Temperature controlled MEMS resonator and method for controlling resonator frequency

• US 7,068,125 B2
• Filed: 03/04/2004
• Issued: 06/27/2006
• Est. Priority Date: 03/04/2004
• 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:
  US10/794,976
• Publication Number:
  US 20050195050A1
• Time in Patent Office: 845 Days
• Field of Search: 333/186, 333/197, 333/198, 333/200, 438/795, 437/171, 437/247, 324/691, 324/703
• US Class Current: 333/186
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01019 Potassium [K]
• CPC Class Codes: H01L 2924/01057 Lanthanum [La]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• 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 9/02338 Suspension means
• CPC Class Codes: H03H 9/02401 by annealing
• CPC Class Codes: H03H 9/02448 of temperature influence
• CPC Class Codes: H03H 9/2426 in combination with other electronic elements
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators
• CPC Class Codes: H03H 9/2473 Double-Ended Tuning Fork [DETF] resonators
• CPC Class Codes: H03H 9/2478 Single-Ended Tuning Fork resonators

Abstract

There are many inventions described and illustrated herein. In one aspect, the present invention is directed to a temperature compensated microelectromechanical resonator as well as fabricating, manufacturing, providing and/or controlling microelectromechanical resonators having mechanical structures that include integrated heating and/or temperature sensing elements. In another aspect, the present invention is directed to fabricate, manufacture, provide and/or control microelectromechanical resonators having mechanical structures that are encapsulated using thin film or wafer level encapsulation techniques in a chamber, and including heating and/or temperature sensing elements disposed in the chamber, on the chamber and/or integrated within the mechanical structures. Other aspects of the inventions will be apparent from the detailed description and claims herein.

Claims

1. A MEMS resonator having a resonant frequency defined in relation to an operating temperature, comprising:

a first substrate anchor including a first electrical contact;

a second substrate anchor including a second electrical contact;

a beam structure disposed between the first and the second substrate anchors and electrically coupled to the first and the second electrical contacts; and

an electrical source, coupled to the first and second electrical contacts, to provide an electrical current to the beam structure and thereby heat the beam structure to maintain the temperature of the beam structure within a predetermined range of temperatures while the MEMS resonator is in operation.

2. The MEMS resonator of claim 1 wherein the beam structure is fixed at a first end to the first substrate anchor and at a second end to the second substrate anchor.

3. The MEMS resonator of claim 1 wherein the electrical source is adapted to provide an electrical current to either the first electrical contact or the second electrical contact and wherein the beam structure includes a conducting or semi-conducting material.

4. The MEMS resonator of claim 1 further including:

a temperature sensor, placed in proximity to the beam structure, to measure temperature; and

control circuitry, coupled to the temperature sensor, to generate control information and provide the control information to the electrical source to maintain the beam structure at the operating temperature or within a predetermined range of temperatures while the MEMS resonator is in operation.

5. The MEMS resonator of claim 4 wherein the control circuitry, in response to temperature data measured by the temperature sensor, generates the control information using a mathematical relationship or data contained in a look-up table.

6. The MEMS resonator of claim 1 wherein the beam structure comprises a single oscillating beam.

7. The MEMS resonator of claim 1 wherein the beam structure comprises a plurality of moveable beams disposed between the first and second substrate anchors.

8. The MEMS resonator of claim 1 wherein at least one of the first and second substrate anchors includes a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

9. The MEMS resonator of claim 1 wherein the beam structure includes a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

10. The MEMS resonator of claim 1 wherein:

the beam structure includes a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients; and

at least one of the first and second substrate anchors includes a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

11. A MEMS resonator having a resonant frequency defined in relation to an operating temperature, comprising:

a first substrate anchor including a first electrical contact;

a second substrate anchor including a second electrical contact;

a first beam, comprising a conductive or semi-conductive material, electrically connected between first and second electrical contacts;

a first moveable beam having a first end that is thermally coupled to the first beam; and

an electrical source, coupled to the first electrical contact, to provide a controlled current to the first electrical contact and thereby heat the first beam.

12. The MEMS resonator of claim 11 further comprising:

a third substrate anchor including a third electrical contact;

a fourth substrate anchor including a fourth electrical contact;

a second beam, comprising a conductive or semi-conductive material, electrically connected between third and fourth electrical contacts;

wherein the first moveable beam includes a second end that is thermally coupled to the second beam; and

wherein the electrical source is further coupled to the third electrical contact to provide a controlled current to the third electrical contact and thereby heat the second beam.

13. The MEMS resonator of claim 12 further including temperature measurement circuitry to determine the resistance of the first moveable beam.

14. The MEMS resonator of claim 13 wherein the temperature measurement circuitry applies an electrical signal to the first moveable beam and measures the response to the electrical signal by the first moveable beam to determine information that is representative of the temperature of the first moveable beam.

15. The MEMS resonator of claim 13 wherein the electrical signal is an AC or DC voltage.

16. The MEMS resonator of claim 13 wherein the electrical signal is an AC or DC current.

17. The MEMS resonator of claim 13 further including control circuitry, coupled to the temperature measurement circuitry, to generate control information and provide the control information to the electrical source to maintain the temperature of the first moveable beam at a predetermined operating temperature or within a predetermined range of temperatures while the MEMS resonator is in operation.

18. The MEMS resonator of claim 17 wherein the control circuitry, in response to information which is representative of the temperature of the first moveable beam, generates the control information using a mathematical relationship or data contained in a look-up table.

