Surface acoustic wave device on composite substrate
A surface acoustic wave device comprising a base substrate, a piezoelectric layer and an electrode layer in between the piezoelectric layer and the base substrate, a comb electrode formed on the piezoelectric layer comprising a plurality of electrode means with a pitch p, defined asp=A, with A being the wavelength of the standing acoustic wave generated by applying opposite potentials to the electrode layer and comb electrode, wherein the piezoelectric layer comprises at least one region located in between the electrode means, in which at least one physical parameter is different compared to the region underneath the electrode means or fingers. A method of fabrication for such surface acoustic wave device is also disclosed. The physical parameter may be thickness, elasticity, doping concentration of Ti or number of protons obtained by proton exchange.
1. A surface acoustic wave device, comprising:
a base substrate;
a piezoelectric layer;
an electrode layer in between the piezoelectric layer and the base substrate; and
a comb electrode formed on the piezoelectric layer comprising a plurality of electrode fingers with a pitch ρ, defined as ρ=λ, with λ being a wavelength of a standing acoustic wave generated by applying opposite potentials to the electrode layer and the comb electrode,
wherein, the piezoelectric layer comprises at least one region located in between the plurality of electrode fingers in which at least one physical parameter is different compared to the region underneath the plurality of electrode fingers; and
wherein either a) a thickness t of the piezoelectric layer is defined by optimization of a coupling between a bulk acoustic wave and the standing acoustic wave generated between the comb electrode and the electrode layer and is on the order or smaller than the wavelength λ of the standing acoustic wave or b) a dimension of the comb electrode is defined by optimization of the coupling between the bulk acoustic wave and the standing acoustic wave generated by the comb electrode.
2. The surface acoustic wave device of claim 1 , wherein the at least one physical parameter of the piezoelectric layer being different in the at least one region is elasticity of the piezoelectric layer.
3. The surface acoustic wave device of claim 1 , wherein the at least one physical parameter of the piezoelectric layer being different in the at least one region is a dopant concentration.
4. The surface acoustic wave device of claim 1 , wherein a thickness t r in the at least one region of the piezoelectric layer is smaller than a thickness t of the piezoelectric layer.
5. The surface acoustic wave device of claim 4 , wherein the piezoelectric layer is present only underneath the plurality of electrode fingers toward the base substrate.
6. The surface acoustic wave device of claim 1 , further comprising a Bragg mirror underneath the piezoelectric layer.
7. The surface acoustic wave device of claim 6 , wherein the electrode layer in between the piezoelectric layer and the base substrate is part of the Bragg mirror.
8. The surface acoustic wave device of claim 6 , wherein the Bragg mirror comprises a plurality of layers of alternating impedance.
9. A frequency filter device comprising a surface acoustic wave device according to claim 1 .
10. A method of fabrication of a surface acoustic wave device, comprising the steps of:
a) providing an electrode layer on top of a base substrate;
b) providing a piezoelectric layer on the electrode layer; and
c) forming an upper comb electrode layer including electrode fingers on the piezoelectric layer;
wherein, in step b), the piezoelectric layer is provided such that the piezoelectric layer comprises at least one region located in between the electrode fingers in which at least one physical parameter is different compared to the region underneath the electrode fingers and wherein step b) comprises a proton exchange in the at least one region of the piezoelectric layer located between the electrode fingers.
11. The method of claim 10 , wherein step b) comprises an etching step for removing part or all of the piezoelectric layer in the region of the piezoelectric layer located between the electrode fingers.
12. The method of claim 10 , wherein step b) comprises an implantation or diffusion of atomic species in the at least one region of the piezoelectric layer located between the electrode fingers.
13. The method of claim 10 , further comprising a step d) of providing a Bragg mirror on or over the base substrate before the step of providing the piezoelectric layer.
14. The method of claim 13 , further comprising forming the Bragg mirror such that the electrode layer is part of the Bragg mirror.
15. The method of claim 13 , wherein at least one of the steps a) to d) comprises a layer transfer process.