Guided SAW device
A guided surface acoustic wave (SAW) device includes a substrate, a piezoelectric layer on the substrate, and a transducer on the piezoelectric layer. The substrate is silicon, and has a crystalline orientation defined by a first Euler angle (ϕ), a second Euler angle (θ), and a third Euler angle (ψ). The first Euler angle (ϕ), the second Euler angle (θ), and the third Euler angle (ψ) are chosen such that a velocity of wave propagation within the substrate is less than 5,400 m/s.
1. A guided surface acoustic wave (SAW) device comprising:
a silicon substrate having a crystalline orientation defined by a first Euler angle (ϕ), a second Euler angle (θ), and a third Euler angle (ψ), wherein the first Euler angle (ϕ), the second Euler angle (θ), and the third Euler angle (ψ) are chosen such that a velocity of wave propagation within the substrate is less than 5,400 m/s;
a piezoelectric layer on the silicon substrate; and
a transducer on the piezoelectric layer.
2. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (100); and
the third Euler angle (ψ) is between one of 18°-72° and 108°-162°.
3. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (110); and
the third Euler angle (ψ) is between one of (0°-34°)+35.264° and (75°-180°)+35.264°.
4. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (111); and
the third Euler angle (ψ) is between 0°-180°.
5. The guided SAW device of claim 1 wherein the piezoelectric layer comprises lithium tantalate.
6. The guided SAW device of claim 5 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.
7. The guided SAW 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.
8. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (100); and
the third Euler angle (ψ) is between one of 18°-25°, 65°-72°, 108°-115°, and 155°-162°.
9. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (110); and
the third Euler angle (ψ) is between one of (30°-34°)+35.264, (75°-80°)+35.264°, and (120°-170°)+35.264°.
10. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (111); and
the third Euler angle (ψ) is between 15°-45°, 75°-105°, and 135°-165°.
11. The guided SAW device of claim 9 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (110); and
the third Euler angle (ψ) is between (137.5°-152.5°)+35.264°.
12. The guided SAW device of claim 10 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (111); and
the third Euler angle (ψ) is between 23°-43°, 77°-97°, and 143°-163°.
13. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (100); and
the third Euler angle (ψ) is between one of 37.5°-52.5° and 127.5°-142.5°.
14. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (110); and
the third Euler angle (ψ) is between (7.5°-22.5°)+35.264°, (87.5°-102.5°)+35.264°, and (137.5°-152.5°)+35.264°.
15. The guided SAW device of claim 1 wherein:
the first Euler angle (ϕ) and the second Euler angle (θ) are fixed according to Miller plane (111); and
the third Euler angle (ψ) is between 23°-43°, 77°-97°, and 143°-163°.
16. The guided SAW device of claim 1 wherein a surface of the substrate on which the piezoelectric layer is provided is modified to reduce carrier lifetimes in the substrate.
17. The guided SAW device of claim 16 wherein the surface of the substrate on which the piezoelectric layer is provided is subjected to ion implantation to reduce carrier lifetimes in the substrate.
18. The guided SAW device of claim 16 wherein a polysilicon layer is provided between the substrate and the piezoelectric layer to reduce carrier lifetimes in the substrate.
19. The guided SAW device of claim 16 wherein a layer of amorphous silicon is provided between the substrate and the piezoelectric layer to reduce carrier lifetimes in the substrate.