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

• US 6,172,797 B1
• Filed: 11/09/1999
• Issued: 01/09/2001
• Est. Priority Date: 06/19/1995
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Huibers, Andrew
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Spector, David N.
• Application Number:
  US09/437,586
• Time in Patent Office: 427 Days
• Field of Search: 359/223, 359/224, 359/290, 359/291, 359/295, 359/298, 359/318, 359/855
• 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:

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

a deflectable element attached to the lower surface of the optically transmissive substrate, the deflectable element comprising a first portion and a second portion such that during a deflection of the deflectable element, the second portion moves towards the lower surface as the first portion moves away from the lower surface, and the deflection is limited by contact between the second portion and the lower surface; and

a circuit substrate positioned below and spaced apart from the lower surface of the optically transmissive substrate.

2. The spatial light modulator of claim 1, wherein the circuit substrate includes an electrode for creating electrostatic attraction between the deflectable element and the circuit substrate.

3. The spatial light modulator of claim 1, further comprising addressing circuitry formed in the circuit substrate and an electrode connected to the addressing circuitry, wherein the electrode is positioned to selectively deflect the deflectable element when a bias voltage is applied between the electrode and the deflectable element.

4. The spatial light modulator of claim 3, wherein the modulator is configured so that when a first electrical potential difference is applied between the deflectable element and the electrode, the deflectable element moves to a fixed deflected position and remains in the fixed deflected position until a second electrical potential difference, less than the first electrical potential difference, is applied between the deflectable element and the electrode.

5. The spatial light modulator of claim 4, wherein the addressing circuitry operating voltage does not exceed approximately five (5) volts.

6. The spatial light modulator of claim 4, wherein the addressing circuitry includes a memory array.

7. The spatial light modulator of claim 6, wherein the memory array comprises DRAM circuits.

8. The spatial light modulator of claim 6, wherein the memory array comprises SRAM circuits.

9. The spatial light modulator of claim 1, wherein the circuit substrate is a portion of a silicon die.

10. The spatial light modulator of claim 1, wherein the optically transmissive substrate comprises quartz.

11. The spatial light modulator of claim 1, wherein the optically transmissive substrate comprises an aperture layer patterned such that light may pass only through a portion of the lower surface of the optically transmissive substrate.

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

13. The spatial light modulator of claim 1, wherein the lower surface is configured to minimize a contact area between the second portion and the lower surface.

14. The spatial light modulator of claim 1, wherein the deflectable element includes a conductive layer.

15. The spatial light modulator of claim 1, wherein the deflectable element includes a layer that is reflective and conductive.

16. The spatial light modulator of claim 1, wherein the deflectable element includes an electrically conductive portion and is deflectable by electrostatic force.

17. The spatial light modulator of claim 1, wherein the deflectable element is electrically coupled to the circuit substrate.

18. The spatial light modulator of claim 1, wherein the deflectable element includes a structural support layer.

19. The spatial light modulator of claim 1, wherein the deflectable element includes an optically transparent support layer and a reflective layer.

20. The spatial light modulator of claim 19, wherein the optically transparent support layer comprises silicon nitride.

21. The spatial light modulator of claim 19, wherein the reflective layer comprises aluminum.

22. The spatial light modulator of claim 1, wherein the first portion of the deflectable element is shaped such that a portion of a second deflectable element fits within the first portion.

23. The spatial light modulator of claim 1, wherein the deflectable element is substantially rigid and is attached to the optically transmissive substrate by a flexible hinge.

24. The spatial light modulator of claim 23, wherein the hinge is a torsion hinge.

25. The spatial light modulator of claim 23, wherein the hinge is relatively elastic compared to the deflectable element.

26. The spatial light modulator of claim 23, wherein the hinge comprises material that has a smaller modulus of elasticity than at least one of the materials in the deflectable element.

27. The spatial light modulator of claim 23, wherein the hinge is thinner than the deflectable element.

28. The spatial light modulator of claim 23, wherein the hinge is comprised of substantially transparent material.

29. The spatial light modulator of claim 23, wherein the hinge lies in a different plane from the deflectable element.

30. The spatial light modulator of claim 23, wherein the hinge is positioned between the deflectable element and the optically transmissive substrate.

31. The spatial light modulator of claim 23, wherein the deflectable element is positioned between the hinge and the optically transmissive substrate.

