Acoustic Wave Resonators, Filters, and Multiplexers

Abstract

To easily achieve excitation in a piston mode.SOLUTION: An acoustic wave resonator 100 comprises: a piezoelectric substrate 10; a pair of comb-shaped electrodes 22 that is provided on the piezoelectric substrate 10 and each includes a plurality of electrode fingers 23 and a bus bar 24 to which the plurality of electrode fingers 23 is connected, wherein leading ends of the plurality of electrode fingers 23 and the bus bars 24 of the comb-shaped electrodes face each other, and a sound velocity of an elastic wave propagating gap areas 33 being an area located between the leading ends of the plurality of electrode fingers 23 and the bus bar 24 is 0.98 or more times and 1.02 or less times the sound velocity of an elastic wave propagating edge areas 32 being an area located at edges in an extension direction of the plurality of electrode fingers 23, in an intersection area 30 being an area where the plurality of electrode fingers 23 of the comb-shaped electrodes intersects with each other; and additional films 42 that are provided on the piezoelectric substrate 10 from the respective edge areas 32 to the gap areas 33 and are not provided in a center area 31 being an area in the intersection area 30 located inside the edge areas 32.SELECTED DRAWING: Figure 2

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 unnecessary signals outside the frequency band used for communication. High-frequency filters use elastic wave resonators such as surface acoustic wave resonators. As a method for reducing spurious signals without compromising the Q value, an elastic wave resonator using a piston mode is known (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-80519 A [Patent Document 2] JP 2020-88459 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the piston mode, the acoustic velocity of the elastic wave in the edge region of the intersection region where the electrode fingers intersect may be set as a low acoustic velocity region where the acoustic velocity is slower than that in the central region located inside the edge region, and the acoustic velocity of the elastic wave in the gap region outside the edge region may be set as a high acoustic velocity region where the acoustic velocity is faster than that in the central region. In this case, the adjustment for achieving the excitation of the piston mode becomes complicated.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to easily realize excitation of piston mode vibration. [Means for solving the problem]

[0006] The present invention provides a piezoelectric substrate, a pair of comb-shaped electrodes provided on the piezoelectric substrate, each of which includes a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, wherein tips of the plurality of electrode fingers face the bus bar, and a speed of sound of an elastic wave propagating through a gap region, which is a region located between the tips of the plurality of electrode fingers and the bus bar, is 0.98 to 1.02 times faster than a speed of sound of an elastic wave propagating through an edge region, which is a region located at an edge in an extension direction of the plurality of electrode fingers, of an intersection region, which is a region where the plurality of electrode fingers intersect, and an additional film provided on the piezoelectric substrate from the edge region to the gap region, and not provided in a central region, which is a region of the intersection region located inside the edge region. In the pair of comb-shaped electrodes, the acoustic velocity of the elastic waves propagating through the edge region and the gap region is slower than the acoustic velocity of the elastic waves propagating through the central region, and the acoustic velocity of the elastic waves propagating through a busbar region, which is a region in which the busbar is located, is faster than the acoustic velocity of the elastic waves propagating through the central region. , an acoustic wave resonator.

[0007] The above-mentioned configuration may further include another additional film provided on the piezoelectric substrate between the tips of the plurality of electrode fingers and the bus bar.

[0008] The present invention provides 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 to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected, wherein tips of the plurality of electrode fingers and tips of the plurality of dummy electrode fingers face each other, and a speed of sound of an elastic wave propagating through a gap region located between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers is 0.98 to 1.02 times faster than a speed of sound of an elastic wave propagating through an edge region located at an edge in an extension direction of the plurality of electrode fingers in an intersection region where the plurality of electrode fingers intersect, and an additional film provided on the piezoelectric substrate from the edge region to the gap region, and not provided in a central region located inside the edge region in the intersection region. In the pair of comb-shaped electrodes, the acoustic velocity of the elastic waves propagating through the edge region and the gap region is slower than the acoustic velocity of the elastic waves propagating through the central region, and the acoustic velocity of the elastic waves propagating through a busbar region, which is a region in which the busbar is located, is faster than the acoustic velocity of the elastic waves propagating through the central region. , acoustic wave resonators.

[0009] The above-mentioned configuration may further include another additional film provided on the piezoelectric substrate between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers.

[0010] In the above configuration, the plurality of electrode fingers may be configured so that the width in the gap region is wider than the width in the intersection region.

[0012] In the above configuration, the acoustic velocity of the elastic wave propagating through the gap region may be 0.98 to 1.00 times the acoustic velocity of the elastic wave propagating through the edge region.

[0013] In the above configuration, the other additional film is Silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium oxide It can be configured as follows.

[0014] In the above configuration, the other additional film is The main component may be silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium.

[0015] In the above configuration, the pair of comb-shaped electrodes is made mainly of aluminum, Another The additional film is mainly composed of silicon oxide, and the thickness of the plurality of electrode fingers is H, the width of the plurality of electrode fingers is W, Another When the cross-sectional area of ​​the additional film in a cross section parallel to the arrangement direction of the plurality of electrode fingers is S, a configuration can be provided that satisfies 1.14×H×W≦S≦1.31×H×W.

[0016] In the above configuration, a length of the gap region in an extension direction of the plurality of electrode fingers can be equal to or less than twice the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

[0017] In the above configuration, the piezoelectric substrate may be a lithium tantalate substrate or a lithium niobate substrate.

[0018] The present invention is a filter including the above-described acoustic wave resonator.

