Time base comprising an integrated micromechanical ring resonator

• US 6,686,807 B1
• Filed: 05/02/2002
• Issued: 02/03/2004
• Est. Priority Date: 11/02/1999
• Status: Expired due to Term

• Current Assignee: Eta SA Fabriques dEbauches (The Swatch Group AG)
• Original Assignee: Eta SA Fabriques dEbauches (The Swatch Group AG)
• Inventors: Kück, Heinz, Platz, Rainer, Giousouf, Metin
• Primary Examiner(s): NGUYEN, MINH T
• Application Number:
  US10/129,193
• Time in Patent Office: 642 Days
• Field of Search: 331/108.C, 331/108.D, 331/116.R, 331/116.M, 331/154, 735/041.8, 735/041.7, 735/040.2, 735/040.8, 735/041.3, 361/283.1
• US Class Current: 331/154
• CPC Class Codes: G01C 19/5712 the devices involving a micromechanical structure
• CPC Class Codes: H03B 5/30 with frequency-determining element being electromechanical resonator

Abstract

A time base having a resonator (4) and an integrated electronic circuit (3) for driving the resonator into oscillation and for producing, in response to this oscillation, a signal having a determined frequency. The resonator is an integrated micromechanical ring resonator (4) supported above a substrate (2) and adapted to oscillate around an axis of rotation (O) substantially perpendicular to the substrate. The ring resonator has a central post (5) extending from the substrate along the axis of rotation, and a free-standing oscillating structure (6) including an outer ring (60) coaxial with the axis of rotation, and a plurality of spring elements (62) disposed symmetrically around the central post and connecting the outer ring to the central post.

Claims

1. A time base comprising a resonator and an integrated electronic circuit for driving said resonator into oscillation and for producing, in response to said oscillation, a signal having a determined frequency, wherein said resonator is an integrated micromechanical ring resonator supported above a substrate and adapted to oscillate, according to a first oscillation mode, around an axis of rotation substantially perpendicular to said substrate, said ring resonator comprising:

a central post extending from said substrate along said axis of rotation;

a free-standing oscillating structure connected to said central post and including;

an outer ring coaxial with said axis of rotation and

a plurality of spring elements disposed symmetrically around said central post and connecting said outer ring to said central post; and

at least one pair of diametrically opposed electrode structures disposed around said outer ring and connected to said integrated electronic circuit,

and wherein said spring elements have a curved shape and are connected substantially perpendicularly to said central post by first junctions, each of said spring elements extending away from said central post in the prolongation of a radial line crossing said axis of rotation.

2. The time base according to claim 1, wherein said electronic circuit is integrated on said substrate together with said micromechanical ring resonator.

3. The time base according to claim 1, wherein said spring elements are connected substantially perpendicularly to said outer ring by second junctions.

4. The time base according to claim 1, wherein said junctions are provided with round fillets.

5. The time base according to claim 1, wherein the number of spring elements is comprised between four and fifty, and preferably is of the order of twenty.

6. The time base according to claim 1, wherein said free-standing oscillating structure further comprises at least one pair of diametrically opposed comb-shaped members disposed around said outer ring and including:

a base member extending radially from said outer ring;

at least a first lateral member extending substantially perpendicularly from a first side of said base member; and

at least a second lateral member extending substantially perpendicularly from a second side of said base member opposite said first side;

and wherein each of said electrode structures comprises;

a first comb-shaped electrode structure meshing with said comb-shaped member and comprising first electrodes adjacent to said first lateral members; and

a second comb-shaped electrode structure meshing with said comb-shaped member and comprising second electrodes adjacent to said second lateral members.

7. The time base according to claim 6, wherein:

said first comb-shaped electrode structures are used to drive said ring resonator into oscillation;

said free-standing oscillating structure is tied via said central post to a fixed potential; and

said second comb-shaped electrode structures are used to sense a signal resulting from the oscillation of said ring resonator,

a constant direct voltage component being added to one or both of said first comb-shaped electrode structures or free-standing oscillating structure.

8. The time base according to claim 6, wherein said lateral members and said electrodes have a shape of an arc of a circle concentric with said outer ring.

9. The time base according to claim 6, wherein at least one stop structure is provided on said substrate adjacent to an outer end of at least one base member in order to limit angular and/or tilt movements and prevent said free-standing oscillating structure from sticking in case of a shock.

10. The time base according to claim 6, wherein extremities of said lateral members and/or extremities of said electrodes are pointed or have a suitably small surface area so as to prevent said free-standing oscillating structure from sticking in case of a shock.

11. The time base according to claim 6, wherein at least one of said lateral members and/or one of said electrodes is longer than the others so as to prevent said free-standing oscillating structure from sticking in case of a shock.

