of the surface acoustic wave excited by the IDT 20 increases, the width of the electrode fingers 23 and the dummy electrode fingers 24 in the X direction increases. In this case, the insulating film 40 may be provided only on the dummy electrode fingers 24 in the region 34a of the dummy region 34. In this way, the position and range of the insulating film 40 in the region 34a of the dummy region 34 can be set appropriately. [Example]

[0073] FIG. 14 is a circuit diagram of a filter 400 according to a fourth embodiment. As shown in FIG. 14, one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 may be an acoustic wave resonator according to the first to third embodiments. The numbers of series resonators and parallel resonators can be set as appropriate. Although a ladder-type filter is shown as an example of the filter, the filter may also be a multimode filter. [Example]

[0074] FIG. 15 is a circuit diagram of a duplexer 500 according to a fifth embodiment. As shown in FIG. 15, a transmit filter 50 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 52 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 50 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 52 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 50 and the receive filter 52 can be the filter of the fourth embodiment. Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0075] 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 described in the claims. [Explanation of symbols]

[0076] 10 Piezoelectric substrate 20 IDT 21 Reflector 22 Comb-shaped electrode 23 Electrode finger 23a Tip of electrode finger 24 dummy electrode fingers 24a Tip of dummy electrode finger 25 Busbar 26 Metal Film 27a, 27b parts 30 Intersection Area 31 Central area 32 Edge Area 33 Gap Region 34 Dummy Area 34a, 34b area 35 Busbar area 40 insulating film 50 Transmission Filter 52 Receive Filter 60 Support substrate 62 insulating film 64 Protective film 100, 110, 120, 200, 300, 1000 Acoustic wave resonators 400 filters 500 Duplexer

Claims

1. a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, wherein first tips of the plurality of electrode fingers and second tips of the plurality of dummy electrode fingers face each other, the plurality of dummy electrode fingers have a first portion located on the second tip side and a second portion located on the opposite side of the first portion from the second tip, and the first portion has a narrower width in a lateral direction than the second portion; an insulating film provided on the piezoelectric substrate from an edge region, which is a region where the electrode fingers of the pair of comb electrodes intersect, to a first region, which is a region where the first portions of the dummy electrode fingers are located, in a dummy region, which is a region where the dummy electrode fingers are located, and is not provided in a central region, which is a region inside the edge region, in the intersection region, and in a second region, which is a region where the second portions of the dummy electrode fingers are located in the dummy region.

2. a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, wherein first tips of the plurality of electrode fingers face second tips of the plurality of dummy electrode fingers, the plurality of dummy electrode fingers have a first portion located on the second tip side and a second portion located on the opposite side of the first portion from the second tip, and the first portion is thinner than the second portion; an insulating film provided on the piezoelectric substrate from an edge region, which is a region where the electrode fingers of the pair of comb electrodes intersect, to a first region, which is a region where the first portions of the dummy electrode fingers are located, in a dummy region, which is a region where the dummy electrode fingers are located, and is not provided in a central region, which is a region inside the edge region, in the intersection region, and in a second region, which is a region where the second portions of the dummy electrode fingers are located in the dummy region.

3. a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each including a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, wherein first tips of the plurality of electrode fingers face second tips of the plurality of dummy electrode fingers, and wherein the acoustic velocity of an elastic wave propagating through a first region located on the side of an intersection region where the plurality of electrode fingers intersect with each other in a dummy region where the plurality of dummy electrode fingers are located is equal to the acoustic velocity of an elastic wave propagating through a second region located on the opposite side of the intersection region from the first region in the dummy region; an insulating film provided on the piezoelectric substrate from an edge region, which is a region of the intersection region located at an edge in the longitudinal direction of the plurality of electrode fingers, to the first region of the dummy region, and not provided in a central region, which is a region of the intersection region located inside the edge region, or in the second region of the dummy region.

4. a piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each of which includes a plurality of electrode fingers, a plurality of dummy electrode fingers, and a bus bar connecting the plurality of electrode fingers and the plurality of dummy electrode fingers, with first tips of the plurality of electrode fingers facing second tips of the plurality of dummy electrode fingers; an insulating film provided on the piezoelectric substrate from an edge region, which is a region located at an edge in a longitudinal direction of the electrode fingers of the pair of comb electrodes in an intersection region where the electrode fingers of the pair of comb electrodes intersect, to a first region, which is a region located on the intersection region side of the dummy region, where the dummy electrode fingers are located, the length in the longitudinal direction in the first region being different in an arrangement direction of the electrode fingers, and the insulating film is not provided in a central region, which is a region located inside the edge region in the intersection region, or in a second region, which is located on the opposite side of the intersection region from the first region in the dummy region.

5. The acoustic wave resonator according to claim 1 , wherein the insulating film is provided on the piezoelectric substrate from the edge region to a boundary between the first region and the second region of the dummy region.

6. 5. The acoustic wave resonator according to claim 1, wherein the acoustic velocity of the acoustic wave propagating through the first region of the dummy region is the same as the acoustic velocity of the acoustic wave propagating through the second region of the dummy region.

7. 5. The elastic wave resonator according to claim 1, wherein the acoustic velocity of an elastic wave propagating through the first region of the dummy region, the acoustic velocity of an elastic wave propagating through the second region of the dummy region, and the acoustic velocity of an elastic wave propagating through the central region of the intersection region are the same.

8. 5. The elastic wave resonator according to claim 1, wherein a length in the longitudinal direction of the plurality of electrode fingers of a gap region, which is a region located between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers, is equal to or less than twice the average pitch of the plurality of electrode fingers of the pair of comb electrodes.

9. A filter comprising the acoustic wave resonator according to claim 1 .

10. A multiplexer including the filter of claim 9.

Images