Micromechanical devices based on piezoelectric resonators

1. A piezoelectrically transduced resonator device comprising:

a wafer including a substrate, a buried oxide layer formed on the substrate, and a device layer formed on the buried oxide layer, the wafer further including an air gap in which portions of the buried oxide layer and device layer have been removed; and

a resonator suspended within the air gap of the wafer above the substrate, the resonator comprising a portion of the device layer, a piezoelectric layer, and top and bottom electrodes contacting top and bottom sides of the piezoelectric layer, wherein the portion of the device layer is not directly connected to the wafer;

wherein the resonator is configured to move relative to the substrate under electrostatic force to tune the frequency of the resonator device when a direct current voltage is applied between the substrate and the portion of the device layer of the resonator.

2. The resonator device of claim 1 , wherein the substrate is made of silicon.

3. The resonator device of claim 1 , wherein the buried oxide layer is made of a thermally grown oxide.

4. The resonator device of claim 1 , wherein the device layer is made of single crystalline silicon.

5. The resonator device of claim 1 , wherein the piezoelectric layer is made of quartz (SiO2), zinc oxide (ZnO), aluminum nitride (AlN), barium titanate (BaTiO3), or lead-zirconate-titanate (PZT).

6. The resonator device of claim 1 , wherein the electrodes are made of a metal material.

7. The resonator device of claim 1 , wherein the electrodes extend out from the resonator to the wafer so as to support the resonator in its suspended state.

8. The resonator device of claim 7 , wherein no component other than the electrodes support the resonator above the substrate.

9. The resonator device of claim 7 , wherein the bottom electrode extends out from the resonator to the wafer in a first direction and the top electrode extends out from the resonator to the wafer in a second direction that is opposite to the first direction.

10. A method for tuning the resonance frequency of a resonator device, the method comprising:

providing a resonator device comprising a silicon-on-insulator wafer that defines an air gap, the resonator device further comprising a resonator suspended within the air gap of the wafer by electrodes that extend between the resonator and the wafer; and

applying a direct current voltage between a substrate of the wafer and a device layer of the resonator to apply an electrostatic force to the resonator that causes it to move relative to the wafer.

11. The method of claim 10 , wherein the electrostatic force pulls the resonator toward the wafer.

12. The method of claim 10 , wherein the movement of the resonator generates stress within the resonator that alters the resonance frequency of the resonator device.

13. The method of claim 10 , further comprising varying the level of the direct current voltage to vary the resonance frequency of the resonator device.

14. The method of claim 10 , wherein the direct current voltage is in the range of 5 to 30 volts.

15. The method of claim 10 , further comprising removing the direct current voltage to return the resonator to its initial state.