This application is related to commonly-assigned application entitled, “FIELD-EMISSION-BASED FLAT LIGHT SOURCE”, filed ______ (Atty. Docket No. US14310). Disclosure of the above-identified application is incorporated herein by reference.
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 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 a light-permeable substrate, a transparent electrically conductive cathode, an electron emitter, an anode layer, a light-reflecting layer, a fluorescent layer. The light-permeable substrate has a surface. The transparent electrically conductive cathode layer is disposed on the surface of the light-permeable substrate. The electron emitter is disposed on the transparent electrically conductive cathode layer. The anode layer faces and is spaced from the transparent electrically conductive cathode layer. A vacuum chamber is formed between the anode layer and the transparent electrically conductive cathode layer. The light-reflecting layer is formed on the anode layer, and faces the transparent electrically conductive cathode layer. 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.
Referring to
The spacers 16 are advantageously made of an insulative material, such as a glass or ceramic material, to provide high strength and to avoid shorting between the electron emitter 12 and the anode layer 15. The anode layer 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 layer 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, usefully, be made of a transparent material such as a transparent glass panel. The transparent electrically conductive cathode layer 112 can, suitably, be made of an indium tin oxide (ITO) film. The electron emitter 12 can, beneficially, include a transparent carbon nanotube film. The thickness of the transparent carbon nanotube film is in the approximate range from 0.5 nanometers to 100 microns. In one useful embodiment, the transparent carbon nanotube film can be fixed on the transparent electrically conductive cathode layer 112 by using an adhesive/glue.
A method for fabricating the transparent carbon nanotube film includes the steps of: (a) providing an array of carbon nanotubes, quite suitably, providing a super-aligned array of carbon nanotubes; (b) selecting a plurality of carbon nanotube segments having a predetermined width from the array of carbon nanotubes by using a tool (e.g., adhesive tape or another tool allowing multiple carbon nanotubes to be gripped and pulled simultaneously); (c) pulling the carbon nanotube segments out of the array of carbon nanotubes at an even/uniform speed to form the carbon nanotube film.
In step (b), quite usefully, the carbon nanotube segments having a predetermined width can be selected by using a wide adhesive tape as the tool to contact the super-aligned array. In step (c), the pulling direction is, usefully, substantially perpendicular to the growing direction of the super-aligned array of carbon nanotubes.
More specifically, during the pulling process, as the initial carbon nanotube segments are drawn out, other carbon nanotube segments are also drawn out end to end, due to the van der Waals attractive force between ends of the adjacent segments. This process of drawing ensures a successive carbon nanotube film can be formed. The carbon nanotubes of the carbon nanotube film are all substantially parallel to the pulling direction, and the carbon nanotube film produced in such manner is able to formed to have a selectable, predetermined width.
It is to be understood that, a plurality of carbon nanotube films can be formed and overlapped with each other to form a multi-layer carbon nanotube film. The aligned directions of the carbon nanotube films can be different. In the multi-layer carbon nanotube film, the number of the layers is arbitrary and depends on the actual needs/use. The layers of carbon nanotube film are combined (i.e., attached to one another) by van de Waals attractive force to form a stable multi-layer film. A thickness of the carbon nanotube film can, suitably, be in the approximate range from 0.5 nanometers to 100 microns.
In the flat light source 10 of the first embodiment, electrons are emitted from the electron emitter 12 and collide with the fluorescent layer 13 on the anode layer 15. Visible light produced by the collisions partially emits directly from the light-permeable substrate 11. The remaining part of the visible light is reflected by the light-reflecting layer 14 and then emits from the light-permeable substrate 11. Due to the transmission step in the vacuum chamber between the light-permeable substrate 11 and the anode layer 15, the uniformity of the luminance is increased.
Referring to
Additionally, a diffuser 27 is disposed on the lower side of the light-permeable substrate 21 and includes a plurality of diffusion (i.e., light-diffusing) structures 272 formed directly thereon. The shape of the diffusion structures 272 of the diffuser 27 can, beneficially, be selected from a group consisting of convex or concave columns, semi-spheres, pyramids, truncated pyramids, and any combination thereof. In one useful embodiment, the diffusion structures 272 are pyramids formed by injection molding.
The lattice-patterned emitters 222 of the electron emitter 22 can be made by a screen printing method, which includes the steps of: (a) providing a carbon nanotube paste and the light-permeable substrate 21 with the transparent electrically conductive cathode layer 224 formed thereon; (b) providing a template with lattice-patterned through holes, and disposing the template on the transparent electrically conductive cathode layer 224; (c) filling the through holes with the carbon nanotube paste; (d) removing the template and, drying and sintering the light-permeable substrate 21 to form the lattice-patterned emitters 222.
In step (a), the carbon nanotube 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, and provide a electrical connection between the carbon nanotubes and the transparent electrically conductive cathode layer. 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.
Quite suitably, the length of the carbon nanotubes is in the approximate range from 5 to 15 microns. The field emission performance will be reduced, when the carbon nanotubes have relatively small length. Whereas, the carbon nanotubes will bend or break when the length thereof are relatively long. The melting point of the low-melting point glass can, beneficially, be in the approximate range from 400° C. to 500° C. The low-melting point glass can be melted in the sintering step, and used to bond the carbon nanotubes to the transparent electrically conductive cathode layer 224.
In step (b), the template can be made by conventional means of screen-printing (e.g. forming a sensitizing layer on a screen and forming the through holes thereon with exposing and profiling steps.). In step (c), the carbon nanotube paste can be put into the through holes by using a rubber blade. In step (d), the light-permeable substrate 21 can be dried in an oven (e.g., via evaporation and/or burn-off at about 75° C.˜120° C.) or in room temperature to eliminate the organic carrier in the carbon nanotube paste. The low-melting point glass can be melted in the sintering step, and used to bond the carbon nanotubes to the transparent electrically conductive cathode layer 224. The melting point of the transparent electrically conductive cathode layer 224 is higher than that of the low-melting point glass.
In one useful embodiment, the step (d) further includes an abrasion step for the emitters 222 after the sintering step, in order to enhance the field emission property thereof. The carbon nanotubes extrude from the paste and have a preferred orientation after the abrasion step.
As the amount of the emitters 222 increases, electron emission will increase but the light output through the light-permeable substrate 21 will decrease. Thus, the distribution density of the emitters 222 is not specifically confined and is set to provide a maximum light output. In one suitable embodiment, the distance between two adjacent emitters 222 is in the approximate range from 10 microns to 10 millimeters. The field-emission-based flat light source 20 in the second embodiment has more uniformity of emitting density and output light than the field-emission-based flat light source 10 in the first embodiment.
Referring to
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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 |
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200710074018.6 | Apr 2007 | CN | national |