Fabrication methods for a piezoelectric micro-electromechanical system (MEMS)
Microelectromechanical System (MEMS) devices and related fabrication methods. A piezoelectric stack is formed on a substrate and is separated from the substrate by a dielectric layer. The piezoelectric stack is formed that includes first and second piezoelectric layers with a first electrode below the first piezoelectric layer, as well as a contact pad and a second electrode between the first and second piezoelectric layers. A first contact is formed that extends through the piezoelectric layers and contact pad to the first electrode. A second contact is formed that extends through the second piezoelectric layer to the second electrode. The contact pad prevents an interface to form between the first and second piezoelectric layers in the contact opening, thus preventing corrosion of the piezoelectric layers during contact formation process.
1. A method for forming a device comprising:
forming a dielectric layer on a substrate;
forming a piezoelectric stack on the dielectric layer, wherein the piezoelectric stack includes a first bottom electrode, a first piezoelectric layer on the first bottom electrode, a second bottom electrode on the first piezoelectric layer, an electrode pad on the first piezoelectric layer, and a second piezoelectric layer on the first piezoelectric layer, the second bottom electrode, and the electrode pad;
patterning the second piezoelectric layer, the electrode pad, and the first piezoelectric layer to form a first via over the first bottom electrode that extends fully through the second piezoelectric layer and the electrode pad and partially through the first piezoelectric layer;
patterning the second piezoelectric layer to form a second via over the second bottom electrode that extends partially through the second piezoelectric layer;
extending, with an etching process, the first via fully through the first piezoelectric layer to the first bottom electrode and the second via fully through the second piezoelectric layer to the second bottom electrode;
forming a first contact in the first via that is electrically coupled to the first bottom electrode, and
forming a second contact in the second via that is electrically coupled to the second bottom electrode.
2. The method of claim 1 further comprising:
forming a top electrode layer on the second piezoelectric layer; and
patterning the top electrode layer to form a first top electrode coupled to the first contact and a second top electrode coupled to the second contact.
3. The method of claim 2 wherein the first top electrode and the second top electrode comprise aluminum copper (AlCu).
4. The method of claim 1 wherein the first bottom electrode and the second bottom electrode comprise molybdenum (Mo).
5. The method of claim 1 wherein the first piezoelectric layer and the second piezoelectric layer comprise aluminum nitride (AlN).
6. The method of claim 1 wherein the etching process is a wet etch.
7. The method of claim 6 wherein the wet etch comprises a tetramethylammonium hydroxide (TMAH) wet etch.
8. The method of claim 1 further comprising:
forming a cavity on a rear side of the substrate to suspend the piezoelectric stack.
9. The method of claim 1 wherein the first via is formed by a first dry etch.
10. The method of claim 9 wherein the second via is formed by a second dry etch after forming the first via.
11. The method of claim 10 wherein the etching process is a wet etch.
12. The method of claim 11 wherein the wet etch comprises a tetramethylammonium hydroxide (TMAH) wet etch.
13. The method of claim 1 wherein the second via is formed by a dry etch.
14. The method of claim 1 wherein the first via and the first contact in the first via are surrounded by the electrode pad.