Singly attached MEMS thermal device and method of manufacture
View Patent ↗An improved MEMS thermal actuator has a cantilevered beam and a conductive circuit having two driving arms, an inner arm adjacent to the cantilevered beam, and an outer arm adjacent to the inner arm. Current flows through the inner and outer arms to heat the conductive circuit, causing it to expand relative to the cantilevered beam. A tether ties the conductive circuit to the cantilevered beam, so that upon expansion, the conductive circuit causes the cantilevered beam to deflect about its anchor point. However, only the inner arm of the driving beam is coupled to the cantilevered beam. Since the outer arm of the conductive circuit is not coupled to the cantilevered beam, the overall stiffness of the actuator may be decreased. In addition, serpentines may be placed in the outer arm of the conductive circuit, in order to further decrease the stiffness of this beam. The actuator may therefore be made more efficient, in that the deflection of the cantilevered beam may be increased for a given input current.
1. A micromechanical device, comprising:
a first cantilevered beam;
a second cantilevered beam adjacent to the first cantilevered beam, and electrically coupled to a current return path, wherein only the second cantilevered beam is attached to the first cantilevered beam by a first dielectric tether, and wherein the second cantilevered beam is configured to expand, thereby driving the first cantilevered beam in a predetermined direction; and
at least one other dielectric tether which couples only the second cantilevered beam to a flexible member that provides the current return path, wherein the current return path is not tethered directly to the first cantilevered beam.
2. The micromechanical device of claim 1 , wherein the flexible member comprises a third cantilevered beam, wherein the second cantilevered beam and the third cantilevered beam comprise portions of an electrical circuit through which current is driven to heat the second cantilevered beam, thereby driving the first cantilevered beam in the predetermined direction.
3. The micromechanical device of claim 2 , further comprising:
an extension on a distal end of the second cantilevered beam, wherein the third cantilevered beam is coupled to the second cantilevered beam at a point inboard of the extension and wherein essentially no current flows through the extension.
4. The micromechanical device of claim 3 , wherein a second dielectric tether couples the first cantilevered beam to the second cantilevered beam at a point over the extension, and wherein the second cantilevered beam is attached by the first dielectric tether to the first cantilevered beam at a point closer to a midpoint than the ends of the second cantilevered beam.
5. The micromechanical device of claim 4 , wherein the third cantilevered beam further comprises at least one serpentine, wherein the distance between the third and the second cantilevered beams increases over some portion of the serpentine, and the third cantilevered beam with the at least one serpentine is substantially more flexible than the second cantilevered beam.
6. The micromechanical device of claim 5 , wherein the at least one other dielectric tether couples the second cantilevered beam to the third cantilevered beam at a point within the at least one serpentine.
7. The micromechanical device of claim 2 , wherein the third cantilevered beam is substantially more flexible than the second cantilevered beam.
8. The micromechanical device of claim 1 , wherein the first and second cantilevered beams and the current return path each comprise nickel or a nickel alloy.
9. The micromechanical device of claim 1 , wherein the first dielectric tether comprises a photopatternable polymer.
10. The micromechanical device of claim 1 , further comprising a gold tip coupled to a distal end of the first cantilevered beam.
11. A micromechanical switch, comprising:
a first micromechanical device of claim 1 ; and
a second micromechanical device of claim 1 , disposed in a substantially orthogonal orientation to the first micromechanical device of claim 1 .
12. A method for manufacturing a micromechanical device, comprising:
forming a first cantilevered beam;
forming a second cantilevered beam adjacent to the first cantilevered beam;
forming a current return path electrically coupled to the second cantilevered beam;
configuring the second cantilevered beam to expand relative to the first cantilevered beam; and
coupling only the second cantilevered beam to the first cantilevered beam with a first dielectric tether, such that the first cantilevered beam is driven in a predetermined direction by the expansion of the second cantilevered beam, and
coupling only the second cantilevered beam to a flexible member with at least one other dielectric tether, wherein the flexible member provides the current return path, and is not coupled directly to the first cantilevered beam.
13. The method of claim 12 , wherein forming the first cantilevered beam, forming the second cantilevered beam, and forming the current return path comprise electroplating at least one of nickel and a nickel alloy.
14. The method of claim 12 , further comprising:
applying a current to the second cantilevered beam and the current return path;
heating the second cantilevered beam; and
driving the first cantilevered beam in the predetermined direction by expansion of the second cantilevered beam.
15. The method of claim 12 , wherein coupling the current return path to the second cantilevered beam comprises:
forming an extension to a distal end of the second cantilevered beam; and
electrically coupling a third cantilevered beam as the flexible member to the second cantilevered beam at a point inboard of the extension.
16. The method of claim 15 , further comprising:
coupling the first cantilevered beam to the second cantilevered beam with a second dielectric tether attached at a point on the extension and another point on the first cantilevered beam and wherein only the second cantilevered beam is attached to the first cantilevered beam by the first dielectric tether.
17. The method of claim 12 , further comprising:
coupling only a third cantilevered beam as the flexible member to the second cantilevered beam with the at least one other dielectric tether, wherein the third cantilevered beam is substantially more flexible than the second cantilevered beam.
18. The method of claim 12 , further comprising:
forming at least one serpentine in a third cantilevered beam as the flexible member; and
coupling the third cantilevered beam to the second cantilevered beam with the at least one other dielectric tether attached to the third cantilevered beam at a point within the serpentine.
19. The method of claim 12 , further comprising:
coupling a gold tip to a distal end of the first cantilevered beam.
20. The method of claim 12 , wherein connecting only the second cantilevered beam to the first cantilevered beam with a first dielectric tether comprises:
applying a photopatternable polymer layer over the substrate;
patterning the layer of photopatternable polymer over and between the first cantilevered beam and the second cantilevered beam; and
baking the photopatternable polymer until it is substantially cured.