Membrane-actuated charge controlled mirror (CCM) projection display

• US 6,031,657 A
• Filed: 12/09/1998
• Issued: 02/29/2000
• Est. Priority Date: 10/15/1998
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Memsolutions, Inc.
• Inventors: Little, Michael J., Robinson, William P., Gifford, Eric A.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): Burke, Margaret
• Application Number:
  US09/208,041
• Time in Patent Office: 447 Days
• Field of Search: 359/293, 359/223, 345/108, 345/109, 353/30, 353/31, 348/740, 348/770, 348/771, 348/772
• US Class Current: 359/293
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

The present invention provides a Schlieren projection system with a large aperture reflective imager. The combination of a beam-addressed CCM design with flat-panel manufacturing techniques configuration produces a large aperture imager that overcomes the problems of limited deflection range, high beam current, electrostatic instability and limited resolution associated with known electrostatically-actuated micromirror targets. The CCM imager includes a thin insulating membrane that decouples the electron beam from the micromirror array. Decoupling also allows the mirror to be designed to optimize reflectivity, exhibit a higher resonant frequency for better video performance, and be fabricated simultaneously with the hinges. The CCM imager is fabricated using flat-panel manufacturing techniques that are ideally suited to producing large aperture devices at low cost.

Claims

1. A projection display, comprising:

a light source that emits light;

a turning mirror that redirects the light;

a field lens that collimates the light;

a large aperture reflective imager that imparts a spatial modulation onto the collimated light, said spatially modulated light being reflected back through said field lens where it is focused onto a plane, said imager comprising

a vacuum cell;

a charge controlled mirror (CCM) mounted in said vacuum cell, comprising,

a glass substrate;

a transparent equipotential layer on said glass substrate;

an array of electrostatically-actuable micromirrors on said equipotential layer that are both held at an reference potential;

an array of insulating posts on said substrate;

a floating-potential insulating membrane supported by said posts above said array of micromirrors; and

a collector grid spaced apart from said insulating membrane opposite said micromirrors and held at a grid potential; and

a source that emits primary electrons that are accelerated through said collector grid and strike portions of said insulating membrane above respective micromirrors causing secondary electrons to be ejected and collected on the collector grid thereby leaving a predetermined charge pattern on said membrane that produces finely-resolved attractive electrostatic forces that cause said micromirrors to pivot and deflect towards the membrane thereby imparting said spatial modulation onto said collimated light;

a Schlieren stop at said plane that converts the spatially modulated beam into an intensity modulated beam; and

a projection lens that collimates the intensity modulated light to form an image.

2. The projection display of claim 1, wherein said light source comprises an arc lamp having an arc of at least 5 mm.

3. The projection display of claim 2, wherein said light source is a metal halide lamp.

4. The projection display of claim 1, wherein said turning mirror and said Schlieren stop are a single integrated structure.

5. The projection display of claim 1, further comprising a color wheel.

6. The projection display of claim 1, wherein said imager comprises at least three micromirrors per image pixel that correspond to red, green and blue, said display further comprising an RGB filter that filters the intensity modulated light from said red, green and blue micromirrors, respectively.

7. The projection display of claim 6, wherein said three micromirrors per image pixel on hinged on three different axes approximately 120°

apart.

8. The projection display of claim 6, wherein said RGB filter circumscribes said Schlieren stop.

9. The projection display of claim 1, wherein said light is split into a plurality of color components, said projection display comprising a like plurality of said large aperture reflective imagers that spatially modulate the respective color components.

10. The projection display of claim 1, wherein said imager further comprises an array of attractor pads on the backside of said membrane that are aligned with said array of micromirrors, said source writing said charge pattern onto said attractor pads such that each micromirror'"'"'s charge is distributed approximately uniformly across the corresponding attractor pad.

11. The projection display of claim 1, wherein said charge pattern increases the localized membrane potentials toward the grid potential so that the potential differences between the membrane and the micromirrors produces the finely-resolved attractive electrostatic forces, said micromirrors being susceptible to snap-over when the potential difference exceeds a threshold potential, said collector grid being biased so that said grid potential is less than said threshold potential.

12. The projection display of claim 1, wherein said array of micromirrors is configured with cloverleaf arrays of four centrally joined cantilever beams that share common post regions on said equipotential layer.

13. The projection display of claim 12, said imager further comprising an array of attractor pads on the backside of said membrane that are aligned with said cantilever beams.

14. The projection display of claim 13, wherein said array of attractor pads includes one said attractor pad per cantilever beam.

15. The projection display of claim 12, wherein said insulating posts are on said substrate in said common posts regions and formed integrally with said membrane.

