Field-emission matrix display based on electron reflections

Information

  • Patent Grant
  • 6674242
  • Patent Number
    6,674,242
  • Date Filed
    Wednesday, March 20, 2002
    22 years ago
  • Date Issued
    Tuesday, January 6, 2004
    20 years ago
Abstract
A Reflective Field Emission Display (FED) system using reflective field emission pixel elements is disclosed. In the FED system disclosed, each pixel elements is composed of at least one edge emitter that is operable to emit electrons and at least one reflector that is operable to first attract and then reflect the emitted electrons onto a transparent layer that is operable to attract the reflected electrons. The transparent anode layer is oppositely positioned with respect to the cathode or emitter edge. In a one aspect of the invention, a phosphor layer interposed between the transparent layer and the pixel element produces a light photon as reflected electrons are attracted to the transparent layer. In another aspect of the invention, a plurality of phosphor layers are applied to the transparent layer to produce a color display when reflected electrons are attracted to the transparent layer.
Description




FIELD OF THE INVENTION




The present invention relates to solid-state displays and more specifically to edge-emitter reflective field emission pixel elements of solid-state displays.




BACKGROUND OF THE INVENTION




Solid state and non-Cathode Ray Tube (CRT) display technologies are well-known in the art. Light Emitting Diode (LED) displays, for example, include semiconductor diode elements that may be arranged in configurations to display alphanumeric characters. Alphanumeric characters are then displayed by applying a potential or voltage to specific elements within the configuration. Liquid Crystal Displays (LCD) are composed of a liquid crystal material sandwiched between two sheets of a polarizing material. When a voltage is applied to the sandwiched materials, the liquid crystal material aligns in a manner to pass or block light. Plasma displays conventionally use a neon/xenon gas mixture housed between sealed glass plates that have parallel electrodes deposited on the surface.




Passive matrix displays and active matrix displays are flat panel displays that are used extensively in laptop and notebook computers. In a passive matrix display, there is a matrix or grid of solid-state elements in which each element or pixel is selected by applying a potential to a corresponding row and column line that forms the matrix or grid. In an active matrix display, each pixel is further controlled by at least one transistor and a capacitor that is also selected by applying a potential to a corresponding row and column line. Active matrix displays provide better resolution than passive matrix displays, but they are considerably more expensive to produce.




While each of these display technologies has advantages, such as low power and lightweight, they also have characteristics that make them unsuitable for many other types of applications. Passive matrix displays have limited resolution, while active matrix displays are expensive to manufacture.




Hence, there is a need for a low-cost, lightweight, high-resolution display that can be used in a variety of display applications.




SUMMARY OF THE INVENTION




A Field Emission Display (FED) device using edge-emitter reflective field emission pixel elements is disclosed. In the FED device disclosed, each pixel element comprises at least one cathode or edge emitter that is operable to emit electrons and at least one reflector that is operable to attract and reflect the emitted electrons. A transparent layer is oppositely positioned to the cathode or emitter and is operable to attract the reflected electrons. A phosphor layer is interposed between the transparent layer and the emitter/reflector elements and produces a photonic response as reflected electrons are attracted to the transparent layer and bombard the phosphor layer. In another aspect of the invention, a plurality of phosphor layers are applied to the transparent layer, which produce different levels of color as reflected electrons are attracted to the transparent layer and bombard corresponding phosphor layers.











BRIEF DESCRIPTION OF THE DRAWINGS




In the drawings:





FIG. 1



a


illustrates a cross-sectional view of a first embodiment of a Field-Emission Display (FED) pixel element in accordance with the principles of the invention;





FIG. 1



b


illustrates a cross-sectional view of a second embodiment of an FED pixel element in accordance with the principles of the invention;





FIG. 2

illustrates a top view of an FED display of two rows and columns using the pixel elements illustrated in

FIG. 1



b;







FIG. 3

illustrates a cross sectional view of FED display shown in

FIG. 2

; and





FIGS. 4



a


and


4




b


illustrate the power supply connection and operational conditions of the FED pixel shown in

FIG. 1



a.













It is to be understood that these drawings are solely for purposes of illustrating the concepts of the invention and are not intended as a definition of the limits of the invention. It will be appreciated that the same reference numerals, possibly supplemented with reference characters where appropriate, have been used throughout to identify corresponding parts.




