# US 2021/0242857 A1 · Acoustic wave filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0242857 A1 - Document ID: US20210242857A1 - Status: Published application - Kind: A1 - Application number: 17/156,756 - Filed: 2021-01-25 - Published: 2021-08-05 - Earliest claimed: 2020-01-31 - Assignees: Murata Manufacturing Co., Ltd. - Applicants: Murata Manufacturing Co., Ltd. - Inventors: Shinichi OKADA - Web page: https://patentgrep.com/patent/US20210242857A1 ## CPC - H03H 9/1457: {Transducers having different finger widths} - H03H 9/02559: {of lithium niobate or lithium-tantalate substrates} - H03H 9/02574: {of combined substrates, multilayered substrates, piezoelectrical layers on not-piezoelectrical substrate} - H03H 9/02637: {Details concerning reflective or coupling arrays} - H03H 9/02834: {of temperature influence (cut angles H03H9/02543)} - H03H 9/02866: {of bulk wave excitation and reflections} - H03H 9/02937: {of chemical damage, e.g. corrosion} - H03H 9/02992: {Details of bus bars, contact pads or other electrical connections for finger electrodes} - H03H 9/14594: {Plan-rotated or plan-tilted transducers} - H03H 9/25: Constructional features of resonators using surface acoustic waves {(devices for manipulating acoustic surface waves in general G10K11/36)} - H03H 9/6483: {Ladder SAW filters} - H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P) ## Abstract An acoustic wave filter includes first and second series-arm resonators, each including an IDT electrode including electrode fingers and a busbar electrode connecting first ends of the electrode fingers to each other. A direction in which second ends of the electrode fingers are aligned with each other crosses a propagation direction of an acoustic wave. The electrode fingers of the IDT electrodes of the first and second series-arm resonators each include an electrode-finger central portion and a wide portion located at the second end and being wider than the electrode-finger central portion. The length of the wide portion of each of the electrode fingers in the first series-arm resonator is greater than the length of the wide portion of each of the electrode fingers in the second series-arm resonator. ## Claims ### Claim 1 An acoustic wave filter comprising: a first series-arm resonator and a second series-arm resonator on a path connecting a first terminal and a second terminal; wherein the first series-arm resonator has a lower anti-resonant frequency than any other series-arm resonator included in the acoustic wave filter; the first series-arm resonator and the second series-arm resonator each include an interdigital transducer (IDT) electrode including a pair of comb teeth-shaped electrodes on a substrate including a piezoelectric layer; electrodes of the pair of comb teeth-shaped electrodes of the first series-arm resonator and electrodes of the pair of comb teeth-shaped electrodes of the second series-arm resonator each include electrode fingers and a busbar electrode, the electrode fingers extending in a direction orthogonal or substantially orthogonal to a propagation direction of an acoustic wave, the busbar electrode connecting first ends of the electrode fingers to each other; a direction in which second ends of the electrode fingers are aligned with each other crosses the propagation direction of the acoustic wave; the electrode fingers of the IDT electrode of the first series-arm resonator and the electrode fingers of the IDT electrode of the second series-arm resonator each include an electrode-finger central portion and a wide portion located at the second end and being wider than the electrode-finger central portion; and a length of the wide portion of each of the electrode fingers in the first series-arm resonator in the direction in which the electrode fingers extend is greater than a length of the wide portion of each of the electrode fingers in the second series-arm resonator in the direction in which the electrode fingers extend. ### Claim 2 (depends on 1) The acoustic wave filter according to claim 1, wherein the length of the wide portion of each of the electrode fingers in the first series-arm resonator is not less than about 0.1λ and not more than about 0.4λ, where λ denotes a wavelength of the acoustic wave. ### Claim 3 (depends on 1) The acoustic wave filter according to claim 1, wherein an intersecting width of the IDT electrode of the first series-arm resonator is not more than about 20λ. ### Claim 4 (depends on 1) The acoustic wave filter according to claim 1, wherein the substrate includes: a piezoelectric layer including two main surfaces, the IDT electrode of each of the first series-arm resonator and the second series-arm resonator being disposed on one of the two main surfaces; a high-acoustic-velocity support substrate, an acoustic velocity of a bulk wave propagating