Deflectable spatial light modulator having superimposed hinge and deflectable element

• US 6,529,310 B1
• Filed: 08/03/2000
• Issued: 03/04/2003
• Est. Priority Date: 09/24/1998
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Huibers, Andrew G., Heureux, Peter J.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Spector, David N.
• Application Number:
  US09/631,536
• Time in Patent Office: 943 Days
• Field of Search: 359/223, 359/291, 359/295, 359/298
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

A spatial light modulator having a substrate holding an array of deflectable (e.g. mirror) elements. The deflectable elements are deflectably coupled to the substrate via corresponding hinges, each hinge being disposed on a side of the deflectable element opposite to the side on which the substrate is disposed. By placing the hinge in this way the fill factor of the array is improved. The hinge can be provided flush against the deflectable element, or it can be provided with a gap between the deflectable element and the hinge. The hinge can be attached via one or more posts or walls connecting to the substrate, and with a flexible or deformable portion that is substantially or entirely hidden from view when viewed through the substrate (e.g. a glass substrate). In one embodiment, the hinge is connected to the undersides of both the substrate and the deflectable element, and connects towards a center part of the deflectable element. In this way, a longer hinge is provided thus reducing strain on any one part of the hinge. Advantages of the present invention include: (1) increased fill factor as the torsion hinge is hidden behind the reflective plate; (2) increased contrast due to fewer scattering optical surfaces exposed, and due to a greater ability to control their angle and geometry; and (3) increased geometric flexibility to optimize electro-mechanical performance and robustness with respect to manufacturing.

Claims

1. A spatial light modulator, comprising in cross section, from top to bottom:

an optically transmissive substrate;

a first gap below the optically transmissive substrate;

a deflectable element below the first gap;

a second gap below the deflectable element; and

a hinge below the second gap.

2. The spatial light modulator of claim 1, wherein the hinge comprises a flexible portion, the flexible portion being hidden from view by the deflectable element when viewed via the optically transmissive substrate.

3. The spatial light modulator of claim 1, wherein both the optically transmissive substrate and the deflectable element have top and bottom surfaces, and wherein the hinge is connected to the bottom surfaces of both the optically transmissive substrate and the deflectable element.

4. The spatial light modulator of claim 3, wherein the hinge is connected to the optically transmissive substrate via posts that extend from the bottom surface of the optically transmissive substrate and past the deflectable element.

5. The spatial light modulator of claim 4, wherein the hinge comprises a flexible portion that is connected to the posts and which extends across the deflectable element and is connected to the bottom surface of the deflectable element.

6. The spatial light modulator of claim 1, further comprising a circuit substrate positioned below and spaced apart from the optically transmissive substrate.

7. The spatial light modulator of claim 1, wherein the deflectable element is held on a bottom surface of the optically transmissive substrate, and wherein the deflectable element has first and second portions such that during deflection of the deflectable element, the second portion of the deflectable element moves towards the bottom surface as the first portion moves away from the bottom surface.

8. The spatial light modulator of claim 7, wherein said circuit substrate comprises an electrode for creating attraction between the deflectable element and the circuit substrate.

9. The spatial light modulator of claim 1, 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.

10. The spatial light modulator of claim 7, 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.

11. The spatial light modulator of claim 10, 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 deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

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

13. The spatial light modulator of claim 12, wherein the deflectable element is reflective.

14. The spatial light modulator of claim 1, wherein the deflectable element is substantially rigid and the hinge is flexible.

15. The spatial light modulator of claim 1, wherein the hinge is a torsion hinge.

16. The spatial light modulator of claim 7, wherein the second portion of the deflectable element is constructed so as to abut against the optically transmissive substrate to thereby limit deflection of the deflectable element.

84. A projection display system, comprising a light source and an array of spatial light modulators according to claims 1, 17, 39, 40 or 62.

17. A spatial light modulator, comprising:

an optically transmissive substrate having thereon a deflectable element, the deflectable element comprising a hinge which is disposed on a side of the deflectable element opposite to that of the optically transmissive substrate.

