Micromirrors and off-diagonal hinge structures for micromirror arrays in projection displays

• US 6,867,897 B2
• Filed: 02/12/2003
• Issued: 03/15/2005
• Est. Priority Date: 01/29/2003
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Patel, Satyadev R., Huibers, Andrew G.
• Primary Examiner(s): Ben, Loha
• Application Number:
  US10/366,297
• Publication Number:
  US 20040125347A1
• Time in Patent Office: 762 Days
• Field of Search: 359/290, 359/291, 359/292, 359/295, 359/298, 359/223, 359/224, 359/855, 359/872, 355/32, 355/35, 353/31, 353/98, 250/216, 216/2, 438/52
• US Class Current: 359/291
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G03B 21/28 Reflectors in projection beam in illumination beam G03B21/2066

Abstract

A spatial light modulator is disclosed, along with methods for making such a modulator, that comprises an array of micromirrors each having a hinge and a micromirror plate held via the hinge on a substrate, the micromirror plate being disposed in a plane separate from the hinge and having a diagonal extending across the micromirror plate, the micromirror plate being attached to the hinge such that the micromirror plate can rotate along a rotation axis that is parallel to, but off-set from the diagonal of the micromirror plate. Also disclosed is a projection system that comprises such a spatial light modulator, as well as a light source, condensing optics, wherein light from the light source is focused onto the array of micromirrors, projection optics for projecting light selectively reflected from the array of micromirrors onto a target, and a controller for selectively actuating the micromirrors in the array.

Claims

1. A spatial light modulator comprising an array of micromirrors, each micromirror comprising:

a hinge; and

a micromirror plate hold via the hinge on a substrate, the micromirror plate being disposed in a plane separate from the hinge and having a diagonal extending across the micromirror plate, the micromirror plate being attached to the huge such that the micromirror plate can rotate along a rotation axis that is parallel to, but oft-set from the diagonal of the micromirror plate.

2. The spatial light modulator of claim 1, wherein the hinge is disposed on an opposite side of the micromirror plate from the substrate.

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

4. The spatial light modulator of claim 3, wherein a second substrate having electrodes and circuitry thereon is positioned proximate to the substrate transmissive to visible light for electrostatically deflecting the micromirrors.

5. The spatial light modulator of claim 2, wherein the micromirror plate is substantially square.

6. The spatial light modulator of claim 2, wherein the micromirror plate has a substantially rhombus shape.

7. The spatial light modulator of claim 2, wherein the micromirror plate has a substantially trapezoidal shape.

8. The spatial light modulator of claim 2, wherein the micromirror plate has a substantially rectangular shape.

9. The spatial light modulator of claim 2, wherein the substrate is a glass or quartz substrate.

10. The spatial light modulator of claim 9, wherein a surface of the substrate is covered with an anti-reflection film.

11. The spatial light modulator of claim 1, wherein the hinge is a torsion hinge and the micromirror plate rotates along an axis of rotation corresponding to the location of the torsion hinge.

12. The spatial light modulator of claim 1, wherein axis of rotation is located 0.5 micrometer or more away from the micromirror plate diagonal.

13. The spatial light modulator of claim 12, wherein axis of rotation is located 1.0 micrometer or more away from the micromirror plate diagonal.

14. The spatial light modulator of claim 13, wherein the axis of rotation is located 2.0 micrometers or more away from the micromirror plate diagonal.

15. The spatial light modulator of claim 1, wherein an edge of the micromirror plate is covered by a light absorbing material.

16. The spatial light modulator of claim 1, that is part of a projection system for forming an image on a target.

17. The spatial light modulator of claim 16, wherein the substrate comprises one or more electrodes and circuitry for electrically controlling the motion of the micromirror plate.

18. The spatial light modulator of claim 1, wherein the micromirror plate is held on the substrate by one or more posts that connect the hinge to the substrate.

19. The spatial light modulator of claim 18, wherein the point of attachment of the hinge to the micromirror plate is not along either diagonal of the micromirror plate.

20. The spatial light modulator of claim 19, wherein the point of attachment of the hinge to the micromirror plate is at least 0.5 micrometer away from the diagonal of the micromirror plate.

21. The spatial light modulator of claim 20, wherein the point of attachment is least 1.0 micrometer away from the diagonal.

22. The spatial light modulator of claim 18, wherein the micromirror plate is held on the substrate by two posts.

23. The spatial light modulator of claim 22, wherein the point of attachment of the hinge to the micromirror plate is not between the two posts.

