Method for adjusting the frequency of a MEMS resonator

• US 20050242904A1
• Filed: 04/28/2004
• Published: 11/03/2005
• Est. Priority Date: 04/28/2004
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Partridge, Aaron, Lutz, Markus
• Granted Patent: US 7,102,467 B2
• Time in Patent Office: Days
• US Class Current: 333/200
• 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 2009/02527 Combined
• CPC Class Codes: H03H 3/0077 by tuning of resonance frequency
• CPC Class Codes: H03H 9/02401 by annealing
• CPC Class Codes: H03H 9/2473 Double-Ended Tuning Fork [DETF] resonators

Abstract

There are many inventions described and illustrated herein. These inventions are directed to a method of fabricating a microelectromechanical resonator having an output frequency that may be adjusted, tuned, set, defined and/or selected whether before and/or after final packaging. In one aspect, the method of the present invention adjusts, tunes, sets, defines and/or selects the frequency of the microelectromechanical resonator by changing and/or removing material from the mechanical structure of the resonator by resistively heating (in a selective or non-selective manner) one or more elements and/or beams of the mechanical structure (for example, the moveable or expandable electrodes and/or frequency adjustment structures).

Claims

1. A method of adjusting the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first substrate anchor including a first electrical contact, a second substrate anchor including a second electrical contact, and a beam structure fixed at a first end by the first substrate anchor and at a second end by the second substrate anchor, and wherein the MEMS resonator includes a first resonant frequency, the method comprising:

selecting a first heating current to apply to the first electrical contact;

applying the first heating current to the MEMS resonator wherein applying the first heating current includes passing the first heating current from the first electrical contact to the second electrical contact to resistively heat the beam structure, wherein, in response, the material of the first beam structure changes to provide a second resonant frequency of the MEMS resonator.

2. The method of claim 1 further including:

measuring the first resonant frequency of the MEMS resonator and wherein the first heating current is selected based on the measured first resonant frequency.

3. The method of claim 1 further including:

measuring the second resonant frequency of the MEMS resonator;

calculating a second heating current to apply to the first electrical contact; and

applying the second heating current to the MEMS resonator wherein applying the second heating current includes passing the second heating current from the first electrical contact to the second electrical contact to resistively heat the beam structure, wherein, in response, the material of the first beam structure changes to provide a third resonant frequency of the MEMS resonator.

4. The method of claim 1 wherein the beam structure comprises a multiple beam tuning fork structure, wherein each beam in the multiple beam tuning fork structure comprises a first end fixed by the first substrate anchor and a second end fixed by the second substrate anchor.

5. The method of claim 1 wherein the first electrical current resistively heats the beam structure to greater than 300°

C.

6. The method of claim 1 wherein the first electrical current resistively heats the beam structure to between approximately 900°

C. and approximately 1200°

C.

7. The method of claim 1 wherein the beam structure comprises a high tension area, wherein the high tension area is resistively heated in response to the first electrical current thereby causing the material of the high tension area to change.

8. The method of claim 1 wherein the beam structure comprises a high tension area, wherein in response to the first heating current, the high tension area is heated to a substantially higher temperature than other portions of the beam structure.

9. A method of adjusting the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first substrate anchor including a first electrical contact, a second substrate anchor including a second electrical contact, and a beam structure fixed at a first end by the first substrate anchor and at a second end by the second substrate anchor, and wherein the MEMS resonator includes a first resonant frequency, the method comprising:

applying a first heating current to the MEMS resonator wherein applying the first heating current includes passing the first heating current from the first electrical contact to the second electrical contact to resistively heat the beam structure, wherein, in response, material of the first beam structure evaporates therefrom to provide a second resonant frequency of the MEMS resonator; and

measuring the second resonant frequency of the MEMS resonator.

10. The method of claim 9 further including:

measuring the first resonant frequency of the MEMS resonator; and

determining the first heating current based on the measured first resonant frequency.

11. The method of claim 9 further including:

measuring the second resonant frequency of the MEMS resonator;

determining a second heating current to apply to the first electrical contact; and

applying the second heating current to the MEMS resonator wherein applying the second heating current includes passing the second heating current from the first electrical contact to the second electrical contact to resistively heat the beam structure, wherein, in response, the material of the first beam structure changes to provide a third resonant frequency of the MEMS resonator.

