Electrostatically actuated micro-electro-mechanical devices and method of manufacture

• US 20020146200A1
• Filed: 03/15/2002
• Published: 10/10/2002
• Est. Priority Date: 03/16/2001
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Hsiao, James Ching-Ming, Shedd, Gordon M., Kirkos, Gregory A., Wang, ChuanChe, Mastrangelo, Carlos Horacio, Waelti, Marc, Kudrle, Thomas David, Bancu, Mirela Gabriela
• Granted Patent: US 6,912,078 B2
• Time in Patent Office: Days
• US Class Current: 385/18
• CPC Class Codes: B81B 3/0062 Devices moving in two or more dimensions, i.e. having special features which allow movement in more than one dimension
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/357 Electrostatic force electrostatic forces controlling reflecting elements in general G02B26/0841
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C
• CPC Class Codes: H01L 2924/19107 off-chip wires
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

One embodiment is directed to a gimbal mechanism for a MEMS mirror device having folded flexure hinges. Another embodiment is directed to a gimbal mechanism having a frame with through-holes or recesses distributed thereabout to reduce weight of said frame. Other embodiments are directed to improved electrode structures for electrostatically actuated MEMS devices. Other embodiments are directed to methods for fabricating electrodes for electrostatically actuated MEMS devices. Other embodiments are directed to methods of fabricating through-wafer interconnect devices. Other embodiments are directed to MEMS mirror array packaging. Other embodiments are directed to electrostatically actuated MEMS devices having driver circuits integrated therewith. Other embodiments are directed to methods of patterning wafers with a plurality of through-holes. Other embodiments are directed to methods of forming moveable structures in MEMS devices. Other embodiments are directed to methods of depositing a thin film on the back of a MEMS device.

Claims

1. A MEMS mirror device, comprising:

a mirror;

a gimbal structure for movably supporting the mirror, the gimbal structure including two pairs of flexure hinges, each pair defining an axis about which said mirror can be rotated, at least some of said flexure hinges having a folded configuration in a cross-section taken generally perpendicular to a respective axis to increase torsional compliance about said respective axis and to decrease compliance in other directions; and

a mechanism for actuating the mirror.

2. The MEMS mirror device of claim 1 wherein each flexure hinge has a generally U-shaped cross-sectional configuration.

3. The MEMS mirror device of claim 1 wherein each flexure hinge has a generally V-shaped cross-sectional configuration.

4. The MEMS mirror device of claim 1 wherein each flexure hinge has multiple folds.

5. The MEMS mirror device of claim 1 wherein said pairs of flexure hinges comprise an inner pair connecting the mirror to an inner gimbal frame, and an outer pair connecting the inner gimbal frame to an outer gimbal frame, and wherein said outer pair have lower torsional compliance compared to the inner pair.

6. The MEMS mirror device of claim 1 wherein each flexure hinge comprises a plurality of springs, and wherein said springs are arranged in a folded configuration in a top view thereof.

7. A MEMS mirror device, comprising:

a mirror;

a gimbal structure for movably supporting the mirror, the gimbal structure including two pairs of flexure hinges, each pair defining an axis about which said mirror can be rotated, said flexure hinges each comprising multiple springs in a folded configuration, each spring also having a folded configuration in a cross-section taken generally perpendicular to a respective axis to increase torsional compliance about said respective axis and to decrease torsional compliance in other directions; and

a mechanism for actuating the mirror.

8. The MEMS mirror device of claim 7 wherein each spring has a generally U-shaped cross-sectional configuration.

9. The MEMS mirror device of claim 7 wherein each spring has a generally V-shaped cross-sectional configuration.

10. The MEMS mirror device of claim 7 wherein each spring has multiple folds.

11. The MEMS mirror device of claim 7 wherein said pairs of flexure hinges comprise an inner pair connecting the mirror to an inner gimbal frame, and an outer pair connecting the inner gimbal frame to an outer gimbal frame, and wherein said outer pair have lower torsional compliance compared to the inner pair.

13. The MEMS mirror device of claim 12, wherein said holes are through-holes to affect air damping of the device.

14. The MEMS mirror device of claim 12, wherein said holes are recesses extending only partly through said movable portion of said support structure.

15. The MEMS mirror device of claim 12, wherein said holes are thinned out areas etched in the structure.

16. The MEMS mirror device of claim 12 wherein said support structure is a gimbal mechanism.

17. The MEMS mirror device of claim 16, wherein said gimbal mechanism comprises an inner and outer frames, and wherein said movable portion comprises said inner frame.

