MEMS structure having a stress inverter temperature-compensated resonator member

• US 7,956,517 B1
• Filed: 09/04/2008
• Issued: 06/07/2011
• Est. Priority Date: 05/10/2007
• Status: Active Grant

• Current Assignee: Silicon Laboratories Incorporated
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Motiee, Mehrnaz, Howe, Roger T., Quevy, Emmanuel P., Bernstein, David H.
• Primary Examiner(s): Dougherty, Thomas M
• Assistant Examiner(s): Gordon, Bryan P
• Application Number:
  US12/204,713
• Time in Patent Office: 1,006 Days
• Field of Search: 310/346, 310/341, 310/367, 310/368, 310/338, 310/321
• US Class Current: 310/346
• CPC Class Codes: B81B 2201/0271 Resonators; ultrasonic resonators
• CPC Class Codes: B81B 3/0072 For controlling internal stress or strain in moving or flexible elements, e.g. stress compensating layers
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 2009/02503 Breath-like, e.g. Lam? mode, wine-glass mode
• CPC Class Codes: H03H 3/0076 for obtaining desired frequency or temperature coefficients
• CPC Class Codes: H03H 9/02338 Suspension means
• CPC Class Codes: H03H 9/2431 Ring resonators
• CPC Class Codes: H03H 9/2463 Clamped-clamped beam resonators
• CPC Class Codes: H03H 9/2473 Double-Ended Tuning Fork [DETF] resonators

Abstract

A MEMS structure having a temperature-compensated resonator member is described. The MEMS structure comprises an asymmetric stress inverter member coupled with a substrate. A resonator member is housed in the asymmetric stress inverter member and is suspended above the substrate. The asymmetric stress inverter member is used to alter the thermal coefficient of frequency of the resonator member by inducing a stress on the resonator member in response to a change in temperature.

Claims

1. A MEMS structure, comprising:

a stress inverter member coupled to a substrate, the stress inverter member having a major axis and a minor axis; and

a resonator member housed in said stress inverter member and suspended above said substrate.

2. The MEMS structure of claim 1, wherein the shape of said stress inverter member is selected from the group consisting of elliptical and diamond-shaped.

3. The MEMS structure of claim 1, wherein the coefficient of thermal expansion (CTE) of said stress inverter member is greater than the CTE of said substrate.

4. The MEMS structure of claim 3, wherein said stress inverter member consists essentially of silicon-germanium, and wherein said substrate consists essentially of silicon.

5. The MEMS structure of claim 1, wherein the thermal coefficient of frequency of said resonator member is negative, and wherein said stress inverter member is for inducing a tensile stress on said resonator member in response to an increase in temperature.

6. The MEMS structure of claim 5, wherein said stress inverter member and said resonator member consist essentially of silicon-germanium, and wherein said substrate consists essentially of silicon.

7. The MEMS structure of claim 1, wherein said stress inverter member is coupled directly to said substrate by a pair of anchor points arranged orthogonally to the longest dimension of said resonator member.

8. A MEMS structure, comprising:

a frame coupled to a substrate by a pair of anchor points, the frame having a major axis and a minor axis and wherein the coefficient of thermal expansion (CTE) of said frame is different from the CTE of said substrate;

a resonator member housed in said frame and suspended above said substrate, wherein said resonator member is, in one plane, completely surrounded by said frame; and

a pair of electrodes coupled with said substrate on either side of said resonator member;

where in response to a first applied stress, the frame is configured to apply a second, opposite, stress to said resonator member.

9. The MEMS structure of claim 8, wherein the shape of said frame is selected from the group consisting of elliptical and diamond-shaped.

10. The MEMS structure of claim 8, wherein the CTE of said stress inverter member is greater than the CTE of said substrate.

11. The MEMS structure of claim 10, wherein said frame consists essentially of silicon-germanium, and wherein said substrate consists essentially of silicon.

12. The MEMS structure of claim 8, wherein said pair of anchor points couples said frame directly to said substrate and is arranged orthogonally to the longest dimension of said resonator member.

13. The MEMS structure of claim 8, wherein the thermal coefficient of frequency of said resonator member is negative, and wherein said stress inverter member is for inducing a tensile stress on said resonator member in response to an increase in temperature.

14. A method for altering the thermal coefficient of frequency of a MEMS structure, comprising:

providing a resonator member housed in a frame coupled to a substrate, the frame having a major axis and a minor axis, wherein said resonator member is suspended above said substrate, and wherein the coefficient of thermal expansion (CTE) of said frame is different from the CTE of said substrate; and

applying a first stress to said frame, wherein, in response to applying said first stress, said frame applies a second, opposite, stress to said resonator member.

15. The method of claim 14, wherein providing said frame comprises providing a frame having a shape selected from the group consisting of elliptical and diamond-shaped, and coupled directly to said substrate by a pair of anchor points.

16. The method of claim 14, wherein applying said second stress reduces the magnitude of the thermal coefficient of frequency of said resonator member.

17. The method of claim 16, wherein said frame applies a tensile stress to said resonator member in response to an increase in temperature.

18. The method of claim 16, wherein said frame applies a compressive stress to said resonator member in response to a decrease in temperature.

19. The method of claim 16, wherein said frame applies a compressive stress to said resonator member in response to an increase in temperature.

20. The method of claim 16, wherein said frame applies a tensile stress to said resonator member in response to a decrease in temperature.

21. The method of claim 14, wherein said resonator member is, in one plane, completely surrounded by said frame.

22. A MEMS structure, comprising:

a stress inverter member coupled to a substrate, the stress inverter member having a first longer axis and a second shorter axis; and

a resonator member housed in said stress inverter member and suspended above said substrate, the resonator member being attached to the stress inverter member between two opposing points on the first longer axis of the stress inverter member, and the stress inverter member being coupled to the substrate by a pair of anchor points that are aligned parallel with the second shorter minor axis.

23. A MEMS structure, comprising:

a frame coupled to a substrate by a pair of anchor points, the frame having a first longer axis and a second shorter axis and wherein the coefficient of thermal expansion (CTE) of said frame is different from the CTE of said substrate;

a resonator member housed in said frame and suspended above said substrate, wherein said resonator member is, in one plane, completely surrounded by said frame, the resonator member being attached to the frame between two opposing points on the first longer axis of the frame, and the frame being coupled to the substrate by a pair of anchor points that are aligned parallel with the second shorter minor axis; and

a pair of electrodes coupled with said substrate on either side of said resonator member.

24. A method for altering the thermal coefficient of frequency of a MEMS structure, comprising:

providing a resonator member housed in a frame coupled to a substrate, the frame having a first longer axis and a second shorter axis, wherein said resonator member is suspended above said substrate, wherein the coefficient of thermal expansion (CTE) of said frame is different from the CTE of said substrate, the resonator member being attached to the frame between two opposing points on the first longer axis of the frame, and the frame being coupled to the substrate by a pair of anchor points that are aligned parallel with the second shorter minor axis; and

applying a first stress to said frame, wherein, in response to applying said first stress, said frame applies a second, opposite, stress to said resonator member.