12. The method of claim 9 wherein the beam structure comprises a multiple beam tuning fork structure, wherein each beam in the multiple beam tuning fork structure comprises a first end fixed by the first substrate anchor and a second end fixed by the second substrate anchor.

13. The method of claim 9 wherein the first electrical current resistively heats the beam structure to greater than 300°

C.

14. The method of claim 9 wherein the first electrical current resistively heats the beam structure to between approximately 900°

C. and approximately 1200°

C.

15. The method of claim 9 wherein the beam structure comprises at least one high tension area, wherein in response to the first heating current, the high tension area is heated to a substantially higher temperature than other portions of the beam structure.

16. The method of claim 9 wherein the beam structure is comprised of a polycrystalline silicon material and the first electrical current resistively heats the beam structure to between approximately 900°

C. and approximately 1200°

C.

17. The method of claim 9 wherein the beam structure is comprised of a polycrystalline silicon material and the first electrical current resistively heats the beam structure to greater than approximately 1200°

C.

18. A method of adjusting the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a beam structure and a frequency adjustment structure, wherein the frequency adjustment structure is comprised of polycrystalline silicon and includes first and second electrical contacts, and wherein the MEMS resonator includes a first resonant frequency, the method comprising:

applying a first heating current to the frequency adjustment structure wherein applying the first heating current includes passing the first heating current from the first electrical contact to the second electrical contact to resistively heat the frequency adjustment structure, wherein, in response, material of the frequency adjustment structure evaporates therefrom and deposits on the beam structure to provide a second resonant frequency of the MEMS resonator; and

measuring the second resonant frequency of the MEMS resonator.

19. The method of claim 18 further including:

measuring the first resonant frequency of the MEMS resonator; and

determining the first heating current based on the measured first resonant frequency.

20. The method of claim 18 further including:

measuring the second resonant frequency of the MEMS resonator;

determining a second heating current to apply to the first electrical contact; and

applying the second heating current to the frequency adjustment structure wherein applying the second heating current includes passing the second heating current from the first electrical contact to the second electrical contact to resistively heat the frequency adjustment structure, wherein, in response, additional material of the frequency adjustment structure deposits on the beam structure to provide a third resonant frequency of the MEMS resonator.

21. The method of claim 18 wherein the beam structure comprises a multiple beam tuning fork structure, wherein each beam in the multiple beam tuning fork structure comprises a first end fixed by a first substrate anchor and a second end fixed by a second substrate anchor.

22. The method of claim 18 wherein the frequency adjustment structure is integrated into a fixed electrode of the MEMS resonator.

23. The method of claim 18 wherein the first electrical current resistively heats the frequency adjustment structure to between 900°

C. and 1200°

C.

24. The method of claim 18 wherein the beam structure comprises at least one high tension area, wherein in response to the first heating current, material of the frequency adjustment structure deposits on the high tension area.

25. The method of claim 18 wherein the beam structure comprises a plurality of high tension areas, wherein in response to the first heating current, a substantial amount of the evaporated material of the frequency adjustment structure deposits on the high tension areas.

26. The method of claim 18 wherein the frequency adjustment structure and the beam structure are comprised of a polycrystalline silicon material and the first electrical current resistively heats the frequency adjustment structure to greater than approximately 900°

C.

27. The method of claim 18 wherein the frequency adjustment structure and the beam structure are comprised of a polycrystalline silicon material and the first electrical current resistively heats the frequency adjustment structure to greater than approximately 1200°

C.

28. The method of claim 27 wherein the frequency adjustment structures are integrated into a fixed electrode.

29. The method of claim 18 wherein the beam structure comprises a plurality of high tension areas, wherein in response to the first heating current, a substantial amount of the evaporated material of the frequency adjustment structure deposits on areas other than the high tension areas.

30. The method of claim 29 wherein the frequency adjustment structure and the beam structure are comprised of a polycrystalline silicon material and the first electrical current resistively heats the frequency adjustment structure to greater than approximately 900°

C.

31. The method of claim 29 wherein the frequency adjustment structure and the beam structure are comprised of a polycrystalline silicon material and the first electrical current resistively heats the frequency adjustment structure to greater than approximately 1200°

C.