12. The time base according to claim 1, wherein said free-standing oscillating structure further comprises at least one pair of diametrically opposed comb-shaped members disposed around said outer ring and including:

a base member extending radially from said outer ring; and

at least a first lateral member extending substantially perpendicularly from a first side of said base member;

and wherein each of said electrode structures comprises;

a comb-shaped electrode structure meshing with said comb-shaped member and comprising first electrodes adjacent to said first lateral members.

13. The time base according to claim 12, wherein

said comb-shaped electrode structures are used to drive said ring resonator into oscillation;

and

said free-standing oscillation structure is tied via said central post to a fixed potential,

a constant direct voltage component being added to one or both of said comb-shaped electrode structures or free-standing oscillating structure, and

sensing being done by detecting a change in impedance at resonance.

14. The time base according to claim 12, wherein said lateral members and said electrodes have a shape of an arc of a circle concentric with said outer ring.

15. The time base according to claim 12, wherein at least one stop structure is provided on said substrate adjacent to an outer end of at least one base member in order to limit angular and/or tilt movements and prevent said free-standing oscillating structure from sticking in case of a shock.

16. The time base according to claim 12, wherein extremities of said lateral members and/or extremities of said electrodes are pointed or have a suitably small surface area so as to prevent said free-standing oscillating structure from sticking in case of a shock.

17. The time base according to claim 12, wherein at least one of said lateral members and/or one of said electrodes is longer than the others so as to prevent said free-standing oscillating structure from sticking in case of a shock.

18. The time base according to claim 1, wherein a conductive pattern having substantially the shape of said free-standing oscillating structure is provided on a surface of said substrate under at least a part of said free-standing oscillating structure, said free-standing oscillating structure and said conductive pattern being put at a same potential.

19. The time base according to claim 1, wherein said free-standing oscillating structure further comprises at least a first pair of diametrically opposed thermally compensating members disposed around said outer ring, said thermally compensating members being adapted to alter a mass moment of inertia of said free-standing oscillating structure as a function of temperature so as to compensate for the effect of temperature on the resonant frequency of the ring resonator.

20. The time base according to claim 19, wherein each of said thermally compensating members comprises a weight member connected to said outer ring by means of a connecting member comprising first and second layers made respectively of first and second materials having different thermal coefficients, said connecting member being adapted to gradually bring said weight member closer to said axis of rotation of rotation when temperature increases, thereby reducing the mass moment of inertia of said free-standing oscillating structure.

21. The time base according to claim 1, further comprising an integrated temperature measuring circuit intended to compensate for the effect of temperature on the frequency of the signal produced by said time base.

22. The time base according to claim 1, further comprising a second micromechanical ring resonator supported above said substrate and adapted to oscillate at a resonant frequency which is different from the resonant frequency of the other resonator, a frequency difference between both resonant frequencies being used for compensating for the effect of temperature on the frequency of the signal produced by said time base.

23. The time base according to claim 1, wherein electrodes are positioned under said free-standing oscillating structure in such a way as to drive and sense a second oscillation mode having a resonant frequency which is different from the resonant frequency of said first oscillation mode, a frequency difference between the resonant frequencies of both oscillation modes being used for compensating for the effect of temperature on the frequency of the signal produced by said time base.

24. The time base according to claim 23, wherein said second oscillation mode is a tilting oscillation mode.

25. The time base according to claim 23, wherein said second oscillation mode is a vertical oscillation mode parallel to said axis of rotation.

26. The time base according to claim 1, wherein said substrate and said ring resonator are made of silicon material.

27. An integrated micro-mechanical ring resonator for a time base, said ring resonator being supported above a substrate and adapted to oscillate around an axis of rotation substantially perpendicular to said substrate, said ring resonator comprising:

a central post extending from said substrate along said axis of rotation;

a free-standing oscillating structure connected to said central post and including;

an outer ring coaxial with said axis of rotation; and

a plurality off spring elements disposed symmetrically around said central post and connecting said outer ring to said central post; and

at least one pair of diametrically opposed electrode structures disposed around said outer ring for connection to an integrated electronic circuit,

wherein said spring elements have a curved shape and are connected substantially perpendicularly to said central post by first junctions, each of said spring elements extending away from said central post in the prolongation of a radial line crossing said axis of rotation.

28. The ring resonator according to claim 27, wherein said spring elements are connected substantially perpendicularly to said outer ring by second junctions.

29. The ring resonator according to claim 27, wherein said junctions are provided with round fillets.

30. The ring resonator according to claim 27, wherein the number of spring elements is comprised between four and fifty, and preferably is of the order of twenty.