Acoustic wave device with velocity reduction cover

1. An acoustic wave resonator comprising:

a piezoelectric layer;

an interdigital transducer electrode over the piezoelectric layer, the interdigital transducer electrode having a central region and first and second edge regions on opposing sides of the central region;

a temperature compensation layer over the interdigital transducer electrode; and

a velocity reduction cover extending over at least a portion of the central region of the interdigital transducer electrode and over at least a portion of the temperature compensation layer, the velocity reduction cover arranged to cause a velocity of an acoustic wave generated by the acoustic wave resonator to be reduced, the velocity reduction cover having a multilayer structure including a first sublayer at least partially located over the central region and disposed over the first and second edge regions, and a second sublayer that extends parallel to the first sublayer and is located only over the first and second edge regions of the interdigital transducer electrode.

2. The acoustic wave resonator of claim 1 wherein the velocity reduction cover includes first and second edge portions, the first edge portion positioned over edge regions of first fingers of the interdigital transducer electrode and the second edge portion positioned over edge regions of second fingers of the interdigital transducer electrode, the velocity reduction cover being thicker in the first and second edge regions than in the central region.

3. The acoustic wave resonator of claim 1 wherein a density of the velocity reduction cover is greater than a density of the temperature compensation layer.

4. The acoustic wave resonator of claim 1 wherein the interdigital transducer electrode and the velocity reduction cover include the same material.

5. The acoustic wave resonator of claim 1 wherein the velocity reduction cover includes a conductive material.

6. The acoustic wave resonator of claim 5 wherein the velocity reduction cover is spaced apart from the interdigital transducer electrode by a distance of 40 nanometers or more.

7. The acoustic wave resonator of claim 5 wherein the velocity reduction cover includes at least one of tungsten, molybdenum, platinum, gold, iridum, ruthenium, titanium, copper, or tantalum.

8. The acoustic wave resonator of claim 5 wherein the velocity reduction cover includes a non-conductive material.

9. The acoustic wave resonator of claim 8 wherein the velocity reduction cover is spaced apart from the interdigital transducer electrode by a distance of 40 nanometers or less.

10. The acoustic wave resonator of claim 8 wherein the velocity reduction cover includes at least one of tantalum pentoxide, titanium oxide, or titanium nitride.

11. The acoustic wave resonator of claim 1 wherein the second sublayer is disposed over the first sublayer and is located within first and second edge regions.

12. The acoustic wave resonator of claim 1 wherein the second sublayer includes a first strip over the first edge region and extending perpendicularly to fingers of the interdigital transducer electrode and a second strip over the second edge region and extending perpendicularly to the fingers of the interdigital transducer electrode.

13. The acoustic wave resonator of claim 12 wherein the first sublayer is patterned to include at least one aperture extending through a portion of the first sublayer that is positioned over the central region.

14. The acoustic wave resonator of claim 1 wherein the piezoelectric layer is a part of a multilayer piezoelectric substrate, the multilayer piezoelectric substrate additionally including a support substrate underlying the piezoelectric layer.

15. An acoustic wave filter comprising:

a temperature compensation layer;

a first acoustic wave resonator including a first interdigital transducer electrode having a central region and first and second edge regions on opposing sides of the central region, and a first velocity reduction cover extending over at least a portion of the central region of the first interdigital transducer electrode and over at least a portion of the temperature compensation layer, the first velocity reduction cover arranged to cause a velocity of an acoustic wave generated by the first acoustic wave resonator to be reduced, the first velocity reduction cover having a multilayer structure including a first sublayer at least partially located over the central region and disposed over the first and second edge regions, and a second sublayer that extends parallel to the first sublayer and is located only over the first and second edge regions of the first interdigital transducer electrode; and

a second acoustic wave resonator including a second interdigital transducer electrode and a second velocity reduction cover extending over at least a portion of a central region of the second interdigital transducer electrode and over at least a second portion of the temperature compensation layer, the second velocity reduction cover arranged to cause a velocity of an acoustic wave generated by the second acoustic wave resonator to be reduced, the first and second acoustic wave resonators being included in a plurality of acoustic wave resonators arranged to filter a radio frequency signal.

16. The acoustic wave filter of claim 15 wherein a density of the first velocity reduction cover is greater than a density of the temperature compensation layer.

17. The acoustic wave filter of claim 15 wherein the first and second interdigital transducer electrodes and the first and second velocity reduction covers include the same material.

18. The acoustic wave filter of claim 15 wherein the first velocity reduction cover includes a conductive material.

19. The acoustic wave filter of claim 15 wherein the first velocity reduction cover includes at least one of tungsten, molybdenum, platinum, gold, iridum, ruthenium, titanium, copper, tantalum, tantalum pentoxide, titanium oxide, or titanium nitride.

20. The acoustic wave filter of claim 15 wherein the second sublayer is disposed over the first sublayer and is located within the first and second edge regions.