19. The MEMS resonator of claim 11 further including:

a temperature sensor, disposed in proximity to the first moveable beam, to measure temperature; and

control circuitry, coupled to the temperature sensor, to generate control information and provide the control information to the electrical source to control the operating temperature of the first moveable beam.

20. The MEMS resonator of claim 19 wherein the control circuitry, in response to temperature data measured by the temperature sensor, generates the control information using a mathematical relationship or data contained in a look-up table.

21. The MEMS resonator of claim 11 further including a second moveable beam having a first end that is thermally coupled to the first beam.

22. The MEMS resonator of claim 21 further comprising:

a third substrate anchor including a third electrical contact;

a fourth substrate anchor including a fourth electrical contact;

a second beam, comprising a conductive or semi-conductive material, electrically connected between third and fourth electrical contacts;

wherein the first and second moveable beams each include a second end that is thermally coupled to the second beam; and

wherein the electrical source is further coupled to the third electrical contact to provide a controlled current to the third electrical contact and thereby heat the second beam.

23. The MEMS resonator of claim 22 wherein the electrical source includes:

a first electrical source, coupled to the first electrical contact, to provide the controlled current to the first electrical contact and thereby heat the first beam; and

a second electrical source, coupled to the third electrical contact, to provide a controlled current to the third electrical contact and thereby heat the second beam.

24. The MEMS resonator of claim 22 wherein the first moveable beam includes a plurality of discrete oscillators, wherein each discrete oscillator comprises a spring and an oscillating mass.

25. The MEMS resonator of claim 22 wherein at least one of the first and second substrate anchors comprises a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

26. The MEMS resonator of claim 21 further including:

a first test contact electrically coupled to the first electrical contact; and

a second test contact electrically coupled to the second electrical contact.

27. The MEMS resonator of claim 26 further comprising temperature measurement circuitry, coupled to the first and second test contacts, to apply an electrical signal thereto to determine information that is representative of the temperature of the first moveable beam.

28. The MEMS resonator of claim 11 wherein the first substrate anchor includes a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

29. The MEMS resonator of claim 11 wherein the first moveable beam includes a plurality of springs and oscillating masses.

30. A method of controlling the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first substrate anchor comprising a first electrical contact, a second substrate anchor comprising 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, the method comprising:

passing a heating current from the first electrical contact to the second electrical contact in order to heat the beam structure; and

adjusting the heating current in relation to an actual operating temperature for the beam structure.

31. The method of claim 30 further including determining information which is representative of the actual operating temperature using a temperature sensor placed in proximity to the beam structure.

32. The method of claim 30 wherein the beam structure comprises a plurality of oscillating beams.

33. The method of claim 30 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.

34. The method of claim 30 wherein at least one of the first and second substrate anchors comprises a composite structure formed from a plurality of materials, wherein at least two of the materials in the plurality of materials have different thermal expansion coefficients.

35. A method of controlling the resonant frequency of a MEMS resonator, wherein the MEMS resonator comprises a first substrate anchor comprising a first electrical contact, a second substrate anchor comprising 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, the method comprising:

passing a heating current from the first electrical contact to the second electrical contact in order to maintain the temperature of the beam structure at the operating temperature or within a predetermined range of temperatures while the MEMS resonator is in operation; and

adjusting the heating current in relation to a calculated resistance of the beam structure.

36. The method of claim 35 further comprising calculating the resistance of the beam structure by applying a measurement voltage across the first electrical contact to the second electrical contact and determining the resistance of the beam structure in relation to the measurement voltage.

37. The method of claim 35 further comprising calculating the resistance of the beam structure by passing a measurement current from the first electrical contact to the second electrical contact and determining the resistance of the beam structure in relation to the measurement current.

38. A method of controlling the resonant frequency of a MEMS resonator at an operating temperature, wherein the MEMS resonator comprises a first substrate anchor fixed between first and second electrical contacts and a beam structure comprising a first end thermally coupled to the first substrate anchor, the method comprising:

heating the first substrate anchor to the operating temperature; and

maintaining the operating temperature of the first substrate anchor in relation to a calculated resistance of the first substrate anchor.

39. The method of claim 38 wherein maintaining the operating temperature of the first substrate anchor further comprises:

applying a measurement voltage across the first and second electrical contacts; and

determining the resistance of the first substrate anchor in relation to the measurement voltage.

40. The method of claim 38 wherein heating the first substrate anchor comprises passing a first heating current from the first electrical contact to the second electrical contact.

41. The method of claim 40 wherein maintaining the operating temperature of the first substrate anchor further comprises:

passing a measurement current between first and second electrical contacts; and

determining the resistance of the first substrate anchor in relation to the measurement current.

42. The method of claim 38 wherein the MEMS resonator further comprises a second substrate anchor fixed between third and fourth electrical contacts, and wherein the beam structure further comprises a second end thermally coupled to the second substrate anchor, the method further comprising:

heating the second substrate anchor to the operating temperature by passing a second heating current from the third electrical contact to the fourth electrical contact; and

maintaining the operating temperature of at least one of the first and second substrate anchors in relation to a calculated resistance of the beam structure.

43. The method of claim 42 wherein maintaining the operating temperature of at least one of the first and second substrate anchors further comprises:

applying a measurement voltage between one electrical contact selected from the first and second electrical contacts and another electrical contact selected from the third and fourth electrical contacts; and

determining the resistance of the beam structure in relation to the measurement voltage.

44. The method of claim 42 wherein maintaining the operating temperature of at least one of the first and second substrate anchors further comprises:

passing a measurement current between one electrical contact selected from the first and second electrical contacts and another electrical contact selected from the third and fourth electrical contacts; and

determining the resistance of the beam structure in relation to the measurement current.