24. The spatial light modulator of claim 22, wherein the two posts are positioned at two ends of the diagonal of the micromirror plate.

25. The spatial light modulator of claim 1, wherein the hinge is disposed between the micromirror plate and the substrate.

26. The spatial light modulator of claim 1, wherein the substrate is a semiconductor substrate.

27. The spatial light modulator of claim 1, wherein the ON state of a micromirror is defined as a point at which the rotation of the micromirror is stopped such that light from the micromirror is capable of being viewed on a target as a pixel in a projected image.

28. The spatial light modulator of claim 27, wherein the micromirror abuts against the substrate or structure patterned on the substrate so that further rotation of the micromirror plate is prevented in the ON state.

29. The spatial light modulator of claim 27, wherein each micromirror comprises a support post for connecting the hinge to the substrate and a stopping mechanism projecting held by the support post for resisting rotation of the micromirror plate.

30. The spatial light modulator of claim 29, wherein when the micromirror plate abuts against the stopping mechanism when it reaches the ON state.

31. The spatial light modulator of claim 27, Wherein the OFF state of the micromirrors is at an angle of at least −

2 degrees relative to the substrate.

32. The spatial light modulator of claim 31, wherein the OFF state of the micromirrors is at an angle of at least −

3 degrees relative to the substrate.

33. The spatial tight modulator of claim 32, wherein a set of electrodes are provided for rotating the micromirror to the ON state, and a second set of electrodes are provided for rotating the micromirror to the OFF state.

34. The spatial light modulator of claim 31, wherein the hinge is part of a hinge support structure that rotatably holds the micromirror plate on the substrate, wherein the hinge support structure is a multilayer structure that has a curved state, due to stress differences between the layers, when the micromirror plate is not electrostatically deflected.

35. The spatial light modulator of claim 1, wherein the hinge is disposed in a plane separate from the plane of the micromirror plate by a gap of at least 0.1 micrometer.

36. The spatial light modulator of claim 1, wherein the micromirror plate has a diagonal length of 25 microns or less.

37. The spatial light modulator of claim 1, wherein the point of attachment of the hinge to the micromirror plate is located at a point away from the diagonal of the micromirror plate at a distance from {fraction (1/40)} to ⅓

the length of the diagonal.

38. The spatial light modulator of claim 37, wherein the point of attachment of the hinge to the micromirror plate is located at a point away from the diagonal of the micromirror plate at a distance from {fraction (1/20)} to ¼

the length of the diagonal.

39. The spatial light modulator of claim 1, wherein each micromirror comprises a support post for connecting the hinge to the substrate and a stopping mechanism projecting held by the support post for resisting rotation of the micromirror plate, wherein the micromirror impacts the stopping mechanism in the ON state, wherein the micromirror plate is a substantially four sided plate having a diagonal and wherein the hinge attaches to the micromirror plate at a point at least 0.5 um away from the diagonal, and wherein the hinge is disposed in a plane separate from the micromirror plate by a gap of at least 0.1 um.

40. The spatial light modulator of claim 1, wherein the hinge comprises a nitride of titanium and/or silicon.

41. A projection system comprising:

a light source;

the spatial light modulator of claim 1;

condensing optics, wherein light from the light source is focused onto the array of micro-mirrors;

projection optics for projecting light selectively reflected from the array of micro-mirrors; and

a controller for selectively actuating micro-mirrors in the array of micro-mirrors.

42. A spatial light modulator comprising an array of micromirrors on a substrate, each micromirror comprising:

two posts;

a hinge; and

a micromirror plate held on the substrate via the hinge and the two posts, the micromirror plate being disposed in a plane separate from the hinge and having a diagonal extending across the micromirror plate, the micromirror plate being attached to the hinge at a point not along a straight line between the two posts.

43. The spatial light modulator of claim 42, wherein the hinge is disposed on an opposite side of the micromirror plate from the substrate.

44. The spatial light modulator of claim 43, wherein the substrate is a substrate transmissive to visible light.

45. The spatial light modulator of claim 44, wherein a second substrate having electrodes and circuitry thereon is positioned proximate to the substrate transmissive to visible light for electrostatically deflecting the micromirrors.