18. The spatial light modulator of claim 17, wherein the hinge comprises a flexible portion, the flexible portion being hidden from view by the deflectable element when viewed via the optically transmissive substrate.

19. The spatial light modulator of claim 17, wherein the hinge is provided flush against the deflectable element, and a gap is provided between the deflectable element and the optically transmissive substrate.

20. The spatial light modulator of claim 17, wherein both the optically transmissive substrate and the deflectable element have top and bottom surfaces, and wherein the hinge is connected to the bottom surfaces of both the optically transmissive substrate and the deflectable element.

21. The spatial light modulator of claim 20, wherein the hinge is connected to the optically transmissive substrate via posts that extend from the bottom surface of the optically transmissive substrate and past the deflectable element.

22. The spatial light modulator of claim 21, wherein the hinge comprises a flexible portion that is connected to the posts and which extends across the deflectable element and is connected to the bottom surface of the deflectable element.

23. The spatial light modulator of claim 22, wherein a gap is disposed between the flexible portion of the hinge and the deflectable element.

24. The spatial light modulator of claim 17, further comprising a circuit substrate positioned below and spaced apart from the optically transmissive substrate.

25. The spatial light modulator of claim 17, wherein the deflectable element is held on a bottom surface of the optically transmissive substrate, and wherein the deflectable element has first and second portions such that during deflection of the deflectable element, the second portion of the deflectable element moves towards the bottom surface as the first portion moves away from the bottom surface.

26. The spatial light modulator of claim 24, wherein said circuit substrate comprises an electrode for creating attraction between the deflectable element and the circuit substrate.

27. The spatial light modulator of claim 26, wherein the deflectable element comprises a reflective layer and an electrode layer which is electrically conductive, the electrode layer being spaced apart from the reflective layer.

28. The spatial light modulator of claim 26, wherein the electrode layer of the deflectable element is connected to the reflective layer via one or more posts or walls therebetween.

29. The spatial light modulator of claim 17, 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.

30. The spatial light modulator of claim 24, wherein the deflectable element is substantially rectangular or square, and wherein the hinge extends across the deflectable element along a diagonal.

31. The spatial light modulator of claim 30, 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 deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

32. The spatial light modulator of claim 17, wherein the deflectable element is held on the optically transmissive substrate via one or more posts, and wherein the one or more posts holds an adjacent deflectable element in the spatial light modulator.

33. The spatial light modulator of claim 31, wherein the deflectable element and/or the electrode comprise a plurality of electrodes capable of receiving different voltage biases.

34. The spatial light modulator of claim 17, wherein the deflectable element comprises a—

plurality of laminated dielectric support layers.

35. The spatial light modulator of claim 17, wherein the deflectable element comprises aluminum.

36. The spatial light modulator of claim 17, wherein the deflectable element is substantially rigid and the hinge is flexible.

37. The spatial light modulator of claim 17, wherein the hinge is a torsion hinge.

38. The spatial light modulator of claim 25, wherein the second portion of the deflectable element is constructed so as to abut against the optically transmissive substrate to thereby limit deflection of the deflectable element.

39. A spatial light modulator comprising:

an optically transmissive substrate which holds on a bottom surface thereof at least one deflectable element via a corresponding at least one torsion hinge, the deflectable element having top and bottom planar surfaces and one or more edges therebetween, the at least one torsion hinge connected to the deflectable element towards a center part of the bottom surface of the deflectable element.

40. A spatial light modulator, comprising:

an optically transmissive substrate having a top surface and a bottom surface;

a deflectable element having a top surface, a bottom surface and one or more edge surfaces; and

a hinge;

wherein the hinge is connected to the optically transmissive substrate only on the bottom surface of the optically transmissive substrate, and wherein the hinge is connected to the deflectable element only on the bottom surface of the deflectable element.

41. The spatial light modulator of claim 40, wherein the hinge comprises a flexible portion, the flexible portion being hidden from view by the deflectable element when viewed via the optically transmissive substrate.

