Patent Application
20080278060
1. Field of the Invention
The present invention relates to a flat light source and, particularly, to a field-emission-based flat light source.
2. Discussion of Related Art
Flat light sources are widely used in many fields, especially in display technology. Many light receiving display devices, such as liquid crystal displays (LCDs), need a flat light source to provide a uniform incidence light. Generally, a flat light source used in LCD converts a linear light source to a flat, area light source through an optical means. However, the conventional flat light source typically inefficiently utilizes light energy.
To improve the efficiency of the light energy utilization, a conventional field-emission-based flat light source is provided. The field-emission-based flat light source includes a cathode electrode, a transparent anode electrode spaced from the cathode electrode, and a fluorescent layer formed on the anode electrode. When a predetermined voltage is applied between the anode electrode and the cathode electrode, electrons are able to emit from the cathode electrode and move to the anode electrode. When the emitted electrons collide against the fluorescent layer, a visible light is produced and transmitted through the transparent anode electrode and to the outside as a flat, area light source.
However, in the conventional field-emission-based flat light source, light emits from the anode electrode directly. The potential non-uniformity of the thickness of the fluorescent layer and/or of the electron emission from the cathode may induce a non-uniformity of light emission of the fluorescent layer. Therefore, the uniformity of luminance of the conventional field-emission-based flat light source is decreased.
What is needed is to provide a field-emission-based flat light source, in which the above problems are eliminated or at least alleviated.
A field-emission-based flat light source includes the following: a light-permeable substrate, a plurality of line-shaped cathodes, an anode, a light-reflecting layer, and a fluorescent layer. The light-permeable substrate has a surface, and the line-shaped cathodes, with a plurality of carbon nanotubes formed and/or deposited thereon, are located on the surface of the light-permeable substrate. The anode faces the cathodes and is spaced from the cathodes to form a vacuum chamber. The light-reflecting layer is formed on the anode and faces the cathode. The fluorescent layer is formed on the light-reflecting layer.
Other advantages and novel features of the present invention of the field-emission-based flat light source will become more apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings.
Many aspects of the present invention of the field-emission-based flat light source can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present field-emission-based flat light source.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present field-emission-based flat light source, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Reference will now be made to the drawings to describe, in detail, embodiments of the present field-emission-based flat light source.
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The spacers 16 are advantageously made of an insulative material, such as a glass or ceramic material, to provide a high strength and to avoid shorting between the cathode and the anode. The anode 15 can, usefully, be made of a conductive material, such as a metal, or of an insulative material with a conductive layer formed thereon. The conductive layer can, beneficially, be made of gold, silver, copper, aluminum, or nickel. The light-reflecting layer 14 can, advantageously, include a light-reflecting sheet or a light-reflecting film coated on the surface of the anode 15. Because of the high reflectivity of silver and/or aluminum, the conductive layer can be used as the light-reflecting layer 14 when the conductive layer is formed of silver and/or aluminum material.
The light-permeable substrate 11 can be made of a transparent material such as a transparent glass panel. The cathode 12 on the light-permeable substrate 11 may includes a plurality of metal wires 122 and a bus electrode 123. The electrical conductive metal wires 122 distributed uniformly on the light-permeable substrate 11 and the diameter is in the approximate range from 10 microns to 1 millimeter. Quite suitably, the material of metal wires 122 can, beneficially, be selected from nickel (Ni), tungsten (W), molybdenum (Mo), titanium (Ti), zirconium (Zr), or other metal and alloy commonly used in electro-vacuum devices. The bus electrode 123 can, advantageously, be made of the same metal, as the metal wires 122 or other metal have better conductivity than the material of the metal wires 122. Carbon nanotubes (CNTs) are disposed on the metal wires 122.
Quite suitably, the bus electrode 123 equally distributes current from electrical power source to each metal wire 122. It is to be understood that the bus electrode 123 is optional. In another embodiment, the metal wire can be contacted to the electrical power source directly, without the bus electrode 123.
In the first embodiment, the metal wires 122 are parallel to each other. As the amount of the metal wires 122 on the light-permeable substrate 11 increases, the electron emission will increase but the light output through the light-permeable substrate 11 will decrease. Thus, the distribution density of the metal wires 122 on the light-permeable substrate 11 is not specifically confined and only needed to provide a maximum light output. In one useful embodiment, the distance between two metal wires 122 is at least about 10 microns to about 10 millimeters.
In the flat light source 10 of the first embodiment, electrons emit from cathode 12 and collide with the fluorescent layer 13 on the anode 15. Visible light produced by the collision of the electrons partially emits directly from the light-permeable substrate 11. The other part of the visible light reflected by the light-reflecting layer 14 and emits from the light-permeable substrate 11. Due to the transmission step in the distance between the light-permeable substrate 11 and the anode 15, the uniformity of the luminance is increased. Further, the cathode 12 may, advantageously, include a transparent conductive layer.
The cathode 12 can be made by the method includes the steps of: (a) providing a carbon nanotube paste; (b) coating the nanotube paste on the surface of the metal wire 122; and (c) fixing the metal wire 122 on the light-permeable substrate 11.
In step (a), the carbon nanotubes paste consists of about 5%˜15% carbon nanotubes, about 10%˜20% conductive metal grains, about 5% low-melting point glass, and about 60% to 80% organic carrier. The material of conductive metal grains can, beneficially, be selected from a group consisting of indium tin oxide (ITO) and silver. The organic carrier is a mixture of terpineol as a solvent, a small amount/percentage of dibutyl phthalate as a plasticizer, and a small amount/percentage of ethyl cellulose as a stabilizer. In the present embodiment, the amount of terpineol, dibutyl phthalate and ethyl cellulose is in the ratio of about 90:5:5. The mixture can be sonicated (i.e., ultrasonically vibrated and mixed) to provide a paste with the above-mentioned paste components uniformly dispersed therein.
The conductive metal grains electrically connect the the metal wires 122 with the transparent conductive layer, as well as the metal wires 122 with the carbon nanotubes formed thereon.
In step (b), the organic carrier is eliminated (e.g., via evaporation and/or burn-off) by drying the coating in an oven (e.g., at about 75° C.˜120° C.) or in room temperature.
In step (c), the metal wires 122 can be fixed on the light-permeable substrate 11 through any of various means, including, for example: bonding the metal wires 122 with the light-permeable substrate 11 using a glue/adhesive or a binder; or sintering the metal wire 122 on the light-permeable substrate 11. The low-melting point glass can be melted through the sintering step. The melting glass bonds the carbon nanotubes on the metal wire 122 and fixes the metal wire 122 on the light-permeable substrate 11. In one useful embodiment, the step (c) further includes an abrasion step after drying and sintering of the metal wire 122, in order to enhance the field emission property. The carbon nanotubes extrude from the paste and have a preferred orientation after the abrasion step.
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The two diffuser plates on the opposing sides of the light-permeable substrate 51 can be formed by, e.g., injection molding (i.e., inject the melted glass into a mold) or glass etching of the initial light-permeable substrate 51. The uniformity of the output light can be elevated through the light-permeable substrate 51, as there are no respective interfaces between it and the two diffuser plates associated therewith, and, of course, the two diffuser plates themselves promote uniform light output, via diffusion.
Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200710074431.2 | May 2007 | CN | national |
This application is related to commonly-assigned application entitled, “FIELD-EMISSION-BASED FLAT LIGHT SOURCE”, filed ______ (Atty. Docket No. US12855). Disclosure of the above-identified application is incorporated herein by reference.