32. The spatial light modulator of claim 1, wherein the deflectable element is deflected to more than one specified angle by applying to an associated electrode in the circuit substrate an electrical potential corresponding with the specified angle.

33. The spatial light modulator of claim 1:

wherein the deflectable element is configured to move from a non-deflected position to a deflected position; and

wherein a portion of the deflectable element reflects light from an optical source to imaging optics when the deflectable element is in the deflected position, the optical source and the imaging optics both located on the same side of the optically transmissive substrate.

34. The spatial light modulator of claim 33:

wherein the deflectable element is configured to move from the non-deflected position to a second deflected position; and

wherein a portion of the deflectable element reflects light from the optical source to second imaging optics when the deflectable element is in the second deflected position, the optical source and the second imaging optics both located on the same side of the optically transmissive substrate.

35. The spatial light modulator of claim 1:

wherein the deflectable element is configured to move from a non-deflected position to a deflected position; and

wherein a portion of the deflectable element reflects light from an optical source to imaging optics when the deflectable element is in the non-deflected position, the optical source and the imaging optics both located on the same side of the optically transmissive substrate.

36. The spatial light modulator of claim 35:

wherein the deflectable element is configured to move from the non-deflected position to a second deflected position; and

wherein a portion of the deflectable element reflects light from the optical source to second imaging optics when the deflectable element is in the second deflected position, the optical source and the second imaging optics both located on the same side of the optically transmissive substrate.

37. The spatial light modulator of claim 1, wherein the second portion is narrower than, and extends from, the first portion.

38. The spatial light modulator of claim 1 wherein the shape of the second portion minimiizes a contact area between the second portion and the optically transmissive substrate.

39. The spatial light modulator of claim 1, wherein the second portion comprises a sharp contact tip configured to contact the optically transmissive substrate when the deflectable element is at a maximum deflection.

40. The spatial light modulator of claim 1, wherein the second portion is coplanar with the first portion.

41. The spatial light modulator of claim 1, wherein the second portion and the lower surface are electrically connected.

42. The spatial light modulator of claim 1, further comprising a voltage source configured to assert a voltage bias to the deflectable element.

43. The spatial light modulator of claim 1, wherein the spatial light modulator is a portion of an array of spatial light modulators.

44. The spatial light modulator of claim 1 further comprising a plurality of reflective deflectable elements each having configurations similar to the deflectable element, wherein selected deflectable elements in the plurality of reflective deflectable elements are grouped in a plurality of subsets, each subset oriented so as to selectively direct incident light at a specific angle.

45. The spatial light modulator of claim 1 further comprising:

a second deflectable element attached to the lower surface of the optically transmissive substrate, the second deflectable element comprising a third portion and a fourth portion such that during a deflection of the second deflectable element, the fourth portion moves towards the lower surface as the third portion moves away from the lower surface, and the deflection of the second deflectable element is limited by contact between the fourth portion and the lower surface.

46. The spatial light modulator of claim 45 wherein the deflectable element and the second deflectable element are configured such that each have essentially the same deflection angle when the second portion and the fourth portion contact the lower surface.

47. A process for directing light comprising:

providing an optically transmissive substrate having a surface;

providing a substantially rigid deflectable element connected to the substrate surface, wherein the deflectable element includes a first portion, a second portion, and a reflective surface, and wherein the deflectable element is configured to be positioned in an undeflected state and in a deflected state, and the second portion moves towards, and can eventually contact, the substrate surface as the first portion moves away from the substrate surface;

positioning the deflectable element in the undeflected state;

shining a light beam from a light source through the substrate onto the reflective surface so that the light beam is reflected through the substrate in a first direction when the deflectable element is in the undeflected state; and

positioning the deflectable element in the deflected state so that the light beam is reflected through the substrate in a second direction when the deflectable element is in the deflected state.

48. The process of claim 47 wherein the light beam reflected in the first direction strikes imaging optics.

49. The process of claim 47 wherein the light beam reflected in the second direction strikes imaging optics.

50. The process of claim 47 further comprising:

providing a circuit substrate below and spaced apart from the optically transmissive substrate;

wherein positioning the deflectable element in the deflected state is done by creating a first electric potential difference between the deflectable element and the circuit substrate, and the deflectable element remains in the deflected state until a second electric potential difference, less than the first electric potential difference, exists between the deflectable element and the circuit substrate.