DETAILED DESCRIPTION OF THE INVENTION





FIG. 1



a


illustrates a cross-sectional view of a Edge-Emitter Field Emission Display (FED) pixel


100


in accordance with the principles of the invention. In this exemplary embodiment, pixel element


100


is fabricated by depositing at least one conductive layer


115


on substrate


120


, e.g. glass. Conductive layer


115


is representative of an electrode that is used to control a voltage applied to pixel elements


100


that are arranged in columns. Conductive line


115


may be any material possessing a high electrical conductivity selected from a group of metals, such as, aluminum, chromium molybdenum, etc. In a preferred embodiment, conductive layer


115


is formed from chromium.




Insulator layer


130


, preferrably silicon dioxide, SiO


2


, is next deposited on conductive layer


115


. Insulator layer


130


electrically isolates conductive layer


115


and is preferably in the range of about 0.5 microns thick. Emitter layer


140


is then deposited on insulating layer


130


. Emitter layer


140


is comprised preferably of a bottom conductive layer


150


and edge emitter layer


170


. Conductive layer


150


is representative of a material to provide an electrical contact to the edge emitter


170


. Emitter or cathode layer


170


is made preferably from an alpha-carbon (α-C) material. Cathode


170


is formed as an edge of a 50-80 nanometer-thick alpha-carbon thin film. Alpha-carbon film is well known to have a low work function for electron emission into a vacuum. In another aspect of the invention, a resistive material, such as alpha-silicon (α-Si), may be imposed between conductive layer


160


and emitter edge


170


.




Pixel well


145


is next created by etching, for example, using photo-resistant patterning, through emitter layer


140


and insulator film layer


130


to expose conductive layer


115


.




Reflector layer


110


is then deposited on exposed conductive layer


115


using known self-aligning metal deposition techniques. In this case, the width of reflector layer


110


is substantially equal to the distance between emitter layer


170


edges. Reflector layer or element


110


may be any material possessing a high electrical conductivity and a high electron reflection efficiency, such as, aluminum, chromium molybdenum, etc. In a preferred embodiment, aluminum (Al) is selected as reflector layer


110


. As will be appreciated, reflector element


110


may be used to control the voltage applied to cathode


140


, and consequently the flow of electrons from emitter edge


170


. In another aspect, without self-aligned reflective layer


110


, conductive layer


115


serves as a reflector.




A transparent electrode (ITO)


180


is deposited on transparent plate


190


, e.g., glass. ITO layer


180


is an optically transparent conductive material, which may be used to provide a known potential in selective areas of ITO


180


.




A phosphor layer


195


is next deposited on ITO


180


. Phosphor layer


195


produces a predetermined or desired level of photonic activity or illumination when activated or bombarded by an impinging electron. In a preferred aspect, phosphor layer is deposited such that it is opposite a corresponding pixel well


145


.




Glass plate or transparent substrate


190


is separated from the emitter edge element


170


by a small distance, preferably in the range of 100-200 microns. The small separation distance prevents any significant broadening of the reflected electron beam. Hence, a small spot of phosphor luminescence and consequently, good display resolution are achieved. Furthermore, the small separation distance prevents the development of multiple electron reflections on top glass


190


. Although not shown, it would be appreciated that a dielectric material, such as SiO


2


, separates transparent substrate


190


and emitter element


170


.




In the operation of the FED pixel element


100


, the application of a positive voltage to conductive layer


115


relative to emitter


150


creates an electrical field that draws electrons from emitter layer


150


to reflective layer


110


. Electrons reflected from reflective layer


110


are then attracted to a positive voltage applied to ITO layer


180


that bombard phosphor layer


195


.




In another aspect of the invention, ITO layer


180


may be formed into electrically isolated conductive stripes arranged in columns, orthogonal to pixel elements formed in rows, as will be further explained. In this aspect, a high constant voltage may be applied to selected electrically conductive lines within ITO layer


180


such that electrons, emitted from selected emitter edges


170


and reflected from reflector layer


110


are attracted to selected conductive lines on ITO


180


. Selective control line activation on the ITO layer


180


is advantageous when different color phosphors are used, as in a color display.




