Method of manufacturing a microelectromechanical system (MEMS) resonator
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.
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.