18. The MEMS mirror device of claim 12, wherein said holes are arranged in a honeycomb lattice-like configuration.

19. The MEMS mirror device of claim 12, wherein said mechanism comprises at least one electrode for electrostatically actuating said mirror.

12. A MEMS mirror device, comprising:

a mirror;

a support structure for movably supporting the mirror, the support structure including a movable portion with a plurality of holes distributed about said movable portion to reduce weight thereof and provide a lower moment of inertia; and

a mechanism for actuating the mirror.

20. A MEMS mirror device, comprising:

a mirror;

a support structure for movably supporting the mirror, said mirror being movable along a given path; and

at least one electrode for electrostatically actuating the mirror, said at least one electrode having at least a portion thereof positioned about the periphery of said mirror and outside of said path.

21. The MEMS mirror device of claim 20 wherein said at least one electrode includes an inner portion positioned beneath said mirror.

22. The MEMS mirror device of claim 21 wherein said inner portion includes a raised portion.

23. The MEMS mirror device of claim 21 wherein said inner portion is sloped.

24. The MEMS mirror device of claim 21 wherein said inner portion is stepped.

25. The MEMS mirror device of claim 20 wherein said at least one electrode comprises a side electrode and has one end proximate the edge of the mirror when said mirror is in an unactuated position.

26. The MEMS mirror device of claim 20 wherein said support structure includes a movable portion, and wherein said at least one electrode and said movable portion are arranged in close alignment.

27. The MEMS mirror device of claim 26 wherein said at least one electrode and said movable portion have a corresponding comb-fingers arrangement.

28. The MEMS mirror device of claim 20 wherein said support structure comprises a gimbal mechanism for rotating said mirror about two axes, and wherein said at least one electrode comprises two pairs of electrodes, each pair for actuating said mirror about one of said axes.

29. The MEMS mirror device of claim 20 further comprising a bump stop to restrict movement of said mirror beyond a given position.

30. A MEMS mirror device, comprising:

a mirror;

a gimbal structure for rotatably supporting the mirror, said mirror being movable along a given path; and

two pairs of electrodes for electrostatically actuating the mirror about said axes, each electrode having at least a portion thereof positioned about the periphery of said mirror and outside of said path.

31. The MEMS mirror device of claim 30 wherein each electrode includes an inner portion positioned beneath said mirror.

32. The MEMS mirror device of claim 31 wherein said inner portion includes a raised portion.

33. The MEMS mirror device of claim 31 wherein said inner portion is sloped.

34. The MEMS mirror device of claim 31 wherein said inner portion is stepped.

35. The MEMS mirror device of claim 30 wherein each electrode has one end proximate an edge of the mirror when said mirror is in an unactuated position.

36. The MEMS mirror device of claim 30 wherein said gimbal structure includes a movable inner frame, and wherein one pair of said electrodes and said movable inner frame are arranged in close alignment.

37. The MEMS mirror device of claim 36 wherein said one pair of electrodes and said movable inner frame have a corresponding comb-fingers arrangement.

38. The MEMS mirror device of claim 30 further comprising a bump stop to restrict movement of said mirror beyond a given position.

39. The MEMS mirror device of claim 38 wherein said bump stop is located between said electrodes.

79. The MEMS mirror device of claim 30 wherein said gimbal structure includes a frame surrounding said mirror, and wherein said frame is curved or angled to provide a range of lever arms during frame movement in order to obtain desired force versus displacement characteristics.

107. The MEMS mirror device of claim 36 wherein said one pair of electrodes and said mirror have a corresponding comb-fingers arrangement.

40. A method of fabricating electrodes for an electrostatically actuated MEMS device, comprising:

providing a wafer;

forming recesses on a first side of said wafer for defining one end of each electrode;

affixing said first side of said wafer to a support substrate;

forming grooves on a second side of said wafer opposite said first side to define an opposite end of said electrodes; and

extending said grooves on said second side to reach said recesses on said first side to define said electrodes.

41. The method of claim 40 wherein said wafer comprises a silicon wafer.

42. The method of claim 40 wherein said support substrate comprises a device that provides for electrical interconnection from one side of a wafer to the other.

43. The method of claim 42 wherein said interconnect device comprises a through-wafer interconnect device having a plurality of through-holes, and wherein said electrodes are each positioned over a through-hole.

44. The method of claim 40 wherein forming grooves and recesses comprises etching said grooves and recesses.

45. The method of claim 40 wherein forming grooves on a second side of said wafer comprises selectively etching said second side using an oxide layer as a mask, and wherein said oxide layer forms a bump stop.

