Field emission charge controlled mirror (FEA-CCM)

• US 6,034,810 A
• Filed: 10/15/1998
• Issued: 03/07/2000
• Est. Priority Date: 04/18/1997
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: Memsolutions, Inc.
• Inventors: Little, Michael J., Robinson, William P., Gifford, Eric A.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): BURKE, MARGARET A
• Application Number:
  US09/172,612
• Time in Patent Office: 509 Days
• Field of Search: 359/293, 359/223, 359/224, 359/298, 359/291, 359/292, 359/295, 359/262, 313/309, 348/781, 348/782
• 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

A bright, high contrast, compact, large area, high-resolution light modulator uses a field emitter array (FEA) to address a charge controlled mirror (CCM). The FEA deposits a charge pattern onto the CCM, which in turn produces electrostatic forces that deflect the micromirrors in accordance with the amount of accumulated charge. The CCM that is used in combination with the FEA can be configured in many different ways to implement different actuation modes, e.g. attractive, repulsive, grid-actuated or membrane-actuated and different charge control modes, e.g. RC decay, RC sustain and charge control.

Claims

1. A light modulator, comprising:

a thin vacuum cell having a transparent faceplate;

a charge controlled mirror (CCM) in said vacuum cell adjacent the interior surface of said faceplate, said CCM comprising an array of electrostatically-actuable micromirrors;

a collector grid in said vacuum cell; and

a field emitter array (FEA) in said vacuum cell that comprises an array of field emitter tips that emit primary electrons, said primary electrons accelerating through said collector grid and striking the backside of the CCM causing secondary electrons to be ejected and collected on the collector grid leaving a charge pattern on the backside of the CCM that produces electrostatic forces that deflect said micromirrors.

2. The light modulator of claim 1, wherein said CCM further comprises a transparent substrate that supports the array of micromirrors and provides the cell'"'"'s faceplate.

3. The light modulator of claim 1, wherein said micromirrors deflect outward away from said faceplate and toward said FEA.

4. The light modulator of claim 3, wherein each said micromirror is mounted on a conductive pad so that said micromirror and said conductive pad are at the same potential.

5. The light modulator of claim 4, wherein said CCM further comprises a buried layer that is held at a fixed potential with respect to said micromirror, said conductive pad having a hole beneath the micromirror so that said micromirror is biased towards said faceplate.

6. The light modulator of claim 3, wherein said CCM further comprises an array of control pads on the backside of said CCM, one of said control pads and the backside of said CCM exhibiting a secondary emission coefficient less than one and the other exhibiting a secondary emission coefficient greater than one, said plurality of field emitter tips alternately delivering primary electrons to said control pads and the backside of said CCM to refresh the charge pattern at a video rate.

7. The light modulator of claim 6, wherein said field emitter tips first deliver charge to said control pads to deflect said mirrors to an erase position and then deliver charge to the backside of the CCM to deflect said mirrors to a next write position.

8. The light modulator of claim 6, wherein said field emitter tips selectively deliver charge to said control pads and the backside of said CCM such that the charge pattern is differentially written onto the CCM causing the mirrors to deflect from one write position to the next.

9. The light modulator of claim 3, wherein the backside of the CCM is coated with a secondary emission material to stabilize its secondary emission coefficient, said FEA emitting primary electrons at different landing energies such that the secondary emission material emits secondary electrons with secondary emission coefficients greater than and less than one to erase and write the charge pattern.

10. The light modulator of claim 3, wherein the backside of the CCM is the surface of the micromirrors facing the FEA, said charge pattern having a negative polarity that causes the micromirrors to be electrostatically attracted toward said collector grid.

11. The light modulator of claim 3, wherein the backside of the CCM is the surface of the micromirrors facing the FEA, each said micromirror comprising a deflectable mirror element that is joined to an underlying base electrode by an inwardly-directed electrically conductive hinge, said deflectable mirror elements being repulsed away from their underlying base electrodes in accordance with the charge pattern.

12. The light modulator of claim 3, wherein said charge pattern is written onto a thin insulating membrane that decouples the micromirrors from said FEA causing said micromirrors to be deflected toward said membrane.

13. The light modulator of claim 1, wherein each said micromirror comprises a deflectable mirror element that is suspended above an underlying reference electrode that is held at a reference potential, said charge pattern creating potential differences between the deflectable mirror elements and their underlying reference electrodes that causes the mirror elements to deflect toward their reference electrodes.

