Bulk acoustic wave resonator filters including a high impedance shunt branch and methods of forming the same
A BAW resonator ladder topology pass-band filter can include a plurality of series branches each including BAW series resonators. A plurality of shunt branches can each include BAW shunt resonators, wherein the plurality of series branches are coupled to the plurality of shunt branches to provide the BAW resonator ladder topology pass-band filter. A high-impedance shunt branch can include a plurality of high-impedance BAW shunt resonators coupled together in-series to provide an impedance for the high-impedance shunt branch that is greater the other shunt branches in the BAW resonator ladder topology pass-band filter.
1. A BAW resonator ladder topology pass-band filter comprising:
a plurality of series branches each including BAW series resonators;
a plurality of shunt branches each including BAW shunt resonators, wherein the plurality of series branches are coupled to the plurality of shunt branches to provide the BAW resonator ladder topology pass-band filter; and
a high-impedance shunt branch including a plurality of high-impedance BAW shunt resonators coupled together in-series to provide an impedance for the high-impedance shunt branch that is greater the other shunt branches in the BAW resonator ladder topology pass-band filter.
2. The BAW resonator ladder topology pass-band filter of claim 1 wherein the high-impedance shunt branch has a resonance frequency f s peak that is greater than respective resonance frequency f s peaks generated by the other shunt branches.
3. The BAW resonator ladder topology pass-band filter of claim 1 wherein each of the plurality of high-impedance BAW shunt resonators included in the high-impedance shunt branch provides an impedance that is at least about twice an impedance of each of the BAW series resonators and each of the BAW shunt resonators in the other shunt branches.
4. The BAW resonator ladder topology pass-band filter of claim 1 wherein the plurality of high-impedance BAW shunt resonators provides a combined impedance of at least about 400 ohms for the high-impedance shunt branch.
5. The BAW resonator ladder topology pass-band filter of claim 1 wherein the high-impedance shunt branch is located at an output of the BAW resonator ladder topology pass-band filter.
6. The BAW resonator ladder topology pass-band filter of claim 1 wherein the high-impedance shunt branch is located at an input of the BAW resonator ladder topology pass-band filter.
7. The BAW resonator ladder topology pass-band filter of claim 1 wherein the high-impedance shunt branch is located between an input of the BAW resonator ladder topology pass-band filter and an output of the BAW resonator ladder topology pass-band filter.
8. The BAW resonator ladder topology pass-band filter of claim 1 wherein the high-impedance shunt branch provides a resonance frequency peak that is aligned with a lower edge of the pass-band of frequencies.
9. The BAW resonator filter of claim 8 wherein the high-impedance shunt branch generates a null in a near-band rejection band of frequencies adjacent to and below the lower edge of the pass-band of frequencies.
10. The BAW resonator ladder topology pass-band filter of claim 1 wherein a surface area of an electrode included in each of the plurality of high-impedance BAW shunt resonators is less than a surface area of any electrode included in the BAW series resonators or any electrode included in the BAW shunt resonators in the other shunt branches.
11. A method of forming a BAW resonator ladder topology pass-band filter, the method comprising:
forming a first upper electrode on an upper surface of a piezoelectric resonator film on a growth substrate in a plurality of series branches of the BAW resonator ladder topology pass-band filter;
forming a second upper electrode on an upper surface of the piezoelectric resonator film on the growth substrate in a plurality of shunt branches of the BAW resonator ladder topology pass-band filter;
forming a third upper electrode on an upper surface of a piezoelectric resonator film on the growth substrate in a high-impedance shunt branch of the BAW resonator ladder topology pass-band filter, wherein a surface area of the third upper electrode is less than a surface area of the first upper electrode and the second upper electrode;
forming a sacrificial layer on the first, second and third upper electrodes;
forming a support layer on the sacrificial layer, the first upper electrode, the second upper electrode and the third upper electrode, and on the upper surface of a piezoelectric resonator film; and
coupling an upper surface of the support layer to a transfer substrate.
12. The method of claim 11 further comprising:
removing the growth substrate to expose a lower surface of the piezoelectric resonator film;
forming a first lower electrode on the lower surface of the piezoelectric resonator film opposite the first upper electrode;
forming a second lower electrode on the lower surface of the piezoelectric resonator film opposite the second upper electrode;
forming a third lower electrode on the lower surface of the piezoelectric resonator film opposite the third upper electrode; and
removing the sacrificial layer.
13. The method of claim 11 wherein the surface area of the third upper electrode is about 50% of the surface area of the first upper electrode and surface area of the second upper electrode.
14. A Bulk Acoustic Wave (BAW) resonator filter comprising:
a BAW resonator pass-band filter, the BAW resonator pass-band filter configured to pass an input signal in a pass-band of frequencies received at an input node of the BAW resonator pass-band filter to an output node of a BAW resonator pass-band filter circuit; and
a high-impedance BAW resonator shunt branch in the BAW resonator pass-band filter circuit including a plurality series coupled BAW resonators in the high-impedance BAW resonator shunt branch.
15. The BAW resonator filter of claim 14 wherein the high-impedance BAW resonator shunt branch has a resonance frequency peak aligned with a lower edge of the pass-band of frequencies.
16. The BAW resonator filter of claim 15 wherein the resonance frequency peak generates a null in a near-band rejection band of frequencies adjacent to and below the lower edge of the pass-band of frequencies.
17. The BAW resonator filter of claim 14 wherein a combined impedance of the high-impedance BAW resonator shunt branch is about 400 Ohms.
18. The BAW resonator filter of claim 17 wherein an impedance of each of the series coupled BAW resonators in the high-impedance BAW resonator shunt branch is about twice an impedance of all other shunt resonators in the ladder topology BAW resonator pass-band filter circuit.
19. The BAW resonator filter of claim 15 wherein the resonance frequency peak of the high-impedance resonator is greater than respective resonance frequency peaks of all other shunt resonators included in the ladder topology BAW resonator pass-band filter circuit.