51. A spatial light modulator fabrication process comprising:

forming a sacrificial layer over an optically transmissive substrate;

forming a hole through said sacrificial layer;

forming and patterning a support layer over said sacrificial layer to define a deflectable element, said deflectable element having a first portion and a second portion such that during a deflection of said deflectable element, said second portion moves toward said substrate as said first portion moves away from said substrate, and said deflection is limited by contact between said second portion and said substrate;

forming and patterning a hinge layer over a portion of said deflectable element to define a hinge such that a portion of said hinge extends through said hole and attaches said deflectable element to said substrate; and

removing said sacrificial layer so that said deflectable element may deflect.

52. The process of claim 51 wherein after said forming and patterning a hinge layer, a reflective conductive layer is formed over both said deflectable element first portion and a portion of said substrate, such that at least part of said reflective conductive layer overlying said first portion is electrically coupled with at least part of said reflective conductive layer overlying said substrate.

53. The process of claim 51 further comprising:

removing a portion of said sacrificial layer to expose a portion of said hinge layer extending through said hole; and

forming a conductive and reflective layer over said deflectable element such that said deflectable element is electrically coupled to a second deflectable element.

54. The process of claim 51 further comprising:

patterning said substrate to define a raised portion such that said deflection is limited by contact between said raised portion and said second portion.

55. A spatial light modulator fabrication process comprising:

forming a first sacrificial layer over an optically transmissive substrate;

forming and patterning a support layer over said first sacrificial layer to define a deflectable element having a first portion and a second portion and to create an exposed portion of said first sacrificial layer, wherein during a deflection of said deflectable element, said second portion moves toward said substrate as said first portion moves away from said substrate, and said deflection is limited by contact between said second portion and said substrate;

forming a second sacrificial layer over the exposed portion of said first sacrificial layer and over said deflectable element;

forming a first hole through said second sacrificial layer and positioned over said deflectable element, and a second hole through both said first sacrificial layer and said second sacrificial layer and positioned away from said deflectable element;

forming and patterning a hinge layer to define a hinge such that a first portion of said hinge extends through said first hole and is coupled with said deflectable element, and such that a second portion of said hinge extends through said second hole and is coupled with said substrate so as to attach said deflectable element to said substrate; and

removing said first sacrificial layer and said second sacrificial layer.

56. A process for the fabrication of a spatial light modulator, the process comprising:

depositing a sacrificial layer over an optically transmissive substrate;

etching a hole through the sacrificial layer;

depositing a reflective layer over the sacrificial layer;

patterning the reflective layer to define a deflectable element, the deflectable element having a first portion and a second portion such that during a deflection of the deflectable element, the second portion moves toward the optically transmissive substrate as the first portion moves away from the optically transmissive substrate, and the deflection is limited by contact between the second portion and the optically transmissive substrate;

connecting the deflectable element to the optically transmissive substrate through the hole;

removing the sacrificial layer so that the deflectable element is free to deflect;

forming addressing circuitry including an electrode on a circuit substrate; and

aligning and joining the optically transmissive substrate and the circuit substrate such that the deflectable element can be selectively deflected by an electric potential applied to the electrode.

57. The process of claim 56 further comprising:

depositing an aperture layer on the optically transmissive substrate before depositing the sacrificial layer; and

patterning the aperture layer to allow light to pass only through a portion of the optically transmissive substrate.

58. The process of claim 56, wherein removing the sacrificial layer comprises etching the sacrificial layer with a XeF₂ gas phase etch.

59. The process of claim 56, wherein depositing the reflective layer comprises:

depositing a first dielectric layer of a first index of refraction; and

depositing a second dielectric layer of a second index of refraction different from the first index of refraction.

60. The process of claim 56 wherein depositing and patterning the reflective layer comprises:

depositing an optically transmissive layer;

patterning the optically transmissive layer; and

depositing a conductive material on the second portion such that the conductive material does not contact the optically transmissive substrate when the second portion contacts the optically transmissive substrate.

61. The process of claim 60, wherein depositing a conductive material comprises depositing the conductive material in a direction, wherein the direction includes a component direction oriented from the first portion towards the second portion of the deflectable element.