Method for controlling piezoelectric coupling coefficient in film bulk acoustic resonators and apparatus embodying the method
View Patent ↗An apparatus such as a thin film resonator has a bottom electrode, a top electrode, and a composite layer between the two electrodes. The composite layer includes a piezoelectric (PZ) layer having a first coupling coefficient and a coupling coefficient control (CCC) layer having a second coupling coefficient. By varying the relative thicknesses of the PZ layer and the CCC layer during the manufacturing process, the coupling coefficient of the resonator can be established (to any value between the first coupling coefficient and the second coupling coefficient) with minimal impact on resonant frequency. Further, it is relatively less difficult to fabricate the PZ layer and the CCC layer having the desired coupling coefficient (as a combination of the first coupling coefficient and the second coupling coefficient) compared to the difficulties of fabrication of a uniform PZ layer having the desired coupling coefficient.
1. An apparatus fabricated on a substrate, the apparatus comprising:
a bottom electrode;
a composite layer on said bottom electrode, said composite layer comprising
a piezoelectric layer having a first coupling coefficient said piezoelectric layer including Aluminum Nitride;
a coupling coefficient control layer having a second coupling coefficient, said coupling coefficient control layer including Aluminum Oxy-Nitride; and
a top electrode above said composite layer.
2. The apparatus recited in claim 1 wherein said coupling coefficient control layer comprises a non-piezoelectric dielectric material.
3. The apparatus recited in claim 1 further comprising a seed layer under said bottom electrode.
4. The apparatus recited in claim 1 further comprising a passivation layer over said top electrode.
5. The apparatus recited in claim 1 wherein said bottom electrode comprises Molybdenum.
6. The apparatus recited in claim 1 wherein the apparatus is fabricated over a cavity.
7. A method of fabricating an apparatus, the method comprising:
fabricating a bottom electrode on a substrate;
fabricating a composite layer on said bottom electrode, said composite layer comprising
a piezoelectric layer having a first coupling coefficient said piezoelectric layer including Aluminum Nitride;
a coupling coefficient control layer having a second coupling coefficient, said coupling coefficient control layer including Aluminum Oxy-Nitride; and
fabricating a top electrode above said composite layer.
8. The method recited in claim 7 wherein said coupling coefficient control layer comprises a non-piezoelectric dielectric material.
9. The method recited in claim 7 further comprising a step of fabricating a seed layer under said bottom electrode.
10. The method recited in claim 7 further comprising a step of fabricating a passivation layer over said top electrode.
11. The method recited in claim 7 wherein said bottom electrode comprises Molybdenum.
12. The method recited in claim 7 wherein the apparatus is fabricated over a cavity.