WO2009143074A2

WO2009143074A2 - Photo-sensitive, bistable, electrowetting light valve

Info

Publication number: WO2009143074A2
Application number: PCT/US2009/044385
Authority: WO
Inventors: Roy Rosser
Original assignee: Roy Rosser
Priority date: 2008-05-18
Filing date: 2009-05-18
Publication date: 2009-11-26
Also published as: WO2009143074A3

Abstract

A photo-sensitive bi-stable, electrowetting light value that may be used as pixel elements in a reflective display. A transparent, isolated electrode is separated from a functional electrode by a suitable layer of photo-conducting material. When a voltage is applied to an "On" pixel, the pixel stays on unless simultaneously illuminated by a suitable source of electromagnetic radiation to the pixel. From the "Off state, the light valve may be switched on by an electrical charge only, as in a regular bi-stable, electrowetting light valve.

Description

TITLE: Photo- sensitive, bistable, electrowetting light valve

INVENTORS: Roy J. Rosser

CROSS REFERENCE TO RELATED APPLICATIONS

[001]This application is related to, and claims priority from, U.S. Provisional Patent application no. 61/054,156 filed on May 18, 2008, by R. Rosser, titled "Photosensitive, bistable, electrowetting light valve" and U.S. Provisional Patent application no. 61/145,564 file on January 18, 2009 by R. Rosser titled "Reusable paper for laser printing" the contents of both of which are hereby incorporated by reference. [002] This application is further related to PCT application PCT/IB2008/052830 filed on July 15, 2008 by R. Rosser titled "Bistable Electrowetting Picture Element", the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

[003] The present invention relates to the field of electrowetting displays. More specifically, the present invention relates to a method, apparatus, and system for bistable, electrowetting picture elements and displays in which at least one of the transitions requires the simultaneous illumination by suitable electro-magnetic radiation.

BACKGROUND OF THE INVENTION

[004] Electrowetting bistable light valves have been described in, for instance, PCT patent application PCT/IB2008/052830 filed on July 15, 2008 by R. Rosser titled

"Bistable Electrowetting Picture Element", the contents of which are hereby incorporated by reference. SUMMARY OF THE INVENTION

Briefly described, the invention provides a photo- sensitive bi- stable, electrowetting light value that may for instance be used as pixel elements in a reflective display. [005] In a preferred embodiment, a transparent, isolated electrode adjacent to the thin, hydrophobic dielectric layer on the "On" side of a more conventional bi-stable, electrowetting light valve is separated from a functional electrode by a suitable layer of photo-conducting material. When a voltage is applied to an "On" pixel, the pixel stays on unless a suitable light is also applied to the pixel. [006] From the "Off state, the light valve may be switched on by an electrical charge only, as in a regular bi-stable, electrowetting light valve. The photo- sensitive bistable, electrowetting light value may also be used as pixels in re-usable photocopying paper. The photo-sensitive bi-stable, electrowetting light value may also be used as re-usable writing paper using a suitable light pen that may simply be a laser. [007] In a further embodiment of the invention the photo-conductive layer has a thin filter between it an the transparent, isolated electrode to limit the range of wavelengths to which it is sensitive. The thin filter may also serve as the reflecting surface of the display and may have wavelength discrimination that limits the light valve to being only sensitive to a narrow band of wavelengths or even a single laser line wavelength. In this way a green laser may draw a green line, a red laser a red line, a blue laser a blue line and a white laser a white line.

[008] These and other features of the invention will be more fully understood by references to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[009] FIGs. IA - ID are schematic representations of a photo- sensitive bi-stable, electrowetting light valve. [001O]FIG. 2 shows a schematic representation of a photo- sensitive bi-stable, electrowetting light valve made sensitive to a particular range of wavelengths. DETAILED DESCRIPTION

[001 I]A preferred embodiment of the invention will now be described in detail by reference to the accompanying drawings in which, as far as possible, like elements are designated by like numbers.

[0012] Figures IA - ID are schematic representations of a photo- sensitive bi-stable, electro wetting light valve 10.

[0013] The photo- sensitive bi-stable, electrowetting light valve 10 include a top transparent electrode 12, two hydrophobic dielectric layers 14, a layer of a polar liquid 16 such as water, a non-polar liquid 18, such as oil, a transparent electrode 20, that may be isolated.

[0014]The polar liquid 16 may contain salts, acids or alkalis to enhance the electrical conductivity of the liquid. The polar liquid 16 may also, or instead, contain additives such as, but not limited to, glycerol or alcohol, or some combination thereof, to allow the device to operate over more extended temperature ranges.

[0015] The non-polar liquid 18 may contain dyes or pigments to facilitate light absorption.