14. The light modulator of claim 13, wherein said charge pattern increases the micromirror potentials toward the potential of the collector grid so that the potential differences between the micromirrors and the reference electrode deflect the mirror elements, said micromirrors being susceptible to snap-over when the potential difference exceeds a threshold potential, said collector grid being biased at a grid potential that is less than said threshold potential.

15. The light modulator of claim 13, wherein said reference electrodes comprise a buried layer that extends beneath all of said micromirrors and is biased at said reference potential, an insulating layer on said buried layer, and an array of electrically isolated conductive pads on said buried layer that support said respective micromirrors so that the conductive pads and the micromirrors are at the same potential, said conductive pads each having an aperture through which the potential differences between the micromirrors and buried layer can deflect the micromirrors.

16. The light modulator of claim 1, further comprising an array of posts that extend from said faceplate to said FEA to hold off atmospheric pressure.

17. A light modulator, comprising:

a thin vacuum cell having a transparent faceplate;

a charge controlled mirror (CCM) having a plurality of electrostatically-actuable electrically isolated micromirrors on said faceplate, each said micromirror having a deflectable mirror element that is joined to an underlying base electrode by an electrically conductive hinge;

a collector grid in said vacuum cell;

a field emitter array (FEA) in said vacuum cell that comprises an array of field emitter tips that emit primary electrons, said primary electrons accelerating through said collector grid and striking the micromirrors causing secondary electrons to be ejected and collected on the collector grid leaving a charge pattern on the array of micromirrors that distributes itself over the mirror element and base electrode to produce electrostatic fringing forces that repel said mirror elements outward away from their respective underlying electrodes.

18. The light modulator of claim 17, wherein said micromirrors exhibit a secondary emission coefficient less than one, further comprising a control pad on each said micromirror that exhibits a secondary emission coefficient greater than one, said plurality of field emitter tips alternately delivering primary electrons to said control pad and said micromirror to refresh the charge pattern at a video rate.

19. The light modulator of claim 18, wherein said field emitter tips first deliver charge to said control pad to deflect said micromirror to an erase position and then deliver charge to the micromirror to deflect it to a next write position.

20. The light modulator of claim 18, wherein said field emitter tips selectively deliver charge to said control pad and the micromirror such that the charge pattern is differentially written onto the array of micromirrors causing the mirrors to deflect from one write position to the next without erasure.

21. A light modulator, comprising:

a thin vacuum cell having a transparent faceplate;

a charge controlled mirror (CCM) having a plurality of electrostatically-actuable electrically isolated micromirrors on said faceplate;

a collector grid biased at a grid potential; and

a field emitter array (FEA) having an array of field emitter tips that emit primary electrons which are accelerated through said collector grid and strike the micromirrors thereby ejecting secondary electrons and depositing a negative charge pattern on said micromirrors,

said collector grid collecting the ejected secondary electrons and producing attractive electrostatic forces that deflect said micromirrors toward said collector grid in accordance with the difference between said grid potential and the respective micromirror potentials induced by said negative charge pattern.

22. The light modulator of claim 21, wherein the collector grid has an array of uniformly sized and spaced cells, at least one per micromirror, that are aligned with a plurality of said field emitter tips on one side and one said micromirror on the other side.

23. The light modulator of claim 21, further comprising a control pad on each said micromirror, said plurality of field emitter tips alternately delivering primary electrons to said control pad and said micromirror to refresh the charge pattern at a video rate.

24. The light modulator of claim 21, wherein the micromirrors are coated with a secondary emission material to stabilize their secondary emission coefficient, said FEA emitting primary electrons at different landing energies such that the secondary emission material emits secondary electrons with secondary emission coefficients greater than and less than one to erase and write the charge pattern.

25. The light modulator of claim 21, further comprising a reference electrode spaced apart from said micromirror array opposite said collector grid, said FEA selectively depositing said negative charge pattern and a positive charge pattern onto said micromirrors so that they respectively deflect toward said collector grid and said reference electrode.

26. The modulator of claim 25, wherein said reference electrode comprises a buried layer on said faceplate beneath said micromirror array, each said micromirror being supported on a conductive pad that assumes the same potential as said mirror, each said conductive pad having a hole through which said anode potential can attract said micromirror.

