MEMS thermal actuator and method of manufacture

• US 20080191303A1
• Filed: 02/14/2007
• Published: 08/14/2008
• Est. Priority Date: 02/14/2007
• Status: Active Grant

• Current Assignee: Innovative Micro Technology Incorporated
• Original Assignee: Innovative Micro Technology Incorporated
• Inventors: Foster, John S., Carlson, Gregory A., Gudeman, Christopher S., Rubel, Paul J.
• Granted Patent: US 7,622,783 B2
• Time in Patent Office: Days
• US Class Current: 257/467
• CPC Class Codes: H01H 1/0036 Switches making use of microelectromechanical systems [MEMS] for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009
• CPC Class Codes: H01H 2001/0047 operable only by mechanical latching
• CPC Class Codes: H01H 2001/0078 with parallel movement of the movable contact relative to the substrate
• CPC Class Codes: H01H 2061/006 Micromechanical thermal relay
• CPC Class Codes: H01H 2061/008 Micromechanical actuator with a cold and a hot arm, coupled together at one end
• CPC Class Codes: H01H 61/04 wherein the thermally-sensitive member is only heated directly

Abstract

A separated MEMS thermal actuator is disclosed which is largely insensitive to creep in the cantilevered beams of the thermal actuator. In the separated MEMS thermal actuator, a inlaid cantilevered drive beam formed in the same plane, but separated from a passive beam by a small gap. Because the inlaid cantilevered drive beam and the passive beam are not directly coupled, any changes in the quiescent position of the inlaid cantilevered drive beam may not be transmitted to the passive beam, if the magnitude of the changes are less than the size of the gap.

Claims

1. A micromechanical actuator, comprising:

a silicon-on-insulator substrate having a device layer formed in a plane;

a material inlaid in the plane of the device layer and configured to move substantially in the plane of the device layer;

a silicon member formed from the device layer of a silicon-on-insulator substrate, configured to move substantially in the plane of the device layer, wherein movement of the inlaid material drives movement of the silicon member.

2. The micromechanical actuator of claim 1, wherein the inlaid material moves about a proximal end, the proximal end being anchored to the silicon-on-insulator substrate, by thermal expansion when a current is driven through the inlaid material.

3. The micromechanical actuator of claim 2, wherein the inlaid material extends substantially through the plane of the device layer, and is coupled at its distal end by a dielectric tether to an adjunct silicon portion.

4. The micromechanical actuator of claim 3, wherein the adjunct silicon portion is separated from the silicon member by an air gap in a quiescent state, and the inlaid material closes the air gap and drives movement of the silicon member when the micromechanical actuator is energized.

5. The micromechanical actuator of claim 4, wherein surfaces which define the air gap comprise at least one of silicon nitride, silicon dioxide, an inlaid metal, an inlaid semiconductor and a hydrofluoric acid etch resistant polymer

6. The micromechanical actuator of claim 1, further comprising a metal contact electrode which overhangs a wall on a distal end of the silicon member, the wall of the silicon member being disposed perpendicularly with respect to the plane of the device layer.

7. The micromechanical actuator of claim 1, further comprising a metal contact electrode inlaid in the plane of the device layer, and contiguous with a distal end of the silicon member.

8. The micromechanical actuator of claim 1, wherein the silicon member is clad with a metal contact material.

9. The micromechanical actuator of claim 6, wherein the inlaid material comprises at least one of gold, a gold alloy, nickel, a nickel alloy, aluminum, permalloy, platinum, copper, ceramic, and glass, the contact electrode comprises at least one of gold, a gold alloy, rhodium, ruthenium, platinum, nickel, a nickel alloy, aluminum and copper, and the silicon member comprises single crystal silicon.

10. A micromechanical switch comprising at least one micromechanical actuator of claim 4 and at least one additional micromechanical actuator, each micromechanical actuator configured to move substantially perpendicularly with respect to the other, in order to make contact between contact electrodes disposed on the distal ends of the micromechanical actuators.

11. An array of micromechanical switches, comprising at least one of the micromechanical switches of claim 10.

12. The array of micromechanical switches of claim 11, wherein electrical contact to the inlaid material is made by vias formed in the silicon-on-insulator substrate.

13. The array of micromechanical switches of claim 12, further comprising a lid wafer with at least one device cavity formed therein, which encloses the array of micromechanical switches.

14. The array of micromechanical switches of claim 13, wherein electrical contact to the micromechanical switches is made by vias formed through the thickness of the lid wafer.

15. A method for forming a micromechanical actuator, comprising:

etching a cavity into a device layer formed in a plane of a silicon-on-insulator substrate;

filling the cavity with an inlaid material, wherein the inlaid material is configured to move substantially in the plane of the device layer;

forming a silicon member from the device layer of the silicon-on-insulator substrate, wherein the silicon member is configured to move substantially in the plane of the device layer about an anchor point; and

etching a dielectric layer of the silicon-on-insulator substrate to release the inlaid material and the silicon member, such that the movement of the inlaid material drives movement of the silicon member.

16. The method of claim 15, further comprising:

planarizing the inlaid material using chemical mechanical polishing, to be substantially flush with the device layer surrounding the inlaid material.

17. The method of claim 15, wherein forming the silicon member from the device layer comprises etching an outline of the silicon member using deep reactive ion etching.

18. The method of claim 15, wherein filling the cavity with the inlaid material comprises plating a material comprising at least one of nickel and a nickel alloy in the cavity of the device layer.

19. The method of claim 15, further comprising:

forming an air gap slot in the device layer of the silicon-on-insulator substrate, which will separate the inlaid material from the silicon member.

20. The method of claim 19, further comprising:

forming at least one additional layer over surfaces defining the air gap slot, wherein a minimum separation of the surfaces of the additional layer defines a minimum dimension of the air gap slot.

21. The method of claim 15, further comprising:

forming a metal electrode over the silicon member, the metal electrode overhanging a wall on a distal end of the silicon member, the wall being oriented substantially perpendicularly with respect to the plane of the device layer.

22. The method of claim 15, further comprising:

etching a cavity into the device layer;

filling the cavity with a conductive contact material, wherein the conductive contact material is configured to move substantially in the plane of the device layer, when released from the dielectric layer, and is contiguous with a distal end of the silicon member.

23. The method of claim 15, further comprising:

forming vias in the silicon-on-insulator substrate, wherein the vias extend at least partially into a handle layer of the silicon-on-insulator substrate;

removing material from the handle layer until the vias extend through the thickness of the silicon-on-insulator substrate.

24. The method of claim 15, further comprising:

forming at least one device cavity in a lid wafer;

bonding the lid wafer to the silicon-on-insulator substrate, such that the inlaid material and the silicon member are sealed in the at least one device cavity.

25. The method of claim 24, further comprising:

forming vias through a thickness of the lid wafer; and

coupling the vias electrically to the inlaid material to energize the inlaid material.

26. An apparatus for forming a micromechanical actuator, comprising:

means for etching a cavity into a device layer formed in a plane of a silicon-on-insulator substrate;

means for filling the cavity with an inlaid material, wherein the inlaid material is configured to move substantially in the plane of the device layer 1;

means for forming a silicon member from the device layer of the silicon-on-insulator substrate, wherein the silicon member is configured to move substantially in the plane of the device layer about an anchor point at its proximal end; and

means for etching a dielectric layer of the silicon-on-insulator substrate to release the inlaid material and the silicon member, such that the movement of the inlaid material drives movement of the silicon member.