Spatial light modulator with hidden comb actuator

• US 20040184132A1
• Filed: 03/22/2003
• Published: 09/23/2004
• Est. Priority Date: 03/22/2003
• Status: Active Grant

• Current Assignee: II-VI Delaware, Inc. (Coherent Corp.)
• Original Assignee: Active Optical Networks, Inc.
• Inventors: Shah, Paren, Novotny, Vlad J.
• Granted Patent: US 6,914,711 B2
• Time in Patent Office: Days
• US Class Current: 359/290
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

Described are Micro-Electro-Mechanical Systems (MEMS) actuators with hidden combs and hinges. The ability to hide the combs renders the actuators useful in digital micro-mirror devices. Comb actuators provide increased torque, which facilitates the use of stiffer, less fragile hinge structures. Also important, comb actuators do not require mechanical stops to define stable states, and thus avoid problems associated with physical contact. The actuators are infinitely variable through a range of angles.

Claims

1. An actuator comprising:

a. a substrate;

b. a fixed comb connected to the substrate and including a plurality of fixed teeth extending in a first plane;

c. a movable comb, including a plurality of movable teeth extending in a second plane;

d. a hinge connected between the substrate and the movable comb, the hinge facilitating movement of the movable comb with respect to the fixed comb; and

e. an actuated member connected to the movable comb and extending in a third plane;

f. wherein the first and second planes extend between the substrate and the third plane.

2. The actuator of claim 1, wherein the first and second planes are coplanar.

3. The actuator of claim 1, wherein the hinge extends along a fulcrum axis substantially parallel to the first and second planes.

4. The actuator of claim 1, further comprising a second movable comb including a second plurality of movable teeth extending in a direction parallel to the first-mentioned plurality of movable teeth.

5. The actuator of claim 4, wherein the second movable comb is disposed in the second plane, and wherein the fulcrum axis extends between the first and second movable combs from a perspective normal to the second plane.

6. The actuator of claim 5, further comprising a bridge connected to the hinge, the first movable comb, and the second movable comb.

7. The actuator of claim 1, further comprising a second fixed comb including a second plurality of fixed teeth extending in a direction parallel to the first-mentioned plurality of fixed teeth.

8. The actuator of claim 7, wherein the first-mentioned fixed teeth are electrically isolated from the second fixed teeth.

9. The actuator of claim 1, wherein the substrate includes an insulating surface, a first electrode connected to the movable comb, and a second electrode connected to the fixed comb.

10. The actuator of claim 1, wherein at least a portion of the movable comb is disposed between the actuated member and the fixed comb.

11. The actuator of claim 1, wherein the actuated member comprises a mirror.

12. The actuator of claim 1, wherein the actuator is one of a plurality of similar actuators in a mirror array.

13. The actuator of claim 1, wherein the actuated member obscures at least a portion of the fixed and movable combs from a perspective normal to the first plane.

14. The actuator of claim 1, wherein an applied voltage potential between the fixed comb and the movable comb moves the movable comb relative to the fixed comb to tilt the actuated member by a fixed deflection angle, and wherein the applied voltage potential defines the fixed deflection angle.

15. The actuator of claim 14, wherein a second applied voltage potential between the fixed comb and the movable comb moves the movable comb relative to the fixed comb to tilt the actuated member by a second fixed deflection angle, and wherein the second applied voltage potential defines the second fixed deflection angle.

16. The actuator of claim 14, wherein the fixed deflection angle corresponds to an “

on”

state.

17. The actuator of claim 1, wherein at least two of the fixed teeth are of different lengths.

18. The actuator of claim 1, wherein at least two of the movable teeth are of different lengths.

19. A spatial light modulator comprising:

a. a plurality of adjacent movable mirror surfaces arranged in an array extending over an array area, each movable mirror surface having an active-surface area;

b. wherein adding the active-surface areas produces a combined active-surface area at least 90 percent of the array area.

20. The spatial light modulator of claim 19, further comprising, for each mirror surface, at least one movable combs connected to the mirror surface;

and a fixed comb interdigitated with the movable comb.

21. The spatial light modulator of claim 20, wherein at least one of the fixed combs is disposed in a first plane and at least one of the movable combs is disposed in a second plane extending between the first plane and at least one of the movable mirror surfaces.

22. The spatial light modulator of claim 20, further comprising a plurality of hinges, each hinge connected to a respective one of the plurality of movable combs.

23. The spatial light modulator of claim 22, wherein the hinge is a torsional hinge.

24. The spatial light modulator of claim 20, further comprising an integrated circuit having a first plurality of contact pads electrically connected to the movable combs and a second collection of contact pads electrically connected to the fixed combs.

25. The actuator of claim 20, wherein at least one of the fixed and movable combs has teeth of different lengths.

26. The actuator of claim 19, wherein at least two of the movable teeth are of different lengths.

27. A projection system comprising:

a. a substrate;

b. a plurality of actuators disposed on the substrate, each actuator including;

i. a fixed comb connected to the substrate and including a plurality of fixed teeth;

ii. a movable comb, including a plurality of movable teeth; and

iii. a hinge connected between the fixed comb and the movable comb, the hinge facilitating movement of the movable comb with respect to the fixed comb; and

c. an array of actuated members, each actuated member including a light-modulating surface connected to at least one of the movable combs;

d. wherein the fixed and movable combs are disposed between the actuated members and the substrate.

28. The projection system of claim 27, wherein the fixed comb defines a first plane, the movable comb defines a second plane, and the first and second planes are coplanar.

29. A method of forming a comb actuator, the method comprising:

a. depositing a first conductive layer;

b. patterning the first conductive layer to define a first comb and an alignment pattern;

c. depositing a first sacrificial layer over the first comb and the alignment pattern;

d. planarizing the first sacrificial layer to expose the first comb;

e. depositing a second conductive layer over the exposed first comb;

f. forming a second mask on the second conductive layer, the second mask aligned to the alignment pattern and defining a second comb; and

g. etching the second conductive layer, leaving the second comb.

30. The method of claim 29, further comprising opening a window in the second conductive layer to uncover the alignment pattern before forming the second mask.

31. The method of claim 29, further comprising:

depositing a second sacrificial layer over the second comb and planarizing the second sacrificial layer to expose the second comb.

32. The method of claim 31, further comprising forming an actuated member over the second comb and removing what remains of the first and second sacrificial layers.

33. The method of claim 29, further comprising depositing a third conductive layer between the first and second conductive layers and patterning the third conductive layer to form a hinge extending between the first and second combs.

34. The method of claim 29, further comprising forming a mirror over the second comb.