Method for adjusting the frequency of a MEMS resonator

• US 7,221,241 B2
• Filed: 07/21/2006
• Issued: 05/22/2007
• Est. Priority Date: 04/28/2004
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Partridge, Aaron, Lutz, Markus
• Primary Examiner(s): Summons; Barbara
• Application Number:
  US11/490,823
• Publication Number:
  US 20060255881A1
• Time in Patent Office: 305 Days
• Field of Search: 333/186, 333/188, 333/197, 333/198, 333/200, 324/691, 324/703, 438/795, 438/50, 438/52
• US Class Current: 333/186
• 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 MEMS device comprising:

a microelectromechanical resonator having a beam structure which includes a resonant frequency;

a frequency adjustment structure, juxtaposed the beam structure, having a plurality of electrical contacts, wherein material of the frequency adjustment structure, in response to being resistively heated by a heating current, evaporates therefrom and deposits on the beam structure to change the resonant frequency of the beam structure; and

wherein the heating current resistively heats the frequency adjustment structure to between approximately 900°

C. and approximately 1200°

C.

2. The MEMS device of claim 1 further including a fixed electrode wherein the frequency adjustment structure is integrated with the fixed electrode.

3. The MEMS device of claim 1 further including a fixed electrode wherein the frequency adjustment structure is disposed adjacent the fixed electrode.

4. The MEMS device of claim 3 wherein the beam structure includes a high tension area and wherein the frequency adjustment structure is disposed adjacent the high tension area.

5. The MEMS device of claim 1 wherein the frequency adjustment structure comprises a monocrystalline silicon.

6. The MEMS device of claim 1 wherein the heating current resistively heats the frequency adjustment structure to greater than 300°

C.

7. The MEMS device of claim 1 wherein the frequency adjustment structure comprises a polycrystalline silicon.

8. The MEMS device of claim 1 wherein the beam structure includes a high tension area and wherein the material deposits substantially on the high tension area.

9. The MEMS device of claim 1 further including a fixed electrode, and wherein the frequency adjustment structure includes (i) a first structure which is integrated with the fixed electrode and (ii) a second structure which is disposed adjacent the fixed electrode.

10. A MEMS device comprising:

a microelectromechanical resonator having (i) a beam structure, which includes a resonant frequency, and (ii) a fixed electrode;

a frequency adjustment structure, having a plurality of electrical contacts, wherein frequency adjustment structure includes a silicon material, and wherein, in response to being resistively heated by a heating current, a portion of the silicon material evaporates therefrom and deposits on the beam structure to change the resonant frequency of the beam structure.

11. The MEMS device of claim 10 wherein the silicon material is a polycrystalline silicon or a monocrystalline silicon.

12. The MEMS device of claim 10 wherein the frequency adjustment structure is integrated with the fixed electrode.

13. MEMS device of claim 10 wherein the frequency adjustment structure is disposed adjacent the fixed electrode.

14. The MEMS device of claim 13 wherein the beam structure includes a high tension area and wherein the frequency adjustment structure is disposed adjacent the high tension area.

15. The MEMS device of claim 10 wherein the beam structure comprises a monocrystalline or polycrystalline silicon.

16. The MEMS device of claim 10 wherein the heating current resistively heats the frequency adjustment structure to greater than 900°

C.

17. The MEMS device of claim 10 wherein the heating current resistively heats the frequency adjustment structure to between approximately 900°

C. and approximately 120°

C.

18. The MEMS device of claim 10 wherein the beam structure includes a high tension area and wherein the silicon material deposits substantially on the high tension area.

19. The MEMS device of claim 10 wherein the frequency adjustment structure includes (i) a first structure which is integrated with the fixed electrode and (ii) a second structure which is disposed adjacent the fixed electrode.

20. The MEMS device of claim 10 wherein the heating current resistively heats the frequency adjustment structure to greater than approximately 900°

C.

21. The MEMS device of claim 10 wherein the heating current resistively heats the frequency adjustment structure to greater than approximately 1200°

C.