[0019] The present invention is a multiplexer including the filter described above. Effect of the Invention

[0020] According to the present invention, excitation of the piston mode can be easily achieved. [Brief description of the drawings]

[0021] [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). [Diagram 2] 2(a) and 2(b) are diagrams showing the sound velocity of a surface acoustic wave in an IDT (Interdigital Transducer) in the first embodiment. [Diagram 3] 3(a) to 3(c) are cross-sectional views illustrating a method for manufacturing the acoustic wave resonator in accordance with the first embodiment. [Figure 4] FIG. 4 is a diagram showing the acoustic velocity of an acoustic wave in an IDT in the first comparative example. [Diagram 5] FIG. 5 is a diagram showing the acoustic velocity of an acoustic wave in an IDT in the second comparative example. [Figure 6] FIG. 6 is a diagram showing the acoustic velocity of an acoustic wave in an IDT in Comparative Example 3. In FIG. [Figure 7] FIG. 7 is a cross-sectional view taken along line BB of FIG. [Figure 8] FIG. 8(a) is a plan view of an acoustic wave resonator according to a first modification of the first embodiment, and FIG. 8(b) is a cross-sectional view taken along line AA of FIG. 8(a). [Figure 9] 9(a) and 9(b) are diagrams showing the acoustic velocity of an acoustic wave in an IDT in the first modification of the first embodiment. [Figure 10] FIG. 10(a) is a plan view of an acoustic wave resonator according to a second modification of the first embodiment, and FIG. 10(b) is a cross-sectional view taken along line AA of FIG. 10(a). [Figure 11] 11(a) is a cross-sectional view taken along line BB in FIG. 10(a), and FIG. 11(b) is a cross-sectional view taken along line CC in FIG. 10(a). [Figure 12] FIG. 12(a) is a plan view of an acoustic wave resonator in accordance with a second embodiment, and FIG. 12(b) is a cross-sectional view taken along line AA of FIG. 12(a). [Figure 13] 13(a) and 13(b) are diagrams showing the acoustic velocity of an acoustic wave in an IDT in Example 2. FIG. [Figure 14] FIG. 14 shows a simulation result of admittance |Y| versus frequency of the acoustic wave resonator in accordance with the second embodiment. [Figure 15] FIG. 15 is a circuit diagram of a filter in accordance with the third embodiment. [Figure 16] FIG. 16 is a block diagram of a duplexer in accordance with the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0023] Fig. 1(a) is a plan view of an acoustic wave resonator 100 in accordance with a first embodiment, and Fig. 1(b) is a cross-sectional view taken along line AA of Fig. 1(a). The arrangement direction of the electrode fingers is the X direction, the extension direction of the electrode fingers is the Y direction, and the thickness direction of the piezoelectric substrate is 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 the piezoelectric substrate. When the piezoelectric substrate is a rotated Y-cut X-propagation piezoelectric substrate, the X direction is the X-axis direction of the crystal orientation.

[0024] 1(a) and 1(b), an acoustic wave resonator 100 includes an interdigital transducer (IDT) 20 and a reflector 21 provided on a piezoelectric substrate 10. The reflector 21 is provided to sandwich the IDT 20 in the X direction. The IDT 20 and the reflector 21 are formed of a metal film 26 on the piezoelectric substrate 10.

[0025] The IDT 20 includes a pair of comb electrodes 22. The comb electrodes 22 include a plurality of electrode fingers 23 and a bus bar 24 to which the plurality of electrode fingers 23 are connected. The tips of the electrode fingers 23 of one comb electrode 22 face the bus bar 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 alternated in at least a part 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 comb electrode 22 is approximately the wavelength λ of the acoustic wave. The pitch D of the plurality of electrode fingers 23 is twice the pitch of the electrode fingers 23 of one comb electrode 22. The reflector 21 reflects the acoustic wave (surface acoustic wave) excited by the electrode fingers 23 of the IDT 20. As a result, the acoustic wave is confined within the intersection region 30 of the IDT 20.

[0026] Intersection region 30 has edge region 32 which is a region located at the edge in the Y direction (region where the tips of electrode fingers 23 are located), and central region 31 which is a region located inside edge region 32 in the Y direction. A region located between the tips of electrode fingers 23 of one comb electrode 22 and busbar 24 of the other comb electrode 22 is gap region 33. A region where busbar 24 is located is busbar region 34.

[0027] An additional film 40 is provided on the piezoelectric substrate 10 between the tips of the electrode fingers 23 of one comb electrode 22 and the bus bar 24 of the other comb electrode 22. The additional film 40 is not provided on or under the electrode fingers 23 adjacent to each other in the X direction. The upper surface of the additional film 40 may be flush with the upper surfaces of the electrode fingers 23, or may have a step. The additional film 40 may be thicker or thinner than the electrode fingers 23. The width of the additional film 40 in the X direction may be the same as, larger than, or smaller than the electrode fingers 23. The additional film 40 is provided to adjust the sound velocity of the surface acoustic wave in the gap region 33, as will be described in detail later.

[0028] An additional film 42 is provided on the piezoelectric substrate 10 so as to cover the electrode fingers 23 and the additional film 40 from the edge region 32 to the gap region 33. The additional film 42 is not provided in the central region 31. As long as the additional film 42 is provided on the electrode fingers 23 and the additional film 40, it does not have to be provided between the electrode fingers 23. The thickness of the additional film 42 on the electrode fingers 23 and the thickness of the additional film 42 on the additional film 40 are approximately the same. "Approximately the same" here means that a difference of the order of manufacturing error is allowed. As will be described in more detail later, the additional film 42 is provided to adjust the sound velocity of the surface acoustic wave in the edge region 32 and the gap region 33.

[0029] The piezoelectric substrate 10 is, for example, a single crystal lithium tantalate (LiTaO 3 ) substrate or single crystal lithium niobate (LiNbO 3 ) substrate, for example, a rotated Y-cut X-propagation lithium tantalate substrate or a rotated Y-cut X-propagation lithium niobate substrate. The piezoelectric substrate 10 is, for example, a 36° to 48° Y-cut X-propagation lithium tantalate substrate.