[0016] Figure IA is a schematic representation of the photo-sensitive bi-stable, electrowetting light valve 10 in an "On" or white state. The non-polar liquid 18 is beaded up, attached to the lower hydrophobic dielectric layer 14 and contained in a hydrophilic sub-pixel.

[0017] Figure IB is a schematic representation of the photo- sensitive bi-stable, electrowetting light valve 10 in transition to an "Off or black state. The photosensitive bi-stable, electrowetting light valve 10 is illuminated with electromagnetic radiation of a suitable wavelength 22 . As a result, a voltage applied between a base electrode 24 and the layer of a polar liquid 16 results in a layer of charge being manifest on the top of the transparent electrode 20 because the layer of photo- conductive material 26 has been made conducing by the electromagnetic radiation of a suitable wavelength 22. [0018] Figure 1C shows the result of the non-polar liquid 18 beading up under the layer of charge manifest on the top of the transparent electrode 20, touching the top hydrophobic dielectric layer 14 and transferring there.

[0019] Figure ID shows that the process may be reversed by simply applying a suitable voltage between the top transparent electrode 12 and the layer of a polar liquid 16.

[0020] Although every reasonable attempt is made in the accompanying drawings to represent the various elements of the embodiments in relative scale, it is not always possible to do so with the limitations of two-dimensional paper. Accordingly, in order to properly represent the relationships of various features among each other in the depicted embodiments and to properly demonstrate the invention in a reasonably simplified fashion, it is necessary at times to deviate from absolute scale in the attached drawings. However, one of ordinary skill in the art would fully appreciate and acknowledge any such scale deviations as not limiting the enablement of the disclosed embodiments. [0021] Figure 2 shows a schematic representation of a photo- sensitive bi- stable, electrowetting light valve made sensitive to a particular range of wavelengths. An optical filter layer 28 is situated between the transparent electrode 20 and the photo- conductive material 26. The photo-conductive material 26 is, therefore, only activated by the appropriate wavelengths of light transmitted by the optical filter layer 28. The optical filter layer 28 is typically a conducting layer, or made conductive by suitable additives.

Industrial Applicability

[0022] The photo-sensitive bi-stable, electrowetting light valve 10 may have industrial applicability in the field of printing, particularly in the field of printing temporary documents in an office environment.

[0023] Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed invention. Modifications may readily be devised by those ordinarily skilled in the art without departing from the spirit or scope of the present invention.

Claims

What is claimed is:

1. A photo- sensitive, bi-stable electowetting light value, comprising: a first fluid and a second fluid , immiscible with each other, within a space between a first surface and a second surface said second fluid being electroconductive or polar; said light valve being electrically switchable from a first state, that remains stable without an applied voltage, and a second state that remains stable without an applied voltage and in which in said first state said first fluid adjoins a first region of said first surface, while in said second state said first fluid adjoins a a second region of said second surface, and wherein said second region is smaller in area than said first region or vice versa; and said light valve being electrically switchable from said second state to said first state only when illuminated with a suitable wavelength of electromagnetic radiation.

2. The device of claim 1 wherein said second surface comprises a wall dividing said second surface into at least two sub-picture regions and wherein said second region comprises one of said sub-picture regions.

3. The device of claim 2 wherein said at least two sub-picture regions have substantially equal areas.

4. The device of claim 1 wherein said second fluid is confined to the space of said light valve.

5. The device of claim 1 further comprising a device comprising a multiplicity of said light valves and wherein said second fluid forms a layer common to a multiplicity of said light valves.

6. The device of claim 5 wherein said light valves have light valve walls extending over a height less than a height of the space between said first surface and said second surface.

7. The device of claim 1 further comprising an absorber or a reflector configured to absorb or reflect light incident on said display device.

8. The device of claim 7 wherein said reflector is diffusive.

9. The device of claim 1 wherein said first fluid ( acts as color filter.

10. The device of claim 1 wherein said first fluid is reflective.

11. The device of claim 1 wherein said first fluid is light absorbing.

12. The device of claim 11 wherein said first fluid comprises a suitable pigment.

13. A photo- sensitive, bi- stable electo wetting display method, comprising: providing a light valve comprising a first fluid and a second fluid , immiscible with each other, within a space between a first surface and a second surface said second fluid being electroconductive or polar; electrically switching said light valve from a first state, that remains stable without an applied voltage, and a second state that remains stable without an applied voltage and in which in said first state said first fluid adjoins a first region of said first surface, while in said second state said first fluid adjoins a a second region of said second surface, and wherein said second region is smaller in area than said first region or vica versa; and electrically switching said light valve from said second state to said first state only when illuminating said light valve with a suitable wavelength of electromagnetic radiation.