As will be appreciated, the gap between the emitter edge


170


and reflector layer


110


can be made extremely small, preferably less than or equal to one (1) micron. In this case, the voltage difference between emitter edge


170


and reflector


110


can be reduced to a level between 30 and 100 volts. The potential of the combined phosphor/ITO


180


is kept at a significantly higher voltage, typically a few hundred volts to attract reflected electrons to corresponding phosphor layers.





FIG. 1



b


illustrates a second embodiment of an FED


200


in accordance with the principles of the invention. In this second embodiment, a plurality of phosphor layers represented as


196


,


197


,


198


are adjacently deposited onto ITO layer


180


for each pixel element. In a preferred embodiment phosphor layers


196


,


197


,


198


, emit a visible light in a band corresponding to one of the primary colors, i.e., red, green, blue. As would be appreciated the selection of colors and the order of the color phosphor layers may be exchanged without altering the scope of the invention.




In this second embodiment of the invention, light emission control is accomplished by applying a high voltage to selective areas of ITO layer


180


, as previously discussed, wherein each selected area corresponds to one of each phosphor layer. In this aspect, different levels of high voltage may be applied to selective areas of ITO layer


180


to attract different amounts of reflected electrons to a corresponding phosphor layer to produce desired levels of color emission.





FIG. 2

illustrates a top view of preferred embodiment of a FED display


500


containing four FED reflective pixel elements in accordance with the principles of the present invention. In this embodiment, cathodes or emitters


140


of pixel elements


501


,


502


are connected in a single row


450


and the cathodes or emitters


140


of pixel elements


503


,


504


are connected a second row


451


. Furthermore, the reflective layers


110


of pixel elements


501


,


503


are connected in a single column


515


, while the reflective layers


110


of pixel element


502


,


504


are connected in a second column


525


.




Also illustrated in this preferred embodiment is emitter


140


distributed throughout a corresponding pixel area


145


as a “comb” having a plurality of tangs, prongs, fingers or digits, represented as digits


171


,


172


,


173


. In this manner, the length of emitter layer


140


, and consequentially emitter layer


170


edge is substantially increased. Similarly, reflective layer


110


is also distributed throughout pixel area


145


as a comb having a plurality of tangs, prongs, fingers or digits,


255


,


256


,


257


,


258


. In this illustrated preferred embodiment, reflective layer


110


digits


255


,


256


,


257


,


258


are interlocked with or fitting between corresponding emitter digits. As will be appreciated, emitter


140


digits


171


,


172


,


173


and reflective layer


110


digits


255


,


256


,


257


,


258


are vertically disposed and offset from each other.





FIG. 3

illustrates a cross-sectional view of pixel elements


501


,


502


in row


450


shown in FIG.


2


. In this illustrated cross-sectional view, reflector layer


110


is shown interlockedly interposed between cathode or emitter layer


140


of pixel


501


and


502


. Also illustrated are columns


515


and


520


adjacent to pixel


501


and


503


, respectively, which are used to apply a voltage to an associated reflective layer


110


. On transparent layer


190


is shown phosphor layers


196


,


197


, and


198


associated with each pixel element. As previously discussed, reflected electrons may be drawn to selected phosphor layers, for example phosphor layer


196


, by selectively applying a high voltage to corresponding ITO layer


181


.




In one aspect of the invention, voltages may be alternatively applied to each ITO layer


181


,


182


,


183


, in a sequential manner for a fixed duration of time related to a frame time. For example, a voltage is applied as illustrated to a single ITO layer


181


, while a low or no voltage is applied to other ITO layers, i.e.,


182


,


183


, in a each corresponding pixel. Hence, electrons are drawn to a single phosphor layer, as illustrated. In a preferred embodiment, voltage is sequentially applied to each ITO layer for one-third (⅓


rd


) of the display frame time. Time-sequential application of voltage is advantageous as the number of drivers is reduced while beam-spreading and pixel cross-talk in the row direction is reduced.





FIGS. 4



a


illustrates the voltage connections and operating conditions of the FED element in accordance with the principles of the present invention.

