Acoustic wave device, filter, and multiplexer
An acoustic wave device includes: a piezoelectric substrate; and a pair of comb-shaped electrodes that is located on the piezoelectric substrate, includes a metal film, and excites a surface acoustic wave, the metal film being mainly composed of a metal having a melting point equal to or higher than a melting point of Pt, the metal film having a first region in which a crystal grain has a columnar shape and a second region that is located on and/or under the first region in a stacking direction and has less crystallinity than the first region or has an amorphous structure.
1. An acoustic wave device comprising:
a piezoelectric substrate; and
a pair of comb-shaped electrodes that is located on the piezoelectric substrate, includes a metal film, and excites a surface acoustic wave, the metal film being mainly composed of a metal having a melting point equal to or higher than a melting point of Pt, the metal film having a first region in which a crystal grain has a columnar shape and a second region that is located on and/or under the first region in a stacking direction and has less crystallinity than the first region or has an amorphous structure.
2. The acoustic wave device according to claim 1 , wherein
when a cross-section is observed with an electron microscope, a ratio of a number of crystal grains having a columnar shape to a number of crystal grains in the first region is 50% or greater.
3. The acoustic wave device according to claim 1 , wherein
the second region is located between the first region and the piezoelectric substrate.
4. The acoustic wave device according to claim 3 , wherein
the second region is in contact with the piezoelectric substrate.
5. The acoustic wave device according to claim 3 , further comprising
an intermediate film that is located between the piezoelectric substrate and the second region, and is mainly composed of a metal having a lower density than Pt.
6. The acoustic wave device according to claim 1 , wherein
the second region has an amorphous structure.
7. The acoustic wave device according to claim 1 , wherein
a thickness of the first region in the stacking direction is greater than a thickness of the second region in the stacking direction.
8. The acoustic wave device according to claim 7 , wherein
the thickness of the second region in the stacking direction is equal to or greater than one-fifth of the thickness of the first region in the stacking direction.
9. The acoustic wave device according to claim 7 , wherein
the thickness of the second region in the stacking direction is equal to or greater than one-tenth of the thickness of the first region in the stacking direction.
10. The acoustic wave device according to claim 1 , wherein
the metal film is mainly composed of at least one of Mo, Ir, Pt, Re, Rh, Ru, Ta, and W.
11. The acoustic wave device according to claim 1 , wherein
the metal film is a Mo film.
12. A filter comprising:
an acoustic wave device including:
a piezoelectric substrate, and
a pair of comb-shaped electrodes that is located on the piezoelectric substrate, includes a metal film, and excites a surface acoustic wave, the metal film being mainly composed of a metal having a melting point equal to or higher than a melting point of Pt, the metal film having a first region in which a crystal grain has a columnar shape and a second region that is located on and/or under the first region in a stacking direction and has less crystallinity than the first region or has an amorphous structure.
13. A multiplexer comprising:
a filter including an acoustic wave device, wherein
the acoustic wave device includes:
a piezoelectric substrate, and
a pair of comb-shaped electrodes that is located on the piezoelectric substrate, includes a metal film, and excites a surface acoustic wave, the metal film being mainly composed of a metal having a melting point equal to or higher than a melting point of Pt, the metal film having a first region in which a crystal grain has a columnar shape and a second region that is located on and/or under the first region in a stacking direction and has less crystallinity than the first region or has an amorphous structure.