Internal electrostatic transduction structures for bulk-mode micromechanical resonators

• US 20060017523A1
• Filed: 06/03/2005
• Published: 01/26/2006
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Howe, Roger T., Bhave, Sunil A.
• Granted Patent: US 7,522,019 B2
• Time in Patent Office: Days
• US Class Current: 333/187
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 2009/02511 Vertical, i.e. perpendicular to the substrate plane
• CPC Class Codes: H03H 9/02259 Driving or detection means
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators

Abstract

An electrostatic transducer for micromechanical resonators, in which the electrode gaps are filled with a dielectric material having a much higher permittivity than air. This internal electrostatic transducer has several advantages over both air-gap electrostatic and piezoelectric transduction; including lower motional impedance, compatibility with advanced scaled CMOS device technology, and extended dynamic range. In one aspect, in order to minimize energy losses, the dielectric material has an acoustic velocity which is matched to that of the resonator material. Internal electrostatic transduction can be adapted to excite and detect either vertical modes (perpendicular to the substrate) or lateral modes (in the plane of the substrate). Its increased transduction efficiency is of particular importance for reducing the motional resistance of the latter.

Claims

1. A micromechanical resonator comprising:

a microresonator body fabricated on a substrate incorporating

an internal electrostatic transducer located approximately at the maximum strain antinode of said microresonator, said electrostatic transducer comprising

a first electrode;

a dielectric layer disposed adjacent to said first electrode; and

a second electrode disposed adjacent to said dielectric layer,

in which the bulk acoustic modes of said micromechanical resonator are transduced.

2. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is oriented in a direction that is substantially perpendicular to the plane of said substrate, so as to enable the excitation and detection of lateral acoustic modes in the microresonator body.

3. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is oriented in a direction that is substantially parallel to the plane of said substrate, so as to enable the excite and detect vertical acoustic modes in the microresonator body.

4. The micromechanical resonator of claim of claim 3 wherein said internal electrostatic transducer is formed by depositing and patterning said electrodes and said dielectric layer.

5. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from a semiconducting crystal and a deposited dielectric layer.

6. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from crystalline silicon and a deposited dielectric layer.

7. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from silicon and a dielectric material with substantially equal acoustic velocity as the silicon.

8. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from silicon and a dielectric material and the dielectric material has a thickness approximately equal to a quarter acoustic wavelength.

9. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from silicon and a dielectric material selected from a group consisting of titanium dioxide, hafnium dioxide, silicon nitride, alumina and silicon dioxide.

10. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from

a conducting material selected from the group consisting of polycrystalline silicon, polycrystalline silicon germanium, and polycrystalline silicon carbide,

and a dielectric material.

11. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is one of an array of transducers.

12. The micromechanical resonator of claim 1 wherein said internal electrostatic transducer is made from silicon and a graded permittivity dielectric embedded in the gap between the resonator and electrodes, configured to excite the shear bulk vibration mode of the micromechanical resonator.

13. A method of forming a lateral mode high frequency electrostatic transducer, comprising:

forming a resonator structure having an array of electrodes, wherein the electrodes are separated from each other by electrode gaps; and

filling the electrode gaps with a dielectric material having a permittivity value that is higher than the permittivity value of air.

14. The method of claim 13 wherein said filling comprises a low pressure chemical vapor deposition process.

15. The method of claim 13 wherein said filling comprises an atomic layer deposition process.

16. The method of claim 13 wherein the dielectric material has an acoustic velocity that is substantially equal to that of the electrodes.

17. The method of claim 13 wherein the dielectric material has a Young'"'"'s modulus-to-density ratio that is substantially equal to that of the resonator structure.

18. The method of claim 13 wherein the dielectric material is selected from a group consisting of titanium dioxide, hafnium dioxide, silicon nitride, alumina and silicon dioxide.

19. A method of forming a lateral mode high frequency electrostatic transducer, comprising:

forming a resonator having an array of electrodes, wherein the electrodes are separated from each other by electrode gaps; and

filling the electrode gaps with a dielectric material having a permittivity value that is higher than the permittivity value of air, wherein the dielectric material is selected from the group consisting of titanium dioxide, hafnium dioxide, silicon nitride, alumina and silicon dioxide,

and wherein the dielectric material has an acoustic velocity that is substantially equal to that of the electrodes.

20. A micromechanical device fabricated by a method, comprising:

forming a resonator having an array of electrodes, wherein the electrodes are separated from each other by electrode gaps; and

filling the electrode gaps with a dielectric material having a permittivity value that is higher than the permittivity value of air.

21. The device of claim 20 wherein said filling comprises a low pressure chemical vapor deposition process.

22. The device of claim 20 wherein said filling comprises an atomic layer deposition process.

23. The device of claim 20 wherein the dielectric material has an acoustic velocity that is substantially equal to that of the resonator structure.

24. The device of claim 20 wherein the dielectric material has Young'"'"'s modulus-to-density ratio that is substantially equal to that of the resonator structure.

25. The device of claim 20 wherein the dielectric material is selected from the group consisting of titanium dioxide, hafnium dioxide, silicon nitride, alumina and silicon dioxide.

26. A micromechanical device fabricated by a method, comprising:

forming a resonator having an array of electrodes, wherein the electrodes are separated from each other by electrode gaps; and

filling the electrode gaps with a dielectric material having a permittivity value that is higher than the permittivity value of air, wherein the dielectric material is selected from the group consisting of titanium dioxide, hafnium dioxide, silicon nitride, alumina and silicon dioxide,

and wherein the dielectric material has an acoustic velocity that is substantially equal to that of the electrodes.