Acoustic wave resonator, filter, multiplexer, and method of fabricating acoustic wave resonator
An acoustic wave resonator includes: a piezoelectric substrate; an IDT located on the piezoelectric substrate and including comb-shaped electrodes facing each other, each of the comb-shaped electrodes including: electrode fingers exciting an acoustic wave; and a bus bar to which the electrode fingers are connected; a dielectric film located on the piezoelectric substrate in an overlap region, where the electrode fingers of one of the comb-shaped electrodes and the electrode fingers of the other overlap, so as to cover the electrode fingers; and an additional film located on the dielectric film in the overlap region and having a density greater than that of the dielectric film, and of which a film thickness in edge regions corresponding to both edges of the overlap region in an extension direction of the electrode fingers is greater than a film thickness in a central region sandwiched between the edge regions in the overlap region.
1. An acoustic wave resonator comprising:
a piezoelectric substrate;
an IDT that is located on the piezoelectric substrate and includes a pair of comb-shaped electrodes facing each other, each of the pair of comb-shaped electrodes including: electrode fingers exciting an acoustic wave; and a bus bar to which the electrode fingers are connected;
a dielectric film that is located on the piezoelectric substrate in an overlap region, in which the electrode fingers of one of the pair of comb-shaped electrodes and the electrode fingers of another one of the pair of comb-shaped electrodes overlap, so as to cover the electrode fingers; and
an additional film that is located on the dielectric film in the overlap region and has a density greater than a density of the dielectric film, and of which a film thickness in edge regions corresponding to both edges of the overlap region in an extension direction of the electrode fingers is greater than a film thickness in a central region sandwiched between the edge regions in the overlap region,
wherein the additional film is a single film that includes no boundary face.
2. The acoustic wave resonator according to claim 1 , wherein
an upper surface of the dielectric film is flat.
3. The acoustic wave resonator according to claim 1 , wherein
the piezoelectric substrate is a lithium niobate substrate, and the dielectric film is a silicon oxide film or a silicon oxide film containing an impurity.
4. The acoustic wave resonator according to claim 3 , wherein
the additional film is a niobium oxide film.
5. The acoustic wave resonator according to claim 3 , wherein
the additional film is a tantalum oxide film.
6. A filter comprising:
the acoustic wave resonator according to claim 1 .
7. A multiplexer comprising:
the filter according to claim 6 .
8. An acoustic wave resonator comprising:
a piezoelectric substrate;
an IDT that is located on the piezoelectric substrate and includes a pair of comb-shaped electrodes facing each other, each of the pair of comb-shaped electrodes including: electrode fingers exciting an acoustic wave; and a bus bar to which the electrode fingers are connected;
a dielectric film that is located on the piezoelectric substrate in an overlap region, in which the electrode fingers of one of the pair of comb-shaped electrodes and the electrode fingers of another one of the pair of comb-shaped electrodes overlap, so as to cover the electrode fingers; and
an additional film that is located on the dielectric film in the overlap region and has a density greater than a density of the dielectric film, and of which a film thickness in edge regions corresponding to both edges of the overlap region in an extension direction of the electrode fingers is greater than a film thickness in a central region sandwiched between the edge regions in the overlap region,
wherein the dielectric film and the additional film are located in a region where the bus bar is formed, and a film thickness of the additional film in the region where the bus bar is formed is equal to or greater than a film thickness of the additional film in the edge regions.
9. The acoustic wave resonator according to claim 8 , wherein
the additional film is a single film that includes no boundary face.
10. The acoustic wave resonator according to claim 8 , further comprising:
a metal film located on the additional film in the region where the bus bar is formed.
11. A filter comprising:
the acoustic wave resonator according to claim 8 .
12. A multiplexer comprising:
the filter according to claim 11 .
13. A method of fabricating an acoustic wave resonator, the method comprising:
forming an IDT including a pair of comb-shaped electrodes facing each other on a piezoelectric substrate, each of the pair of comb-shaped electrodes including: electrode fingers exciting an acoustic wave; and a bus bar to which the electrode fingers are connected;
forming a dielectric film on the piezoelectric substrate in an overlap region, in which the electrode fingers of one of the pair of comb-shaped electrodes and the electrode fingers of another one of the pair of comb-shaped electrodes overlap, so that the dielectric film covers the electrode fingers;
forming, on the dielectric film in the overlap region, an additional film that has a density greater than a density of the dielectric film and of which a film thickness in edge regions corresponding to both edges of the overlap region in an extension direction of the electrode fingers is greater than a film thickness in a central region sandwiched between the edge regions in the overlap region; and
thinning the additional film substantially uniformly,
wherein the additional film is a single film that includes no boundary face.