Reflective spatial light modulator with deflectable elements formed on a light transmissive substrate

• US 6,538,800 B2
• Filed: 01/09/2002
• Issued: 03/25/2003
• Est. Priority Date: 06/19/1995
• Status: Expired due to Fees

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Huibers, Andrew G.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Spector, David N.
• Application Number:
  US10/043,703
• Publication Number:
  US 20020122239A1
• Time in Patent Office: 440 Days
• Field of Search: 359/223, 359/291, 359/295, 359/298
• US Class Current: 359/291
• 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 first substrate that is bonded to a second substrate;

the first substrate being an optically transmissive substrate and having a plurality of deflectable micromirror elements thereon;

the second substrate being a silicon substrate with addressing circuitry and a plurality of electrodes for causing deflection of the deflectable micromirror elements on the first substrate.

2. The spatial light modulator of claim 1, wherein each electrode is positioned to selectively deflect a corresponding deflectable element when a bias voltage is applied between the electrode and the corresponding deflectable element.

3. The spatial light modulator of claim 1, wherein each of the deflectable elements is reflective and comprises a metallic layer.

4. The spatial light modulator of claim 3, wherein each of the deflectable elements further comprises a structural support layer.

5. The spatial light modulator of claim 1, wherein the deflectable elements further comprise:

a substantially rigid plate which is attached to the optically transmissive substrate with one or more torsion hinges located along an edge of the plate, whereby the plate is operable to rotate about the edge.

6. The spatial light modulator of claim 5, further comprising a means for limiting the area of contact between each of the deflectable element and the optically transmissive substrate.

7. The spatial light modulator of claim 1, wherein the optically transmissive substrate comprises an aperture layer, whereby light may pass only through a portion of the optically transmissive substrate.

8. The spatial light modulator of claim 1, wherein the optically transmissive substrate comprises fixed optical elements.

9. The spatial light modulator of claim 1, wherein each of the deflectable elements comprises an electrically conductive portion and is deflectable by electrostatic force.

10. The spatial light modulator of claim 1, further comprising a means for electrically connecting each of the deflectable elements to the silicon substrate.

11. The spatial light modulator of claim 1, wherein each of the deflectable elements is substantially rigid and is attached to the optically transmissive substrate by flexible hinges.

12. The spatial light modulator of claim 1, wherein each of the deflectable elements comprises a plurality of reflective deflectable elements, and wherein the plurality of reflective deflectable elements are grouped in a plurality of subsets, each subset oriented so as to selectively direct incident light into a specific angle.

13. The spatial light modulator of claim 1, wherein each of the deflectable elements is composed of a laminate including a metallic layer.

14. The spatial light modulator of claim 1, wherein the electrodes are positioned for creating electrostatic attraction of the deflectable elements on the optically transmissive substrate.

15. The spatial light modulator of claim 1, wherein the electrodes are aluminum electrodes.

16. The spatial light modulator of claim 1, wherein the deflectable elements are electrically conductive.

17. The spatial light modulator of claim 2, wherein:

the deflectable elements are electrically connected in rows;

the electrodes are electrically connected in columns that cross the rows at pixel locations;

whereby individual pixels may be turned on and off by selectively applying appropriate row and column biases and creating electrostatic attraction.

18. The spatial light modulator of claim 1, wherein the optically transmissive substrate contains an aperture layer, wherein said aperture layer allows light to pass only through a subset of the substrate area.

19. The spatial light modulator of claim 1, wherein claim each of the deflectable elements further comprises a mirror stop rigidly connected to the mirror such that when the angle increases, a free end of the mirror stop moves closer to the optically transmissive substrate.

20. The spatial light modulator of claim 19, wherein the mirror stop is structured such that a free end of the mirror is separate from the silicon substrate when the free end of the mirror stop is in contact with the optically transmissive substrate.

21. The spatial light modulator of claim 20, wherein each of said deflectable elements is connected to the silicon substrate by a hinge such that each of the deflectable elements is free to rotate about a corresponding hinge, wherein the mirror stop is connected to the hinge opposite the mirror.

22. The spatial light modulator of claim 19, wherein the mirror stop comprises a sharp contact tip configured to contact the optically transmissive substrate when the angle is at a maximum value.

