Process of making a BAW resonator bi-layer top electrode
A piezoelectric layer is coupled to a bottom electrode in a method of fabricating a piezoelectric resonator. A bottom metal layer of a top electrode is deposited on the piezoelectric layer. The bottom metal layer is patterned and etched. A top metal layer of the top electrode is deposited on the etched bottom metal layer. The top metal layer is patterned and etched. An interconnect metal layer is deposited on the etched top metal layer and the piezoelectric layer such that the interconnect metal layer isolates the bottom metal layer from subsequent etch steps.
1. A method of fabricating a piezoelectric resonator, the method comprising:
a. providing a bottom electrode and a piezoelectric layer coupled to the bottom electrode;
b. depositing a bottom metal layer of a top electrode in direct contact with the piezoelectric layer;
c. patterning and etching the bottom metal layer;
d. depositing a top metal layer of the top electrode in direct contact with the etched bottom metal layer;
e. patterning and etching the top metal layer; and
f. depositing an interconnect metal layer in direct contact with the etched top metal layer, in direct contact with the etched bottom metal layer, and in direct contact with the piezoelectric layer such that the interconnect metal layer isolates the etched bottom metal layer from subsequent etch steps.
2. The method of claim 1 further comprising patterning and etching the interconnect metal layer such that the bottom metal layer of the top electrode is isolated from the etching.
3. The method of claim 1 wherein the interconnect metal layer is patterned such that all edges of the top electrode including the top metal layer and the bottom metal layer remain covered by the interconnect metal layer after a subsequent etch steps.
4. The method of claim 1 wherein the interconnect metal layer comprises a first interconnect metal layer and a second interconnect metal layer.
5. The method of claim 4 wherein the first interconnect metal layer comprises titanium tungsten.
6. The method of claim 4 wherein the second interconnect metal layer comprises aluminum copper or copper.
7. The method of claim 1 wherein the interconnect metal layer comprises titanium tungsten, tungsten, or molybdenum.
8. The method of claim 1 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.
9. The method of claim 1 wherein the piezoelectric resonator comprises a bulk acoustic wave resonator.
10. The method of claim 1 wherein the bottom metal layer comprises a refractory metal.
11. The method of claim 10 wherein the bottom metal layer comprises molybdenum.
12. The method of claim 10 wherein the bottom metal layer comprises ruthenium, tungsten, platinum, osmium, rhenium or iridium.
13. The method of claim 1 wherein the top metal layer comprises aluminum, gold, platinum, or an aluminum alloy composition.
14. The method of claim 1 wherein the top metal layer comprises a metal alloy composition.