Double substrate reflective spatial light modulator with self-limiting micro-mechanical elements

• US 20050168795A1
• Filed: 03/24/2005
• Published: 08/04/2005
• Est. Priority Date: 06/19/1995
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Venture Lending & Leasing IV Incorporated
• Inventors: Huibers, Andrew G.
• Granted Patent: US 6,975,444 B2
• Time in Patent Office: Days
• US Class Current: 359/290
• CPC Class Codes: G02B 26/08 for controlling the direction of light in light guides G02B6/35
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

A spatial light modulator includes an upper optically transmissive substrate held above a lower substrate containing addressing circuitry. One or more electrostatically deflectable elements are suspended by hinges from the upper substrate. In operation, individual mirrors are selectively deflected and serve to spatially modulate light that is incident to, and then reflected back through, the upper substrate. Motion stops may be attached to the reflective deflectable elements so that the mirror does not snap to the bottom substrate. Instead, the motion stop rests against the upper substrate thus limiting the deflection angle of the reflective deflectable elements.

Claims

1. A spatial light modulator, comprising:

a silicon substrate;

an optically transmissive substrate bonded to the silicon substrate and defining a gap therebetween, with an array of micromirrors disposed within the gap;

wherein the micromirrors are mechanically deflectable in a digital manner and are capable of being selectively deflected to spatially modulate light that is incident to, and then reflected back through, the optically transmissive substrate;

wherein each micromirror comprises a rigid mirror and a torsion hinge;

SRAM or DRAM circuitry on the silicon substrate at each micromirror location;

electrodes on the silicon substrate and connected to the SRAM or DRAM circuitry and for electrostatically attracting corresponding micromirrors;

wherein the electrodes are disposed closer to the corresponding micromirrors than the circuitry; and

wherein the mirror and torsion hinge are disposed in different layers with the torsion hinge crossing the mirror and attaching at a point on the mirror.

2. The spatial light modulator of claim 1, wherein the gap between the silicon substrate and the optically transmissive substrate is partially evacuated.

3. The spatial light modulator of claim 2, wherein the micromirrors are square.

4. The spatial light modulator of claim 3, wherein the silicon substrate and optically transmissive substrate are bonded together with a spacer and adhesive.

5. The spatial light modulator of claim 4, wherein the adhesive is an epoxy.

6. The spatial light modulator of claim 1, further comprising a conducting transparent layer on the optically transmmissive substrate.

7. The spatial light modulator of claim 6, wherein the conducting transparent layer actively pulls the micromirrors to the optically transmissive substrate to their OFF state.

8. The spatial light modulator of claim 6, wherein the conducting transparent layer is indium tin oxide.

9. The spatial light modulator of claim 1, wherein an aperture layer is provided.

10. The spatial light modulator of claim 9, wherein the aperture layer allows light to pass only through a subset of the optically transmissive substrate.

11. The spatial light modulator of claim 5, wherein an opaque aperture layer is provided on the optically transmissive substrate to selectively block light from passing therethrough.

12. The spatial light modulator of claim 6, wherein a single electrode per micromirror is provided on the silicon substrate.

13. The spatial light modulator of claim 9, wherein the aperture layer is a sputtered and etched layer on the light transmissive substrate.

14. The spatial light modulator of claim 1, wherein each micromirror comprises a motion stop.

15. The spatial light modulator of claim 14, wherein the micromirrors are bistable and are deflected between ON and OFF positions.

16. The spatial light modulator of claim 14, wherein the motion stop is at the same potential as the mirror.

17. The spatial light modulator of claim 14, wherein two motion stops per micromirror are provided.

18. The spatial light modulator of claim 15, wherein the mirror has a reflecting layer comprising aluminum.

19. The spatial light modulator of claim 18, further comprising multiple substantially transparent layers on the mirror to enhance reflectivity of the mirror.

20. The spatial light modulator of claim 18, wherein the micromirrors are electrically coupled to the silicon substrate.

21. The spatial light modulator of claim 20, wherein the hinge is thinner than the mirror.

22. The spatial light modulator of claim 21, wherein the hinge lies in a separate plane from the mirror.

23. The spatial light modulator of claim 22, wherein the micromirrors are configured to move to a deflected position wherein a portion of the micromirror reflects light from an optical source to imaging optics when the micromirror is in the deflected position, the optical source and the imaging optics both located on the same side of the optically transmissive substrate.

24. A spatial light modulator, comprising:

a silicon substrate;

an optically transmissive substrate bonded to the silicon substrate and defining a gap therebetween, with an array of micromirrors disposed within the gap;

wherein the micromirrors are mechanically deflectable in a digital manner and are capable of being selectively deflected to spatially modulate light that is incident to, and then reflected back through, the optically transmissive substrate;

wherein each micromirror comprises a rigid mirror and a hinge;

RAM circuitry on the silicon substrate at each micromirror location;

electrodes on the silicon substrate and connected to the RAM circuitry and for electrostatically attracting corresponding micromirrors;

wherein the optically transmissive substrate and the silicon substrate are bonded together with spacers and epoxy.

25. The spatial light modulator of claim 24, wherein the electrodes are disposed closer to the corresponding micromirrors than the RAM circuitry.

26. The spatial light modulator of claim 25, wherein the RAM circuitry is DRAM circuitry.

27. The spatial light modulator of claim 24, wherein the mirror and torsion hinge are disposed in different layers with the torsion hinge crossing the mirror and attaching at a point.

28. The spatial light modulator of claim 24, wherein an aperture layer is provided.

29. The spatial light modulator of claim 28, wherein the aperture layer allows light to pass only through a subset of the optically transmissive substrate.

30. The spatial light modulator of claim 25, wherein an opaque aperture layer is provided on the optically transmissive substrate to selectively block light from passing therethrough.

31. The spatial light modulator of claim 24, further comprising a conducting transparent layer on the optically transmmissive substrate.

32. The spatial light modulator of claim 31, wherein the conducting transparent layer actively pulls the micromirrors to the optically transmissive substrate to their OFF state.

33. The spatial light modulator of claim 31, wherein the conducting transparent layer is indium tin oxide.

34. The spatial light modulator of claim 24, further comprising a voltage source configured to assert a voltage bias to the deflectable element.

35. The spatial light modulator of claim 24, wherein the RAM circuitry is SRAM circuitry.

36. The spatial light modulator of claim 24, wherein the hinge and mirror are disposed in different planes and wherein the mirror has an axis or rotation about the hinge.

37. The spatial light modulator of claim 36, further comprising planar optical componenets on the optically transmissive substrate.

38. The spatial light modulator of claim 24, wherein the hinge comprises silicon nitride.

39. A projection system comprising:

an optical source for providing light;

a spatial light modulator for spatially modulating light from the light source;

imaging optics for receiving light from the spatial light modulator;

wherein the spatial light modulator comprises;

a silicon substrate;

an optically transmissive substrate bonded to the silicon substrate and defining a gap therebetween, with an array of micromirrors disposed within the gap;

wherein the micromirrors are mechanically deflectable in a digital manner and are capable of being selectively deflected to spatially modulate light that is incident to, and then reflected back through, the optically transmissive substrate;

wherein each micromirror comprises a rigid mirror and a torsion hinge;

SRAM or DRAM circuitry on the silicon substrate at each micromirror location;

electrodes on the silicon substrate and connected to the SRAM or DRAM circuitry and for electrostatically attracting corresponding micromirrors;

wherein the electrodes are disposed closer to the corresponding micromirrors than the circuitry; and

wherein the mirror and torsion hinge are disposed in different layers with the torsion hinge crossing the mirror and attaching at a point on the mirror.