23. The spatial light modulator of claim 19, wherein the mirror stop is coplanar with the mirror.

24. The spatial light modulator of claim 19, wherein the mirror stop and the optically transmissive substrate are electrically connected.

25. A spatial light modulator comprising:

an optically transmissive substrate having an upper surface and a lower surface;

a plurality of reflective deflectable elements attached to the lower surface of said optically transmissive substrate;

a silicon substrate positioned below, parallel, and spaced apart from the lower surface of said optically transmissive substrate, said silicon substrate containing a plurality of electrodes and electronic circuitry for selective actuation of the deflectable elements attached to said optically transmissive substrate.

26. The spatial light modulator of claim 25, wherein the electrodes are connected to the electronic circuitry, wherein each electrode is positioned to selectively deflect a corresponding deflectable element when a bias voltage is applied between the electrode and the corresponding deflectable element.

27. The spatial light modulator of claim 25, wherein each of the deflectable elements is reflective and comprises a metallic layer.

28. The spatial light modulator of claim 27, wherein each of the deflectable elements further comprises a structural support layer.

29. The spatial light modulator of claim 25, wherein the deflectable elements further comprise:

a substantially rigid plate which is attached to the optically transmissive substrate with one or more torsion hinges located along an edge of the plate, whereby the plate is operable to rotate about the edge.

30. The spatial modulator of claim 29, further comprising a means for limiting the area of contact between each of the deflectable elements and the optically transmissive substrate.

31. The spatial light modulator of claim 25, wherein the optically transmissive substrate comprises an aperture layer, whereby light may pass only through a portion of the lower surface of the optically transmissive substrate.

32. The spatial light modulator of claim 25, wherein the optically transmissive substrate comprises fixed optical elements.

33. The spatial light modulator of claim 25, wherein each of the deflectable elements comprises an electrically conductive portion and is deflectable by electrostatic force.

34. The spatial light modulator of claim 25, further comprising a means for electrically connecting each of the deflectable elements to the silicon substrate.

35. The spatial light modulator of claim 25, wherein each of the deflectable elements is substantially rigid and is attached to the optically transmissive substrate by flexible hinges.

36. The spatial light modulator of claim 25, wherein each of the deflectable elements comprises a plurality of reflective deflectable elements, and wherein the plurality of reflective deflectable elements are grouped in a plurality of subsets, each subset oriented so as to selectively direct incident light into a specific angle.

37. The spatial light modulator of claim 27, wherein each of the deflectable elements is composed of a laminate including a metallic layer.

38. The spatial light modulator of claim 25, wherein the silicon substrate comprises an electrode for creating electrostatic attraction between each of the deflectable elements and the optically transmissive substrate.

39. The spatial light modulator of claim 25, further comprising aluminum electrodes on the silicon substrate for causing deflection of the deflectable elements on the optically transmissive substrate.

40. The spatial light modulator of claim 25, wherein the deflectable elements are electrically conductive.

41. The spatial light modulator of claim 40, wherein:

the deflectable elements are electrically connected in rows;

the electrodes are electrically connected in columns that cross the rows at pixel locations;

whereby individual pixels may be turned on and off by selectively applying appropriate row and column biases and creating electrostatic attraction.

42. The spatial light modulator of claim 25, wherein the optically transmissive substrate contains an aperture layer, wherein said aperture layer allows light to pass only through a subset of the substrate area.

43. The spatial light modulator of claim 25, wherein each of the deflectable elements further comprises a mirror stop rigidly connected to the mirror such that when the angle increases, a free end of the mirror stop moves closer to the optically transmissive substrate.

44. The spatial light modulator of claim 43, wherein the mirror stop is structured such that a free end of the mirror is not in contact with the silicon substrate when the free end of the mirror stop is in contact with the optically transmissive substrate.

45. A process for operating a spatial light modulator comprising:

asserting a bias voltage between addressing electrodes connected to circuitry and a reflective deflectable element, the addressing circuitry being contained in a silicon substrate, the reflective deflectable element being attached to a lower surface of an optically transmissive substrate, the silicon substrate disposed below, but separated from, the optically transmissive substrate.

46. The process of claim 45, wherein asserting a bias voltage comprises:

asserting a negative voltage to the reflective deflectable element; and

asserting a positive voltage from 0 to 5 volts to the addressing circuitry.