Surface acoustic wave (SAW) resonator
View Patent ↗A surface acoustic wave (SAW) resonator includes a piezoelectric layer disposed over a substrate, and a plurality of electrodes disposed over the first surface of the piezoelectric layer. A layer is disposed between the substrate and the piezoelectric layer. A silicon layer disposed between a first surface of the layer and a second surface of the piezoelectric layer. A first surface of the silicon layer has a smoothness sufficient to foster atomic bonding between the first surface of the silicon layer and the second surface of the piezoelectric layer.
1. A surface acoustic wave (SAW) resonator structure, comprising:
a substrate having a first surface and a second surface, the first surface having a plurality of features;
a piezoelectric layer disposed over the substrate, the piezoelectric layer having a first surface and a second surface;
a plurality of electrodes disposed over the first surface of the piezoelectric layer, the plurality of electrodes configured to generate surface acoustic waves in the piezoelectric layer; and
a layer disposed over the first surface of the substrate, the layer having a first surface and a second surface; and
a polycrystalline silicon layer having a first surface and a second surface, the polycrystalline silicon layer being disposed between the first surface of the layer and the second surface of the piezoelectric layer, the first surface of the polycrystalline silicon layer having a smoothness sufficient to foster atomic bonding between the first surface of the polycrystalline silicon layer and the second surface of the piezoelectric layer, wherein the plurality of features reflect acoustic waves and reduce an incidence of spurious modes in the piezoelectric layer.
2. A SAW resonator structure as claimed in claim 1 , wherein the layer is disposed beneath the second surface of the polycrystalline silicon layer, the first surface of the layer having a smoothness sufficient to foster atomic bonding between the first surface of the layer and the second surface of the polycrystalline silicon layer.
3. A SAW resonator structure as claimed in claim 1 , wherein the polycrystalline silicon layer has a thickness in a range of approximately 100 Å to approximately λ/3 where λ is a wavelength of surface acoustic waves generated in the piezoelectric layer.
4. A SAW resonator structure as claimed in claim 1 , wherein the reflected acoustic waves destructively interfere with acoustic waves in the piezoelectric layer.
5. A SAW resonator structure as claimed in claim 1 , wherein the features in the first surface of the substrate are substantially pyramidal in shape.
6. A SAW resonator structure as claimed in claim 5 , wherein the features are substantially not in a regular pattern.
7. A SAW resonator structure as claimed in claim 5 , wherein the features have a height of approximately one-fourth of a wavelength (¼ λ) of a spurious mode.
8. A SAW resonator structure as claimed in claim 5 , wherein the features have a height in a range of approximately 0.25 μm to approximately 1.5 μm.
9. A SAW resonator structure as claimed in claim 5 , wherein the features have a height in a range of approximately 0.1 μm to approximately 2.50 μm.
10. A SAW resonator structure as claimed in claim 5 , wherein the features have a plurality of heights, and each of the pluralities of heights is approximately a height in a range of approximately one-fourth of a wavelength (¼ λ) of the spurious modes.
11. A SAW resonator structure as claimed in claim 1 , wherein the layer comprises an oxide material.
12. A SAW resonator structure as claimed in claim 11 , wherein the oxide material comprises silicon dioxide (SiO 2 ).
13. A SAW resonator structure as claimed in claim 11 , wherein the first surface of the layer has a root-mean-square (RMS) variation in height of approximately 0.1 Å to approximately 10.0 Å.
14. A surface acoustic wave (SAW) filter comprising a plurality of SAW resonator structures, one or more of the plurality of SAW resonator structures comprising:
a substrate having a first surface and a second surface, the first surface having a plurality of features;
a piezoelectric layer disposed over the substrate, the piezoelectric layer having a first surface and a second surface;
a plurality of electrodes disposed over the first surface of the piezoelectric layer, the plurality of electrodes configured to generate surface acoustic waves in the piezoelectric layer, and
a layer disposed over the first surface of the substrate, the layer having a first surface and a second surface; and
a polycrystalline silicon layer having a first surface and a second surface, the polycrystalline silicon layer being disposed between the first surface of the layer and the second surface of the piezoelectric layer, the first surface of the polycrystalline silicon layer having a smoothness sufficient to foster atomic bonding between the first surface of the polycrystalline silicon layer and the second surface of the piezoelectric layer, wherein the plurality of features reflect acoustic waves and reduce an incidence of spurious modes in the piezoelectric layer.