through the high-acoustic-velocity support substrate being higher than an acoustic wave velocity of an acoustic wave propagating through the piezoelectric layer; and a low-acoustic-velocity film disposed between the high-acoustic-velocity support substrate and the piezoelectric layer, an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film being lower than an acoustic velocity of an acoustic wave propagating through the piezoelectric layer. ### Claim 5 (depends on 1) The acoustic wave filter according to claim 1, further comprising: a third series-arm resonator disposed on the path, the first series-arm resonator and the third series-arm resonator being connected in series; wherein the third series-arm resonator has a lower anti-resonant frequency than the second series-arm resonator; the third series-arm resonator includes an IDT electrode including a pair of comb teeth-shaped electrodes provided on a substrate including a piezoelectric layer; electrodes of the pair of comb teeth-shaped electrodes of the third series-arm resonator each include electrode fingers and a busbar electrode, the electrode fingers extending in the direction orthogonal or substantially orthogonal to the propagation direction of the acoustic wave, the busbar electrode connecting first ends of the electrode fingers to each other; a direction in which second ends of the electrode fingers are aligned with each other crosses the propagation direction of the acoustic wave; the electrode fingers of the IDT electrode of the third series-arm resonator each include an electrode-finger central portion and a wide portion located at the second end and being wider than the electrode-finger central portion; and a length of the wide portion of each of the electrode fingers in the third series-arm resonator in the direction in which the electrode fingers extend is greater than the length of the wide portion of each of the electrode fingers in the second series-arm resonator in the direction in which the electrode fingers extend. ### Claim 6 (depends on 1) The acoustic wave filter according to claim 1, further comprising a plurality of the second series-arm resonators. ### Claim 7 (depends on 1) The acoustic wave filter according to claim 1, further comprising a parallel-arm resonator disposed on a path connecting a reference terminal and a node at which the first series-arm resonator and the second series-arm resonator are connected. ### Claim 8 (depends on 7) The acoustic wave filter according to claim 7, further comprising a plurality of the parallel-arm resonators. ### Claim 9 (depends on 7) The acoustic wave filter according to claim 7, wherein the first series-arm resonator, the second series-arm resonator, and the parallel-arm resonator define a ladder band-pass filter. ### Claim 10 (depends on 1) The acoustic wave filter according to claim 1, wherein each of the first and second series-arm resonators is a surface acoustic wave resonator. ### Claim 11 (depends on 1) The acoustic wave filter according to claim 1, wherein each of the first and second series-arm resonators includes a reflector disposed on both sides of the respective first or second series-arm resonator in the propagation direction. ### Claim 12 (depends on 1) The acoustic wave filter according to claim 1, wherein each of the IDT electrodes of the first and second series-arm resonators includes an adhesive layer on the piezoelectric layer and a main electrode layer on the adhesive layer. ### Claim 13 (depends on 12) The acoustic wave filter according to claim 12, wherein the adhesive layer includes Ti as a main component. ### Claim 14 (depends on 12) The acoustic wave filter according to claim 12, wherein the main electrode layer includes Al as a main component and a Cu content of about 1%. ### Claim 15 (depends on 1) The acoustic wave filter according to claim 1, wherein each of the IDT electrodes of the first and second series-arm resonators is covered with a protective layer. ### Claim 16 (depends on 15) The acoustic wave filter according to claim 15, wherein the protective layer includes silicon dioxide as a main component. ### Claim 17 (depends on 1) The acoustic wave filter according to claim 1, wherein the piezoelectric layer is made of a θ°-rotated Y cut X SAW propagation LiTaO3 piezoelectric single crystal. ### Claim 18 (depends on 1) The acoustic wave filter according to claim 1, wherein the piezoelectric layer has a thickness of about 600 nm. ### Claim 19 (depends on 4) The acoustic wave filter according to claim 4, wherein the high-acoustic-velocity support substrate is a silicon substrate having a thickness of about 125 μm. ### Claim 20 (depends on 4) The acoustic wave filter according to claim 4, wherein the low-acoustic-velocity film includes silicon dioxide as a main component and has a thickness of about 670 nm.