Methods of fabricating a membrane with improved mechanical integrity
Methods for fabricating robust films across a patterned underlying layer's edges or steps are disclosed. The novel methods diminish the negative effects of electrode steps or edges on the integrity of a membrane. Thus, the methods are particularly applicable to membrane release technology. The height of the step or edge is eliminated or reduced to increase the mechanical integrity of the film.
1. A method of forming a thin film acoustic device having a piezoelectric film between a base electrode and a second electrode that enable application of an electric field to the piezoelectric film, the method comprising:
(a) providing a substrate;
(b) forming the base electrode as a stair-step shaped electrode by;
(b1) depositing a plurality of conducting layers on the substrate wherein any odd conducting layer is composed of a first conducting material and any even conducting layer is composed of a conducting material, which is different from the first conducting material, such that adjacent layers of the odd and even conducting layers have different etch profiles from each other;
(b2) selectively laterally etching one of the conducting layers;
(b3) selectively laterally etching an other of the conducting layers directly below the one conducting layer; and
(b4) stopping step (b3) at a point where the other of the conducting layers is etched less than the one conducting layer to form a step of the stair-step shaped electrode;
(c) depositing the piezoelectric film on the base electrode; and
(d) forming the second electrode over the piezoelectric film.
2. The method of claim 1 , wherein the piezoelectric film serves as a support membrane for the device.
3. The method of claim 1 , wherein the plurality of conducting layers comprises at least two of the odd conducting layers and at least two of the even conducting layers.
4. The method of claim 3 , wherein each said step in the stair-step shaped electrode is formed between an even conducting layer and an adjacent odd conducting layer having different lateral dimensions.
5. The method of claim 4 , wherein each said step in the stair-step shaped electrode comprises an adjacent pair of one odd conducting layer and one even conducting layer having equivalent lateral dimensions.