Methods and apparatus for a MEMS varactor
View Patent ↗A micro-electro mechanical system (MEMS) variable capacitor (varactor) generally includes a substrate ( 102 ), a first capacitive plate ( 112 ) formed on the substrate, a flexible structure ( 150 ) coupled to the substrate, a second capacitive plate ( 116 ) and a first electrode ( 122 ) formed on the flexible structure; a package seal ( 104 ) coupled to the substrate and having a second electrode ( 106 ) formed thereon, wherein the distance between the first capacitive plate and the second capacitive plate (and hence, the capacitance of the structure) is responsive to a bias voltage applied to the electrodes.
1. A MEMS varactor device comprising:
a substrate;
a first capacitive plate formed on said substrate;
a flexible structure coupled to the substrate;
a second capacitive plate and a first electrode formed on the flexible structure; and
a package seal coupled to the substrate and having a second electrode formed thereon, wherein a distance between the first capacitive plate and the second capacitive plate is responsive to a bias voltage applied between the first electrode and the second electrode.
2. The device of claim 1 , further including a third electrode formed on the substrate.
3. The device of claim 2 , wherein the second electrode and the third electrode are substantially aligned.
4. The device of claim 1 , wherein the package seal has an external surface, and wherein the second electrode is formed on the external surface.
5. The device of claim 1 , wherein the package seal has an internal surface, the second electrode is formed on the internal surface, and a dielectric layer is formed on the second electrode.
6. The device of claim 1 , wherein the flexible structure is a rectangular structure.
7. The device of claim 6 , wherein the flexible structure is coupled to the substrate at two opposite sides of the rectangular structure.
8. The device of claim 6 , wherein the flexible structure is coupled to the substrate at each corner of the rectangular structure.
9. The device of claim 1 , wherein the first electrode comprises a plurality of electrode segments.
10. The device of claim 1 , wherein the first electrode comprises a single electrode segment substantially surrounding the second capacitive plate.
11. A method for forming a MEMS varactor device, comprising:
providing a substrate;
forming a first capacitive plate on the substrate;
forming a flexible structure coupled to the substrate;
forming a second capacitive plate and a first electrode on the flexible structure;
forming a package seal coupled to the substrate, wherein the package seal encapsulates the first capacitive plate and the flexible structure; and
forming a second electrode on the package seal.
12. The method of claim 11 , wherein the second electrode is formed on an external surface of the package seal.
13. The method of claim 11 , wherein the second electrode is formed on an internal surface of the package seal, further including forming a dielectric layer on the second electrode.
14. The method of claim 11 , wherein forming the flexible structure includes forming a substantially rectangular structure having a perimeter, wherein the rectangular structure is anchored to the substrate at two or more points along its perimeter.
15. The method of claim 11 , further including forming a third electrode on the substrate.
16. The method of claim 15 , further including forming one or more conductive traces to the first electrode, the second electrode, the third electrode, the first capacitive plate, and the second capacitive plate.
17. A MEMS varactor comprising:
a substrate;
a first capacitive plate and a bottom electrode formed on the substrate;
a flexible structure coupled to the substrate;
a second capacitive plate and a middle electrode formed on the flexible structure, wherein the second capacitive plate and the first capacitive plate are separated by an inter-plate distance;
a package seal coupled to the substrate, said package seal encompassing the first capacitive plate and the flexible structure;
a top electrode formed on the package seal; and
wherein the inter-plate distance is configured to increase when a bias voltage is applied between the top electrode and the middle electrode, and is configured to decrease when a bias voltage is applied between the middle electrode and the bottom electrode.
18. The MEMS varactor of claim 17 , wherein the flexible structure comprises a dielectric material.
19. The MEMS varactor of claim 17 , wherein the shape of the flexible structure is selected from the group consisting of a cantilever structure, a bridge structure, and a trampoline structure.
20. The MEMS varactor of claim 17 , wherein the middle electrode comprises a single electrode segment substantially encompassing the first capacitive plate.