Micromechanical structures having a capacitive transducer gap filled with a dielectric and method of making same

• US 20070046398A1
• Filed: 08/28/2006
• Published: 03/01/2007
• Est. Priority Date: 08/29/2005
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Lin, Yu-Wei, Li, Sheng-Shian, Xie, Yuan, Nguyen, Clark
• Granted Patent: US 7,551,043 B2
• Time in Patent Office: Days
• US Class Current: 333/186
• CPC Class Codes: H03H 2009/02354 applied along the periphery, e.g. at nodal points of the ring
• CPC Class Codes: H03H 2009/02503 Breath-like, e.g. Lam? mode, wine-glass mode
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 9/2436 Disk resonators

Abstract

Micromechanical structures having at least one lateral capacitive transducer gap filled with a dielectric and method of making same are provided. VHF and UHF MEMS-based vibrating micromechanical resonators filled with new solid dielectric capacitive transducer gaps to replace previously used air gaps have been demonstrated at 160 MHz, with Q'"'"'s˜20,200 on par with those of air-gap resonators, and motional resistances (R_x'"'"'s) more than 8× smaller at similar frequencies and bias conditions. This degree of motional resistance reduction comes about via not only the higher dielectric constant provided by a solid-filled electrode-to-resonator gap, but also by the ability to achieve smaller solid gaps than air gaps. These advantages with the right dielectric material may now allow capacitively-transduced resonators to match to the 50-377Ω impedances expected by off-chip components (e.g., antennas) in many wireless applications without the need for high voltages.

Claims

1. A micromechanical device comprising:

a micromechanical resonator fabricated on a substrate and having a motional resistance;

a micromechanical electrode, the resonator and the electrode defining a capacitive transducer gap; and

a dielectric having a permittivity value that is higher than the permittivity value of air disposed in the gap to decrease the motional resistance of the resonator.

2. The device of claim 1 wherein the dielectric is a liquid.

3. The device of claim 1 wherein the dielectric is selected from a group comprising titanium dioxide, hafnium dioxide, silicon nitride, and BST.

4. The device of claim 1 wherein the dielectric is a porous solid material.

5. The device of claim 1 wherein the resonator is operable in a wine-glass mode.

6. The device of claim 1 wherein the dielectric is dimensioned so that its electrode-to-resonator thickness corresponds to an effective quarter-wavelength of the resonance frequency of the resulting electrode-dielectric-resonator structure.

7. A method of forming an electrostatic transducer, comprising:

forming a micromechanical electrode structure;

forming a micromechanical resonator structure on a substrate, wherein the electrode structure is separated from the resonator structure by a capacitive transducer gap; and

filling the gap with a dielectric having a permittivity value that is higher than the permittivity value of air.

8. The method of claim 7 wherein the dielectric is selected from a group comprising titanium dioxide, hafnium dioxide, silicon nitride, and BST.

9. The method of claim 7 wherein the resonator structure is operable in a wine-glass mode.

10. The method of claim 7 wherein the dielectric is a liquid.

11. The method of claim 7 wherein the dielectric is a porous solid material.

12. The method of claim 7 wherein the dielectric is dimensioned so that its dielectric-to-resonator thickness corresponds to an effective quarter-wavelength of the resonance frequency of the resulting electrode-dielectric-resonator structure.