MEMS resonator having at least one resonator mode shape
The invention relates to a MEMS resonator having at least one mode shape comprising: a substrate ( 2 ) having a surface ( 12 ), and a resonator structure ( 1 ), wherein the resonator structure ( 1 ) is part of the substrate ( 2 ), characterized in that the resonator structure ( 1 ) is defined by a first closed trench ( 3 ) and a second closed trench ( 3 ), the first trench ( 3 ) being located inside the second trench ( 3 ) so as to form a tube structure ( 1 ) inside the substrate ( 2 ), and the resonator structure ( 1 ) being released from the substrate ( 2 ) only in directions parallel to the surface ( 12 ). The invention further relates to a method of manufacturing such a MEMS resonator.
1. A MEMS resonator having at least one resonator mode shape, the MEMS resonator comprising a substrate having a surface, and a resonator structure, characterized in that the resonator structure is part of the substrate, and further characterized in that the resonator structure is defined by a first closed trench and a second closed trench, the first trench being located inside the second trench so as to form a tube structure inside the substrate, and the resonator structure being released from the substrate only in directions parallel to the surface.
2. A MEMS resonator as claimed in claim 1 , characterized in that the first closed trench and the second closed trench have a circular shape so as to form a circular tube structure.
3. A MEMS resonator as claimed in claim 2 , characterized in that the first closed trench and the second closed trench are located concentrically with respect to each other so as to form the tube structure in such a manner that it has a constant thickness in all radial directions parallel to the surface.
4. A MEMS resonator as claimed in claim 1 , characterized in that the height of the tube structure, the height being defined by the depth of said first and second closed trenches, is more than two times the thickness of the tube structure.
5. A MEMS resonator according to claim 1 , characterized in that the first and second closed trenches are non-circular so as to form a tube structure having a varying thickness in radial directions parallel to the surface for compensating for a difference in the Young's modulus of the substrate material in said directions.
6. A MEMS resonator as claimed in claim 1 , characterized in that an actuator electrode is located on a sidewall of one of said closed trenches, the actuator electrode being arranged for actuating the resonator.
7. A MEMS resonator as claimed in claim 6 , characterized in that the actuator electrode is provided along the full length of said closed trench.
8. A MEMS resonator as claimed in claim 6 , characterized in that the actuator electrode is also arranged for sensing movement of the resonator.
9. A MEMS resonator as claimed in claim 6 , characterized in that a sensing electrode is located on a sidewall of the other of said closed trenches.
10. A MEMS oscillator comprising a MEMS resonator as claimed in claim 6 .
11. A MEMS filter comprising a single MEMS resonator as claimed in claim 6 .
12. A method of manufacturing a MEMS resonator having at least one mode shape comprising the following steps:
providing a substrate having a surface;
forming a first closed trench in the substrate;
forming a second closed trench in the substrate, the second closed trench surrounding the first closed trench so as to form a tube structure;
implanting dopant atoms into the substrate for making the resonator structure conductive and for defining an electrode;
providing a dielectric layer on the substrate and on all sidewalls of said trenches;
providing a conductive layer on the substrate and in said trenches;
patterning said conductive layer such that an opening is formed at the location of the tube structure locally exposing the dielectric layer, the patterning further being such that a separate inner electrode inside the first trench and a separate outer electrode inside the second trench are formed;
selectively partially removing the dielectric layer from the opening for forming a first gap between said inner electrode and the tube structure, and for forming a second gap between said outer electrode and the tube structure.