FIG. 4



b


illustrates that the field emission current posses an extremely sharp field dependence and a pronounced emission threshold. Thus, it is possible to sub-divide the total cathode-reflector voltage difference into a constant voltage Vo and a variable voltage ΔV, which may be pulsed. Constant voltage Vo may be applied to the emitter as a negative voltage or a zero voltage, which may indicate a particular row is not activated. A positive variable voltage ΔV may then be applied to reflector


110


to activate the emission at the row-column intersection. Furthermore, a zero voltage as a column voltage corresponds to the non-activated pixel. Hence, a pixel is in its on-state when a negative voltage Vo relative to the reflector is applied to the row containing emitter


140


and a positive ΔV voltage is applied to the column containing reflector


110


.




As is well known in the art, masking for example, using photo-resistance masks is accomplished over that portion of the metal that is not to be removed, while maintaining expose the unwanted portion. The exposed portion is then removed by subjecting the multi-layer structure to a metal etching process. There are several different etching processes available to those skilled in the art. Furthermore, the term “deposited” as used in this written description includes means for forming or growing on a material layer on a surface by exposing the surface to the material. Vapor deposition, thermal growth, oxidation and sputtering are examples of deposition processes that can be used in accordance with the principles of the present invention.




As would be understood by those skilled in the art, a sold-state flat panel display using laterally reflected pixel elements disclosed herein may be formed by arranging a plurality of pixel elements, for example, pixel


100


, emitter layers


140


electrically connected in rows and reflector layers


110


and


310


are arranged in columns. Pixel elements may then be selected to produce an image viewable through transparent layer


185


by the application of voltages to selected rows and columns. Control of selected rows and columns may be performed by any means, for example, a processor, through appropriate row controller circuitry and column controller circuitry. As will be appreciated, a processor may be any means, such as a general purpose or special purpose computing system, or may be a hardware configuration, such as a dedicated logic circuit, integrated circuit, Programmable Array Logic, Application Specific Integrated circuit that provides known voltage outputs on corresponding row and column lines in response to known inputs.




While there has been shown, described, and pointed out, fundamental novel features of the present invention as applied to preferred embodiments thereof, it will be understood that various omissions and substitutions and changes in the apparatus described, in the form and details of the devices disclosed, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated.



