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

• US 20050174625A1
• Filed: 03/24/2005
• Published: 08/11/2005
• Est. Priority Date: 06/19/1995
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Huibers, Andrew G.
• Granted Patent: US 7,027,207 B2
• Time in Patent Office: Days
• 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 substrate that is transmissive to visible light;

a silicon substrate;

wherein the silicon substrate and the substrate that is transmissive to visible light are bonded together forming a gap between the substrates; and

a plurality of deflectable elements enclosed within the gap.

2. The spatial light modulator of claim 1, wherein deflectable elements are microelectromechanical deflectable elements.

3. The spatial light modulator of claim 2, wherein the substrate that is transmissive to visible light is glass.

4. The spatial light modulator of claim 3, wherein the substrates are bonded together with the spacer therebetween using an adhesive.

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

6. The spatial light modulator of claim 5, wherein the deflectable elements are mirror plates.

7. The spatial light modulator of claim 6, wherein each mirror plate is attached to a hinge such that the mirror plate is operable to rotate.

8. The spatial light modulator of claim 7, wherein the hinge is a torsion hinge.

9. The spatial light modulator of claim 8, wherein the mirror plate comprise a first and second portions such that during the rotation of the mirror plate, the second portion moves towards the glass substrate and the first portion moves away from the glass substrate;

and wherein the hinge and the mirror plate are positioned in different planes.

10. The spatial light modulator of claim 9, further comprising circuitry and electrodes on the silicon substrate for deflecting the mirror plates.

11. The spatial light modulator of claim 10, wherein the circuitry comprises SRAM circuits to drive the electrodes.

12. The spatial light modulator of claim 11, wherein a spacer is positioned outside the plurality of deflectable elements.

13. The spatial light modulator of claim 12, wherein the deflectable element is reflective and comprises a metallic layer.

14. The spatial light modulator of claim 13, further comprising an aperture layer whereby light may pass only through a portion of the optically transmissive substrate.

15. The spatial light modulator of claim 14, wherein the aperture layer is opaque.

16. The spatial light modulator of claim 15, wherein the hinge is structured such that when a force is applied to the mirror plate bending occurs in the hinge, and, as a result, an angle between the mirror plate and the light transmissive substrate changes.

17. The spatial light modulator of claim 16, wherein the hinge is disposed between the mirror plate and the silicon substrate.

18. The spatial light modulator of claim 17, comprising in cross section, from top to bottom:

the substrate transmissive to visible light;

a first gap below the light transmissive substrate;

the deflectable element below the first gap;

a second gap below the deflectable element; and

the hinge below the second gap.

19. The spatial light modulator of claim 18, wherein the hinge extends across the deflectable element between the electrode and the deflectable element and connects to the deflectable element towards a center part of the deflectable element.

20. The spatial light modulator of claim 19, wherein the modulator is configured so that when a first electrical potential difference is applied between the deflectable element and a corresponding electrode, the deflectable element moves to a deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

21. The spatial light modulator of claim 20, wherein deflectable element comprises a first portion and a second portion such that during deflection of the deflectable element, the second portion moves towards the light transmissive substrate as the first portion moves away from the light transmissive substrate.

22. The spatial light modulator of claim 21, further comprising one or more passivation layers on the silicon substrate.

23. The spatial light modulator of claim 22, wherein the electrodes on the silicon substrate are disposed closer to the light transmissive substrate than the circuitry.

24. The spatial light modulator of claim 23, wherein the deflectable elements are electrically connected in rows, the electrodes are electrically connected in columns that cross the rows at the deflectable element locations, whereby individual mirrors may be turned on and off by selectively applying appropriate row and column biases and creating electrostatic attraction.

25. A spatial light modulator, comprising:

a substrate that is transmissive to visible light;

a silicon substrate;

wherein the silicon substrate and the substrate that is transmissive to visible light are bonded together with a spacer therebetween forming a gap between the substrates; and

a plurality of deflectable elements encapsulated within the gap.

26. The spatial light modulator of claim 25, wherein the deflectable elements are electrically connected in rows, the electrodes are electrically connected in columns that cross the rows at the deflectable element locations, whereby individual mirrors may be turned on and off by selectively applying appropriate row and column biases and creating electrostatic attraction.

27. The spatial light modulator of claim 26, wherein the electrodes on the silicon substrate are disposed closer to the light transmissive substrate than the circuitry.

28. The spatial light modulator of claim 27, wherein the hinge is structured such that when a force is applied to the mirror plate bending occurs in the hinge, and, as a result, an angle between the mirror plate and the light transmissive substrate changes.

29. The spatial light modulator of claim 28, wherein the deflectable element is reflective and comprises a metallic layer.

30. The spatial light modulator of claim 29, wherein the spacer is positioned outside the plurality of deflectable elements.

31. The spatial light modulator of claim 30, further comprising circuitry and electrodes on the silicon substrate for deflecting the deflectable elements.

32. The spatial light modulator of claim 31, wherein the circuitry comprises SRAM circuits to drive the electrodes.

33. The spatial light modulator of claim 32, wherein the deflectable elements are mirror plates.

34. The spatial light modulator of claim 33, wherein each mirror plate is attached to a hinge such that the mirror plate is operable to rotate.

35. The spatial light modulator of claim 34, wherein the silicon and light transmissive substrates are bonded together with the spacer therebetween using an adhesive.

36. The spatial light modulator of claim 35, wherein the adhesive is epoxy.

37. The spatial light modulator of claim 36, wherein deflectable elements are microelectromechanical deflectable elements.

38. The spatial light modulator of claim 37, wherein the substrate that is transmissive to visible light is glass.

39. The spatial light modulator of claim 38, further comprising an opaque layer whereby light may pass only through a portion of the optically transmissive substrate.

40. The spatial light modulator of claim 39, further comprising one or more passivation layers on the silicon substrate.

41. The spatial light modulator of claim 40, wherein deflectable element comprises a first portion and a second portion such that during deflection of the deflectable element, the second portion moves towards the light transmissive substrate as the first portion moves away from the light transmissive substrate.

42. The spatial light modulator of claim 41, wherein the modulator is configured so that when a first electrical potential difference is applied between the deflectable element and a corresponding electrode, the deflectable element moves to a deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

43. The spatial light modulator of claim 42, wherein the hinge extends across the deflectable element between the electrode and the deflectable element and connects to the deflectable element towards a center part of the deflectable element.

44. The spatial light modulator of claim 43, comprising in cross section, from top to bottom:

the substrate transmissive to visible light;

a first gap below the light transmissive substrate;

the deflectable element below the first gap;

a second gap below the deflectable element; and

the hinge below the second gap.

45. The spatial light modulator of claim 44, wherein the hinge is disposed between the mirror plate and the silicon substrate.

46. The spatial light modulator of claim 45, wherein the hinge is a torsion hinge.

47. The spatial light modulator of claim 46, wherein the mirror plate comprise a first and second portions such that during the rotation of the mirror plate, the second portion moves towards the glass substrate and the first portion moves away from the glass substrate;

and wherein the hinge and the mirror plate are positioned in different planes.

48. The spatial light modulator of claim 47, wherein a single electrode on the silicon substrate is provided for electrostatically attracting a corresponding mirror plate.

49. The spatial light modulator of claim 47, further comprising a conducting transparent layer on the light transmissive substrate for actively pulling the mirror plate to an OFF state.