[0030] Metal film 26 is a film containing, for example, aluminum (Al), copper (Cu), or molybdenum (Mo) as a main component. An adhesive film such as a titanium (Ti) film or a chromium (Cr) film may be provided between electrode fingers 23 and bus bars 24 and piezoelectric substrate 10. The adhesive film is thinner than electrode fingers 23 and bus bars 24. An insulating film may be provided so as to cover electrode fingers 23. In this case, additional films 40 and 42 may be provided on the insulating film. The insulating film may function as a protective film.

[0031] The additional film 40 is, for example, silicon oxide (SiO 2 ), tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5However, a film mainly made of other materials may be used as long as it is possible to adjust the sound velocity of the elastic wave propagating through the gap region 33. When the additional film 40 is a metal film such as aluminum or titanium, an insulating film is provided between the additional film 40 and the electrode fingers 23 and the bus bar 24; this will be described later.

[0032] The additional film 42 is, for example, silicon oxide (SiO 2 ), tantalum oxide (Ta 2 O 5 ), niobium oxide (Nb 2 O 5 The additional film 42 may be a film mainly composed of the same material as the additional film 40, or a film mainly composed of a different material, as long as the sound velocity of the elastic wave propagating through the edge region 32 and the gap region 33 can be adjusted. When the additional film 42 is a metal film such as aluminum or titanium, an insulating film is provided between the additional film 42 and the electrode fingers 23 and the bus bar 24, which will be described later.

[0033] 2(a) and 2(b) are diagrams showing the acoustic velocity of an acoustic wave in the IDT 20 in the first embodiment. FIG. 2(a) shows a state before the additional film 42 is provided, and FIG. 2(b) shows a state after the additional film 42 is provided. As shown in FIG. 2(a), the additional film 40 is provided on the piezoelectric substrate 10 between the tip of the electrode finger 23 and the bus bar 24, so that the acoustic velocities of the surface acoustic waves propagating through the central region 31, the edge region 32, and the gap region 33 are substantially the same. In other words, the additional film 40 is provided with its material, thickness, and / or width adjusted so that the acoustic velocity of the surface acoustic wave propagating through the gap region 33 is substantially the same as the acoustic velocity of the surface acoustic wave propagating through the central region 31 and the edge region 32.

[0034] 2(b), by providing the additional film 42 from the edge region 32 to the gap region 33, the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 becomes slower than the sound velocity of the surface acoustic wave propagating through the central region 31. That is, the additional film 42 is provided with its material, thickness, and / or width adjusted so that the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 becomes appropriately slower than the sound velocity of the surface acoustic wave propagating through the central region 31. The sound velocity of the surface acoustic wave propagating through the central region 31 is, for example, greater than 1.02 times and less than 1.035 times the sound velocity of the surface acoustic wave propagating through the edge region 32.

[0035] Because the additional film 40 makes the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 substantially the same, even after the additional film 42 is provided, the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 remain substantially the same. "Substantially the same" means, for example, that the sound velocity of the surface acoustic wave propagating through the gap region 33 is 0.98 to 1.02 times the sound velocity of the surface acoustic wave propagating through the edge region 32.

[0036] [Manufacturing method] 3(a) to 3(c) are cross-sectional views showing a method for manufacturing the acoustic wave resonator 100 according to the first embodiment. As shown in FIG. 3(a), 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 and a reflector 21 are formed on the piezoelectric substrate 10, the IDT 20 including a pair of comb-shaped electrodes 22 including a plurality of electrode fingers 23 and a bus bar 24. A gap 44 is formed between the tip of the electrode fingers 23 and the bus bar 24. The metal film 26 is formed by, for example, a sputtering method, a vacuum deposition method, a CVD (Chemical Vapor Deposition) method, or the like. The metal film 26 is patterned by, for example, a photolithography technique and an etching technique.

[0037] As shown in FIG. 3(b), the additional film 40 is formed in the gap 44 between the tip of the electrode finger 23 and the bus bar 24. The additional film 40 is formed, for example, by forming a mask layer having an opening corresponding to the gap 44 on the piezoelectric substrate 10, depositing the additional 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 additional film 40 is deposited by, for example, sputtering, vacuum deposition, or CVD.

[0038] As shown in FIG. 3(c), the additional film 42 is formed so as to cover the electrode fingers 23 and the additional film 40 from the edge region 32 to the gap region 33. The additional film 42 is formed, for example, by forming a mask layer having openings corresponding to the edge region 32 and the gap region 33 on the piezoelectric substrate 10, depositing the additional film 42 using the mask layer as a mask, and then removing the mask layer. The mask layer is made of, for example, a photoresist. The additional film 42 is deposited by, for example, a sputtering method, a vacuum deposition method, or a CVD method. In this way, the acoustic wave resonator 100 in accordance with the first embodiment is formed.

[0039] [Comparative Example] Fig. 4 is a diagram showing the sound velocity of an acoustic wave in the IDT 20 in Comparative Example 1. As shown in the upper diagram of Fig. 4, in Comparative Example 1, no additional film is provided between the tip of the electrode finger 23 and the bus bar 24, and a gap 44 is formed. The additional film 42 is provided only in the edge region 32, and not in the gap region 33.

[0040] Since no additional film is provided between the tip of electrode finger 23 and bus bar 24, and additional film 42 is provided only in edge region 32, as shown in the lower diagram of Figure 4, the sound velocity of surface acoustic waves propagating through edge region 32 is slower than the sound velocity of surface acoustic waves propagating through central region 31, and the sound velocity of surface acoustic waves propagating through gap region 33 is faster than the sound velocity of surface acoustic waves propagating through central region 31.