Claims
  • 1. A reflective emission pixel comprising:a substrate layer; at least one reflective layer, an emitter layer positioned on said substrate layer having an edge for electron emission extending above said at least one reflective layer, wherein said at least one reflective layer is at a first positive potential to attract electrons from said emitter layer; a transparent electrode layer oppositely positioned, and electrically isolated from, said at least one emitter layer, said transparent electrode layer having a second potential to attract electrons reflected from said at least one reflective layer; and at least one phosphor layer on said transparent electrode layer oppositely positioned to said at least one reflective layer.
  • 2. The pixel as recited in claim 1, further comprising:a connectivity layer associated with each of said at least one reflective layer, said connectivity layer positioned between said at least one reflective layer and said substrate layer.
  • 3. The pixel as recited in claim 2, wherein said connectivity layer is selected from the group consisting of: chromium, niobium, vanadium, aluminum, molybdenum, gold, silver, copper.
  • 4. The pixel as recited in claim 1, wherein said reflective layer is selected from the group consisting of: aluminum, chromium, niobium, vanadium, gold, silver, copper.
  • 5. The pixel as recited in claim 1, wherein said emitter layer further comprising:a conductive layer; and a resistive layer in electrical contact with said conductive layer.
  • 6. The pixel as recited in claim 5, wherein said resistive layer is an alpha-carbon material.
  • 7. The pixel as recited in claim 1, wherein said at least one phosphor layer is selected from a group that emits a distinct wavelength when activated.
  • 8. The pixel as recited in claim 7, wherein said distinct wavelength is selected from the group consisting: red, green, blue.
  • 9. The pixel as recited in claim 1, wherein said emitter layer is distributed within said pixel to increase the edge of said emitter layer.
  • 10. The pixel as recited in claim 1, wherein said emitter layer and said at least one reflective layer are each subdivided into a plurality of digits.
  • 11. The pixel as recited in claim 10, wherein said emitter layer digits and said at least one reflective layer digits are interlockingly positioned.
  • 12. The pixel as recited in claim 1, wherein said second potential is selectively applied to selected areas of said transparent electrode layer.
  • 13. The pixel as recited in claim 1, wherein said first potential includes a known constant potential and a potential applied as a pulse.
  • 14. The pixel as recited in claim 12, wherein said second potential is applied sequentially to said selected areas.
  • 15. The pixel as recited in claim 14, wherein said second potential is applied for a known duration.
  • 16. A reflective field edge emission display (FED) system comprising:a FED display comprising: a plurality of reflective edge emission pixel elements arranged in a matrix of N rows and M columns, each of said pixel elements containing an emitter element and a reflector element, said reflector element operable to reflect electrons extracted from said emitter element and; a transparent electrode layer, oppositely positioned to and electrically isolated from said plurality of pixel elements, operable to attract said reflected electrons, at least one phosphor layer deposited on said transparent electrode layer positioned between said transparent electrode layer and said pixel elements; a row controller operable to apply a known value of a first potential to selected ones of said N rows of associated emitter elements; a column controller operable to apply a constant portion of said first potential to selected ones of said M columns; means to select at least one of said N rows and at least one of said M columns; and means to selectively apply a second potential to said transparent electrode layer.
  • 17. The system as recited in claim 16, wherein said at least one phosphor layer is selected from a group that emits a distinct wavelength when activated.
  • 18. The system as recited in claim 17, wherein said distinct wavelength is selected from the group consisting of: red, green, blue.
  • 19. The system as recited in claim 16, wherein said pixel emitter element is distributed within said pixel.
  • 20. The system as recited in claim 16, wherein said pixel element emitter and said associated reflector are subdivided into a plurality of digits.
  • 21. The system as recited in claim 20, wherein said plurality of emitter digits and said plurality of reflector digits are offset and interlockingly positioned.
  • 22. The system as recited in claim 16, wherein said edge emitter further comprises:a conductive layer; and a resistive layer in electrical contact with said conductive layer.
  • 23. The system as recited in claim 22, wherein said resistive layer is an alpha-carbon material.
  • 24. The system as recited in claim 16, wherein said second potential is applied in a sequential manner.
  • 25. The system as recited in claim 24, wherein said second potential is applied for a known period of time.
  • 26. A method for fabricating a reflective FED pixel element comprising the steps of:depositing on a first substrate; at least one reflective layer having a high efficiency of electron reflection; an insulating layer on said reflective layer; an emitter layer on said insulating layer; etching a well through said deposited emitter and insulating layers to expose said at least one reflective layer such that said emitter layer has at least one edge that extends into said well; depositing on a transparent substrate; a transparent layer having a high electrical conductivity; at least one phosphor layer; and aligning and electrically isolating said second transparent substrate and said first substrate wherein said at least one phosphor layer is oppositely positioned to said at least one reflective layer.
  • 27. The method as recited in claim 26, wherein the step of depositing said emitter layer comprises the steps of:depositing a conductive layer on said insulating layer; depositing a resistive layer on said conductive layer, wherein said resistive layer is an alpha-carbon and in electrical contact with said conductive layer.
