US-20260128729-A1 - ACOUSTIC WAVE DEVICE

US20260128729A1US 20260128729 A1US20260128729 A1US 20260128729A1US-20260128729-A1

Abstract

An acoustic wave device includes a first substrate including first and second main surfaces, a second substrate including a third main surface, a functional electrode on the third main surface, a support portion between the first and third main surfaces to provide a space therebetween, and via conductors in the first substrate and extending from the first main surface toward the second main surface. The support portion includes first and second metal films in contact with each other. In plan view of the first main surface, a region of the first metal film includes a region of the second metal film and an area of the first metal film is larger than an area of the second metal film, and a hardness of the second metal film is greater than a hardness of the first metal film.

Inventors

Masaaki Matsumori
Kentaro Fujinaga

Assignees

MURATA MANUFACTURING CO., LTD.

Dates

Publication Date: 20260507
Application Date: 20251231
Priority Date: 20230809

Claims (20)

1 . An acoustic wave device comprising: a first substrate including a first main surface and a second main surface facing away from each other; a second substrate including a third main surface facing the first main surface; a functional electrode on the third main surface; a support portion between the first main surface and the third main surface and providing a space between the first main surface and the third main surface; and a via conductor located in the first substrate and extending from the first main surface toward the second main surface; wherein the support portion includes: a first metal film in contact with the via conductor and provided on the first main surface; and a second metal film in contact with the first metal film and provided on an opposite side of the via conductor with the first metal film therebetween; in plan view of the first main surface, a region of the first metal film includes a region of the second metal film, and an area of the first metal film is larger than an area of the second metal film; and a hardness of the second metal film is greater than a hardness of the first metal film.
2 . The acoustic wave device according to claim 1 , wherein the support portion further includes a third metal film on the third main surface, connected to the functional electrode, and in contact with the second metal film; and a hardness of the third metal film is greater than the hardness of the first metal film.
3 . The acoustic wave device according to claim 1 , wherein the first metal film includes a first main electrode layer, a first diffusion barrier layer, and a first joint layer in order from a first main surface side; the second metal film includes a second joint layer, a second diffusion barrier layer, and a second main electrode layer in order from the first main surface side; and the first joint layer and the second joint layer are joined to each other.
4 . The acoustic wave device according to claim 3 , wherein an angle between a side surface of the first diffusion barrier layer and a first plane parallel to the first main surface is smaller than an angle between a side surface of the first main electrode layer and the first plane.
5 . The acoustic wave device according to claim 4 , wherein a portion of the side surface of the first main electrode layer is covered with the first diffusion barrier layer.
6 . The acoustic wave device according to claim 4 , wherein an area of a joint interface between the first main electrode layer and the first diffusion barrier layer is larger than an area of a joint interface between the first joint layer and the first diffusion barrier layer.
7 . The acoustic wave device according to claim 4 , wherein the first diffusion barrier layer includes titanium.
8 . The acoustic wave device according to claim 3 , wherein an angle between a side surface of the second diffusion barrier layer and a first plane parallel to the first main surface is smaller than an angle between a side surface of the second main electrode layer and the first plane.
9 . The acoustic wave device according to claim 8 , wherein a portion of the side surface of the second main electrode layer is covered with the second diffusion barrier layer.
10 . The acoustic wave device according to claim 8 , wherein an area of a joint interface between the second main electrode layer and the second diffusion barrier layer is larger than an area of a joint interface between the second joint layer and the second diffusion barrier layer.
11 . The acoustic wave device according to claim 8 , wherein the second diffusion barrier layer includes titanium.
12 . The acoustic wave device according to claim 3 , wherein an element with a highest weight ratio of metal elements of the second joint layer is the same as an element with a highest weight ratio of metal elements of the first joint layer.
13 . The acoustic wave device according to claim 3 , wherein in plan view of the first main surface: a region of the first metal film includes a region of the second metal film; a region of the second diffusion barrier layer includes a region of the second joint layer, and an area of the second diffusion barrier layer is larger than an area of the second joint layer; a region of the second main electrode layer includes the region of the second diffusion barrier layer, and an area of the second main electrode layer is larger than the area of the second diffusion barrier layer; a linear expansion coefficient of the second joint layer is greater than a linear expansion coefficient of the second diffusion barrier layer; and a linear expansion coefficient of the second main electrode layer is greater than the linear expansion coefficient of the second joint layer.
14 . The acoustic wave device according to claim 1 , wherein the second substrate has piezoelectricity; an interdigital transducer (IDT) electrode is provided on the third main surface; the IDT electrode includes a plurality of first electrode fingers and a plurality of second electrode fingers in parallel to each other; a first busbar electrode connects ends of the plurality of first electrode fingers to each other; and a second busbar electrode that connects ends of the plurality of second electrode fingers to each other and faces the first busbar electrode with the plurality of first electrode fingers and the plurality of second electrode fingers therebetween; and the functional electrode includes the plurality of first electrode fingers and the plurality of second electrode fingers.