[0041] 5 is a diagram showing the acoustic velocity of an elastic wave in the IDT 20 in Comparative Example 2. As shown in the upper and lower diagrams in FIG. 5, in Comparative Example 2, the distance between the tip of the electrode finger 23 and the bus bar 24 is narrowed. In other words, the length of the gap region 33 in the Y direction is shortened. The length of the gap region 33 in the Y direction is, for example, 1λ or less. The other configurations are the same as those of Comparative Example 1.

[0042] In Comparative Example 1, the length of gap region 33 in the Y direction is long. In this case, in the piston mode, edge region 32 functions as a low sound velocity region, and gap region 33 functions as a high sound velocity region. In Comparative Example 2, the length of gap region 33 in the Y direction is short in order to reduce the size of the acoustic wave resonator and / or to suppress diffraction loss. In this case, in the piston mode, edge region 32 may function as a low sound velocity region, and busbar region 34 may function as a high sound velocity region.

[0043] In this way, depending on the length of the gap region 33 in the Y direction, the gap region 33 may function as a high sound velocity region, or the busbar region 34 may function as a high sound velocity region. Therefore, in order to establish excitation of the piston mode, the sound velocity of the surface acoustic wave propagating through the gap region 33 and / or the sound velocity of the surface acoustic wave propagating through the busbar region 34 must be adjusted according to the length of the gap region 33 in the Y direction. This makes the adjustments required to establish excitation of the piston mode complicated.

[0044] 6 is a diagram showing the sound velocity of an acoustic wave in the IDT 20 in Comparative Example 3. As shown in the upper diagram of FIG. 6, in Comparative Example 3, the additional film 42 is provided from the edge region 32 to the gap region 33. The other configurations are the same as those of Comparative Example 1. As shown in the lower diagram of FIG. 6, since the additional film 42 is provided from the edge region 32 to the gap region 33, the sound velocity of the surface acoustic wave propagating in the gap region 33 is slower than that of Comparative Example 1.

[0045] 6 shows an example in which the sound velocity of the surface acoustic wave propagating through the gap region 33 is slower than that of the surface acoustic wave propagating through the central region 31, but depending on the level of the mass loading effect of the additional film 42 (the effect of reducing the sound velocity due to the mass loading on the piezoelectric substrate 10), the sound velocity of the surface acoustic wave propagating through the gap region 33 may be faster than that of the surface acoustic wave propagating through the central region 31. When the sound velocity of the surface acoustic wave propagating through the gap region 33 is slower than that of the surface acoustic wave propagating through the central region 31, the busbar region 34 functions as a high sound velocity region. When the sound velocity of the surface acoustic wave propagating through the gap region 33 is faster than that of the surface acoustic wave propagating through the central region 31, the gap region 33 functions as a high sound velocity region. In this way, in order to achieve the piston mode excitation, the sound velocity of the surface acoustic wave propagating through the gap region 33 and / or the sound velocity of the surface acoustic wave propagating through the busbar region 34 must be adjusted in accordance with the mass loading effect of the additional film 42, which makes the adjustments required to achieve the piston mode excitation complicated.

[0046] On the other hand, according to the first embodiment, as shown in FIG. 2(b), the acoustic velocity of the elastic wave propagating through the gap region 33 is 0.98 to 1.02 times the acoustic velocity of the elastic wave propagating through the edge region 32. The additional film 42 is provided from the edge region 32 to the gap region 33, and is not provided in the center region 31. As a result, regardless of the length of the gap region 33 in the Y direction and the degree of the mass loading effect by the additional film 42, the edge region 32 and the gap region 33 function as low acoustic velocity regions, and the busbar region 34 functions as a high acoustic velocity region. Therefore, the complexity of the adjustment for establishing the excitation of the piston mode is suppressed, and the excitation of the piston mode can be easily realized. For example, the requirements for establishing the excitation of the piston mode include the length of the low acoustic velocity region in the Y direction and the acoustic velocity of the elastic wave propagating through the low acoustic velocity region, which can be adjusted by the length of the additional film 42 in the Y direction and the thickness of the additional film 42. The sound velocity of the elastic wave propagating through the gap region 33 is preferably 0.985 to 1.015 times the sound velocity of the elastic wave propagating through the edge region 32, more preferably 0.99 to 1.01 times, and even more preferably 0.995 to 1.005 times.

[0047] In order to realize 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 region 32. The total Y-direction length of the edge region 32 is preferably 5λ or less (e.g., ¼ or less of the aperture length), more preferably 2λ or less (e.g., 1 / 10 or less of the aperture length). The Y-direction length of each edge region 32 is preferably 0.1λ or more (e.g., 1 / 200 or more of the aperture length), more preferably 0.5λ or more (e.g., 1 / 40 or more of the aperture length). The edge region 32 may be provided only on one side of the central region 31. The total Y-direction length of the gap region 33 is preferably 5λ or less (e.g., ¼ or less of the aperture length), more preferably 2λ or less (e.g., 1 / 10 or less of the aperture length). The length of each gap region 33 in the Y direction is preferably 0.1λ or more (eg, 1 / 200 or more of the aperture length), and more preferably 0.5λ or more (eg, 1 / 40 or more of the aperture length).

[0048] 1(a) and 1(b), an additional film 40 is provided on the piezoelectric substrate 10 between the tip of the electrode finger 23 and the bus bar 24. This makes it possible to slow down the sound velocity of the elastic wave propagating through the gap region 33 so that the sound velocity of the elastic wave propagating through the gap region 33 becomes substantially the same as the sound velocity of the elastic wave propagating through the edge region 32.