42. The spatial light modulator of claim 41, wherein a first gap is provided between the hinge and the deflectable element, and a second gap is provided between the deflectable element and the optically transmissive substrate.

43. The spatial light modulator of claim 40, wherein both the optically transmissive substrate and the deflectable element have top and bottom surfaces, and wherein the hinge is connected to the bottom surfaces of both the optically transmissive substrate and the deflectable element.

44. The spatial light modulator of claim 43, wherein the hinge is connected to the optically transmissive substrate via posts that extend from the bottom surface of the optically transmissive substrate and past the deflectable element.

45. The spatial light modulator of claim 44, wherein the hinge comprises a flexible portion that is connected to the posts and that extends across the deflectable element and is connected to the bottom surface of the deflectable element.

46. The spatial light modulator of claim 45, wherein a gap is disposed between the flexible portion of the hinge and the deflectable element.

47. The spatial light modulator of claim 40, further comprising a circuit substrate positioned below and spaced apart from the optically transmissive substrate.

48. The spatial light modulator of claim 40, wherein the deflectable element is held on a bottom surface of the optically transmissive substrate, and wherein the deflectable element has first and second portions such that during deflection of the deflectable element, the second portion of the deflectable element moves towards the bottom surface as the first portion moves away from the bottom surface.

49. The spatial light modulator of claim 47, wherein said circuit substrate comprises an electrode for creating attraction between the deflectable element and the circuit substrate.

50. The spatial light modulator of claim 49, wherein said electrode is positioned directly below the deflectable element.

51. The spatial light modulator of claim 49, wherein the electrode is positioned below the deflectable element, and a hinge connects the deflectable element to the transparent substrate.

52. The spatial light modulator of claim 40, 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.

53. The spatial light modulator of claim 47, 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.

54. The spatial light modulator of claim 53, 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 deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

55. The spatial light modulator of claim 40, wherein the deflectable element includes a conductive layer.

56. The spatial light modulator of claim 55, wherein the deflectable element is reflective.

57. The spatial light modulator of claim 40, wherein the deflectable element comprises a structural support layer.

58. The spatial light modulator of claim 40, wherein the deflectable element comprises aluminum.

59. The spatial light modulator of claim 40, wherein the deflectable element is substantially rigid and the hinge is flexible.

60. The spatial light modulator of claim 59, wherein the hinge is a torsion hinge.

61. The spatial light modulator of claim 48, wherein the second portion of the deflectable element is constructed so as to abut against the optically transmissive substrate to thereby limit deflection of the deflectable element.

62. A spatial light modulator, comprising:

an optically transmissive substrate extending in a plane substantially horizontally;

a deflectable element extending in a plane substantially horizontally and spaced apart from and substantially parallel to the optically transparent substrate; and

a connector that allows for deflectable connection of the deflectable element to the optically transparent substrate;

wherein the connector comprises a first end attached to the optically transparent substrate, a vertical portion extending from the first end and past the plane of the deflectable element, a hinge portion extending in a plane substantially parallel to and spaced apart from the deflectable element, and a second end connecting the hinge portion to the deflectable element.

63. The spatial light modulator of claim 62, wherein the hinge comprises a flexible portion, the flexible portion being hidden from view by the deflectable element when viewed via the optically transmissive substrate.

64. The spatial light modulator of claim 62, wherein a first gap is provided between the hinge and the deflectable element, and a second gap is provided between the deflectable element and the optically transmissive substrate.

65. The spatial light modulator of claim 62, wherein both the optically transmissive substrate and the deflectable element have top and bottom surfaces, and wherein the hinge is connected to the bottom surfaces of both the optically transmissive substrate and the deflectable element.

66. The spatial light modulator of claim 65, wherein the hinge is connected to the optically transmissive substrate via posts that extend from the bottom surface of the optically transmissive substrate and past the deflectable element.

67. The spatial light modulator of claim 66, wherein the hinge comprises a flexible portion that is connected to the posts and that extends across the deflectable element and is connected to the bottom surface of the deflectable element.

68. The spatial light modulator of claim 67, wherein a gap is disposed between the flexible portion of the hinge and the deflectable element.