  • 28. The method as recited in claim 27, further comprising the step of:depositing a conductive layer between said reflective layer and said first substrate.
  • 29. The method as recited in claim 26, wherein said reflective layer is selected from the group consisting of: gold, silver, aluminum, copper, chromium, niobium, vanadium, molybdenum.
  • 30. The method are recited in claim 27, wherein said conductive layer is selected from the group consisting of: gold, silver, aluminum, copper, chromium, niobium, vanadium, molybdenum.
  • 31. The pixel as recited in claim 5, further comprising:a second resistive material imposed between said conductive layer and said resistive layer.
  • 32. The pixel as recited in claim 31, wherein said resistive layer is an alpha-silicon material.
  • 33. The system as recited in claim 22, further comprising:a second resistive material imposed between said conductive layer and said resistive layer.
  • 34. The system as recited in claim 23, wherein said resistive layer is an alpha-silicon material.
  • 35. The method as recited in claim 26, further comprising the step of:depositing a second resistive layer between said conductive layer and said resistive layer.
  • 36. The method as recited in claim 35, wherein said second resistive layer is an alpha-silicon material.
  • 37. A reflective emission pixel comprising:a substrate layer; at least one reflective layer; a connectivity layer associated with each of said at least one reflective layer, said connectivity layer positioned between said at least one reflective layer and said substrate layer. an emitter layer positioned on said substrate layer having an edge for electron emission extending above at least one reflective layer, wherein said at least one reflective layer is at a first positive potential to attract electrons from said emitter layer; a transparent electrode layer oppositely positioned, and electrically isolated from, said at least one emitter layer, said transparent electrode layer having a second potential to attract electrons reflected from said at least one reflective layer; and at least on phosphor layer on said transparent electrode layer oppositely positioned to said at least one reflective layer.
  • 38. The pixel as recited in claim 37, wherein said connectivity layer is selected from the group consisting of: chromium, niobium, vanadium, aluminum, molybdenum, gold, silver, copper.
  • 39. The pixel as recited in claim 37, wherein said reflective layer is selected from the group consisting of: aluminum, chromium, niobium, vanadium, gold, silver, copper.
  • 40. The pixel as recited in claim 37, wherein said emitter layer further comprising:a conductive layer; and a resistive layer in electrical contact with said conductive layer.
  • 41. The pixel as recited in claim 40, wherein said resistive layer is an alpha-carbon material.
  • 42. The pixel as recited in claim 37, wherein said at least one phosphor layer is selected from a group of phosphors that emits a distinct wavelength when activated.
  • 43. The pixel as recited in claim 42, wherein said distinct wavelength is selected from the group consisting of: red, green, blue.
  • 44. The pixel as recited in claim 37, wherein said emitter layer is distributed within said pixel to increase the edge of the emitter layer.
  • 45. The pixel as recited in claim 37, wherein said emitter layer and said at least one reflective layer are each subdivided into a plurality of digits.
  • 46. The pixel as recited in claim 45, wherein said emitter layer digits and said at least one reflective layer digits are interlockingly positioned.
  • 47. The pixel as recited in claim 37, wherein said second potential is selectively applied to selected areas of said transparent electrode layer.
  • 48. The pixel as recited in claim 37, wherein said fist potential includes a known constant potential and a potential applied as a pluse.
  • 49. The pixel as recited in claim 47, wherein said second potential is applied sequentially to said selected areas.
  • 50. The pixel as recited in claim 49, wherein said second potential is applied for a known duration.
  • 51. A reflective emission pixel comprising:a substrate layer; at least one reflective layer; an emitter layer positioned on said substrate layer having an edge for electron emission extending above said at least one reflective layer; means to apply a first potential to said at least one reflective layer, wherein said first positive potential operates to attract electrons from said emitter layer a transparent electrode layer oppositely positioned, and electrically isolated from, said at least one emitter layer; means to apply a second potential to said transparent layer, wherein second potential is operable to attract electrons reflected from said at least one reflective layer; and at least one phosphor layer on said transparent electrode layer oppositely positioned to said at least one reflective layer.
  • 52. The pixel as recited in claim 51, further comprising:a connectivity layer associated with each of said at least one reflective layer, said connectivity layer positioned between said at least one reflective layer and said substrate layer.
PRIORITY FILING DATE

This application claims the benefit of the earlier filing date, under 35 U.S.C. §119, of U.S. Provisional Patent Applications; Ser. No. 60/277,171, entitled “New Edge-Emission Matrix Display,” filed on Mar. 20, 2001; Ser. No. 60/284,864, entitled “Field-Emission Matrix Display Based on Electron Reflections,” filed on Apr. 19, 2001; and Ser. No. 60/355,683, entitled, “New Features in Edge Emitter Field Emission Display”, filed on Feb. 7, 2002, of which are incorporated by reference herein. This application relates to commonly assigned patent applications: Ser. No. 10.102,467 entitled “Field-Emission Matrix Display Based on Lateral Electron Reflection,” filed on Mar. 20, 2002; and Ser. No. 10/102,467 entitled “Improved Method for Fabricating Edge Emitter Field Emission Displays,” filed on Mar. 20, 2002, the disclosures of which are incorporated by reference herein.

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Provisional Applications (3)
Number Date Country
60/277171 Mar 2001 US
60/284864 Apr 2001 US
60/355683 Feb 2002 US