[0049] In the first embodiment, the additional film 40 is a film mainly composed of silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium. By providing such an additional film 40 on the piezoelectric substrate 10 between the tip of the electrode finger 23 and the bus bar 24, the sound velocity of the elastic wave propagating through the gap region 33 can be made substantially the same as the sound velocity of the elastic wave propagating through the edge region 32. When the additional film 40 is a compound such as silicon oxide, tantalum oxide, or niobium oxide, the total ratio of the elements constituting the compound to the total of the elements contained in the additional film 40 is 50 at% (atomic %) or more, and may be 80 at% or more. The ratio of each element constituting the compound is 10 at% or more, and may be 20 at% or more. When the additional film 40 is a simple substance such as aluminum or titanium, the ratio of the simple substance element to the total of the elements contained in the additional film 40 is 50 at% or more, and may be 80 at% or more.

[0050] In the first embodiment, the sound velocity of the elastic wave propagating through the gap region 33 is preferably 0.98 to 1.00 times the sound velocity of the elastic wave propagating through the edge region 32. This allows the gap region 33 and the edge region 32 to function as low sound velocity regions more reliably. The sound velocity of the elastic wave propagating through the gap region 33 is preferably 0.985 to 1.00 times the sound velocity of the elastic wave propagating through the edge region 32, more preferably 0.99 to 1.00 times, and even more preferably 0.995 to 1.00 times.

[0051] FIG. 7 is a cross-sectional view taken along line BB of FIG. 1(a). In FIG. 7, for clarity, the additional film 42 is omitted. As shown in FIG. 7, the width of the electrode finger 23 in the X direction is W, and the thickness of the electrode finger 23 is H. The cross-sectional area of ​​the cross section of the additional film 40 parallel to the X direction is S. When the comb-shaped electrode 22 is formed mainly from aluminum and the additional film 40 is formed mainly from silicon oxide, it is preferable that the cross-sectional area S satisfies 1.14×H×W≦S≦1.31×H×W. The reason for this will be explained below.

[0052] The mass loading effect of the silicon oxide film, which reduces the acoustic velocity of the elastic wave by mass loading on the piezoelectric body, is about 87.5% of that of the aluminum film. Therefore, when the silicon oxide film and the aluminum film have the same width, the film thickness required for the silicon oxide film to have the same mass loading effect is about 1.14 times that of the aluminum film. For example, when the silicon oxide film and the aluminum film have the same width, in order to obtain the same mass loading effect as an aluminum film having a film thickness of 0.1λ, the film thickness of the silicon oxide film is 0.1λ×1.14=0.114λ. Therefore, when the width of the electrode finger 23 mainly made of aluminum is W, the thickness is H, and the cross-sectional area of ​​the additional film 40 mainly made of silicon oxide is S, the mass loading effect of the electrode finger 23 and the additional film 40 is the same by satisfying S=1.14×H×W. Therefore, the acoustic velocity of the elastic wave propagating through the gap region 33 can be made the same as the acoustic velocity of the elastic wave propagating through the edge region 32.

[0053] Also, in order to reduce the acoustic velocity of the elastic wave by 2% by the mass loading effect, the thickness needs to be about 1.15 times thicker than the original film thickness. For example, assume that the silicon oxide film and the aluminum film have the same width, and the thickness of the silicon oxide film is 0.114λ to obtain the same mass loading effect as an aluminum film with a thickness of 0.1λ. In this case, in order to reduce the acoustic velocity of the elastic wave by 2% by increasing the mass loading film of the silicon oxide film, the film thickness of the silicon oxide needs to be 0.114λ×1.15=0.131λ. From this, when the width W and thickness H of the electrode finger 23 mainly made of aluminum are each, and the cross-sectional area S of the additional film 40 mainly made of silicon oxide is each, by satisfying S=1.31×H×W, the acoustic velocity of the elastic wave propagating through the gap region 33 where the additional film 40 is provided becomes 2% slower than the acoustic velocity of the elastic wave propagating through the intersection region 30 where the electrode fingers 23 intersect.

[0054] For this reason, by satisfying 1.14×H×W≦S≦1.31×H×W, the sound speed of the elastic wave propagating through the gap region 33 can be made to be 0.98 to 1.00 times the sound speed of the elastic wave propagating through the edge region 32.

[0055] In the first embodiment, the length of the gap region 33 in the Y direction may be 2 times (1λ) or less of the average pitch D of the plurality of electrode fingers 23. In this case, similar to the second comparative example, the size of the acoustic wave resonator can be reduced and / or the diffraction loss can be suppressed. In the second comparative example, when the length of the gap region 33 in the Y direction is 1λ or less, the high acoustic velocity region may become the gap region 33 or the busbar region 34. In the first embodiment, the low acoustic velocity region becomes the edge region 32 and the gap region 33, and the high acoustic velocity region becomes the busbar region 34. From the viewpoint of the size reduction of the acoustic wave resonator and / or the suppression of the diffraction loss, the length of the gap region 33 in the Y direction may be 1.5 times (0.75λ) or less of the average pitch D of the plurality of electrode fingers 23, or may be 1 time (0.5λ) or less. The average pitch D of the plurality of electrode fingers 23 can be calculated by dividing the width of the IDT 20 in the X direction by the number of the electrode fingers 23.

