Bulk acoustic wave resonators having convex surfaces, and methods of forming the same

1. A method, comprising:

forming an electrode of a bulk acoustic wave (BAW) resonator on at least one of a semiconductor substrate, a sacrificial layer, or an acoustic reflector; and

forming a piezoelectric layer of the BAW resonator on the electrode, in which the electrode covers entirely a surface of the piezoelectric layer, and the piezoelectric layer has a convex portion with a non-uniform thickness.

2. The method of claim 1 , wherein the surface of the piezoelectric layer is a planar surface, and the convex portion has a convex surface opposing the planar surface.

3. The method of claim 1 , wherein forming the piezoelectric layer on the electrode includes:

forming a piezoelectric material on the electrode; and

setting a shape of the piezoelectric material to form the piezoelectric layer having the convex portion.

4. The method of claim 3 , wherein the shape is a first shape, and setting the first shape of the piezoelectric material includes:

setting a second shape of a photoresist material on the piezoelectric material; and

etching the photoresist material having the second shape and the piezoelectric material to set the first shape of the piezoelectric material.

5. The method of claim 4 , wherein the second shape is based on a rate of etching of the piezoelectric material and the photoresist material.

6. The method of claim 4 , wherein setting a second shape of a photoresist material includes performing a gray-scale lithography operation on the photoresist material.

7. The method of claim 4 , wherein setting a second shape of a photoresist material includes performing a shaped lithography operation on the photoresist material.

8. The method of claim 4 , wherein setting a second shape of a photoresist material includes performing a sloped lithography operation on the photoresist material.

9. The method of claim 4 , wherein the convex portion is a first convex portion, and setting a second shape of a photoresist material includes forming a second convex portion on the photoresist material.

10. The method of claim 9 , wherein the first and second convex portions have convex surfaces of different curvatures.

11. The method of claim 1 , wherein the piezoelectric layer includes aluminum nitride.

12. The method of claim 1 , wherein the piezoelectric layer includes zinc oxide.

13. The method of claim 1 , wherein the electrode is a first electrode, and the method further comprises forming a second electrode of the BAW on the piezoelectric layer.

14. The method of claim 1 , further comprising:

mounting the semiconductor substrate or the acoustic reflector having the piezoelectric layer and the electrode thereon on an integrated circuit.

15. The method of claim 14 , further comprising: forming an interconnect between the electrode and the integrated circuit.

16. The method of claim 15 , wherein the interconnect includes a bond wire.

17. The method of claim 13 , wherein the surface is a first surface, and the second electrode covers entirely a second surface of the piezoelectric layer opposite the first surface.

18. The method of claim 1 , wherein the convex portion has a first thickness at a center and a second thickness on two sides of the center, the second thickness being smaller than the first thickness.

19. The method of claim 1 , wherein the convex portion has a plano-convex shape.

20. The method of claim 1 , wherein the BAW resonator is part of an integrated circuit.