Integrated coupled resonator filter and bulk acoustic wave devices
View Patent ↗A method for manufacturing a filter device is provided. The filter device comprises a coupled resonator at a first site, a shunt resonator at a second site and a series resonator at a third site, the coupled resonator comprising a first and a second resonator. The method comprising a step of providing a substrate with a piezoelectric layer sandwiched between a first electrode and a first part of a second electrode at the first site and the second site, the piezoelectric layer sandwiched between the first electrode and a second part of the second electrode at the third site. The method further comprising the step of forming a coupling layer on the second electrode, the step of forming a further piezoelectric layer sandwiched between a further first electrode and a further second electrode at the third site and the step of removing the coupling layer at the second and third sites.
1. A coupled resonator filter device, comprising:
a substrate;
a coupled resonator filter comprising a first bulk acoustic wave (BAW) resonator, a second BAW resonator and an acoustic coupling layer disposed between the first BAW resonator and the second BAW resonator, the second BAW resonator comprising a second port with a first terminal and a second terminal; and
a filter section comprising a BAW resonator electrically connecting the first BAW resonator of the coupled resonator filter with a first terminal and a second terminal of a first port, wherein the first and second BAW resonators of the coupled resonator filter are acoustically coupled and the first BAW resonator of the coupled resonator filter and the BAW resonator of the filter section are arranged at different sites of a piezoelectric layer.
2. The coupled resonator filter device according to claim 1 , wherein the first BAW resonator of the coupled resonator filter is formed between the substrate and the second BAW resonator of the coupled resonator filter.
3. The coupled resonator filter device according to claim 1 , wherein the filter section comprises: a shunt resonator and a series resonator, wherein the shunt resonator is connected in parallel to the first BAW resonator of the coupled resonator filter and the series resonator is connected in series between the first terminal of the first port and one of the electrodes of the first BAW resonator of coupled resonator filter.
4. The coupled resonator filter device according to claim 3 , further comprising: a further coupled resonator filter comprising a first BAW resonator and a second BAW resonator, which are acoustically coupled, wherein the first BAW resonator of the further coupled resonator filter is formed between the second BAW resonator of the further coupled resonator filter and the substrate and is electrically connected in parallel to the first BAW resonator of the coupled resonator filter, and wherein the second port further comprises a third terminal and the second BAW resonator of the further coupled resonator filter is electrically connected in series between the second and third terminals of the second port.
5. The coupled resonator filter device according to claim 4 , wherein the second terminal of the second port comprises a ground output, and wherein the first and the third terminals of the second port comprise a signal output so that an output signal of the first terminal is phase shifted by 180° to an output signal at the third terminal of the second port and the output signal at the second port comprises a balanced output signal.
6. The coupled resonator filter device according to claim 5 , wherein in operation the coupled resonator filter device performs a single-to-balanced mode conversion for signals from the first port to the second port.
7. The coupled resonator filter device according to claim 1 , wherein the substrate comprises acoustical mirrors at sites, where the first BAW resonator of the coupled resonator filter is formed and where the BAW resonator of the filter section is formed, the acoustical mirrors comprising a layer assembly of alternating materials of high and low acoustic impedances, and wherein the first and second BAW resonators of the coupled resonator filter are acoustically coupled by a further layer assembly of coupling layers of alternating high and low acoustic impedances.
8. The coupled resonator filter device as claimed in claim 1 , wherein the acoustic coupling layer comprises a low acoustic impedance layer and a high acoustic impedance layer.