15. A SAW filter as claimed in claim 14 , wherein the layer is disposed beneath the second surface of the polycrystalline silicon layer, the first surface of the layer having a smoothness sufficient to foster atomic bonding between the first surface of the layer and the second surface of the polycrystalline silicon layer.
16. A SAW filter as claimed in claim 14 , wherein the polycrystalline silicon layer has a thickness in a range of approximately 100 Å to approximately λ/3 where λ is a wavelength of surface acoustic waves generated in the piezoelectric layer.
17. A SAW filter as claimed in claim 14 , wherein the reflected acoustic waves destructively interfere with acoustic waves in the piezoelectric layer.
18. A SAW filter as claimed in claim 14 , wherein the features in the first surface of the substrate are substantially pyramidal in shape.
19. A SAW filter as claimed in claim 18 , wherein the features are substantially not in a regular pattern.
20. A SAW filter as claimed in claim 18 , wherein the features have a height of approximately one-fourth of a wavelength (¼ λ) of a spurious mode.
21. A SAW filter as claimed in claim 20 , wherein the features have a height in a range of approximately 0.25 μm to approximately 1.5 μm.
22. A SAW filter as claimed in claim 20 , wherein the features have a height in a range of approximately 0.1 μm to approximately 2.50 μm.
23. A SAW filter as claimed in claim 14 , wherein the features have a plurality of heights, and each of the pluralities of heights is approximately a height in a range of approximately one-fourth of a wavelength (¼ λ) of the spurious modes.
24. A SAW filter as claimed in claim 14 , wherein the SAW filter is a ladder filter, comprising the plurality of SAW resonator structures.
25. A SAW filter as claimed in claim 14 , wherein the layer comprises an oxide material.
26. A SAW filter as claimed in claim 25 , wherein the oxide material comprises silicon dioxide (SiO 2 ).
27. A SAW filter as claimed in claim 25 , wherein the first surface of the layer has a root-mean-square (RMS) variation in height of approximately 1.0 Å to approximately 10.0 Å or less.
28. A SAW filter as claimed in claim 14 , wherein two or more of the plurality of SAW resonator structures are configured in a series and shunt configuration.
29. A surface acoustic wave (SAW) resonator structure, comprising:
a substrate having a first surface and a second surface, the first surface having a plurality of features;
a piezoelectric layer disposed over the substrate, the piezoelectric layer having a first surface and a second surface;
a plurality of electrodes disposed over the first surface of the piezoelectric layer, the plurality of electrodes configured to generate surface acoustic waves in the piezoelectric layer; and
a layer disposed over the first surface of the substrate, the layer having a first surface and a second surface; and
a silicon layer comprising a first surface and a second surface, and having a thickness in a range of approximately 100 Å to approximately λ/3 where λ is a wavelength of the surface acoustic waves generated in the piezoelectric layer, the silicon layer being disposed between the first surface of the layer and the second surface of the piezoelectric layer, the first surface of the silicon layer having a smoothness sufficient to foster atomic bonding between the first surface of the silicon layer and the second surface of the piezoelectric layer, wherein the plurality of features reflect acoustic waves and reduce an incidence of spurious modes in the piezoelectric layer.
30. A SAW resonator structure as claimed in claim 29 , wherein the features in the first surface of the substrate are substantially pyramidal in shape.
31. A SAW resonator structure as claimed in claim 30 , wherein the features are substantially not in a regular pattern.
32. A SAW resonator structure as claimed in claim 30 , wherein the features have a height of approximately one-fourth of a wavelength (¼ λ) of a spurious mode.
33. A SAW resonator structure as claimed in claim 30 , wherein the features have a height in a range of approximately 0.25 μm to approximately 1.5 μm.
34. A SAW resonator structure as claimed in claim 30 , wherein the features have a height in a range of approximately 0.1 μm to approximately 2.50 μm.
35. A SAW resonator structure as claimed in claim 30 , wherein the features have a plurality of heights, and each of the pluralities of heights is approximately a height in a range of approximately one-fourth of a wavelength (¼ λ) of the spurious modes.
36. A SAW resonator structure as claimed in claim 29 , wherein the layer comprises an oxide material.
37. A SAW resonator structure as claimed in claim 36 , wherein the oxide material comprises silicon dioxide (SiO 2 ).
38. A SAW resonator structure as claimed in claim 36 , wherein the first surface of the layer has a root-mean-square (RMS) variation in height of approximately 0.1 Å to approximately 10.0 Å.