Single crystal silicon micromirror and array

• US 6,541,831 B2
• Filed: 01/18/2001
• Issued: 04/01/2003
• Est. Priority Date: 01/18/2000
• Status: Expired due to Term

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: MacDonald, Noel C., Lee, Seung B.
• Primary Examiner(s): Everhart, Caridad
• Application Number:
  US09/761,860
• Publication Number:
  US 20010044165A1
• Time in Patent Office: 803 Days
• Field of Search: 257/482, 257/682, 257/680, 257/415, 257/417
• US Class Current: 257/415
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

A micromirror is fabricated in a substrate by defining a mirror platform on a first side of the substrate, defining an actuator structure corrected to the platform on a second side of the substrate, and then releasing the mirror platform for motion with the actuator. The actuator may be a comb drive structure having interdigitated movable finger electrodes connected to the mirror platform and stationary finger electrodes mounted on the substrate. The movable and stationary finger electrodes preferably are asymmetrical, and when activated, controllably move the mirror platform either horizontally or vertically with respect to the surface of the substrate.

The comb drive structure may be connected at one of its ends to a torsional support beam secured to the substrate, for torsional motion of the mirror platform with respect to the substrate. Alternatively, the comb drive may be connected at both ends to spaced torsional support beams for vertical motion of the platform with respect to the substrate. In the latter case, the actuator preferably includes spaced hinges to allow expansion of the actuator length.

Claims

1. A micromirror, comprising:

a substrate having a through cavity;

a micromirror platform fabricated from said substrate and located in said cavity;

an actuator including a comb drive fabricated from said substrate and suspended in said cavity for motion with respect to said substrate; and

at least one support connected to suspend said platform from said actuator for motion with the actuator.

2. The micromirror of claim 1, wherein said actuator is suspended for torsional motion of said platform with respect to said substrate.

3. The micromirror, of claim 2, wherein said actuator is secured to a beam extending across said cavity.

4. The micromirror of claim 3, wherein said beam is secured to a first end of said actuator, a second end of said actuator being free for torsional motion about said beam.

5. The micromirror of claim 1, wherein said comb drive includes movable fingers on said actuator interdigitated with stationary fingers on said substrate, said movable and stationary fingers having different heights.

6. The micromirror of claim 1, wherein said comb drive in assymetrical.

7. The micromirror of claim 1, wherein said actuator is suspended for vertical motion of said mirror platform with respect to said substrate.

8. The micromirror of claim 7, wherein said actuator is connected between two spaced beams extending across said cavity.

9. The micromirror of claim 8, wherein said actuator includes a backbone connected between said beams, and multiple transverse movable fingers on said backbone interdigitated with multiple stationary fingers on said substrate to form a comb-type drive for said actuator.

10. The micromirror of claim 9, wherein said backbone is expandable.

11. The micromirror of claim 8, wherein said actuator includes an expandable backbone connected between said beams, and an asymmetric drive for moving said backbone vertically with respect to said substrate.

12. The micromirror of claim 8, wherein said actuator includes a segmented backbone connected between said spaced beams.

13. The micromirror of claim 12, wherein said segmented backbone includes a first segment secured at a first end to a first one of said spaced beams, a second segment secured at a first end to a second one of said spaced beams, and a third segment connected between said first and second segments.

14. The micromirror of claim 13, further including a first hinge connecting said first segment to said third segment and a second hinge connecting said second segment to said third segment.

15. The micromirror of claim 14, further including a controllable drive mounted on said third segment for producing vertical motion of said third segment.

16. The micromirror of claim 15, wherein said support for said platform is secured to said third segment of said backbone.

17. The micromirror of claim 15, wherein each of said first and second hinges includes first and second parallel bars interconnected to produce torsional motion of said first and second segments about said first and second beams, respectively, and concurrent changes in the length of said backbone upon vertical motion of said third segment.

18. The micromirror of claim 17, wherein said controllable drive is an asymmetric comb drive.

19. The micromirror of claim 17, wherein said asymmetric comb drive includes interdigitated movable and stationary fingers having different effective heights.

20. The micromirror of claim 19, wherein each of said movable and stationary fingers incorporates a silicon core having an electrically insulating top and sidewall coating covered by a metal layer, to form an electrode.

21. The micromirror of claim 20, wherein the thickness of the top electrically insulating coating on said movable fingers in different than the thickness of the top electrically insulating coating on said stationary fingers to produce said different effective finger heights.

22. The micromirror of claim 20, wherein said silicon core of said movable fingers has a different height than the silicon core of said stationary fingers to produce said different effective finger heights.

23. A micromirror comprising:

a substrate having a through cavity;

a micromirror platform fabricated from said substrate and located in said cavity;

a beam extending across said cavity;

an actuator fabricated from said substrate and suspended in said cavity for motion with respect to said substrate, a first end of said actuator being secured to said beam and a second end of said actuator being free for torsional motion about said beam in said cavity;

at least one support connected to suspend said platform from said actuator for motion with the actuator;

wherein said actuator includes a backbone connected to said beam, and multiple transverse movable fingers on said backbone interdigitated with multiple stationary fingers on said substrate to form a comb-type drive for said actuator.

24. A microelectromechanical mirror structure, comprising:

a substrate having a cavity;

at least one support beam secured to said substrate and extending into said cavity;

an elongated actuator beam having an end portion connected to, and substantially perpendicular to, said support beam, extending into said cavity, and movable in said cavity with respect to said substrate;

a mirror platform mounted on said actuator beam and movable with said beam; and

a driver mounted on said substrate and activatable to drive said actuator beam to controllably move said platform.

25. The structure of claim 24, further including first and second spaced-apart support beams secured to said substrate and extending across said cavity, said actuator beam having first and second end portions connected to said first and second support beams, respectively.

26. The structure of claim 25, further including first and second expansion hinges connecting said first and second end portions of said actuator beam to said first and second support beams, respectively.

27. The structure of claim 26, wherein each said expansion hinge incorporates a pair of spaced, parallel, interconnected high aspect ratio bars.

28. The structure of claim 27, wherein said support beams, actuator beam and expansion hinges are substantially coplanar, and wherein said expansion hinge is connected to permit expansion of the length of said actuator beam and out-of-plane motion of said actuator beam upon activation of said driver.

29. The structure of claim 28, wherein said mirror structure is part of an array of similar mirror structures fabricated in a common substrate.

30. The structure of claim 29, further including address lines for the drivers for each mirror structure is said array for selectively actuating said drivers.

31. The structure of claim 28, wherein each said expansion hinge includes a first bar connected to its corresponding support beam and a second bar connected to its corresponding end portion of said actuator beam to permit torsional motion of said support beam and to accommodate said expansion of the length of said actuator beam upon activation of said driver.

32. The structure of claim 24, wherein said actuator beam is a cantilever having a first end portion secured to said support beam and having a second free end portion extending into said cavity, said driver being activatable to pivot said actuator about said support beam.

33. The structure of claim 24, wherein said support beam and said actuator beam are substantially coplanar with a top surface of said substrate and said mirror platform is integral with said actuator beam and extends through said cavity, a surface of said mirror platform being substantially coplanar with a bottom surface of said substrate.

34. The structure of claim 33, wherein said actuator beam is a cantilever having a first end portion secured to said support beam and having a second free end portion extending into said cavity, said driver being actuatable to pivot said actuator about said support beam.