[0056] [Variations] FIG. 8(a) is a plan view of an acoustic wave resonator 110 according to a first modification of the first embodiment, and FIG. 8(b) is a cross-sectional view taken along the line AA of FIG. 8(a). As shown in FIGS. 8(a) and 8(b), in acoustic wave resonator 110, additional film 40 is not provided between the tip of electrode finger 23 and bus bar 24, and additional film 42 is provided from edge region 32 to gap region 33 between the tip of electrode finger 23 and bus bar 24. The thickness of additional film 42 between the tip of electrode finger 23 and bus bar 24 is approximately the same as the thickness of additional film 42 on electrode finger 23. The term "approximately the same" used here means that a difference of the order of manufacturing error is allowed. The width (length in the X direction) of electrode finger 23 in gap region 33 is larger than the width (length in the X direction) in intersection region 30. That is, electrode finger 23 has wide portion 27 in gap region 33 that is wider than the width in intersection region 30. For example, the width of the electrode fingers 23 in the gap region 33 (the width of the wide portion 27) may be 1.2 to 2.0 times, 1.3 to 1.8 times, or 1.4 to 1.6 times the width of the electrode fingers 23 in the intersection region 30. The other configurations are the same as those in the first embodiment, and therefore the description will be omitted.

[0057] 9(a) and 9(b) are diagrams showing the acoustic velocity of an acoustic wave in the IDT 20 in the first modified example of the first embodiment. FIG. 9(a) shows a state before the additional film 42 is provided, and FIG. 9(b) shows a state after the additional film 42 is provided. As shown in FIG. 9(a), the width of the electrode fingers 23 is wider in the gap region 33 than in the intersection region 30, so that the acoustic velocities of the surface acoustic waves propagating in the central region 31, the edge region 32, and the gap region 33 are substantially the same. In other words, the width of the electrode fingers 23 in the gap region 33 is adjusted so that the acoustic velocity of the surface acoustic wave propagating in the gap region 33 is substantially the same as the acoustic velocities of the surface acoustic wave propagating in the central region 31 and the edge region 32.

[0058] 9(b), by providing the additional film 42 from the edge region 32 to the gap region 33, the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 becomes slower than the sound velocity of the surface acoustic wave propagating through the central region 31. In other words, the additional film 42 is provided with its material, thickness, and / or width adjusted so that the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 is appropriately slower than the sound velocity of the surface acoustic wave propagating through the central region 31.

[0059] Since the width of the electrode fingers 23 in the gap region 33 is large, the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 are substantially the same, even after the additional film 42 is provided, the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 are substantially the same. As described above, "substantially the same" refers to, for example, the case where the sound velocity of the surface acoustic wave propagating through the gap region 33 is 0.98 to 1.02 times the sound velocity of the surface acoustic wave propagating through the edge region 32.

[0060] In the first embodiment, the additional film 40 is provided between the tip of the electrode finger 23 and the bus bar 24 so that the acoustic velocity of the elastic wave propagating through the gap region 33 is substantially equal to the acoustic velocity of the elastic wave propagating through the edge region 32, but this is not limited to the above. As in the first modified example of the first embodiment, the acoustic velocity of the elastic wave propagating through the gap region 33 may be substantially equal to the acoustic velocity of the elastic wave propagating through the edge region 32 by widening the width of the electrode finger 23 in the gap region 33. In addition, the acoustic velocity of the elastic wave propagating through the gap region 33 may be substantially equal to the acoustic velocity of the elastic wave propagating through the edge region 32 by a method other than the above. In addition, the acoustic velocity of the elastic wave propagating through the gap region 33 may be substantially equal to the acoustic velocity of the elastic wave propagating through the edge region 32 by both providing the additional film 40 and widening the width of the electrode finger 23 in the gap region 33.

[0061] FIG. 10(a) is a plan view of an acoustic wave resonator 120 according to a second modification of the first embodiment, and FIG. 10(b) is a cross-sectional view taken along line AA of FIG. 10(a). FIG. 11(a) is a cross-sectional view taken along line BB of FIG. 10(a), and FIG. 11(b) is a cross-sectional view taken along line CC of FIG. 10(a). In FIG. 10(a), the insulating film 46 is partially omitted for clarity. As shown in FIG. 10(a), FIG. 10(b), FIG. 11(a), and FIG. 11(b), in the acoustic wave resonator 120, the insulating film 46 is provided on the surfaces of the electrode fingers 23 and the bus bar 24, and the additional film 40 and the additional film 42 are provided on the insulating film 46. Therefore, the insulating film 46 is provided between the additional film 40 and the electrode fingers 23 and the bus bar 24 in the Y direction, and the additional film 40 is not in direct contact with the electrode fingers 23 and the bus bar 24. An insulating film 46 is provided between the additional film 42 and the electrode fingers 23 and bus bar 24, and the additional film 42 is not in direct contact with the electrode fingers 23 and bus bar 24. The other configurations are the same as those in the first embodiment, so a description thereof will be omitted.

[0062] A metal film such as aluminum or titanium may be used for the additional film 40. In this case, an insulating film 46 may be provided between the additional film 40 and the electrode fingers 23 and the bus bar 24, thereby electrically insulating the additional film 40 from the electrode fingers 23 and the bus bar 24. Similarly, a metal film such as aluminum or titanium may be used for the additional film 42. In this case, an insulating film 46 may be provided between the additional film 42 and the electrode fingers 23 and the bus bar 24, thereby electrically insulating the additional film 42 from the electrode fingers 23 and the bus bar 24.

[0063] Incidentally, since the film thickness of the insulating film 46 is thin (for example, 0.1 λ or less), even if the insulating film 46 is provided, the effect on the excitation conditions of the piston mode is negligibly small.

