Surface acoustic wave device

1. A surface acoustic wave device, comprising:

a piezoelectric substrate; and

a pair of interdigital transducer electrodes, including:

a pair of busbars, provided on the piezoelectric substrate, and

a plurality of electrode fingers, mutually extending into a comb shape from the respective busbar towards the opposed busbar,

wherein the pair of interdigital transducer electrodes includes an alternating region as a region where the electrode fingers connected to one busbar and the electrode fingers connected to the other busbar are alternately provided, when viewed along an arranged direction of the plurality of electrode fingers,

wherein when a region on an end portion side of the alternating region and a region including distal end portions of the plurality of electrode fingers is referred to as an edge region, a propagation velocity of a surface acoustic wave in the edge region is slower than a propagation velocity of a surface acoustic wave in the alternating region, and

a propagation velocity of a surface acoustic wave in a busbar region as a region where the pair of busbars are disposed is faster than the propagation velocity of the surface acoustic wave in the alternating region;

wherein a thickness of a metal film that constitutes the pair of busbars is thinner than a thickness of a metal film that constitutes the electrode finger to make the propagation velocity of the surface acoustic wave in the busbar region faster than the propagation velocity of the surface acoustic wave in the alternating region.

2. The surface acoustic wave device according to claim 1 , wherein

a propagation velocity adjusting film is provided in the edge region to make the propagation velocity of the surface acoustic wave slower than the propagation velocity of the surface acoustic wave in the alternating region.

3. The surface acoustic wave device according to claim 1 , wherein

the electrode finger positioned in the edge region includes a widened portion to make the propagation velocity of the surface acoustic wave slower than the propagation velocity of the surface acoustic wave in the alternating region.

4. The surface acoustic wave device according to claim 1 , wherein

with respect to a distance d between center lines of adjoiningly arranged electrode fingers, a width between an end portion of the alternating region and the busbar when viewed along an extending direction of the electrode fingers is in a range of 0.1d to 2d.

5. The surface acoustic wave device according to claim 1 , wherein

a density of a metal film that constitutes the pair of busbars is smaller than a density of a metal film that constitutes the electrode finger to make the propagation velocity of the surface acoustic wave in the busbar region faster than the propagation velocity of the surface acoustic wave in the alternating region.

6. The surface acoustic wave device according to claim 1 , wherein

a dielectric film is provided on an upper layer side with respect to the interdigital transducer electrode, and

the dielectric film has a temperature-frequency characteristic whose frequency varies in a direction opposite to a direction of a temperature-frequency characteristic of the piezoelectric substrate.

7. The surface acoustic wave device according to claim 6 , wherein

a thickness of the dielectric film provided in the busbar region is thinner than a thickness of the dielectric film provided in an electrode finger region where the plurality of electrode fingers are arranged to make the propagation velocity of the surface acoustic wave in the busbar region faster than the propagation velocity of the surface acoustic wave in the alternating region.

8. The surface acoustic wave device according to claim 6 , wherein

the dielectric film provided in the busbar region is configured from a dielectric material having a propagation velocity of the surface acoustic wave faster than a propagation velocity of the surface acoustic wave of the dielectric film provided in an electrode finger region where the electrode finger is arranged to make the propagation velocity of the surface acoustic wave in the busbar region faster than the propagation velocity of the surface acoustic wave in the alternating region.

9. The surface acoustic wave device according to claim 6 , wherein

the dielectric film is provided in an electrode finger region where the electrode finger is arranged, and the dielectric film is not provided in the busbar region to make the propagation velocity of the surface acoustic wave in the busbar region faster than the propagation velocity of the surface acoustic wave in the alternating region.

10. The surface acoustic wave device according to claim 6 , wherein

the piezoelectric substrate is made of LiNbO 3 or LiTaO 3 , and

the dielectric film is made of silicon oxide, silicon oxynitride, or fluorine-doped silicon oxide.

11. The surface acoustic wave device according to claim 1 , wherein

for each of the pair of busbars, a plurality of dummy electrodes is provided between the distal end portions of the plurality of electrode fingers connected to the one busbar, and the other busbar, and

the plurality of dummy electrodes extends from the other busbar separately from the distal end portions.

12. The surface acoustic wave device according to claim 11 , wherein

a propagation velocity adjusting film is provided to decrease the propagation velocity of the surface acoustic wave, and the propagation velocity adjusting film is provided in a dummy region as a region where the dummy electrode is provided.

13. The surface acoustic wave device according to claim 1 , further comprising:

an upper layer film, being provided on an uppermost layer of the surface acoustic wave device to cause the surface acoustic wave device to have a weather resistance or to perform a frequency adjustment.

14. The surface acoustic wave device according to claim 13 , wherein the upper layer film is made of silicon nitride.