47. The method of claim 46 wherein the glass wafer comprises a Pyrex wafer.

48. The method of claim 46 wherein forming the holes comprises powder blasting the holes on opposite sides of said wafer.

49. The method of claim 48 wherein said holes have an hour-glass like configuration to more securely hold conductive plugs.

46. A method of fabricating a through-wafer interconnect device for use with a MEMS device, comprising:

providing a glass wafer;

forming holes through the wafer using powder blasting; and

filling or lining the holes with an electrically conductive material.

50. A method of fabricating a through-wafer interconnect device for use with a MEMS device, comprising:

forming holes through a wafer;

electroplating conductive material through said holes; and

lapping both sides of the wafer to prepare wafer surfaces for subsequent photolithography processes.

51. The method of claim 50 further comprising attaching the wafer to a carrier wafer prior to the step of electroplating, and removing the carrier wafer from the wafer prior to lapping a side of said wafer to which said carrier wafer is attached.

52. The method of claim 50 wherein said wafer comprises a glass wafer.

53. The method of claim 50 wherein said wafer comprises a Pyrex wafer.

54. A method of fabricating a through-wafer interconnect device for a MEMS device, comprising:

selectively implanting a side of a silicon wafer with P-type dopant comprising Boron;

bonding the side of the silicon wafer to a wafer having a plurality of holes therethrough, said holes being aligned with doped portions of said silicon wafer; and

dissolving the silicon wafer, leaving silicon membranes extending over said holes.

55. An electrostatically actuated MEMS mirror array apparatus, comprising:

an array of electrostatically actuated MEMS mirror devices; and

an angled transparent window bonded to said array for passage therethrough of optical signals.

56. The apparatus of claim 55 wherein said transparent window comprises a glass window.

57. The apparatus of claim 55 wherein said transparent window comprises a Pyrex window.

58. The apparatus of claim 55 wherein said window is bonded to interconnect wafer on which said array of electrostatically actuated MEMS mirror devices is supported.

60. The package of claim 59 wherein the MEMS mirror array device includes a MEMS mirror array and one or more ASIC controllers attached thereto.

61. The package of claim 60 further comprising a thermally conductive material between said ASIC controllers and said base for heat dissipation.

62. The package of claim 59 further comprising passive electronic components in said package.

63. The package of claim 59 wherein the base comprises a metal base with a ceramic substrate laminated thereon.

64. The package of claim 63 wherein the coefficient of thermal expansion of the metal base generally matches that of the ceramic substrate.

65. The package of claim 59 wherein said seal ring comprises metal alloy.

66. The package of claim 65 wherein the seal ring has a coefficient of thermal expansion generally matching that of the base and lid.

67. The package of claim 66 wherein the seal ring is electrically connected to a conductive and grounded plane formed by the base.

68. The package of claim 59 wherein said lid is hermetically sealed to said base.

69. The package of claim 59 wherein said window of the lid surface is covered with a transparent, electrically conductive layer.

70. The package of claim 69 wherein said conductive layer comprises indium tin oxide.

71. The package of claim 69 wherein said lid comprises metal and said conductive layer is electrically connected to the lid.

72. The package of claim 71 wherein said conductive layer is electrically connected to the lid using an electrically conductive material disposed between the window and the lid.

73. The package of claim 59 wherein a Faraday cage is formed around the MEMS mirror array device to protect the MEMS mirror array device from electrostatic and electromagnetic interference.

102. The package of claim 59 wherein the MEMS mirror array device is electrically connected to said base by a combination of flip chip bump bonding and wire-bonding.

103. The package of claim 59 wherein the thickness of said window of the lid and the distance between said window and the MEMS mirror array device is optimized to avoid negative optical interference between light reflected from said window and any other light beams.

59. A MEMS mirror array package, comprising:

a base;

a MEMS mirror array device on said base;

a lid including a window, said lid covering said base and said MEMS mirror array device; and

a seal ring between said lid and said base.

74. An electrostatically actuated MEMS mirror array apparatus, comprising:

an array of electrostatically actuated MEMS mirror devices; and

a plurality of driver circuits integrated in said mirror array apparatus, each driver circuit associated with one or more of said mirror devices to control movement of respective mirrors.

75. The apparatus of claim 74 wherein said driver circuits comprise ASIC (Application Specific Integrated Circuit) controllers.

76. The apparatus of claim 74 wherein said driver circuits are attached to a back-side of the array.

77. The apparatus of claim 76 wherein each driver circuit controls a plurality of mirror devices using time-division multiplexing.

