BAW RESONATOR WITH COIL INTEGRATED IN HIGH IMPEDANCE LAYER OF BRAGG MIRROR OR IN ADDITIONAL HIGH IMPEDANCE METAL LAYER BELOW RESONATOR

1 . A bulk acoustic wave (BAW) resonator of a solidly mounted resonator (SMR) type, the BAW resonator comprising:

a substrate, a Bragg mirror, a bottom electrode, a piezoelectric layer and a top electrode;

wherein the Bragg mirror comprises alternating mirror layers of high acoustic impedance and low acoustic impedance where at least two high impedance layers are present;

wherein a first planar coil is formed from one of the high impedance mirrors layer or from an additional metal layer arranged between the substrate and a low impedance mirror layer; and

wherein the planar coil is electrically coupled to the resonator.

2 . The BAW resonator of claim 1 :

wherein the coil is formed from an additional high impedance layer;

wherein the additional high impedance layer and the high impedance mirror layers comprise the same material; and

wherein high impedance layers are embedded between dielectric low-impedance layers.

3 . The BAW resonator of claim 1 , further comprising:

two additional metal layers with a respective first or second planar coil formed therein, wherein the first and second planar coil are circuited in series with each other.

4 . The BAW resonator of claim 1 :

wherein the material of the high impedance layers comprises a metal chosen from W, Mo and Al; and

wherein the material of the low impedance layers is silicon oxide.

5 . The BAW resonator of claim 1 :

wherein an active resonator region is defined to be a region where bottom electrode, piezoelectric layer and top electrode overlap each other;

wherein an active resonator area is the area of the active resonator region when projected normal to the top surface of the substrate; and

wherein the planar coil is coupled to the bottom or top electrode by conducting vias guided through the stack of mirror layer at a position that is outside the active resonator area.

6 . The BAW resonator of claim 1 :

wherein the planar coil is a planar winding that has a first end in the middle of the winding and a second end; and

wherein the first end is connected by a first via to a first electrode of the resonator and the second end of the planar coil is connected by a second via to the second electrode of the resonator, wherein first and second electrode are selected from bottom electrode and top electrode.

7 . The BAW resonator of claim 1 :

wherein a respective first planar coil and a respective second planar coil are arranged one above the other but are separated by a low impedance layer of a dielectric; and

wherein the first and second planar coil are circuited in series with each other by a via connecting the first ends in the middles of the respective windings.

8 . The BAW resonator of claim 1 , wherein the materials of the electrodes of the resonator are chosen from the group comprising W, Mo or Al.

9 . The BAW resonator of claim 1 :

wherein the coil comprises a first winding formed in a first metal layer and a second winding formed in a second metal layer;

wherein the two windings are circuited in series with each other by a via connecting the first ends in the middles of the respective windings; and

wherein a first one of the second ends of the series connection of the two windings are connected to the bottom electrode while the second one of the second ends is connected to the top electrode to circuit the coil in parallel to the BAW resonator.

10 . The BAW resonator of claim 1 , wherein at least one of the high impedance mirror layers is grounded.