Temperature compensation for silicon MEMS resonator

• US 6,987,432 B2
• Filed: 04/16/2003
• Issued: 01/17/2006
• Est. Priority Date: 04/16/2003
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Partridge, Aaron, Lutz, Markus
• Primary Examiner(s): Callahan, Timothy P.
• Assistant Examiner(s): Nguyen, Hai L.
• Application Number:
  US10/414,793
• Publication Number:
  US 20040207489A1
• Time in Patent Office: 1,007 Days
• Field of Search: 333186-188, 333/133, 333/197, 333/219, 331/154, 84D/IG.21, 310/309
• US Class Current: 333/186
• CPC Class Codes: B81B 2201/0271 Resonators; ultrasonic resonators
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• 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 9/02338 Suspension means
• CPC Class Codes: H03H 9/02417 involving adjustment of the transducing gap
• CPC Class Codes: H03H 9/02448 of temperature influence
• CPC Class Codes: H03H 9/2457 Clamped-free beam resonators
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators

Abstract

Thermally induced frequency variations in a micromechanical resonator are actively or passively mitigated by application of a compensating stiffness, or a compressive/tensile strain. Various composition materials may be selected according to their thermal expansion coefficient and used to form resonator components on a substrate. When exposed to temperature variations, the relative expansion of these composition materials creates a compensating stiffness, or a compressive/tensile strain.

Claims

1. A method of compensating for thermally induced frequency variations in a microelectromechanical resonator having a desired resonance frequency, wherein the microelectromechanical resonator comprises an oscillating beam and a counterelectrode, the method comprising:

determining an actual operating frequency of the micromechanical resonator; and

applying a compensating stiffness to the oscillating beam in relation to the actual operating frequency and the desired resonance frequency so that the resonator provides the desired resonance frequency over a range of temperatures, wherein applying a compensating stiffness includes applying an electrostatic force to the oscillating beam via the counterelectrode.

2. The method of claim 1 wherein the distance between the oscillating beam and the counterelectrode is a working gap, and wherein applying a compensating stiffness further includes changing the working gap between the oscillating beam and the counterelectrode.

3. The method of claim 2 wherein applying a compensating stiffness further includes increasing the working gap between the oscillating beam and the counterelectrode.

4. The method of claim 2 wherein applying a compensating stiffness further includes decreasing the working gap between the oscillating beam and the counterelectrode.

5. The method of claim 1 wherein the oscillating beam is separated from the counterelectrode by a working gap, and wherein applying the electrostatic force to the beam further comprises:

moving the counterelectrode in relation to the oscillating beam to adjust the working gap in relation to the actual operating frequency of the resonator.

6. The method of claim 5 wherein moving the electrode further comprises:

physically moving the counterelectrode in relation to the oscillating beam using a mechanical extension mechanism.

7. The method of claim 1 further including fabricating the microelectromechanical resonator using CMOS compatible materials.

8. The method of claim 1 wherein applying the electrostatic force further comprises changing a voltage applied to the counterelectrode.

9. The method of claim 8 wherein determining the actual operating frequency further comprises:

measuring at least one of the resonator frequency and the operating temperature of the resonator; and

wherein changing the voltage applied to the counterelectrode is in relation to the at least one of the resonator frequency and the operating temperature.

10. The method of claim 8 wherein applying the electrostatic force further includes increasing a voltage applied to the counterelectrode.

11. The method of claim 8 wherein applying the electrostatic force further includes decreasing a voltage applied to the counterelectrode.

12. The method of claim 8 wherein determining the actual operating frequency further comprises measuring the resonator frequency and wherein changing the voltage applied to the counterelectrode is in relation to the resonator frequency.

13. The method of claim 8 wherein determining the actual operating frequency further comprises measuring the operating temperature of the resonator and wherein changing the voltage applied to the counterelectrode is in relation to the operating temperature of the resonator.

14. A method of compensating for thermally induced frequency variations in a microelectromechanical resonator disposed on or in a substrate and having a desired resonance frequency, wherein the microelectromechanical resonator comprises counterelectrode and a laterally oscillating beam which oscillates in a direction that is substantially parallel to the substrate, the method comprising:

determining an actual operating frequency of the microelectromechanical resonator; and

applying a compensating stiffness to the laterally oscillating beam in relation to the actual operating frequency and the desired resonance frequency so that the resonator provides the desired resonance frequency over a range of temperatures, wherein applying a compensating stiffness includes applying an electrostatic force to the laterally oscillating beam via the counterelectrode.

15. The method of claim 14 further including fabricating the microelectromechanical resonator using CMOS compatible materials.

16. The method of claim 14 wherein the oscillating beam is separated from the counterelectrode by a working gap, and wherein applying the electrostatic force to the beam further comprises moving the counterelectrode in relation to the oscillating beam to adjust the working gap in relation to the actual operating frequency of the resonator.

17. The method of claim 16 wherein moving the electrode further comprises physically moving the counterelectrode in relation to the oscillating beam using a mechanical extension mechanism.

18. The method of claim 14 wherein the distance between the laterally oscillating beam and the counterelectrode is a working gap, and wherein applying a compensating stiffness further includes changing the working gap between the laterally oscillating beam and the counterelectrode.

19. The method of claim 18 wherein applying a compensating stiffness further includes increasing the working gap between the oscillating beam and the counterelectrode.

20. The method of claim 18 wherein applying a compensating stiffness further includes decreasing the working gap between the laterally oscillating beam and the counterelectrode.

21. The method of claim 14 wherein applying the electrostatic force further comprises changing a voltage applied to the counterelectrode.

22. The method of claim 21 wherein determining the actual operating frequency further comprises:

measuring at least one of the resonator frequency and the operating temperature of the resonator; and

wherein changing the voltage applied to the counterelectrode is in relation to the at least one of the resonator frequency and the operating temperature.

23. The method of claim 22 wherein applying the electrostatic force further includes increasing a voltage applied to the counterelectrode.

24. The method of claim 22 wherein applying the electrostatic force further includes decreasing a voltage applied to the counterelectrode.

25. The method of claim 22 wherein determining the actual operating frequency further comprises measuring the resonator frequency and wherein changing the voltage applied to the counterelectrode is in relation to the resonator frequency.

26.The method of claim 22 wherein determining the actual operating frequency further comprises measuring the operating temperature of the resonator and wherein changing the voltage applied to the counterelectrode is in relation to the operating temperature of the resonator.