78. The apparatus of claim 76 wherein each driver circuit controls a plurality of mirror devices using serial digital input.

80. A method of patterning a wafer having a plurality of through-holes, comprising:

spinning a material on said wafer;

slowly baking said wafer so that said material forms a membrane over each of said through-holes; and

patterning the wafer.

81. The method of claim 80 wherein said material comprises polyimide.

82. The method of claim 80 wherein said material comprises a polymer.

83. The method of claim 80 wherein said material comprises BCB.

84. A method of forming a movable structure in a MEMS device, comprising:

holding the structure at only edges thereof using a polymer; and

applying a dry etch to remove said polymer and release said structure.

85. The method of claim 84 wherein said polymer comprises polyimide.

86. The method of claim 84 wherein said dry etch is performed using a dry plasma gas.

87. The method of fabricating a MEMS mirror device, comprising:

depositing a reflective material on a mirror structure;

depositing a sacrificial layer on said reflective material;

fabricating a mirror device using said mirror structure; and

removing said sacrificial layer.

88. The method of claim 87 wherein said reflective material comprises gold.

89. The method of claim 87 wherein said sacrificial layer comprises titanium.

90. A method of fabricating a MEMS structure comprising:

depositing oxide on a wafer and selectively removing it;

depositing polysilicon on the remaining oxide;

selectively removing the polysilicon using the oxide as an etch stop; and

removing the remaining oxide.

91. A gimbal mechanism for movably supporting a structure, the gimbal mechanism including two pairs of flexure hinges, each pair defining an axis about which said structure can be rotated, said flexure hinges each having a folded configuration in a cross-section taken generally perpendicular to a respective axis to increase torsional compliance about said respective axis and to decrease compliance in other directions.

92. The gimbal mechanism of claim 91 wherein each flexure hinge has a generally U-shaped cross-sectional configuration.

93. The gimbal mechanism of claim 91 wherein each flexure hinge has a generally V-shaped cross-sectional configuration.

94. The gimbal mechanism of claim 91 wherein each flexure hinge has multiple folds.

95. The gimbal mechanism of claim 91 wherein said pairs of flexure hinges comprise an inner pair connecting the structure to an inner gimbal frame, and an outer pair connecting the inner gimbal frame to an outer gimbal frame, and wherein said outer pair have lower torsional compliance compared to the inner pair.

96. The gimbal mechanism of claim 91 wherein each flexure hinge comprises a plurality of springs, and wherein said springs are arranged in a folded configuration in a top view thereof.

97. A gimbal mechanism for movably supporting a structure, the gimbal mechanism including two pairs of flexure hinges, each pair defining an axis about which said structure can be rotated, said flexure hinges each comprising multiple springs in a folded configuration, each spring also having a folded configuration in a cross-section taken generally perpendicular to a respective axis to increase torsional compliance about said respective axis and to decrease torsional compliance in other directions.

98. The gimbal mechanism of claim 97 wherein each spring has a generally U-shaped cross-sectional configuration.

99. The gimbal mechanism of claim 97 wherein each spring has a generally V-shaped cross-sectional configuration.

100. The gimbal mechanism of claim 97 wherein each spring has multiple folds.

101. The gimbal mechanism of claim 97 wherein said pairs of flexure hinges comprise an inner pair connecting the structure to an inner gimbal frame, and an outer pair connecting the inner gimbal frame to an outer gimbal frame, and wherein said outer pair have lower torsional compliance compared to the inner pair.

104. A method of fabricating a through-wafer interconnect device for a MEMS device, comprising:

providing a silicon-on-insulator wafer having a device layer and a handle layer;

bonding the device layer of the silicon-on-insulator wafer to a wafer having a plurality of through-holes;

dissolving the handle layer of the silicon-on-insulator wafer; and

selectively etching away the device layer to leave silicon membranes extending over said through-holes.

105. A method of depositing a thin film on the back of a MEMS device, comprising:

forming a shadow mask from a silicon wafer;

positioning the shadow mask on the back of the device; and

evaporating material forming said thin film through said shadow mask.

106. The method of claim 105 wherein said material comprises gold.

108. A method of fabricating a MEMS mirror-gimbal structure, comprising:

providing a silicon-on-insulator wafer having a device layer and a handle layer;

patterning the device layer to form flexure hinges of a gimbal mechanism;

performing selective epitaxial growth of silicon on said device layer to form a thickened silicon layer; and

patterning the thickened silicon layer to form a mirror and a gimbal frame of said gimbal mechanism.