46. The spatial light modulator of claim 43, wherein the substrate is a glass or quartz substrate.

47. The spatial light modulator of claim 46, wherein a surface of the substrate is covered with an anti-reflection film.

48. The spatial light modulator of claim 43, wherein the micromirror plate is substantially square.

49. The spatial light modulator of claim 43, wherein the micromirror plate has a substantially rhombus shape.

50. The spatial light modulator of claim 43, wherein the micromirror plate has a substantially trapezoidal shape.

51. The spatial light modulator of claim 43, wherein the micromirror plate has a substantially rectangular shape.

52. The spatial light modulator of claim 42, wherein the hinge is a torsion hinge and the micromirror plate rotates along an axis of rotation corresponding to the location of the torsion hinge.

53. The spatial light modulator of claim 42, wherein axis of rotation is located 0.5 micrometer or more away from the micromirror plate diagonal.

54. The spatial light modulator of claim 53, wherein the axis of rotation is located 1.0 micrometer or more away from the micromirror plate diagonal.

55. The spatial light modulator of claim 54, wherein the axis of rotation is located 2.0 micrometers or more away from the micromirror plate diagonal.

56. The spatial light modulator of claim 42, wherein an edge of the micromirror plate is covered by a light absorbing material.

57. The spatial light modulator of claim 42, that is part of a projection system for forming an image on a target.

58. The spatial light modulator of claim 57, wherein the substrate comprises one or more electrodes and circuitry for electrically controlling the motion of the micromirror plate.

59. The spatial light modulator of claim 42, wherein the micromirror plate is held on the substrate by one or more posts that connect the hinge to the substrate.

60. The spatial light modulator of claim 59, wherein the point of attachment of the hinge to the micromirror plate is not along the diagonal of the micromirror plate.

61. The spatial light modulator of claim 60, wherein the point of attachment of the hinge to the micromirror plate is at least 0.5 micrometer away from the diagonal of the micromirror plate.

62. The spatial light modulator of claim 61, wherein the point of attachment is at least 1.0 micrometer away from the diagonal.

63. The spatial light modulator of claim 59, wherein the wherein the micromirror plate is held on the substrate by two posts.

64. The spatial light modulator of claim 63, wherein the point of attachment of the hinge to the micromirror plate is not between the two posts.

65. The spatial light modulator of claim 63, wherein the two posts are positioned at two ends of the diagonal of the micromirror plate.

66. The spatial light modulator of claim 42, wherein the hinge is disposed between the micromirror plate and the substrate.

67. The spatial light modulator of claim 42, wherein the substrate is a semiconductor substrate.

68. The spatial light modulator of claim 42, wherein the ON state of a micromirror is defined as a point at which the rotation of the micromirror is stopped such that light from the micromirror is capable of being viewed on a target as a pixel in a projected image.

69. The spatial light modulator of claim 68, wherein the micromirror abuts against the substrate or structure patterned on the substrate so that further rotation of the micromirror plate is prevented in the ON state.

70. The spatial light modulator of claim 68, wherein each micromirror comprises a support post for connecting the hinge to the substrate and a stopping mechanism projecting held by the support post for resisting rotation of the micromirror plate.

71. The spatial light modulator of claim 70, wherein when the micromirror plate abuts against the stopping mechanism when it reaches the ON state.

72. The spatial light modulator of claim 68, wherein the OFF state of the micromirrors is at an angle of at least −

2 degrees relative to the substrate.

73. The spatial light modulator of claim 72, wherein the OFF state of the micromirrors is at an angle of at least −

3 degrees relative to the substrate.

74. The spatial light modulator of claim 73, wherein a set of electrodes are provided for rotating the micromirror to the ON state, and a second set of electrodes are provided for rotating the micromirror to the OFF state.

75. The spatial light modulator of claim 72, wherein the hinge is part of a hinge support structure that rotatably holds the micromirror plate on the substrate, wherein the hinge support structure is a multilayer structure that has a curved state, due to stress differences between the layers, when the micromirror plate is not electrostatically deflected.

76. The spatial light modulator of claim 42, wherein the hinge is disposed in a plan, separate from the micromirror plate by a gap of at least 0.1 micrometer.

77. The spatial light modulator of claim 42, wherein the micromirror plate has a diagonal length or 25 microns or less.

78. The spatial light modulator of claim 42, wherein the point of attachment of the hinge to the micromirror plate is located at a point away from the diagonal of the micromirror plate at a distance from {fraction (1/40)} to ⅓

the length of the diagonal.

