Method for temperature compensation in MEMS resonators with isolated regions of distinct material

• US 8,464,418 B2
• Filed: 12/15/2009
• Issued: 06/18/2013
• Est. Priority Date: 03/09/2007
• Status: Active Grant

• Current Assignee: Semiconductor Manufacturing International (Shanghai) Corporation (Semiconductor Manufacturing International Corporation)
• Original Assignee: Silicon Laboratories Incorporated
• Inventors: Quevy, Emmanuel P., Bernstein, David H.
• Primary Examiner(s): Tugbang, A. Dexter
• Application Number:
  US12/638,919
• Publication Number:
  US 20100093125A1
• Time in Patent Office: 1,281 Days
• Field of Search: 29/253.5, 295/94, 298/52, 438/50, 438/329, 438/424, 438/429, 438/430, 438/FOR.227, 438/FOR.291, 257/742, 257/773
• US Class Current: 29/594
• CPC Class Codes: B81C 1/00349 Creating layers of material on a substrate
• CPC Class Codes: B81C 1/00523 Etching material
• CPC Class Codes: B81C 1/0069 Thermal properties, e.g. improve thermal insulation
• CPC Class Codes: G02B 6/358 Latching of the moving element, i.e. maintaining or holding the moving element in place once operation has been performed; includes a mechanically bistable system
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 2009/2442 Square resonators
• CPC Class Codes: H03H 3/0076 for obtaining desired frequency or temperature coefficients
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/2457 Clamped-free beam resonators
• CPC Class Codes: Y10T 29/42 Piezoelectric device making
• CPC Class Codes: Y10T 29/49005 Acoustic transducer
• CPC Class Codes: Y10T 29/49165 by forming conductive walled aperture in base

Abstract

MEMS resonators containing a first material and a second material to tailor the resonator'"'"'s temperature coefficient of frequency (TCF). The first material has a different Young'"'"'s modulus temperature coefficient than the second material. In one embodiment, the first material has a negative Young'"'"'s modulus temperature coefficient and the second material has a positive Young'"'"'s modulus temperature coefficient. In one such embodiment, the first material is a semiconductor and the second material is a dielectric. In a further embodiment, the quantity and location of the second material in the resonator is tailored to meet the resonator TCF specifications for a particular application. In an embodiment, the second material is isolated to a region of the resonator proximate to a point of maximum stress within the resonator. In a particular embodiment, the resonator includes a first material with a trench containing the second material.

Claims

1. A method of forming a MEMS resonator device, comprising:

forming a first structural material on a substrate;

forming a trench in the first structural material;

forming in the trench, a second structural material having a different Young'"'"'s modulus temperature coefficient than the first structural material;

patterning a resonator comprising both the first and second structural materials; and

anchoring the patterned resonator to an anchor;

where the second material is confined to a region of the resonator having a longest dimension that is shorter than a distance between the anchor and a point of the resonator furthest from the anchor.

2. The method of claim 1, wherein forming the first and second structural materials on the substrate further comprises depositing films at a temperature below 500°

C.

3. The method of claim 1, wherein forming the first structural material comprises depositing a polycrystalline silicon germanium alloy and wherein forming the second structural material comprises depositing silicon dioxide.

4. The method of claim 1, wherein forming the first structural material comprises depositing an silicon dioxide and wherein forming the second structural material comprises depositing a polycrystalline silicon germanium alloy.

5. The method of claim 1, wherein the trench in the first structural material is defined through lithography and etch to have a dimension required to compensate the temperature coefficient of frequency of the resonator.

6. The method of claim 1, wherein forming the second structural material in the trench further comprises:

filling the trench with the second structural material to form a void-free structure; and

removing the second structural material from the top surface of the first structural material with at least one of an etch back and chemical-mechanical polish.

7. The method of claim 1, wherein the second structural material in the trench forms a spacer on the sidewalls of the trench and patterning the resonator removes the first structural material from a portion of the spacer to form a spacer ring attached to a sidewall of the resonator.

8. The method of claim 7, further comprising isotropically etching the second structural material to remove the portions of the ring not attached to the sidewall of the resonator.

9. The method of claim 1, where the first material has a negative Young'"'"'s modulus temperature coefficient and the second material has a positive Young'"'"'s modulus temperature coefficient.

10. The method of claim 1, where the first material is a semiconductor and the second material is a dielectric.

11. The method of claim 1, where the top surface of the first material is planar with the top surface of the second material.

12. The method of claim 1, where the resonator is a beam;

and where the region of the resonator to which the second material is confined includes a point of maximum flexural stress within the resonator when the resonator is made to resonate.

13. The method of claim 1, where the resonator is a beam;

and where the region of the resonator to which the second material is confined includes a point of maximum stress within the resonator and excludes a point of maximum displacement when the resonator is made to resonate.

14. The method of claim 1, where the resonator is a bulk mode resonator;

and where the region of the resonator to which the second material is confined is an isolated block completely surrounded by the first material.

15. The method of claim 1, where the second material stiffens the resonator region to which the second material is confined as a function of temperature to tune a temperature coefficient of frequency of the resonator in a manner at least partially decoupled from the resonator temperature coefficient.

16. The method of claim 1, where an edge of the second material farthest from the anchor is disposed a first distance from the anchor, the first distance being less than a distance between the anchor and a point of maximum displacement during resonance.

17. The method of claim 16, further comprising forming the plurality of trenches in the first structural material such that the plurality of trenches are arranged in a radial array about the anchor.

18. The method of claim 16, where the first material has a negative Young'"'"'s modulus temperature coefficient and the second material has a positive Young'"'"'s modulus temperature coefficient.

19. The method of claim 16, where the top surface of the first material is planar with the top surface of the second material.

20. A method of forming a MEMS resonator, comprising:

forming a first structural material on a substrate;

forming a trench in the first structural material;

forming in the trench, a second structural material having a different Young'"'"'s modulus temperature coefficient than the first structural material; and

patterning a resonator comprising both the first and second structural materials;

where the second material is isolated to a region of the resonator proximate to a point of maximum stress within the resonator during operation.

21. A method of forming a MEMS resonator, comprising:

forming a first structural material on a substrate;

forming a trench in the first structural material;

forming in the trench, a second structural material having a different Young'"'"'s modulus temperature coefficient than the first structural material; and

patterning a resonator comprising both the first and second structural materials;

where the resonator is a bulk-mode resonator, and where the method further comprises;

forming a plurality of trenches in the first structural material, the plurality of trenches being arranged in a radial array; and

forming the second structural material in the plurality of trenches.