Surface acoustic wave device on device on composite substrate

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 a region underneath the plurality of electrode fingers; and

wherein the at least one physical parameter of the piezoelectric layer being different in the at least one region is one of elasticity of the piezoelectric layer and a dopant concentration.

2. The surface acoustic wave device of claim 1 , further comprising a Bragg mirror underneath the piezoelectric layer.

3. The surface acoustic wave device of claim 2 , wherein the electrode layer is between the piezoelectric layer and the base substrate, and the electrode layer is part of the Bragg mirror.

4. The surface acoustic wave device of claim 2 , wherein the Bragg mirror comprises a plurality of layers of alternating impedance.

5. 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.

6. The surface acoustic wave device of claim 1 , wherein 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.

7. The surface acoustic wave device of claim 1 , wherein a dimension of the comb electrode is defined by optimization of a coupling between a bulk acoustic wave and the standing acoustic wave generated by the comb electrode.

8. A frequency filter device comprising the surface acoustic wave device according to claim 1 .

9. 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 a region underneath the electrode fingers, and

wherein step b) comprises one of an implantation or diffusion of atomic species in the region of the piezoelectric layer located between the electrode fingers and an etching step for removing part of the piezoelectric layer in the region of the piezoelectric layer located between the electrode fingers.

10. The method of claim 9 , further comprising a step d) of providing a Bragg mirror on or over the base substrate before the step of providing the piezoelectric layer.

11. The method of claim 10 , further comprising forming the Bragg mirror such that the electrode layer is part of the Bragg mirror.

12. The method of claim 10 , wherein at least one of the steps a) to d) comprises a layer transfer process.

13. The method of claim 9 , wherein step b) comprises a proton exchange in the at least one region of the piezoelectric layer located between the electrode fingers.