Piezoelectric resonator operating in thickness shear mode

1. Acoustic wave resonator device comprising a resonant layer that comprises a series of laterally adjacent areas of first and second dielectric materials, of which one or both materials are piezoelectric, wherein either:

(a) the first dielectric material is a piezoelectric and the second dielectric material is a non-piezoelectric; or

(b) the first and second dielectric materials are piezoelectrics of different piezoelectric properties;

wherein the piezoelectric material is AlN, ZnO or GaN; and

wherein the resonator comprises an electrode system configured for excitation of shear thickness resonance of acoustic waves.

2. Acoustic wave resonator device of claim 1 (a) wherein the second dielectric material is a disordered piezoelectric material with substantially no net piezoelectric effect.

3. Acoustic wave resonator device of claim 1 (b) wherein the first dielectric material is a piezoelectric of first polarity and the second dielectric material is a piezoelectric of opposite polarity or of different polarity.

4. Acoustic wave resonator device of claim 1 wherein the resonant layer is supported on a reflector composed of series of layers of high acoustic impedance material(s) alternating with layers of low acoustic impedance material(s).

5. Acoustic wave resonator device of claim 4 wherein the reflector comprises at least one of AlN, Al2O3, Ta2O5, HfO2 or W as high impedance material and SiO2 as low impedance material.

6. Acoustic wave resonator device of claim 1 wherein the resonant layer is a membrane with mechanically free surfaces.

7. Acoustic wave resonator device of claim 1 comprising an electrode system configured for in-phase electric field production in the plane of piezoelectric parts of the resonant layer.

8. Acoustic wave resonator device of claim 1 comprising interdigitated electrodes.

9. Acoustic wave resonator device of claim 1 comprising a patterned electrodes system consisting of patterned electrodes made of an electrically-conductive first material separated by an electrically non-conductive second material with similar mechanical properties to the first material.

10. Acoustic wave resonator device of claim 9 wherein the first material of the electrodes is based on Al and the second material is SiO2.

11. A media sensing apparatus comprising an acoustic wave resonator device of claim 1 .

12. A media sensing apparatus for liquid immersion comprising an acoustic wave resonator device of claim 1 .

13. A piezoelectric transformer comprising:

an input part;

a matching part; and

an output part,

wherein the input part comprises an acoustic wave resonator device of claim 1 , the output part comprises a piezoelectric material and the matching part is arranged to acoustically couple the input and output parts.

14. The piezoelectric transformer of claim 13 wherein the output part is made of AlN or ZnO.

15. The piezoelectric transformer of claim 13 wherein the matching part is made of SiO2.

16. Acoustic wave resonator device comprising a resonant layer that

comprises a series of laterally adjacent areas of first and second dielectric materials, of which one or both materials are piezoelectric, wherein either:

(a) the first dielectric material is a piezoelectric and the second dielectric material is a non-piezoelectric; or

(b) the first and the second dielectric materials are piezoelectrics of different piezoelectric properties;

wherein the piezoelectric material is AlN, ZnO or GaN; and

wherein the resonator comprises an electrode system configured for excitation of a pure shear thickness resonance of the acoustic waves.