Acoustic wave device, resonator and filter

1. An acoustic wave device comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate; and

a first dielectric film provided so as to cover the comb electrodes such that empty spaces contact fingers of the comb electrodes.

2. The acoustic wave device as claimed in claim 1 wherein the empty spaces are provided above the fingers of the comb electrodes, and

wherein the empty spaces contact the upper surface of the fingers of the comb electrodes and are formed between the comb electrodes and the first dielectric film.

3. The acoustic wave device as claimed in claim 1 , wherein the empty spaces are located between two adjacent fingers of the comb electrodes, and

wherein the empty spaces contact the side surface of the fingers of the comb electrodes.

4. The acoustic wave device as claimed in claim 3 , wherein the empty spaces are located between two adjacent fingers of the comb electrodes so as to connect the two adjacent fingers.

5. The acoustic wave device as claimed in claim 1 , wherein the empty spaces are located above the fingers of the comb electrodes and between two adjacent fingers of the comb electrodes,

wherein the empty spaces contact the upper surface and the side surface of the fingers of the comb electrodes, and

wherein the empty spaces are formed between the comb electrodes and the first dielectric film.

6. The acoustic wave device as claimed in claim 1 further comprising a second dielectric film provided between the piezoelectric substrate and the comb electrodes.

7. The acoustic wave device as claimed in claim 6 , wherein the second dielectric film comprises a material identical to that included in the first dielectric film.

8. The acoustic wave device as claimed in claim 6 , wherein the second dielectric film includes a material having a higher dielectric constant than the first dielectric film.

9. The acoustic wave device as claimed in claim 6 , wherein the second dielectric film includes an aluminum oxide film.

10. The acoustic wave device as claimed in claim 6 , wherein the first dielectric film contacts the piezoelectric film between adjacent fingers of the comb electrodes.

11. The acoustic wave device as claimed in claim 1 , further comprising a third dielectric film provided on the first dielectric film.

12. The acoustic wave device as claimed in claim 11 , wherein the third dielectric film has a propagation velocity of an acoustic wave that is greater than that of an acoustic wave propagated in the first dielectric film.

13. The acoustic wave device as claimed in claim 11 , wherein the third dielectric film includes an aluminum oxide film.

14. The acoustic wave device as claimed in claim 1 , wherein the piezoelectric substrate comprises one of lithium niobate and lithium tantalate.

15. The acoustic wave device as claimed in claim 1 , wherein the comb electrodes comprise copper.

16. An acoustic wave device comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate; and

a first dielectric film provided so as to cover the comb electrodes such that empty spaces are located above fingers of the comb electrodes and are formed in the first dielectric film,

wherein the first dielectric film is located between the fingers of the comb electrodes and the empty spaces.

17. A resonator comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate;

reflection electrodes between which the comb electrodes are provided; and

a first dielectric film provided so as to cover the comb electrodes and the reflection electrodes such that empty spaces contact fingers of the comb electrodes and fingers of the reflection electrodes.

18. A resonator comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate;

reflection electrodes between which the comb electrodes are provided; and

a first dielectric film provided so as to cover the comb electrodes and the reflection electrodes such that empty spaces do not contact fingers of the comb electrodes and do not contact fingers of the reflection electrodes,

wherein the empty spaces are formed in the first dielectric film, and

wherein the first dielectric film is located between the fingers of the comb electrodes and the empty spaces, and between the reflection electrodes and the empty spaces.

19. A filter comprising multiple resonators including a resonator comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate;

reflection electrodes between which the comb electrodes are provided; and

a first dielectric film provided so as to cover the comb electrodes and the reflection electrodes such that empty spaces contact fingers of the comb electrodes and fingers of the reflection electrodes.

20. A filter comprising multiple resonators including a resonator comprising:

a piezoelectric substrate;

comb electrodes formed above the piezoelectric substrate;

reflection electrodes between which the comb electrodes are provided; and

a first dielectric film provided so as to cover the comb electrodes and the reflection electrodes such that empty spaces do not contact fingers of the comb electrodes and do not contact fingers of the reflection electrodes,

wherein the empty spaces are formed in the first dielectric film, and

wherein the first dielectric film is located between the fingers of the comb electrodes and the empty spaces, and between the reflection electrodes and the empty spaces.