Guided acoustic wave device
A guided acoustic wave device includes a substrate, a lithium tantalate layer on the substrate, and a transducer on the lithium tantalate film. The lithium tantalate has a crystalline orientation defined by (YXl)Θ°, where Θ is between 10° and 37°. The inventors discovered that limiting the crystalline orientation of the lithium tantalate in this manner provides significant increases in the electromechanical coupling coefficient of the acoustic wave device, thereby increasing bandwidth and improving performance.
1. A guided acoustic wave device comprising:
a substrate comprising one of quartz and silicon;
a lithium tantalate layer on the substrate, the lithium tantalate layer having a crystalline orientation defined by (YXl)Θ°, where Θ is between 10° and 37°; and
a transducer on the lithium tantalate layer.
2. The guided acoustic wave device of claim 1 wherein the transducer is an interdigital transducer comprising:
a first comb electrode comprising a first bus bar and a first plurality of electrode fingers extending transversely from the first bus bar; and
a second comb electrode comprising a second bus bar and a second plurality of electrode fingers extending transversely from the second bus bar such that:
the first bus bar is parallel to the second bus bar;
the first plurality of electrode fingers extend from the first bus bar towards the second bus bar;
the second plurality of electrode fingers extend from the second bus bar towards the first bus bar; and
the first plurality of electrode fingers are interleaved with the second plurality of electrode fingers.
3. The guided acoustic wave device of claim 2 wherein:
a distance between adjacent electrode fingers of one of the first comb electrode and the second comb electrode defines a center frequency wavelength (λ) of the guided acoustic wave device; and
a thickness of the lithium tantalate layer is less than 2λ.
4. A device according to claim 3 wherein the first comb electrode and the second comb electrode are essentially perpendicular to an X axis of the lithium tantalate layer.
5. The guided acoustic wave device of claim 3 wherein the thickness of the lithium tantalate layer is between 0.10λ and 0.45λ.
6. The guided acoustic wave device of claim 5 wherein Θ is between 10° and 35°.
7. The guided acoustic wave device of claim 5 wherein Θ is between 21° and 35°.
8. The guided acoustic wave device of claim 7 wherein the thickness of the lithium tantalate layer is between 0.15λ and 0.35λ.
9. The guided acoustic wave device of claim 3 wherein Θ is between 10° and 35°.
10. The guided acoustic wave device of claim 9 wherein the thickness of the lithium tantalate layer is between 0.15λ and 0.35λ.
11. The guided acoustic wave device of claim 1 wherein Θ is between 10° and 35°.
12. The guided acoustic wave device of claim 11 wherein the thickness of the lithium tantalate layer is between 0.15λ and 0.35λ.
13. The guided acoustic wave device of claim 3 wherein:
the substrate comprises quartz with a propagation that is close to a Z axis thereof;
the guided acoustic wave device comprises one or more dielectric layers between the substrate and the lithium tantalate layer; and
the thickness of the lithium tantalate layer is between 0.15λ and 0.35λ.
14. The guided acoustic wave device of claim 3 wherein:
the substrate comprises Si(111); and
the guided acoustic wave device further comprises one or more silicon oxide layers between the substrate and the lithium tantalate layer.
15. The guided acoustic wave device of claim 1 wherein the substrate comprises quartz.
16. The guided acoustic wave device of claim 15 further comprising one or more dielectric layers between the substrate and the lithium tantalate layer.
17. The guided acoustic wave device of claim 1 wherein the substrate comprises Si(111).
18. The guided acoustic wave device of claim 17 further comprising one or more oxide layers between the substrate and the lithium tantalate layer.
19. The guided acoustic wave device of claim 1 wherein Θ is between 15° and 30°.
20. The guided acoustic wave device of claim 1 wherein Θ is between 10° and 35°.
21. A guided acoustic wave device comprising:
a substrate comprising one of quartz and silicon;
a lithium tantalate layer on the substrate; and
an interdigital transducer on the lithium tantalate layer, wherein:
the interdigital transducer comprises a first comb electrode and a second comb electrode;
a distance between adjacent electrode fingers of one of the first comb electrode and the second comb electrode defines a center frequency wavelength (λ) of the guided acoustic wave device;
the transducer comprises a patterned metal layer having a thickness (h); and
a crystalline orientation of the lithium tantalate layer is defined by
(
YXl
)
θ°
where
22
-
1.2
h
λ
≤
Θ
≤
37
+
0.6
h
λ
-
0.08
(
h
λ
)
2
.
22. The guided acoustic wave device of claim 21 further comprising one or more oxide layers between the substrate and the lithium tantalate layer.
23. The guided acoustic wave device of claim 21 wherein the substrate comprises one of (YXl)90° quartz and (111) silicon.