69. The spatial light modulator of claim 62, further comprising a circuit substrate positioned below and spaced apart from the optically transmissive substrate.

70. The spatial light modulator of claim 62, wherein the deflectable element is held on a bottom surface of the optically transmissive substrate, and wherein the deflectable element has first and second portions such that during deflection of the deflectable element, the second portion of the deflectable element moves towards the bottom surface as the first portion moves away from the bottom surface.

71. The spatial light modulator of claim 69, wherein said circuit substrate comprises an electrode for creating attraction between the deflectable element and the circuit substrate.

72. The spatial light modulator of claim 71, wherein said circuit substrate is an opaque silicon substrate.

73. The spatial light modulator of claim 72, wherein the silicon substrate is a VLSI/CMOS substrate.

74. The spatial light modulator of claim 62, 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.

75. The spatial light modulator of claim 69, further comprising addressing circuitry formed in the circuit substrate that resembles a low-density DRAM.

76. The spatial light modulator of claim 75, 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 deflected position and remains in the deflected position until a second electrical potential difference is applied between the deflectable element and the electrode.

77. The spatial light modulator of claim 62, wherein the deflectable element comprises LPCVD-deposited silicon nitride, silicon oxide, amorphous silicon or polysilicon.

78. The spatial light modulator of claim 77, wherein the deflectable element further comprises a conductive and reflective metal layer.

79. The spatial light modulator of claim 78, wherein the deflectable element comprises a laminate support structure comprising a plurality of structural support layers disposed between the conductive and reflective metal layer and the optically transmissive substrate.

80. The spatial light modulator of claim 78, wherein the deflectable element comprises aluminum.

81. The spatial light modulator of claim 62, wherein the deflectable element is substantially rigid and the hinge is flexible.

82. The spatial light modulator of claim 62, wherein the hinge is a torsion hinge.

83. The spatial light modulator of claim 70, wherein the second portion of the deflectable element is constructed so as to abut against the optically transmissive substrate to thereby limit deflection of the deflectable element.

85. A method comprising the acts of:

providing a substrate;

forming a first sacrificial layer above the transparent substrate;

forming a deflectable element layer above the first sacrificial layer;

forming a second sacrificial layer above the deflectable element layer;

forming a hinge above the second sacrificial layer; and

removing the first and second sacrificial layers.

86. The method for making a spatial light modulator according to claim 85, wherein the hinge is formed to connect to both the substrate and the deflectable element layer, such that upon removal of the first and second sacrificial layers, the deflectable element is deflectably coupled to the substrate.

87. The method according to claim 86, wherein the substrate is a light transmissive substrate for allowing a light beam to pass therethrough, and the deflectable element is positioned for deflecting the light beam.

88. The method according to claim 85, further comprising the act of removing a portion of the second sacrificial layer prior to forming the hinge, such that upon forming the hinge, the hinge connects, via the removed portion, to the deflectable element.

89. The method according to claim 85, wherein the deflectable element layer comprises a reflective material.

90. The method according to claim 85, wherein the deflectable element layer comprises a light reflective and conductive layer.

91. The method according to claim 87, wherein the light transmissive substrate is glass.

92. The method according to claim 85, wherein the first and second sacrificial layers comprise silicon.

93. The method according to claim 85, wherein the hinge comprises silicon nitride.

94. The method according to claim 85, further comprising the act of patterning the deflectable element layer prior to forming the second sacrificial layer.

95. The method according to claim 94, further comprising the act of patterning the hinge prior to removal of the sacrificial layers.

96. The method according to claim 85, wherein the sacrificial layers are removed with a noble gas fluoride and/or a halogen fluoride.

97. The method according to claim 85, wherein part of the sacrificial layers is removed with plasma, and a part of the sacrificial layers is removed with a non-plasma vapor etch.

98. The method according to claim 85, further comprising the act of forming a circuit substrate and bonding the circuit substrate to the substrate having the deflectable element deflectably coupled thereto.

99. The method according to claim 98, wherein a spatial light modulator is formed.