Quartz orientation for guided SAW devices
Guided Surface Acoustic Wave (SAW) devices with improved quartz orientations are disclosed. A guided SAW device includes a quartz carrier substrate, a piezoelectric layer on a surface of the quartz carrier substrate, and at least one interdigitated transducer on a surface of the piezoelectric layer opposite the quartz carrier substrate. The quartz carrier substrate includes an orientation that provides improved performance parameters for the SAW device, including electromechanical coupling factor, resonator quality factor, temperature coefficient of frequency, and delta temperature coefficient of frequency.
1. A Surface Acoustic Wave (SAW) device, comprising:
a quartz carrier substrate;
a piezoelectric layer on a surface of the quartz carrier substrate; and
at least one Interdigitated Transducer (IDT) on a surface of the piezoelectric layer opposite the quartz carrier substrate;
wherein a cut plane for the quartz carrier substrate comprises a crystalline orientation having Euler angles (α, β, γ) of at least one of the following;
α is in a range of −55° to −65°, β is in a range of 18° to 28°, and γ is in a range of 85° to 95°; or
α is in a range of −5° to 5°, β is in a range of −18° to −28°, and γ is in a range of −85° to −95°; or
α is in a range of 55° to 65°, β is in a range of 18° to 28°, and γ is in a range of 85° to 95°.
2. The SAW device of claim 1 wherein the crystalline orientation of the plane is rotated along the propagation direction in a range of 0° to 30°, or in a range of 150° to 210°, or in a range of 330° to 360°.
3. The SAW device of claim 1 wherein a bulk acoustic velocity of the quartz carrier substrate in the propagation direction is larger than a velocity of a SAW of the SAW device.
4. The SAW device of claim 1 wherein a thickness of the piezoelectric layer is less than two times an IDT period of the at least one IDT.
5. The SAW device of claim 1 wherein a thickness of the piezoelectric layer is less than one times an IDT period of the at least one IDT.
6. The SAW device of claim 1 wherein a thickness of the piezoelectric layer is less than about seventy percent of an IDT period of the at least one IDT.
7. The SAW device of claim 1 wherein the at least one IDT comprises Aluminum or an Aluminum alloy.
8. The SAW device of claim 1 wherein a thickness of the at least one IDT is less than about fifteen percent of an IDT period.
9. The SAW device of claim 1 wherein a thickness of the at least one IDT is in a range of from three percent to fourteen percent of an IDT period.
10. The SAW device of claim 1 wherein the piezoelectric layer comprises Lithium Tantalate with an orientation between Y and Y+60°.
11. The SAW device of claim 1 wherein the piezoelectric layer comprises Lithium Niobate with an orientation between Y−20° and Y+60°.
12. The SAW device of claim 1 further comprising one or more layers on the surface of the quartz carrier substrate between the quartz carrier substrate and the piezoelectric layer.
13. The SAW device of claim 12 wherein the one or more layers comprise at least one layer of Silicon Oxide.
14. The SAW device of claim 13 wherein the Silicon Oxide is doped with a dopant containing Fluoride or Boron atoms.
15. The SAW device of claim 1 wherein the at least one IDT is embedded inside one or more dielectric layers.
16. The SAW device of claim 15 wherein the one or more dielectric layers comprise Silicon Oxide.
17. The SAW device of claim 16 wherein the Silicon Oxide is doped with a dopant containing Fluoride or Boron atoms.
18. The SAW device of claim 1 wherein a cut-off frequency is at least 1.07 times greater than a resonance frequency.