27. A light modulator, comprising:

a vacuum cell having a transparent faceplate;

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

an array of electrostatically-actuable pivotable micromirrors on said faceplate that are held at an reference potential;

an array of insulating posts on said faceplate;

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

a collector grid that is spaced apart from said membrane opposite said array of micro mirrors; and

a field emitter array (FEA) that is supported on said insulating posts in said vacuum cell and emits primary electrons that are accelerated through said collector grid and strike the backside of said insulating membrane causing secondary electrons to be ejected and collected on the collector grid thereby leaving a charge pattern on said membrane that produces finely-resolved attractive electrostatic forces that cause said micromirrors to pivot and deflect toward the membrane.

28. The light modulator of claim 27, further comprising a transparent equipotential layer between said faceplate and said array of micromirrors that shields said micromirrors from charge accumulation on said faceplate.

29. The light modulator of claim 28, further comprising a conductive grid on said equipotential layer that ensures electrical continuity between said micromirrors.

30. The light modulator of claim 28, wherein said equipotential layer has an array of holes beneath respective micromirrors, further comprising:

an insulative layer beneath said equipotential layer; and

a buried conductive layer between said insulative layer and said faceplate that is held at a constant potential, said constant potential creating an electric field through said holes with respect to said reference potential that establishes a constant attractive force on said micromirrors that biases them downward toward said faceplate.

31. The light modulator of claim 27, further comprising:

an array of conductive pads on the backside of said membrane that are aligned with said array of micromirrors, said FEA writing said charge pattern onto said conductive pads such that each micromirror'"'"'s charge is distributed uniformly across the corresponding conductive pad.

32. The light modulator of claim 31, further comprising:

an array of conductive pads on the frontside of said membrane facing and aligned with said array of micromirrors, said conductive pads on the membrane'"'"'s backside and frontside forming an array of series capacitors so that charge deposited on said backside conductive pads produces mirror charges on said frontside conductive pads opposite said micromirrors.

33. The light modulator of claim 32, further comprising a control pad on said backside conductive pads, which exhibit opposite secondary emission coefficients.

34. The light modulator of claim 27, wherein the membrane is coated with a secondary emission material to stabilize its secondary emission coefficient, said FEA emitting primary electrons at different landing energies such that the secondary emission material emits secondary electrons with secondary emission coefficients greater than and less than one to erase and write the charge pattern.

35. A light modulator, comprising

a thin vacuum cell having a transparent faceplate;

a charge controlled mirror (CCM) in said vacuum cell adjacent the interior surface of said faceplate, said CCM comprising an array of electrostatically-actuable micromirrors in which each micromirror comprises a deflectable mirror element that is supported above an underlying reference electrode that is held at a reference potential, said micromirrors being susceptible to snap-over when the potential difference between the mirror element and the reference electrode exceeds a threshold potential;

a collector grid in said vacuum cell that is biased at a grid potential below said threshold potential; and

a field emitter array (FEA) in said vacuum cell that comprises an array of field emitter tips that emit primary electrons, said primary electrons accelerating through said collector grid and striking the micromirrors causing secondary electrons to be ejected and collected on the collector grid leaving a charge pattern on the mirror elements that increases their potentials toward said grid potential thereby producing electrostatic forces that deflect said mirror elements toward said reference electrode.

36. The light modulator of claim 35, wherein said reference electrodes comprise a buried layer that extends beneath all of said micromirrors and is biased at said reference potential, an insulating layer on said buried layer, and an array of electrically isolated conductive pads on said buried layer that support said respective micromirrors so that the conductive pads and the micromirrors are at the same potential, said conductive pads each having an aperture through which the potential differences between the micromirrors and buried layer can deflect the micromirrors.

37. The light modulator of claim 35, further comprising a control pad on each said micromirror, said plurality of field emitter tips alternately delivering primary electrons to said control pad and said micromirror to refresh the charge pattern at a video rate.

38. The light modulator of claim 35, wherein the micromirrors are coated with a secondary emission material to stabilize their secondary emission coefficient, said FEA emitting primary electrons at different landing energies such that the secondary emission material emits secondary electrons with secondary emission coefficients greater than and less than one to refresh the charge pattern at a video rate.