Temperature compensation mechanism for a micromechanical ring resonator

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, said resonator being an integrated micromechanical ring resonator 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 connected to said central post by means of a plurality of spring elements; and

electrode structures disposed around said outer ring and connected to said integrated electronic circuit,

wherein said free-standing oscillating structure further comprises a plurality of thermally compensating members, said thermally compensating members being distinct from the spring elements and 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.

2. The time base according to claim 1 , wherein said thermally compensating members are attached to said outer ring on its inner side or outer side.

3. The time base according to claim 1 , wherein said free-standing oscillating structure comprises at least a first pair of diametrically opposed thermally compensating members attached to said outer ring.

4. The time base according to claim 1 , wherein each of said thermally compensating members comprises a weight member connected to said free-standing oscillating structure 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 when temperature increases, thereby reducing the mass moment of inertia of said free-standing oscillating structure.

5. The time base according to claim 4 , wherein said first material is silicon and said second material is a metal.

6. The time base according to claim 5 , wherein said metal is aluminium.

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

8. The time base according to claim 1 , wherein the thermally compensating members are attached to the free-standing oscillating structure at one end, and are free at their other end.

9. A resonator in the form of an integrated micromechanical ring resonator 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; and

a free-standing oscillating structure connected to said central post and including an outer ring coaxial with said axis of rotation and connected to said central post by means of a plurality of spring elements,

wherein said free-standing oscillating structure further comprises a plurality of thermally compensating members, said thermally compensating members being adapted to reduce a mass moment of inertia of said free-standing oscillating structure with increasing temperature so as to compensate for the effect of temperature on the resonant frequency of the ring resonator.

10. The resonator according to claim 9 , wherein said thermally compensating members are attached to said outer ring on its inner side or outer side.

11. The resonator according to claim 10 , wherein at least two diametrically opposed thermally compensating members are attached to the outer ring.

12. The resonator according to claim 9 , wherein each of said thermally compensating members comprises a weight member connected to said free-standing oscillating structure 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 when temperature increases, thereby reducing the mass moment of inertia of said free-standing oscillating structure.

13. The resonator according to claim 12 , wherein said first material is silicon and said second material is a metal.

14. The resonator according to claim 13 , wherein said metal is aluminium.

15. The resonator according to claim 9 , wherein said substrate 2 and said ring resonator 4 are made of silicon material.

16. 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, said resonator being an integrated micromechanical ring resonator 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 connected to said central post by means of a plurality of spring elements; and

electrode structures disposed around said outer ring and connected to said integrated electronic circuit,

wherein said free-standing oscillating structure further comprises a plurality of thermally compensating members, said thermally compensating members being adapted to reduce a mass moment of inertia of said free-standing oscillating structure with increasing temperature so as to compensate for the effect of temperature on the resonant frequency of the ring resonator.

17. The time base according to claim 16 , wherein the thermally compensating members are attached to the free-standing oscillating structure at one end, and are free at their other end.