Filter device including longitudinally coupled resonator elastic wave filter and elastic wave resonator

Patent metadata

Field	Value
Publication number	US-10469055-B2
Application number	US-201715830015-A
Country	US
Kind code	B2
Filing date	Dec 4, 2017
Priority date	Jun 24, 2015
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

A filter device includes a longitudinally coupled resonator elastic wave filter that includes IDT electrodes including low acoustic velocity regions in outer side portions of center regions of the IDT electrodes and high acoustic velocity regions in outer side portions of the low acoustic velocity regions in a direction orthogonal or substantially orthogonal to an elastic wave propagation direction, and defines and functions as a first bandpass filter, and elastic wave resonators that are electrically connected to the longitudinally coupled resonator elastic wave filter.

First claim

What is claimed is:

1. A filter device comprising:
a longitudinally coupled resonator elastic wave filter that includes a plurality of first IDT electrodes including low acoustic velocity regions in outer side portions of center regions of the first IDT electrodes and high acoustic velocity regions in outer side portions of the low acoustic velocity regions in a direction orthogonal or substantially orthogonal to an elastic wave propagation direction, and defines and functions as a first bandpass filter;
an elastic wave resonator that is electrically connected to the longitudinally coupled resonator elastic wave filter;
a piezoelectric film including LiTaO 3 ; and
a high acoustic velocity member with an acoustic velocity of propagating bulk waves, which is higher than an acoustic velocity of elastic waves propagating in the piezoelectric film; wherein
the piezoelectric film is laminated directly or indirectly on the high acoustic velocity member;
the plurality of first IDT electrodes are longitudinally coupled and connected on one surface of the piezoelectric film;
the elastic wave resonator includes a second IDT electrode located on one surface of the piezoelectric film;
the second IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers which interpose with the first electrode fingers;
a film thickness of the piezoelectric film is equal to or smaller than about 10λ when a wavelength determined by a pitch of the first and second electrode fingers of the second IDT electrode is λ; and
a direction connecting front ends of the plurality of first electrode fingers and a direction connecting front ends of the plurality of second electrode fingers define an inclination angle of ν with respect to a propagation direction φ of elastic waves excited by the second IDT electrode, which is determined by Euler Angles (ϕ, θ, φ) of the LiTaO 3 , where ν is a positive value of larger than 0°.

2. The filter device according to claim 1 , wherein a thickness of the piezoelectric film is equal to or smaller than about 1.5λ.

3. The filter device according to claim 1 , wherein the elastic wave resonator includes a plurality of elastic wave resonators electrically connected to define a second bandpass filter.

4. The filter device according to claim 3 , wherein the second bandpass filter is a ladder filter.

5. The filter device according to claim 3 , wherein the filter device is a duplexer including the longitudinally coupled resonator elastic wave filter as a reception filter and the second bandpass filter as a transmission filter.

6. The filter device according to claim 3 , wherein the first bandpass filter and the second bandpass filter are provided on a single chip component.

7. The filter device according to claim 3 , wherein
the first bandpass filter is provided in a first chip component;
the second bandpass filter is provided on a second chip component; and
the first chip component is different from the second chip component.

8. The filter device according to claim 7 , wherein the first chip component and the second chip component are both mounted on a mounting substrate.

9. The filter device according to claim 1 , wherein a low acoustic velocity film with an acoustic velocity of propagating bulk waves, which is lower than the acoustic velocity of the elastic waves propagating in the piezoelectric film, is laminated between the high acoustic velocity member and the piezoelectric film, and the piezoelectric film is laminated indirectly on the high acoustic velocity member.

10. The filter device according to claim 1 , wherein the piezoelectric film is laminated directly on the high acoustic velocity member.

11. The filter device according to claim 1 , wherein
each of the first IDT electrodes includes a first busbar, a second busbar spaced away from the first busbar, a plurality of first electrode fingers base ends of which are electrically connected to the first busbar and front ends of which extend toward the second busbar, and a plurality of second electrode fingers base ends of which are connected to the second busbar and front ends of which extend toward the first busbar; and
in each of the first IDT electrodes of the longitudinally coupled resonator elastic wave filter:
when a direction orthogonal or substantially orthogonal to a direction in which the first and second electrode fingers extend is a width direction, at least one of each of the first and second electrode fingers includes large width portions with larger dimensions in the width direction than dimensions of portions of the first and second electrode fingers at a center in a lengthwise direction at at least one side of the base end side and the front end side relative to the center in the lengthwise direction;
at least one of the first and second busbars includes a plurality of cavities which are located along a lengthwise direction of the first or second busbar; and
each of the first and second busbars includes an inner busbar portion which is located at a side of the first or second electrode fingers relative to the cavities and extends in the lengthwise direction of the first and second busbars, a center busbar portion in which the cavities are provided, and an outer busbar portion located at an opposite side to the inner busbar portion with the center busbar portion interposed between the outer busbar portion and the inner busbar portion.

12. The filter device according to claim 11 , wherein the inner busbar portion includes a band shape extending in the elastic wave propagation direction.

13. The filter device according to claim 11 , wherein both of the first electrode fingers and the second electrode fingers include the large width portions.

14. The filter device according to claim 1 , wherein
each of the first IDT electrodes includes a first busbar, a second busbar spaced away from the first busbar, a plurality of first electrode fingers base ends of which are electrically connected to the first busbar and front ends of which extend toward the second busbar, and a plurality of second electrode fingers base ends of which are connected to the second busbar and front ends of which extend toward the first busbar;
when a region in which the plurality of first electrode fingers and the plurality of second electrode fingers overlap with each other in the elastic wave propagation direction is an intersection region, the intersection region includes the center regions in the direction orthogonal or substantially orthogonal to the elastic wave propagation direction and the low acoustic velocity regions provided in the outer side portions of the center regions;
the first and second electrode fingers are increased in thickness in the low acoustic velocity regions; and
an acoustic velocity in the low acoustic velocity regions is lower than the acoustic velocity in the center regions.

15. The filter device according to claim 1 , wherein
each of the first IDT electrodes includes a first busbar, a second busbar spaced away from the first busbar, a plurality of first electrode fingers base ends of which are electrically connected to the first busbar and front ends of which extend toward the second busbar, and a plurality of second electrode fingers base ends of which are connected to the second busbar and front ends of which extend toward the first busbar; and
a dielectric film that lowers an acoustic velocity is laminated on the first and second electrode fingers in the low acoustic velocity regions.

16. The filter device according to claim 15 , wherein the dielectric film laminated on

Assignees

• Murata Manufacturing Co

Inventors

• Iwamoto Hideki
• Okada Keiji
• Takamine Yuichi
• Takai Tsutomu

Classifications

• H03H9/6483

  Ladder SAW filters · CPC title

• H03H9/6436

  having one acoustic track only · CPC title

• H03H9/145

  for networks using surface acoustic waves · CPC title

• H03H9/72 Primary

  Networks using surface acoustic waves · CPC title

• H03H9/132

  characterized by a particular shape · CPC title