[0064] In the first modification of the first embodiment, similarly to the second modification of the first embodiment, an insulating film 46 may be provided between the additional film 42 and the electrode fingers 23 and between the additional film 42 and the bus bar 24 . EXAMPLES

[0065] 12(a) is a plan view of an acoustic wave resonator 200 according to a second embodiment, and FIG. 12(b) is a cross-sectional view taken along line AA of FIG. 12(a). As shown in FIG. 12(a) and FIG. 12(b), in the acoustic wave resonator 200, the comb-shaped electrode 22 includes a plurality of electrode fingers 23, a plurality of dummy electrode fingers 25, and a bus bar 24 to which the plurality of electrode fingers 23 and the plurality of dummy electrode fingers 25 are connected. The tips of the electrode fingers 23 of one comb-shaped electrode 22 face the tips of the dummy electrode fingers 25 of the other comb-shaped electrode 22. An additional film 40 is provided on the piezoelectric substrate 10 between the tips of the electrode fingers 23 of one comb-shaped electrode 22 and the tips of the dummy electrode fingers 25 of the other comb-shaped electrode 22. The additional film 40 is not provided on or under the electrode fingers 23 adjacent to each other in the X direction. The upper surface of additional film 40 may be flush with the upper surfaces of electrode fingers 23 and dummy electrode fingers 25, or may have a step. Additional film 40 may be thicker or thinner than electrode fingers 23 and dummy electrode fingers 25. The width of additional film 40 in the X direction may be the same as, larger than, or smaller than those of electrode fingers 23 and dummy electrode fingers 25. Acoustic wave resonator 200 has intersection region 30 having central region 31 and edge region 32, gap region 33, busbar region 34, and, in addition, dummy region 35 between gap region 33 and busbar region 34 where dummy electrode fingers 25 are located. The other configurations are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0066] 13(a) and 13(b) are diagrams showing the acoustic velocity of an acoustic wave in the IDT 20 in the second embodiment. FIG. 13(a) shows a state before the additional film 42 is provided, and FIG. 13(b) shows a state after the additional film 42 is provided. As shown in FIG. 13(a), the additional film 40 is provided between the tip of the electrode finger 23 and the tip of the dummy electrode finger 25, so that the acoustic velocities of the surface acoustic waves propagating through the central region 31, the edge region 32, the gap region 33, and the dummy region 35 are substantially the same. In other words, the additional film 40 is provided with its material, thickness, and / or width adjusted so that the acoustic velocity of the surface acoustic wave propagating through the gap region 33 is substantially the same as the acoustic velocity of the surface acoustic wave propagating through the central region 31, the edge region 32, and the dummy region 35.

[0067] 13(b), by providing the additional film 42 from the edge region 32 to the gap region 33, the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 becomes slower than the sound velocity of the surface acoustic wave propagating through the central region 31 and the dummy region 35. In other words, the additional film 42 is provided with its material, thickness, and / or width adjusted so that the sound velocity of the surface acoustic wave propagating through the edge region 32 and the gap region 33 is appropriately slower than the sound velocity of the surface acoustic wave propagating through the central region 31 and the dummy region 35.

[0068] Because the additional film 40 makes the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 substantially the same, even after the additional film 42 is provided, the sound velocity of the surface acoustic wave propagating through the gap region 33 and the sound velocity of the surface acoustic wave propagating through the edge region 32 remain substantially the same. "Substantially the same" means, for example, that the sound velocity of the surface acoustic wave propagating through the gap region 33 is 0.98 to 1.02 times the sound velocity of the surface acoustic wave propagating through the edge region 32.

[0069] [simulation] A simulation was performed to evaluate the spurious response of acoustic wave resonator 200 in accordance with Example 2. The simulation conditions were as follows. Piezoelectric Substrate 10:42° Y-cut X-propagation Lithium Tantalate Substrate IDT 20 and reflector 21: Aluminum film with a thickness of 200 nm Additional film 40: Silicon oxide film with a thickness of 228 nm Additional film 42: Silicon oxide film with a thickness of 80 nm Elastic wave wavelength λ: 2μm Length of edge region 32 in Y direction: 0.7λ Length of gap region 33 in Y direction: 1λ Difference in sound velocity between edge region 32 and gap region 33: 0% Difference in sound speed between the center area 31 and the edge area 32: 2.5%

[0070] Fig. 14 shows a simulation result of admittance |Y| versus frequency for acoustic wave resonator 200 in accordance with Example 2. As shown in Fig. 14, acoustic wave resonator 200 in accordance with Example 2 shows results in which spurious responses in dashed line region 60 are suppressed.

[0071] According to the second embodiment, as shown in FIG. 13(b), the sound velocity of the elastic wave propagating through the gap region 33 is 0.98 to 1.02 times the sound velocity of the elastic wave propagating through the edge region 32. The additional film 42 is provided from the edge region 32 to the gap region 33, and is not provided in the central region 31. As a result, similar to the first embodiment, the edge region 32 and the gap region 33 function as low sound velocity regions, and the busbar region 34 functions as a high sound velocity region, regardless of the length of the gap region 33 in the Y direction and the degree of the mass loading effect of the additional film 42. Therefore, the complexity of the adjustment for achieving the excitation of the piston mode is suppressed, and the excitation of the piston mode can be easily achieved.

[0072] 12(a) and 12(b), an additional film 40 is provided on piezoelectric substrate 10 between the tips of electrode fingers 23 and dummy electrode fingers 25. This makes it possible to slow down the acoustic velocity of the elastic waves propagating through gap region 33 so that the acoustic velocity of the elastic waves propagating through gap region 33 becomes substantially the same as the acoustic velocity of the elastic waves propagating through edge region 32.

[0073] Also in Example 2, similarly to Example 1, additional film 40 is a film containing silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium as a main component. By providing such additional film 40 between the tips of electrode fingers 23 and dummy electrode fingers 25, the sound velocity of the elastic wave propagating through gap region 33 can be made substantially the same as the sound velocity of the elastic wave propagating through edge region 32.

