Acoustic wave device
A through-hole that extends from an upper surface of a cover opposite a support to a lower surface of the support facing a substrate is provided in the support and the cover. The through-hole overlaps a portion of a wiring line in a plan view. An acoustic wave device further includes an electrode film that is electrically connected to the wiring line in the through-hole, and a protective layer that includes an insulating material and that covers a portion of the electrode film. The protective layer is connected to the cover and the support in the through-hole. Differences in thermal expansion coefficients between the protective layer and the cover and between the protective layer and the support are smaller than a difference in thermal expansion coefficients between the protective layer and the electrode film.
1. An acoustic wave device comprising:
a substrate;
a functional element that is provided on the substrate;
a wiring line that is provided on the substrate and that is electrically connected to the functional element;
a support that is made of an insulating material and that is provided around the functional element on the substrate; and
a cover that is made of an insulating material, that covers the functional element, and that faces the substrate with the support interposed between the substrate and the cover; wherein
a through-hole that extends from a first surface of the cover opposite the support to a second surface of the support that faces the substrate is provided in the support and the cover;
the through-hole overlaps a portion of the wiring line in a plan view;
the acoustic wave device further includes:
an electrode film that is provided on the first surface and in the through-hole and that is electrically connected to the wiring line in the through-hole; and
a protective layer that is made of an insulating material and that covers at least a portion of the first surface and a portion of the electrode film;
the protective layer is connected to at least of the cover and the support in the through-hole; and
a difference in thermal expansion coefficients between the protective layer and the at least one of the cover and the support is smaller than a difference in thermal expansion coefficients between the protective layer and the electrode film.
2. The acoustic wave device according to claim 1 , wherein the protective layer is connected to the cover and the support in the through-hole.
3. The acoustic wave device according to claim 2 , wherein an inner wall surface around the through-hole includes a third surface of the cover that faces the substrate and a fourth surface of the support that is adjacent to the third surface; and
the protective layer is connected to the third surface and the fourth surface.
4. The acoustic wave device according to claim 1 , wherein the protective layer is connected to the substrate in the through-hole.
5. The acoustic wave device according to claim 1 , wherein the functional element includes at least one interdigital transducer electrode.
6. The acoustic wave device according to claim 5 , wherein the at least one interdigital transducer electrode defines a surface acoustic wave resonator.
7. The acoustic wave device according to claim 1 , wherein a metallic layer is provided between the wiring line and the functional element.
8. The acoustic wave device according to claim 1 , wherein the insulating material of the support is a synthetic resin or a photosensitive resin.
9. The acoustic wave device according to claim 1 , wherein the insulating material of the cover is an epoxy resin or polyimide.
10. The acoustic wave device according to claim 1 , wherein a hollow space is defined by the substrate, the support, and the cover, and the functional element is located in the hollow space.
11. The acoustic wave device according to claim 1 , wherein the support and the cover are integrally provided.
12. The acoustic wave device according to claim 1 , wherein the electrode film is a multilayer film that includes a seed layer and a plating layer provided on the seed layer.
13. The acoustic wave device according to claim 1 , wherein the protective layer covers an entirety or substantially an entirety of the first surface.
14. The acoustic wave device according to claim 1 , wherein the difference in thermal expansion coefficients between the protective layer and the at least one of the cover and the support is between about 0 and about 10×10 −6 /K; and
the difference in thermal expansion coefficients between the protective layer and the electrode film is between about 30×10 −6 /K and about 50×10 −6 /K.