16. A projection display, comprising:

a light source that emits light;

a tuning mirror that redirects the light;

a first optical component that reflects a first color component of said light and passes the remaining light;

a second optical component that reflects a second color component of the light passed by said first optical component and passes the remaining light;

a third optical component that reflect a third color component of the light passed by said second optical component;

a plurality of field lens that respectively collimate the first, second and third color components of light;

a plurality of large aperture reflective imagers that impart respective spatial modulations onto the collimated first, second and third color components of light, said spatially modulated components being reflected back through the respective field lenses and said third, second and first optical elements where said components are focused onto a plane, said imagers each comprising

a vacuum cell;

a charge controlled mirror (CCM) mounted in said vacuum cell, comprising,

a glass substrate;

a transparent equipotential layer on said glass substrate;

an array of electrostatically-actuable micromirrors on said equipotential layer that are both held at an reference potential;

an array of insulating posts on said substrate;

a floating-potential insulating membrane supported by said posts above said array of micromirrors; and

a collector grid spaced apart from said insulating membrane opposite said micromirrors and held at a grid potential; and

a source that emits primary electrons that are accelerated through said collector grid and strike portions of said insulating membrane above respective micromirrors causing secondary electrons to be ejected and collected on the collector grid thereby leaving a predetermined charge pattern on said membrane that produces finely-resolved attractive electrostatic forces that cause said micromirrors to pivot and deflect towards the membrane thereby imparting said spatial modulation onto said collimated light;

a Schlieren stop at said plane that converts the spatially modulated components into intensity modulated beams; and

a projection lens that collimates the intensity modulated beams to form a color image.

17. The projection display of claim 16, wherein said light source comprises an arc lamp having an arc of at least 5 mm.

18. The projection display of claim 17, wherein said light source is a metal halide lamp.

19. The projection display of claim 16, wherein said turning mirror and said Schlieren stop are a single integrated structure.

20. The projection display of claim 16, wherein each said imager further comprises an array of attractor pads on the backside of said membrane that are aligned with said array of micromirrors, said source writing said charge pattern onto said attractor pads such that each micromirror'"'"'s charge is distributed approximately uniformly across the corresponding attractor pad.

21. The projection display of claim 16, wherein said charge pattern increases the localized membrane potentials toward the grid potential so that the potential differences between the membrane and the micromirrors produces the finely-resolved attractive electrostatic forces, said micromirrors being susceptible to snap-over when the potential difference exceeds a threshold potential, said collector grid being biased so that said grid potential is less than said threshold potential.

22. The projection display of claim 16, wherein said array of micromirrors is configured with cloverleaf arrays of four centrally joined cantilever beams that share common post regions on said equipotential layer.

23. The projection display of claim 22, said imager further comprising an array of attractor pads on the backside of said membrane that are aligned with said cantilever beams.

24. The projection display of claim 23, wherein said array of attractor pads includes one said attractor pad per cantilever beam.

25. The projection display of claim 22, wherein said insulating posts are on said substrate in said common posts regions and formed integrally with said membrane.

26. A projection display, comprising:

a light source that emits light;

a turning mirror that redirects the light;

a field lens that collimates the light;

a large aperture reflective imager that imparts a red, green and blue spatial modulation onto the collimated light in response to the red, green and blue components of a video addressing signal, said spatially modulated light being reflected back through said field lens where it is focused onto a plane, said imager comprising

a vacuum cell;

a charge controlled mirror (CCM) mounted in said vacuum cell, comprising,

a glass substrate;

a transparent equipotential layer on said glass substrate;

an array of electrostatically-actuable hinged micromirrors on said equipotential layer that are both held at an reference potential, said micromirrors being configured so that each image pixel has at least a red, a green and a blue micromirror;

an array of insulating posts on said substrate;

a floating-potential insulating membrane supported by said posts above said array of micromirrors; and

a collector grid spaced apart from said insulating membrane opposite said micromirrors and held at a grid potential; and

a source that emits primary electrons that are accelerated through said collector grid and strike portions of said insulating membrane above respective micromirrors causing secondary electrons to be ejected and collected on the collector grid thereby leaving a predetermined charge pattern on said membrane that produces finely-resolved attractive electrostatic forces that cause said micromirrors to pivot and deflect towards the membrane thereby imparting said red, green and blue spatial modulation onto said collimated light;

a Schlieren stop at said plane that converts the spatially modulated beam into an intensity modulated beam;

a red, green and blue color filter that converts the intensity modulated beam into red, green and blue intensity modulated beams; and

a projection lens that collimates the intensity modulated light to form a color image.

27. The projection display of claim 26, wherein said red, green and blue micromirrors are hinged on three different axis so that the spatially modulated light reflected off of the red, green and blue micromirrors passes through respective red, green and blue portions of the color filter.

28. The projection display of claim 27, wherein said color filter circumscribes said Schlieren stop.

29. The projection display of claim 26, where said light source is a metal halide lamp.

30. The projection display of claim 26, wherein said array of micromirrors is configured with cloverleaf arrays of four centrally joined cantilever beams that share common post regions on said equipotential layer.

31. The projection display of claim 30, said imager further comprising an array of attractor pads on the backside of said membrane that are aligned with said cantilever beams.

32. The projection display of claim 31, wherein said array of attractor pads includes one said attractor pad per cantilever beam.

33. The projection display of claim 30, wherein said insulating posts are on said substrate in said common posts regions and formed integrally with said membrane.