Device including a micromechanical resonator having an operating frequency and method of extending same

• US 6,249,073 B1
• Filed: 01/13/2000
• Issued: 06/19/2001
• Est. Priority Date: 01/14/1999
• Status: Expired due to Term

• 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: Wang, Kun, McCorquodale, Michael, Nguyen, Clark T. -C.
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US09/482,670
• Time in Patent Office: 523 Days
• Field of Search: 310/309
• US Class Current: 310/309
• CPC Class Codes: H01H 2059/0072 with stoppers or protrusions for maintaining a gap, reducing the contact area or for preventing stiction between the movable and the fixed electrode in the attracted position
• CPC Class Codes: H01H 59/0009 making use of micromechanics
• CPC Class Codes: H03H 3/0078 involving adjustment of the transducing gap
• CPC Class Codes: H03H 9/24 Constructional features of resonators of material which is not piezoelectric, electrostrictive, or magnetostrictive
• CPC Class Codes: H03H 9/2452 Free-free beam resonators
• CPC Class Codes: H03H 9/462 Microelectro-mechanical filters
• CPC Class Codes: H03H 9/465 in combination with other electronic elements

Abstract

A flexural-mode, micromechanical resonator utilizing a non-intrusive support structure to achieve measured Q'"'"'s as high as 8,400 at VHF frequencies from 30-90 MHz is manufactured using polysilicon surface micromachining technology. Also, a method for extending the operating frequency of the resonator as well as other types of micromechanical resonators is disclosed. One embodiment of the method is called a differential-signaling technique. The other embodiment of the method is called a dimple-down technique. The support structure includes one or more torsional-mode support springs in the form of beams that effectively isolate a resonator beam from its anchors via quarter-wavelength impedance transformations, minimizing anchor dissipation and allowing the resonator to achieve high Q with high stiffness in the VHF frequency range. The resonator also includes one or more spacers in the form of dimples formed on the flexural resonator beam or the substrate. In operation, the dimples determine a capacitive-transducer gap of the resonator. When a large DC-bias voltage is applied between a drive electrode and the resonator beam, the dimples provide a predetermined minimum distance between the flexural resonator beam and the drive electrode.

Claims

1. A micromechanical resonator device having an operating frequency, a resonator formed on a substrate and a support structure anchored to the substrate to support the resonator above the substrate characterized in that:

the support structure is attached at at least one nodal point of the resonator and the support structure and the resonator are both dimensioned so that the resonator is isolated during resonator vibration wherein energy losses to the substrate are substantially eliminated and wherein the resonator device is a high-Q resonator device.

2. The device as claimed in claim 1 wherein the support structure includes at least one beam attached to a nodal point of the resonator.

3. The device as claimed in claim 1 further comprising at least one drive electrode formed on the substrate to allow electrostatic excitation of the resonator wherein the resonator and the at least one drive electrode define a capacitive transducer gap therebetween.

4. The device as claimed in claim 3 further comprising at least one spacer having a height, each spacer extending between the resonator and the substrate at a nodal point wherein the size of the gap is based on the height of the at least one spacer during pull down of the resonator.

5. The device as claimed in claim 1 wherein the device is a silicon-based resonator device.

6. The device as claimed in claim 1 wherein the device is a diamond-based resonator device.

7. The device as claimed in claim 3 further comprising a sense electrode formed on the substrate to sense output current.

8. A method for extending the operating frequency of a micromechanical resonator device including a resonator having a fundamental resonant mode formed on a substrate and a support structure anchored to the substrate to support the resonator above the substrate, the method comprising:

forcing different portions of the resonator to move in opposite directions at the same time so that the resonator vibrates in a resonant mode, m, higher than the fundamental resonant mode wherein the resonator has m+1 nodal points and wherein the support structure is attached to the nodal points so that the resonator is isolated during resonator vibration.

9. The method as claimed in claim 8 wherein the micromechanical resonator device includes a plurality of drive electrodes spaced along the resonator to allow electrostatic excitation of the resonator and wherein the step of forcing includes the steps of applying an in-phase signal to one of the drive electrodes to deflect a first portion of the resonator in a first direction and applying an out-of-phase signal to the other drive electrode to deflect a second portion of the resonator in a second direction opposite the first direction to force the resonator into a correct mode shape.

10. The method as claimed in claim 8 wherein the support structure includes m+1 beams dimensioned based on the operating frequency and wherein one of the beams is attached at each of the nodal points of the resonator so that the resonator sees substantially no resistance to transverse or torsional motion.

11. The method as claimed in claim 8 wherein the micromechanical resonator device includes a drive electrode formed on the substrate to allow electrostatic excitation of the resonator and wherein the step of forcing includes the step of applying a signal to the drive electrode, the resonator and the drive electrode define a capacitive transducer gap therebetween and wherein the micromechanical resonator further includes m+1 spacers having a height and which extend between the resonator and the substrate at the m+1 nodal points and wherein the m+1 spacers force the resonator into a correct mode shape during the application of the signal to the drive electrode.

12. The method as claimed in claim 11 wherein the micromechanical resonator device includes a sense electrode formed on the substrate to sense output current.

13. The method as claimed in claim 11 wherein the support structure includes less than m+1 beams dimensioned based on the operating frequency of the resonator device and wherein the beams are attached to the nodal points of the resonator so that the resonator sees substantially no resistance to transverse or torsional motion.

14. The method as claimed in claim 8 wherein the support structure includes a single beam.