Loaded series resonators for adjusting frequency response of acoustic wave resonators

1. An acoustic wave filter device comprising:

an acoustic wave filter element comprising input electrodes and output electrodes located on a top surface of a piezoelectric layer;

a first resonator comprising a first resonator top electrode on the top surface of the piezoelectric layer and a first resonator bottom electrode on a bottom surface of the piezoelectric layer, the first resonator having a first notch in resonator impedance at a first frequency, wherein one of the top and the bottom electrodes of the first resonator is electrically connected to the acoustic wave filter element; and

a second resonator coupled to the acoustic wave filter element and comprising a second resonator top electrode on the top surface of the piezoelectric layer, a second resonator bottom electrode on the bottom surface of the piezoelectric layer, wherein the second resonator has a second thickness that is different from a first thickness of the first resonator such that the second resonator has a second notch in resonator impedance at a second frequency that is different from the first frequency, and wherein one of the top and the bottom electrodes of the second resonator is electrically connected to the acoustic wave filter element,

wherein the first frequency is an anti-resonance frequency of the first resonator, and the second frequency is an anti-resonance frequency of the second resonator, and

wherein both the first and the second frequencies are within a sideband of resonator impedance of the acoustic wave filter element.

2. The acoustic wave filter device of claim 1 , wherein the second thickness is greater than the first thickness due to at least one of: the second resonator top electrode being thicker than the first resonator top electrode, the second resonator bottom electrode being thicker than the first resonator bottom electrode, or the piezoelectric layer within the second resonator being thicker than the piezoelectric layer within the first resonator.

3. The acoustic wave filter device of claim 1 , wherein the second resonator is thicker than the first resonator in multiple layers of corresponding resonator top electrodes, corresponding resonator bottom electrodes, corresponding piezoelectric layers, or corresponding mass loading layers on the corresponding top electrodes in the first and the second resonators.

4. The acoustic wave filter device of claim 1 , wherein the first frequency and the second frequency differ by at least 1%.

5. The acoustic wave filter device of claim 1 , wherein the first resonator bottom electrode is electrically coupled to the input electrodes, and the second resonator bottom electrode is electrically coupled to the output electrodes.

6. The acoustic wave filter device of claim 1 , wherein the first resonator top electrode is an uppermost layer of the first resonator.

7. The acoustic wave filter device of claim 1 , further comprising a first mass loading layer on the first resonator top electrode.

8. The acoustic wave filter device of claim 7 , further comprising a second mass loading layer on the second resonator top electrode, wherein the first mass loading layer and the second mass loading layer have a same material but have different thicknesses.

9. The acoustic wave filter device of claim 7 , further comprising a second mass loading layer on the second resonator top electrode, wherein the first mass loading layer and the second mass loading layer are different materials with different density and/or different stiffness.

10. The acoustic wave filter device of claim 7 , wherein the first mass loading layer covers only a portion of the first resonator top electrode.

11. The acoustic wave filter device of claim 7 , further comprising a second mass loading layer on the second resonator top electrode, wherein the first mass loading layer covers the first resonator top electrode and the second mass loading layer covers only a portion of the second resonator top electrode.

12. The acoustic wave filter device of claim 7 , wherein the first mass loading layer is a different material than the first resonator top electrode.

13. The acoustic wave filter device of claim 7 , wherein the first mass loading layer is a same material as the first resonator top electrode, and the first resonator top electrode and second resonator top electrode have different thicknesses.

14. The acoustic wave filter device of claim 1 , wherein the first resonator bottom electrode is electrically connected to the acoustic wave filter element by a first conductive via extending through the piezoelectric layer, and the second resonator bottom electrode is electrically connected to the acoustic wave filter element by a second conductive via extending through the piezoelectric layer.

15. The acoustic wave filter device of claim 1 , wherein the input electrodes, the output electrodes, the first resonator electrode, and the second resonator electrode are provided by separate portions of a same electrode layer on the top surface of the piezoelectric layer.

16. The acoustic wave filter device of claim 1 , wherein a thickness of the piezoelectric layer and a gap width between the input and output electrodes is such that application of a radio frequency voltage between the input electrodes and the counter-electrode will create symmetric and antisymmetric acoustic thickness-extensional resonance modes in the piezoelectric layer.

17. The acoustic wave filter device of claim 1 , comprising a counter-electrode located on the bottom surface of the piezoelectric layer below the input electrodes and the output electrodes.

18. The acoustic wave filter device of claim 17 , wherein the acoustic wave filter element is a laterally acoustically coupled bulk acoustic wave (LBAW) filter.