BAW resonator bi-layer top electrode with zero etch undercut
View Patent ↗A piezoelectric resonator includes a multi-layer top electrode configured such that a top most layer protects the underlying layers from subsequent etching, thereby preventing etch undercut of the top-most layer. In one embodiment, the multi-layer top electrode is configured as a bi-layer, so that the upper layer of the bi-layer stack protects all sides of the underlying layer from subsequent etch process steps. In an alternative embodiment, at least the perimeter of a multi-layer top electrode is completely covered with overlapping interconnect metal.
1. A piezoelectric resonator comprising:
a. a bottom electrode;
b. a piezoelectric layer coupled to the bottom electrode; and
c. a top electrode coupled to the piezoelectric layer, wherein the top electrode comprises a bottom metal layer and a top metal layer configured such that the top metal layer isolates the bottom metal layer from subsequent etch steps.
2. The piezoelectric resonator of claim 1 wherein the bottom metal layer comprises a refractory metal.
3. The piezoelectric resonator of claim 2 wherein the bottom metal layer comprises molybdenum.
4. The piezoelectric resonator of claim 2 wherein the bottom metal layer comprises ruthenium, tungsten, platinum, osmium, rhenium or iridium.
5. The piezoelectric resonator of claim 1 wherein the top metal layer comprises aluminum, gold, platinum, or an aluminum alloy composition.
6. The piezoelectric resonator of claim 1 wherein the top metal layer comprises a metal alloy composition.
7. The piezoelectric resonator of claim 1 further comprising an interconnect metal layer coupled to the top metal layer.
8. The piezoelectric resonator of claim 7 wherein the interconnect metal layer is physically isolated from the bottom metal layer of the top electrode.
9. The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises a first interconnect metal layer and a second interconnect metal layer.
10. The piezoelectric resonator of claim 9 wherein the first interconnect metal layer comprises titanium tungsten.
11. The piezoelectric resonator of claim 9 wherein the second interconnect metal layer comprises aluminum copper or copper.
12. The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises titanium tungsten, tungsten, or molybdenum.
13. The piezoelectric resonator of claim 7 wherein the interconnect metal layer comprises a metal material that is selectively etched relative to a material of the top metal layer of the top electrode.
14. The piezoelectric resonator of claim 1 wherein the piezoelectric resonator comprises a bulk acoustic wave resonator.
15. The piezoelectric resonator of claim 1 wherein:
the bottom metal layer comprises a top surface, a bottom surface opposite the top surface, and a sidewall surface disposed around the perimeter of the bottom metal layer between the top surface and the bottom surface; and
the top metal layer completely overlaps the bottom metal layer, wherein the top metal layer covers the entire sidewall surface of the bottom metal layer.
16. A piezoelectric resonator comprising:
a. a bottom electrode;
b. a piezoelectric layer coupled to the bottom electrode;
c. a top electrode coupled to the piezoelectric layer, wherein the top electrode comprises a bottom metal layer and a top metal layer; and
d. an interconnect metal layer coupled to the top electrode and configured such that the metal interconnect layer isolates the bottom metal layer from a metal interconnect etch step.
17. The piezoelectric resonator of claim 16 wherein the interconnect metal layer is configured to cover a perimeter of the top electrode such that the bottom metal layer is isolated.
18. The piezoelectric resonator of claim 16 wherein the bottom metal layer comprises a refractory metal.
19. The piezoelectric resonator of claim 18 wherein the bottom metal layer comprises molybdenum.
20. The piezoelectric resonator of claim 18 wherein the bottom metal layer comprises ruthenium, tungsten, platinum, osmium, rhenium or iridium.
21. The piezoelectric resonator of claim 16 wherein the top metal layer comprises aluminum, gold, platinum, or an aluminum alloy composition.
22. The piezoelectric resonator of claim 16 wherein the top metal layer comprises a metal alloy composition.
23. The piezoelectric resonator of claim 16 wherein the interconnect metal layer is configured to be in physical contact with the top metal layer and the bottom metal layer of the top electrode.
24. The piezoelectric resonator of claim 16 wherein the interconnect metal layer comprises a first interconnect metal layer and a second interconnect metal layer.
25. The piezoelectric resonator of claim 24 wherein the first interconnect metal layer comprises titanium tungsten.
26. The piezoelectric resonator of claim 24 wherein the second interconnect metal layer comprises aluminum copper or copper.
27. The piezoelectric resonator of claim 16 wherein the interconnect metal layer comprises titanium tungsten, tungsten, or molybdenum.
28. The piezoelectric resonator of claim 16 wherein the interconnect metal layer comprises a metal material that is selectively etched relative to a material of the top metal layer of the top electrode.
29. The piezoelectric resonator of claim 16 wherein the piezoelectric resonator comprises a bulk acoustic wave resonator.
30. The piezoelectric resonator of claim 16 wherein:
the bottom metal layer comprises a top surface, a bottom surface opposite the top surface, and a sidewall surface disposed around the perimeter of the bottom metal layer between the top surface and the bottom surface; and
the interconnect metal layer covers the entire sidewall surface of the bottom metal layer.