Method of manufacturing a microelectromechanical system (MEMS) resonator

• US 8,667,665 B2
• Filed: 07/31/2012
• Issued: 03/11/2014
• Est. Priority Date: 12/21/2007
• Status: Active Grant

• Current Assignee: SiTime Corporation (Megachips Corporation)
• Original Assignee: SiTime Corporation (Megachips Corporation)
• Inventors: Hagelin, Paul Merritt, Grosjean, Charles
• Primary Examiner(s): Kim, Paul D
• Application Number:
  US13/562,684
• Publication Number:
  US 20120295384A1
• Time in Patent Office: 588 Days
• Field of Search: 295/921, 295/94, 295/95, 296/091, 298/31, 298/46, 310330-332, 310/340, 310/344, 310/345, 333186-189
• US Class Current: 29/594
• 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

One embodiment of the present inventions sets forth a method for decreasing a temperature coefficient of frequency (TCF) of a MEMS resonator. The method comprises lithographically defining slots in the MEMS resonator beams and filling the slots with a compensating material (for example, an oxide) wherein the temperature coefficient of Young'"'"'s Modulus (TCE) of the compensating material has a sign opposite to a TCE of the material of the resonating element.

Claims

1. A method of manufacturing a microelectromechanical system (MEMS) resonator having a reduced magnitude of thermal coefficient of frequency (TCF) wherein the MEMS resonator includes a resonating element which oscillates, the method comprising:

fabricating one or more slots within the resonating element;

providing a liner material within the one or more slots; and

providing a compensating material (a) on or over the liner material and (b) in the one or more slots, wherein a temperature coefficient of Young'"'"'s Modulus (TCE) of the compensating material has a sign opposite to a TCE of a material comprising the resonating element.

2. The method of claim 1, wherein the one or more slots are defined in a region of the resonating element subject to larger stresses relative to other regions of the MEMS resonator.

3. The method of claim 2, wherein the resonating element oscillates via an extensional and/or flexural mode.

4. The method of claim 1, wherein an outside sidewall of the resonating element has a serrated surface.

5. The method of claim 4, wherein the serrated surface comprises teeth.

6. The method of claim 5, wherein the resonating element is configured to oscillate in a tuning fork fashion during operation, and a region proximate to the base of the teeth is the region subject to the largest flexural stresses.

7. The method of claim 1, wherein the one or more slots are filled completely with the compensating material.

8. The method of claim 1, wherein the liner material includes silicon.

9. The method of claim 8, wherein the silicon is a polysilicon.

10. The method of claim 1, wherein the liner material includes a silicon nitride.

11. The method of claim 10, further comprising providing a low stress cap layer on the compensating material.

12. The method of claim 11, wherein the low-stress cap layer comprises silicon.

13. The method of claim 1, wherein providing the liner material within the one or more slots further includes depositing the liner material on a silicon oxide layer exposed at a bottom of the one or more slots.

14. The method of claim 13, wherein the liner material comprises a silicon or silicon nitride.

15. The method of claim 13, further comprising removing excess of the compensating material from the surfaces of the resonating element such that the compensating material remains substantially only within the one or more slots within the resonating element.

16. The method of claim 15, further comprising providing a cap material on the compensating material within the one or more slots.

17. The method of claim 16, wherein the cap material comprises silicon.

18. The method of claim 16, wherein the one or more slots are filled completely with the compensating material.

19. The method of claim 1, wherein the compensating material comprises oxide.

20. The method of claim 19, wherein the one or more slots are filled with oxide through one of the processes of (i) oxide growth, (ii) oxide deposition, or (iii) a combination of oxide growth and oxide deposition.