Temperature stable MEMS resonator

• US 9,548,720 B1
• Filed: 09/23/2015
• Issued: 01/17/2017
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: SiTime Corporation (Megachips Corporation)
• Original Assignee: SiTime Corporation (Megachips Corporation)
• Inventors: Hagelin, Paul M., Grosjean, Charles I.
• Primary Examiner(s): Gannon, Levi
• Application Number:
  US14/863,337
• Time in Patent Office: 482 Days
• Field of Search: 310/311, 310/315, 310/341, 310/346, 310/370, 331/66, 331/154, 331/156, 331/176, 333186-189, 333/197, 333/200, 333/219, 333/219.1, 333/234
• US Class Current: 1/1
• CPC Class Codes: H02N 1/00 Electrostatic generators or motors using a solid moving electrostatic charge carrier
• CPC Class Codes: H03B 5/30 with frequency-determining element being electromechanical resonator
• CPC Class Codes: H03B 5/32 being a piezoelectric resonator selection of piezoelectric material H10N30/00
• CPC Class Codes: H03H 2009/02251 Design
• CPC Class Codes: H03H 2009/02283 Vibrating means
• CPC Class Codes: H03H 2009/02291 Beams
• CPC Class Codes: H03H 2009/02299 Comb-like, i.e. the beam comprising a plurality of fingers or protrusions along its length
• CPC Class Codes: H03H 2009/02322 Material
• CPC Class Codes: H03H 2009/0233 comprising perforations
• CPC Class Codes: H03H 2009/02496 Horizontal, i.e. parallel to the substrate plane
• CPC Class Codes: H03H 2009/155 using MEMS techniques
• CPC Class Codes: H03H 3/0072 of microelectro-mechanical resonators or networks micromembranes or microbeams B81B2203/01; manufacture of microstructural devices in general B81C
• CPC Class Codes: H03H 3/0073 Integration with other electronic structures
• CPC Class Codes: H03H 3/0076 for obtaining desired frequency or temperature coefficients
• CPC Class Codes: H03H 9/02244 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/02433 Means for compensation or elimination of undesired effects
• CPC Class Codes: H03H 9/02448 of temperature influence
• CPC Class Codes: H03H 9/125 Driving means, e.g. electrodes, coils
• CPC Class Codes: H03H 9/21 Crystal tuning forks
• CPC Class Codes: H03H 9/2405 of microelectro-mechanical resonators
• CPC Class Codes: H03H 9/2468 : Tuning fork resonators
• CPC Class Codes: H03H 9/2484 : with two fork tines, e.g. Y-beam cantilever
• CPC Class Codes: H10N 30/01 : Manufacture or treatment
• CPC Class Codes: H10N 30/04 : Treatments to modify a piezoelectric or electrostrictive property, e.g. polarisation characteristics, vibration characteristics or mode tuning
• CPC Class Codes: Y10T 29/42 : Piezoelectric device making
• CPC Class Codes: Y10T 29/49002 : Electrical device making
• CPC Class Codes: Y10T 29/49005 : Acoustic transducer
• CPC Class Codes: Y10T 29/4902 : Electromagnet, transformer or inductor
• CPC Class Codes: Y10T 29/4908 : Acoustic transducer

Abstract

A resonant member of a MEMS resonator oscillates in a mechanical resonance mode that produces non-uniform regional stresses such that a first level of mechanical stress in a first region of the resonant member is higher than a second level of mechanical stress in a second region of the resonant member. A plurality of openings within a surface of the resonant member are disposed more densely within the first region than the second region and at least partly filled with a compensating material that reduces temperature dependence of the resonant frequency corresponding to the mechanical resonance mode.

Claims

1. A microelectromechanical system (MEMS) resonator comprising:

a resonant member that oscillates at a resonant frequency and in a mechanical resonance mode in which the resonant member is subject to non-uniform regional stresses such that a first level of mechanical stress in a first region of the resonant member is higher than a second level of mechanical stress in a second region of the resonant member, the resonant member having (i) a first surface that spans the first and second regions, and (ii) a plurality openings formed in the first surface and disposed more densely within the first region than the second region; and

a compensating material disposed within each of the openings in the first surface to reduce temperature dependence of the resonant frequency of the resonant member.

2. The MEMS resonator of claim 1 wherein the compensating material is characterized by a temperature coefficient of Young'"'"'s Modulus (TCE) having a sign opposite that of a TCE of the resonant member.

3. The MEMS resonator of claim 1 further comprising a capping material disposed over the openings.

4. The MEMS resonator of claim 3 wherein the compensating material comprises an oxide and the capping material comprises silicon.

5. The MEMS resonator of claim 1 wherein the resonant member has a second surface opposite the first surface and wherein at least one of the openings in the first surface extends to a depth less than a distance between the first and second surfaces along an axis normal to the first and second surfaces.

6. The MEMS resonator of claim 1 further comprising a liner material disposed in at least one of the plurality of openings.

7. The MEMS resonator of claim 1 wherein the resonant member has a second surface opposite the first surface and wherein at least one of the openings in the first surface of the resonant member extends into the resonant member without reaching the second surface.

8. The MEMS resonator of claim 1 wherein the resonant member has a second surface opposite the first surface and wherein at least one of the openings in the first surface extends through the resonant member from the first surface to the second surface.

9. The MEMS resonator of claim 1 wherein each of the plurality of openings in the first surface of the resonant member is formed by removal of a constituent material of the resonant member.

10. The MEMS resonator of claim 1 wherein the resonant member comprises silicon and the compensating material comprises an oxide.

11. A method of fabricating a microelectromechanical system (MEMS) resonator, the method comprising:

forming a resonant member capable of oscillating at a resonant frequency and in a mechanical resonance mode in which one or more regions of the resonant member are subject to higher levels of mechanical stress than other regions of the resonant member;

forming a plurality of openings in a first surface of the resonant member predominantly within the one or more regions subject to higher levels of mechanical stress; and

disposing a compensating material within the openings in the first surface that reduces temperature dependence of the resonant frequency of the resonant member.

12. The method of claim 11 wherein disposing the compensating material within the openings comprises disposing within at least one of the openings a compensating material characterized by a temperature coefficient of Young'"'"'s Modulus (TCE) having a sign opposite that of a TCE of the resonant member.

13. The method of claim 11 further comprising disposing a capping material within the openings over the compensating material.

14. The method of claim 13 wherein disposing the compensating material within the openings comprises disposing an oxide within the openings, and wherein disposing the capping material within the openings over the compensating material comprises disposing silicon within the openings over the oxide.

15. The method of claim 11 wherein the resonant member has a second surface opposite the first surface and wherein forming the plurality of openings in the first surface of the resonant member comprises extending at least one of openings in the first surface to a depth less than a distance between the first and second surfaces along an axis normal to the first and second surfaces.

16. The method of claim 11 further comprising disposing a liner material in at least one of the plurality of openings.

17. The method of claim 11 wherein the resonant member has a second surface opposite the first surface and wherein forming the plurality of openings in the first surface comprises extending at least one of the openings into the resonant member without reaching the second surface.

18. The method of claim 11 wherein the resonant member has a second surface opposite the first surface and wherein forming the plurality of openings in the first surface comprises extending at least one of the openings through the resonant member from the first surface to the second surface.

19. The method of claim 11 wherein forming the plurality of openings in the first surface comprises removal of a constituent material of the resonant member.

20. The method of claim 11 wherein forming the resonant member comprises forming a silicon resonant member from a silicon substrate, and wherein disposing the compensating material within the openings in the first surface of the resonant member comprises disposing an oxide within the openings.