ACOUSTIC WAVE RESONATOR HAVING ANTIRESONANT CAVITY

1 . An acoustic wave resonator structure, comprising:

substrate having a first surface and a second surface;

a piezoelectric layer disposed over the substrate, the piezoelectric layer having a first surface, and a second surface comprising a plurality of features;

a plurality of electrodes disposed over the first surface of the piezoelectric layer, the plurality of electrodes configured to generate surface acoustic waves in the piezoelectric layer; and

a layer disposed between the first surface of the substrate and the second surface of the piezoelectric layer, the layer having a first surface and a second surface, the second surface of the layer being on contact with the second surface of the substrate, and having a smoothness sufficient to foster atomic bonding between the second surface of the layer and the first surface of the substrate, wherein the layer and the piezoelectric layer have a combined thickness (H) selected so an anti-resonance (AR) condition exists between the first surface of the piezoelectric layer and the second surface of the layer for an undesired bulk vertical shear mode.

2 . The acoustic wave resonator structure of claim 1 , wherein a pitch of the plurality of electrodes is selected to be one-half of a wavelength (λ/2) of a desired resonant mode.

3 . The acoustic wave resonator structure of claim 2 , wherein the combined is equal to approximately to a correction factor (n) times the pitch of the plurality of electrodes, wherein n is an integer in the range of approximately 5 to approximately 20.

4 . The acoustic wave resonator structure of claim 3 , wherein the correction factor is a ratio of a velocity of the undesired bulk vertical shear mode in the piezoelectric layer to a velocity of the desired resonant mode.

5 . The acoustic wave resonator structure as claimed in claim 1 , wherein at least some of the plurality of features have substantially slanted sides.

6 . The acoustic wave resonator structure as claimed in claim 5 , wherein at least some of the plurality of features are substantially not in a regular pattern.

7 . The acoustic wave resonator structure as claimed in claim 5 , wherein the at least some of the plurality of features have a height of approximately one-fourth of a wavelength (¼λ) of a spurious mode.

8 . The acoustic wave resonator structure as claimed in claim 5 , wherein the at least some of the plurality of features have a plurality of heights, and each of the pluralities of heights is approximately a height in the range of approximately one-fourth of a wavelength (¼λ) of one of the plurality of spurious modes.

9 . The acoustic wave resonator structure as claimed in claim 1 , wherein the layer comprises an oxide material.

10 . The acoustic wave resonator structure as claimed in claim 9 , wherein the oxide material comprises silicon dioxide (SiO 2 ).

11 . The acoustic wave resonator structure as claimed in claim 10 , wherein the second surface of the layer has a root-mean-square (RMS) variation in height of approximately 0.1 Å to approximately 10.0 Å.

12 . The acoustic wave resonator structure as claimed in claim 1 , wherein the layer comprises one of ZnO 2 , HfO 2 , AlN, Y 2 O 3 , Yb 2 O 3 , Cr 2 O 3 , Sc 2 O 3 .

13 . An acoustic wave filter comprising a plurality of acoustic wave resonator structures, one or more of the plurality of acoustic wave resonator structures comprising:

substrate having a first surface and a second surface;

a piezoelectric layer disposed over the substrate, the piezoelectric layer having a first surface, and a second surface, comprising a plurality of features;

a plurality of electrodes disposed over the first surface of the piezoelectric layer, the plurality of electrodes configured to generate surface acoustic waves in the piezoelectric layer; and

a layer disposed between the first surface of the substrate and the second surface of the piezoelectric layer, the layer having a first surface and a second surface, the second surface of the layer being on contact with the second surface of the substrate, and having a smoothness sufficient to foster atomic bonding between the second surface of the layer and the first surface of the substrate, wherein the layer and the piezoelectric layer have a combined thickness (H) selected so an anti-resonance (AR) condition exists between exists between the first surface of the piezoelectric layer and the second surface of the layer for an undesired bulk vertical shear mode.

14 . The acoustic wave filter of claim 13 , wherein the acoustic wave filter has a roll-off at a high frequency side of a passband of approximately 0.5 to approximately 0.6 times a guard band.

15 . The acoustic wave filter of claim 14 , wherein the passband rolls off from approximately 2.5 dB to approximately 50 dB.

16 . The acoustic wave filter of claim 13 , wherein the pitch is selected to be one-half of a wavelength (λ/2) of a desired resonant mode.

17 . The acoustic wave filter of claim 16 , wherein the combined thickness is equal to approximately to a correction factor (n) times the pitch of the plurality of electrodes, wherein n is an integer in the range of approximately 5 to approximately 20.

18 . The acoustic wave filter of claim 17 , wherein the correction factor is a ratio of a velocity of the undesired bulk vertical shear mode in the piezoelectric layer to a velocity of the desired resonant mode.

19 . A acoustic wave filter as claimed in claim 13 , wherein at least some of the plurality of features in the first surface of the substrate have substantially slanted sides.

20 . A acoustic wave filter as claimed in claim 13 , wherein the plurality of features are substantially not in a regular pattern.