22. A method of adjusting the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first electrical contact, a second electrical contact, and a beam structure coupled to at least one substrate anchor, and wherein the MEMS resonator includes a first resonant frequency, the method comprising;

determining a first heating current to apply to the first electrical contact, wherein the first heating current is determined using the first resonant frequency; and

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 beam structure changes to provide a second resonant frequency of the MEMS resonator.

23. The method of claim 22 further including:

measuring the second resonant frequency of the MEMS resonator;

determining a second heating current; and

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 beam structure changes to provide a third resonant frequency of the MEMS resonator.

24. The method of claim 22 wherein the beam structure includes a multiple beam tuning fork structure, wherein each beam in the multiple beam tuning fork structure includes a first end fixed by a first substrate anchor.

25. The method of claim 22 wherein the first heating current resistively heats the beam structure to greater than 300°

C.

26. The method of claim 22 wherein the beam structure includes a high tension area, wherein the high tension area is resistively heated in response to the first heating current thereby causing the material of the high tension area to change.

27. The method of claim 22 wherein the beam structure includes 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.

28. A method of adjusting the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first electrical contact, a second electrical contact, and a beam structure fixed to a substrate via a substrate anchor, and wherein the MEMS resonator includes a first resonant frequency, the method comprising:

passing a 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 beam structure evaporates therefrom to provide a second resonant frequency of the MEMS resonator, wherein the first heating current resistively heats at least a portion of the beam structure to between approximately 900°

C. and approximately 1200°

C.; and

measuring the second resonant frequency of the MEMS resonator.

29. The method of claim 28 further including applying a 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 beam structure changes to provide a third resonant frequency of the MEMS resonator.

30. The method of claim 29 further including determining the second heating current using the measured second resonant frequency.

31. The method of claim 28 wherein the beam structure includes a multiple beam tuning fork structure, wherein each beam in the multiple beam tuning fork structure includes a first end fixed by a first substrate anchor.

32. The method of claim 28 wherein the beam structure includes 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.

33. 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 includes polycrystalline silicon and includes first and second electrical contacts, and wherein the MEMS resonator includes a first resonant frequency, the method comprising:

passing a first heating current from the first electrical contact to the second electrical contact to resistively heat the frequency adjustment structure, wherein, in response, polycrystalline silicon 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.

34. The method of claim 33 further including:

measuring the first resonant frequency of the MEMS resonator; and

determining the first heating current using the measured first resonant frequency.

35. The method of claim 33 further including:

determining a second heating current; 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.

36. The method of claim 33 wherein the frequency adjustment structure is integrated with a fixed electrode of the MEMS resonator.

37. The method of claim 33 wherein the beam structure includes a high tension area, wherein in response to the first heating current, material of the frequency adjustment structure deposits on the high tension area.

38. The method of claim 33 wherein the beam structure includes 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.

39. The method of claim 33 wherein the frequency adjustment structure and the beam structure includes polycrystalline silicon material.

40. A MEMS device comprising:

a microelectromechanical resonator having (i) a beam structure which includes a resonant frequency, and (ii) a fixed electrode;

a frequency adjustment structure, juxtaposed the beam structure, having a plurality of electrical contacts, wherein material of the frequency adjustment structure, in response to being resistively heated by a heating current, evaporates therefrom and deposits on the beam structure to change the resonant frequency of the beam structure; and

wherein the frequency adjustment structure includes (i) a first structure which is integrated with the fixed electrode and (ii) a second structure which is disposed adjacent the fixed electrode.

41. The MEMS device of claim 40 wherein the beam structure includes a high tension area and wherein the frequency adjustment structure is disposed adjacent the high tension area.

42. The MEMS device of claim 40 wherein the frequency adjustment structure comprises a monocrystalline silicon.

43. The MEMS device of claim 40 wherein the heating current resistively heats the frequency adjustment structure to greater than 300°

C.

44. The MEMS device of claim 40 wherein the frequency adjustment structure comprises a polycrystalline silicon.

45. The MEMS device of claim 40 wherein the beam structure includes a high tension area and wherein the material deposits substantially on the high tension area.

46. The MEMS device of claim 40 wherein the heating current resistively heats the frequency adjustment structure to greater than approximately 900°

C.

47. The MEMS device of claim 40 wherein the heating current resistively heats the frequency adjustment structure to greater than approximately 1200°

C.