# US 10,122,344 B2 · Surface acoustic wave filter

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- Number: US 10,122,344 B2
- Document ID: US10122344B2
- Status: Granted
- Kind: B2
- Application number: 15/079,259
- Filed: 2016-03-24
- Published: 2016-09-29
- Granted: 2018-11-06
- Earliest claimed: 2015-03-26
- Assignees: Murata Manufacturing Co., Ltd.
- Applicants: Murata Manufacturing Co., Ltd.
- Inventors: Norihiko Nakahashi; Koji Miyamoto
- Web page: https://patentgrep.com/patent/US10122344B2

## CPC

- H03H 9/6483: {Ladder SAW filters}
- H03H 9/0009: {using surface acoustic wave devices}
- H03H 9/02818: {Means for compensation or elimination of undesirable effects}
- H03H 9/02866: {of bulk wave excitation and reflections}
- H03H 9/14541: {Multilayer finger or busbar electrode}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

A ladder-type surface acoustic wave filter includes interdigital transducer electrodes disposed on a LiTaO3 piezoelectric substrate, and series resonators and parallel resonators defined by the interdigital transducer electrodes, and utilizes a leaky wave that propagates on the LiTaO3 piezoelectric substrate. A bandwidth ratio indicating a bandwidth of a passband of the ladder-type surface acoustic wave filter is about 2.5% or greater, and a cutoff frequency due to bulk wave radiation of one of the parallel resonators, is in a frequency range higher than the passband.

## Claims

### Claim 1

A surface acoustic wave filter comprising:
a LiTaO3 piezoelectric substrate; and
interdigital transducer electrodes disposed on the LiTaO3 piezoelectric substrate; wherein
the surface acoustic wave filter is a ladder-type surface acoustic wave filter including series resonators and parallel resonators defined by the interdigital transducer electrodes and utilizes a leaky wave that propagates on the LiTaO3 piezoelectric substrate; wherein
a bandwidth ratio that indicates a bandwidth of a passband of the surface acoustic wave filter is about 2.5% or greater;
a cutoff frequency at which bulk wave radiation of one of the parallel resonators increases is in a frequency range higher than the passband;
a normalized film thickness that is a ratio of a film thickness of the interdigital transducer electrodes of the parallel resonator to a repetitive pitch of a plurality of electrode fingers of the interdigital transducer electrodes of the parallel resonator is greater than or equal to about 9.0% and less than or equal to about 13.0%; and
a duty ratio that is a ratio of a line width of the plurality of electrode fingers to a sum of the line width and a space width between the plurality of electrode fingers is greater than or equal to about 0.3 and less than or equal to about 0.8.

### Claim 2 (depends on 1)

The surface acoustic wave filter according to claim 1, wherein the bandwidth ratio is about 3.0% or greater.

### Claim 3 (depends on 1)

The surface acoustic wave filter according to claim 1, wherein the normalized film thickness and the duty ratio are in a range of a region A illustrated in FIG. 10.