15 . The acoustic wave device according to claim 14 , wherein the second substrate includes a support substrate and a piezoelectric film including the third main surface; and d/p is about 0.5 or less, where d is a thickness of the piezoelectric film, and p is an electrode finger pitch of the IDT electrode.
16 . The acoustic wave device according to claim 14 , wherein the support portion further includes a third metal film on the third main surface, connected to the functional electrode, and in contact with the second metal film; the third metal film includes the first busbar electrode and the second busbar electrode; and a hardness of the third metal film is greater than a hardness of the first metal film.
17 . The acoustic wave device according to claim 1 , wherein the functional electrode includes a first planar electrode, a piezoelectric thin film, and a second planar electrode in order from the third main surface.
18 . The acoustic wave device according to claim 1 , wherein the first substrate includes silicon.
19 . The acoustic wave device according to claim 1 , wherein in plan view of the first main surface: the region of the first metal film includes a region of the via conductor, and the area of the first metal film is larger than an area of the via conductor; and the region of the second metal film includes the region of the via conductor, and the area of the second metal film is larger than the area of the via conductor.
20 . The acoustic wave device according to claim 2 , wherein, in plan view of the third main surface, a region of the third metal film includes the region of the second metal film, and an area of the third metal film is larger than the area of the second metal film.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to Japanese Patent Application No. 2023-129696 filed on Aug. 9, 2023 and is a Continuation application of PCT Application No. PCT/JP2024/027431 filed on Jul. 31, 2024. The entire contents of each application are hereby incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to acoustic wave devices. 2. Description of the Related Art Japanese Unexamined Patent Application Publication No. 2018-137742 discloses an electronic device including a piezoelectric thin-film resonating unit, a first substrate (piezoelectricity substrate) on which the piezoelectric thin-film resonating unit is disposed, a second substrate (lid substrate) sandwiching the piezoelectric thin-film resonating unit between the first substrate and the second substrate, a thin film of a high resistivity material formed on the second substrate, and a via conductor provided in the first substrate. According to this, signals from the piezoelectric thin-film resonating unit can be input and output from a first substrate side while the signals are prevented from being coupled to the second substrate. When the via conductor is formed as a structure for inputting and outputting signals of the piezoelectric thin-film resonating unit (acoustic wave resonating unit) by machining the substrate made of a piezoelectric material, degradation of signals of the acoustic wave resonating unit is a concern. In contrast, a structure for inputting and outputting signals of the acoustic wave resonating unit by forming the via conductor in the lid substrate may be used. In this structure, however, to reduce or prevent the degradation of signals of the acoustic wave resonating unit, it is necessary to improve the joint strength of the support portion connected to the via conductor and the electrode of the piezoelectricity substrate while ensuring a space between the piezoelectricity substrate and the lid substrate. SUMMARY OF THE INVENTION Example embodiments of the present invention provide acoustic wave devices each including support portion with improved joint strength. According to an example embodiment of the present invention, an acoustic wave device includes a first substrate including a first main surface and a second main surface facing away from each other, a second substrate including a third main surface facing the first main surface, a functional electrode on the third main surface, a support portion between the first main surface and the third main surface to provide a space between the first main surface and the third main surface, and a via conductor located in the first substrate and extending from the first main surface toward the second main surface, in which the support portion includes a first metal film in contact with the via conductor and located on the first main surface, and a second metal film in contact with the first metal film and located on an opposite side of the via conductor with the first metal film therebetween, in plan view of the first main surface, a region of the first metal film includes a region of the second metal film, and an area of the first metal film is larger than an area of the second metal film, and a hardness of the second metal film is greater than a hardness of the first metal film. According to example embodiments of the present invention, acoustic wave devices each including a support portion with improved joint strength are provided. The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the example embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an acoustic wave device according to an example embodiment of the present invention. FIG. 2A is a first plan view of an acoustic wave device according to an example embodiment of the present invention. FIG. 2B is a second plan view of an acoustic wave device according to an example embodiment of the present invention. FIG. 2C is a third plan view of an acoustic wave device according to an example embodiment of the present invention. FIG. 3A indicates a plan view and a cross-sectional view schematically illustrating a first example of an acoustic wave resonator of an acoustic wave device according to an example embodiment of the present invention. FIG. 3B is a cross-sectional view schematically illustrating a second example of an acoustic wave resonator of an acoustic wave device according to an example embodiment of the present invention. FIG. 3C is a cross-sectional view schematically illustrating a third example of an acoustic wave resonator of an acoustic wave device according to an example embodiment of the present invention. FIG. 3D is a cross-sectional view schematically illustrating a fourth example of an acoustic wave resonat