[0074] In the second embodiment, the acoustic velocity of the elastic wave propagating through the busbar region 34 may be slower than the acoustic velocity of the elastic wave propagating through the central region 31. In this case, the acoustic velocity of the elastic wave propagating through the dummy region 35 is made faster than the acoustic velocity of the elastic wave propagating through the central region 31, so that the dummy region 35 can be excited in the piston mode.

[0075] In the first and second embodiments, the piezoelectric substrate 10 may be bonded onto a support substrate. In this case, an insulating layer such as silicon oxide, aluminum oxide, and / or aluminum nitride may be provided between the piezoelectric substrate 10 and the support substrate. EXAMPLES

[0076] Fig. 15 is a circuit diagram of a filter 300 according to a third embodiment. As shown in Fig. 15, the filter 300 has one or more series resonators S1 to S4 connected in series and one or more parallel resonators P1 to P3 connected in parallel between an input terminal Tin and an output terminal Tout. The acoustic wave resonator of the first or second embodiment can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators of the ladder filter can be set as appropriate. The filter may be a multimode filter. EXAMPLES

[0077] FIG. 16 is a block diagram of a duplexer 400 according to a fourth embodiment. As shown in FIG. 16, in the duplexer 400, a transmission filter 50 is connected between a common terminal Ant and a transmission terminal Tx, and a reception filter 52 is connected between the common terminal Ant and a reception terminal Rx. The transmission filter 50 passes a signal in a transmission band among high-frequency 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 52 passes a signal in a reception band among high-frequency 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 50 and the reception filter 52 can be the filter 300 according to the third embodiment.

[0078] Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0079] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to such specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0080] 10 Piezoelectric substrate 20 IDT 21 Reflector 22 Comb-shaped electrode 23 Electrode finger 24 Busbar 25 Dummy electrode finger 26 Metal Film 27 Wide section 30 Intersection Area 31 Central area 32 Edge Area 33 Gap Region 34 Busbar Area 35 Dummy Area 40 Additional membrane 42 Additional membrane 44 void 46 Insulating Film 50 Transmission Filter 52 Receiving Filter 100, 110, 120, 200 Acoustic Wave Resonator 300 Filters 400 Duplexer

Claims

1. A piezoelectric substrate; a pair of comb-shaped electrodes provided on the piezoelectric substrate, each including a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are connected, wherein tips of the plurality of electrode fingers face each other and the bus bar, and the sound speed of an elastic wave propagating through a gap region located between the tips of the plurality of electrode fingers and the bus bar is 0.98 to 1.02 times faster than the sound speed of an elastic wave propagating through an edge region located at an edge in an extension direction of the plurality of electrode fingers within an intersection region where the plurality of electrode fingers intersect; an additional film provided on the piezoelectric substrate from the edge region to the gap region, and not provided in a central region of the intersection region that is located on the inside of the edge region; The pair of comb electrodes form an elastic wave resonator in which the speed of sound of elastic waves propagating through the edge region and the gap region is slower than the speed of sound of elastic waves propagating through the central region, and the speed of sound of elastic waves propagating through a busbar region, which is the region in which the busbar is located, is faster than the speed of sound of elastic waves propagating through the central region.

2. The acoustic wave resonator according to claim 1 , further comprising another additional film provided on the piezoelectric substrate between tips of the plurality of electrode fingers and the bus bar.

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 to which the plurality of electrode fingers and the plurality of dummy electrode fingers are connected, wherein tips of the plurality of electrode fingers and tips of the plurality of dummy electrode fingers face each other, and the acoustic velocity of an elastic wave propagating through a gap region located between the tips of the plurality of electrode fingers and the tips of the plurality of dummy electrode fingers is 0.98 to 1.02 times the acoustic velocity of an elastic wave propagating through an edge region located at an edge in an extension direction of the plurality of electrode fingers within an intersection region where the plurality of electrode fingers intersect; an additional film provided on the piezoelectric substrate from the edge region to the gap region, and not provided in a central region of the intersection region that is located on the inside of the edge region; The pair of comb electrodes form an elastic wave resonator in which the speed of sound of elastic waves propagating through the edge region and the gap region is slower than the speed of sound of elastic waves propagating through the central region, and the speed of sound of elastic waves propagating through a busbar region, which is the region in which the busbar is located, is faster than the speed of sound of elastic waves propagating through the central region.

4. 4. The acoustic wave resonator according to claim 3, further comprising another additional film provided on the piezoelectric substrate between tips of the plurality of electrode fingers and tips of the plurality of dummy electrode fingers.

5. The acoustic wave resonator according to claim 1 , wherein the electrode fingers have a width in the gap region greater than a width in the intersection region.

6. The acoustic wave resonator according to claim 1 , wherein a sound velocity of the acoustic wave propagating through the gap region is 0.98 to 1.00 times a sound velocity of the acoustic wave propagating through the edge region.

7. The elastic wave resonator described in claim 2, wherein the other additional film is primarily composed of silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium.

8. The elastic wave resonator described in claim 4, wherein the other additional film is primarily composed of silicon oxide, tantalum oxide, niobium oxide, aluminum, or titanium.

9. The pair of comb-shaped electrodes is made mainly of aluminum, The other additional film is mainly composed of silicon oxide, 9. The elastic wave resonator according to claim 7 or 8, wherein 1.14×H×W≦S≦1.31×H×W is satisfied, where H is a thickness of the plurality of electrode fingers, W is a width of the plurality of electrode fingers, and S is a cross-sectional area of ​​the other additional film in a cross section parallel to the arrangement direction of the plurality of electrode fingers.

10. 10. The acoustic wave resonator according to claim 1, wherein a length of the gap region in an extension direction of the plurality of electrode fingers is equal to or less than twice an average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

11. The acoustic wave resonator according to claim 1 , wherein the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate.

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

13. A multiplexer including a filter according to claim 12.

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