79. The spatial light modulator of claim 68, wherein the point of attachment of the hinge to the micromirror plate is located at a point away from the diagonal of the micromirror plate at a distance from {fraction (1/20)} to ¼

the length of the diagonal.

80. The spatial light modulator of claim 42, wherein each micromirror comprises a support post for connecting the hinge to the substrate and a stopping mechanism projecting held by the support post for resisting rotation of the micromirror plate, wherein the micromirror impacts the stopping mechanism in the ON state, wherein the micromirror plate is a substantially four sided plate having a diagonal, and wherein the hinge attaches to the micromirror plate at a point at least 0.5 um away from the diagonal, and wherein the hinge is disposed in a plane separate from the mirror plate by a gap of at least 0.1 um.

81. The spatial light modulator of claim 42, wherein the hinge comprises a nitride of titanium and/or silicon.

82. A projection system comprising:

a light source;

the spatial light modulator of claim 42;

condensing optics, wherein light from the light source is focused onto the array of micro-mirrors;

projection optics for projecting light selectively reflected from the array of micro-mirrors; and

a controller for selectively actuating micro-mirrors in the array of micro-mirrors.

83. A method comprising:

providing a substrate;

depositing a first sacrificial layer on the substrate;

on the first sacrificial layer, forming a micromirror plate having a diagonal;

depositing a second sacrificial layer on the micromirror plate;

patterning the first and second sacrificial layers to form two vias down to the substrate and a via down to the micromirror plate, the three vias forming a triangle;

forming a hinge-structure comprising posts in the three vias and a hinge structure therebetween for connecting the micromirror plate to the substrate; and

removing the first and second sacrificial layers.

84. The method of claim 83, wherein the sacrificial layers comprise amorphous silicon.

85. The method of claim 84 wherein the sacrificial layers are removed with a spontaneous gas phase chemical etchant.

86. The method of claim 85, wherein the etchant is a noble gas fluoride or an interhalogen.

87. The method of claim 83, wherein the sacrificial layers comprise a polymer.

88. A method comprising:

providing a substrate;

depositing a first sacrificial layer on the substrate;

on the first sacrificial layer, forming a micromirror plate having a diagonal;

depositing a second sacrificial layer on the micromirror plate;

forming a hinge-structure on the substrate that attaches to the micromirror plate at a point not along the diagonal, the hinge structure for holding the micromirror plate above the substrate such that the micromirror plate can rotate by means of a rotation axis that is parallel to, but off-set from the diagonal of the micromirror plate; and

removing the first and second sacrificial layers.

89. The method of claim 88, wherein the sacrificial layers comprise amorphous silicon.

90. The method of claim 89, wherein the sacrificial layers are removed with a spontaneous gas phase chemical etchant.

91. The method of claim 90, wherein the etchant is a noble gas fluoride or an interhalogen.

92. The method of claim 88, wherein the sacrificial layers comprise a polymer.

93. A reflective micromirror device, comprising:

a substrate;

a micromirror plate held on the substrate for reflecting incident light; and

a hinge-structure connecting the micromirror plate to the substrate, wherein the hinge structure is a multilayer structure having layers of different intrinsic stress such that the hinge structure is curved due to the difference in intrinsic stress.

94. The reflective micromirror device of claim 93, wherein one layer of the multilayer structure is compressive and another layer of the multilayer structure is tensile.

95. A method for forming a micromirror for a spatial light modulator, comprising:

providing a substrate;

depositing a first sacrificial layer on the substrate;

forming a micromirror plate on the first sacrificial layer for reflecting an incident light;

depositing a second sacrificial layer on the micromirror plate;

forming a hinge-structure on the second sacrificial layer for connecting the micromirror plate to the substrate, wherein the forming of the hinge structure comprises depositing a first hinge-structure layer having an intrinsic positive tensile-strain, and depositing a second hinge-structure layer on the first layer, wherein the second layer has an intrinsic negative compression strain; and

removing the first and second sacrificial layers such that the first and second hinge-structure layers are curved at their natural resting stales due to the difference in intrinsic strain, such that the micromirror plate is held by the hinge-structure in a position not parallel to the substrate.

96. The method of claim 95, wherein the first hinge structure layer is deposited by chemical vapor deposition.

97. The method of claim 96, wherein the second hinge structure layer is deposited by physical vapor deposition.

98. The method of claim 96, wherein the second hinge structure layer is a reactively sputtered ceramic layer and the first hinge structure layer is a ceramic layer deposited by chemical vapor deposition.