Reduced micromirror mirror gaps for improved contrast ratio

• US 6,028,690 A
• Filed: 11/23/1998
• Issued: 02/22/2000
• Est. Priority Date: 11/26/1997
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Huffman, James D., Miller, Rodney D., Carter, Duane E., Meier, Robert E., Ray, Brian L.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US09/197,723
• Time in Patent Office: 456 Days
• Field of Search: 359/224, 359/225, 359/290, 359/291, 359/295
• US Class Current: 359/224.1
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means

Abstract

A micromirror array fabricated on a semiconductor substrate 708. The micromirrors in the micromirror array logically divided into an interior active region 704 which selectively modulates light striking the mirrors in the interior active region 704, and an exterior border region 702 for producing a dark border around the image produced by the interior active region 704. A gap between each mirror allows adjacent mirrors to rotate. The gap 712 between mirrors in the interior active region 704 of the array is larger than the gap 710 between at least some of the mirrors in the exterior border region 702. The smaller gap 710 in the exterior region 702 is enabled by restricting mirrors in the exterior region 702 to a single direction of rotation.

Claims

1. A micromirror array comprising:

a substrate having electrical components fabricated on a first surface of said substrate; and

an array of micromechanical light modulator elements, each micromechanical light modulator element comprising an addressing circuit and a mirror supported by and spaced apart from said substrate, each of said mirrors separated from adjacent mirrors by a gap, said array forming an inner light modulating region and an outer border region surrounding said inner light modulating region;

wherein said gap is smaller between at least some mirrors in said outer border region than between mirrors in said inner light modulating region.

2. The micromirror array of claim 1, said mirrors operable to rotate about an axis parallel to said substrate surface, said mirrors in said inner light modulating region operable to rotate in two directions about said axis, said mirrors in said outer border region operable to rotate only in one direction about said axis.

3. The micromirror array of claim 1, wherein said gap between at least two adjacent mirrors in said outer border region is too small to permit said at least two adjacent mirrors to rotate independently without interference.

4. The micromirror array of claim 1, said outer border region comprising a buffer region adjacent a portion of said inner light modulating region, said buffer region comprising mirrors spacer apart by gaps as large as the gaps between mirrors in said inner light modulating region.

5. The micromirror array of claim 1, wherein said mirrors are spaced closer together in said outer border region.

6. The micromirror array of claim 1, wherein said mirrors in said outer border region are larger than said mirrors in said inner light modulating region.

7. The micromirror array of claim 1, said mirrors in said outer border region being larger than said mirrors in said inner light modulating region while said distance between said micromechanical light modulator elements in said outer border region and said micromechanical modulator elements in said inner light modulating region is equal.

8. The micromirror array of claim 1, further comprising:

two address electrodes for each modulator element in said inner light modulating region, said two address electrodes on said substrate surface, one said address electrode on each side of said axis to enable said mirror element to rotate in either direction about said axis.

9. The micromirror array of claim 1, further comprising:

one address electrode for each modulator element in said outer border region, said address electrode on said substrate surface on one side of said axis to enable said mirror element to rotate toward said address electrode about said axis.

10. A method of forming a micromechanical light modulator array, said method comprising:

forming landing electrode/mirror bias structures and address electrodes on a semiconductor substrate;

depositing a first spacer layer on said semiconductor substrate;

patterning said first spacer layer to define hinge support spacervia locations;

depositing a metal hinge layer over said first spacer layer;

forming at least one hinge etch mask on said metal hinge layer;

depositing a metal yoke layer on said metal hinge layer and said hinge etch masks;

patterning said metal hinge layer and said metal yoke layer to form at least one hinge and at least one hinge yoke attached to said hinge;

depositing a second spacer layer over said metal yoke layer;

patterning said second spacer layer to define mirror support spacervia locations;

depositing a metal mirror layer over said second spacer layer;

patterning said metal mirror layer to define an array of micromirrors, said array of micromirrors forming an interior active region and an exterior border region, each said micromirror separated from adjacent micromirrors by a mirror gap, wherein said mirror gap between micromirrors in said interior active region is larger than said mirror gap between at least some of the micromirrors in said exterior border region; and

removing said first and said second spacer layers.

11. The method of claim 10, said step of patterning said metal mirror layer step further comprising:

forming a small mirror gap between at least two adjacent micromirrors in said exterior border region, said small mirror gap being too small to allow said at least two adjacent micromirrors independently to rotate about an axis formed by said at least one hinge.

12. A display system comprising:

a light source for producing a light beam along a light path; and

a micromirror device in said light path for selectively reflecting portions of said light beam along a second light path toward an image plane, said micromirror device comprising;

a substrate having electrical components fabricated on a first surface of said substrate; and

an array of micromechanical light modulator elements, each micromechanical light modulator element comprising an addressing circuit and a mirror supported by and spaced apart from said substrate, each of said mirrors separated from adjacent mirrors by a gap, said array forming an inner light modulating region and an outer border region surrounding said inner light modulating region;

wherein said gap is smaller between mirrors in said outer border region than between mirrors in said inner light modulating region.

13. The display system of claim 12 further comprising:

a projection lens in said second light path form receiving said selectively reflected light and focusing said selectively reflected light on said image plane.

14. The display system of claim 12 further comprising:

a controller for providing image data to said micromirror device.

15. The display system of claim 12 further comprising:

a source lens for focusing light from said light source onto said micromirror device.