Single crystal silicon micromirror and array

• US 20010044165A1
• Filed: 01/18/2001
• Published: 11/22/2001
• Est. Priority Date: 01/18/2000
• Status: Active Grant

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: MacDonald, Noel C., Lee, Seung B.
• Granted Patent: US 6,541,831 B2
• Time in Patent Office: Days
• US Class Current: 438/52
• 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 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 4

, 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.

6. The micromirror of

claim 1

, wherein said actuator includes a comb drive.

7. The micromirror of

claim 6

, 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.

8. The micromirror of

claim 6

, wherein said comb drive is asymmetrical.

9. The micromirror of

claim 1

, wherein said actuator is suspended for vertical motion of said mirror platform with respect to said substrate.

10. The micromirror of

claim 9

, wherein said actuator is connected between two spaced beams extending across said cavity.

11. The micromirror of

claim 10

, 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.

12. The micromirror of

claim 11

, wherein said backbone is expandable.

13. The micromirror of

claim 10

, 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.

14. The micromirror of

claim 10

, wherein said actuator includes a segmented backbone connected between said spaced beams.

15. The micromirror of

claim 14

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

16. The micromirror of

claim 15

, 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.

17. The micromirror of

claim 16

, further including a controllable drive mounted on said third segment for producing vertical motion of said third segment.

18. The micromirror of

claim 17

, wherein said support for said platform is secured to said third segment of said backbone.

19. The micromirror of

claim 17

, 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.

20. The micromirror of

claim 19

, wherein said controllable drive is an asymmetric comb drive.

21. The micromirror of

claim 19

, wherein said asymmetric comb drive includes interdigitated movable and stationary fingers having different effective heights.

22. The micromirror of

claim 21

, 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.

23. The micromirror of

claim 22

, 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.

24. The micromirror of

claim 22

, 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.

25. A method for fabrication of a movable micromirror, comprising:

coating top and bottom parallel surfaces of a wafer with an electrically insulating layer;

coating at least a portion of said bottom surface with a reflective surface;

forming in said bottom surface a trench surrounding a mirror platform including said reflective surface;

forming in said top surface an actuator structure having a movable portion connected to said mirror structure; and

releasing said mirror platform from said wafer for motion with said actuator.

26. The method of

claim 25

, wherein forming said actuator includes fabricating multiple movable stationary interdigitated fingers having different effective heights for producing relative vertical motion of said movable and stationary fingers.

27. The method of

claim 26

, wherein fabricating fingers having different effective heights includes fabricating said movable and stationary fingers with different core heights.

28. The method of

claim 26

, wherein fabricating fingers having different effective heights includes fabricating said movable and stationary fingers with the same core heights and with top surface oxide layers of different thicknesses.

29. The method of

claim 26

, wherein forming said actuator includes fabricating movable and stationary interdigitated fingers having silicon cores with the same height, coating the tops of the cores of said movable and stationary fingers with different thicknesses of an insulating layer;

and metallizing said fingers to produce interdigitated electrodes having different effective heights.

30. The method of

claim 26

, wherein forming said actuator includes fabricating movable and stationary interdigitated fingers having silicon cores of differing heights;

coating said fingers with an electrically insulating layer; and

metallizing said fingers to produce interdigitated electrodes having different effective heights.