Patent Application
20120133270
This application claims all benefits accruing under 35 U.S.C. §119 from China Patent Application No. 201010564731.0, filed on Nov. 29, 2010 in the China Intellectual Property Office, the disclosure of which is incorporated herein by reference. This application is related to applications entitled, “PIXEL TUBE FOR FIELD EMISSION DISPLAY”, filed **** (Atty. Docket No. US34847); and “FIELD EMISSION UNIT AND PIXEL TUBE FOR FIELD EMISSION DISPLAY”, filed **** (Atty. Docket No. US36435).
1. Technical Field
The present disclosure relates to a pixel tube for field emission display.
2. Description of Related Art
Field emission displays (FEDs) are based on the emission of electrons in a vacuum. Electrons are emitted from micron-sized tips in a strong electric field, the electrons are accelerated to collide with a fluorescent material, which then emits visible light. Field emission displays are thin, light weight, and provide high levels of brightness.
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios) (greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features tend to make carbon nanotubes ideal candidates for electron emitter in field emission displays. Generally, a carbon nanotube wire drawn from a carbon nanotube array is used as an electron emitter after being cut by a blade. However, because the carbon nanotube wire has a planar end surface and low electron emission efficiency, the luminous efficiency of the field emission display is low.
What is needed, therefore, is to provide a high luminous efficiency pixel tube for field emission display.
Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one.
References will now be made to the drawings to describe, in detail, various embodiments of the present pixel tube for field emission display.
Referring to
The sealed container 102 defines a vacuum space to accommodate the cathode 104, the phosphor layer 110, and the anode 112. The cathode 104 and the anode 112 are spaced from each other. The cathode terminal 116 is electrically connected to the cathode 104 and extends from the inside to the outside of the sealed container 102. The anode terminal 114 is electrically connected to the anode 112 and extends from the inside to the outside of the sealed container 102. When a voltage is applied between the anode 112 and the cathode 104, a number of electrons can be emitted from the cathode 104. The electrons can strike the phosphor layer 110 to luminesce under the electric field force of the anode 112. Thus, the pixel tube 100 lights.
The sealed container 102 includes a plurality of walls and defines an inner space in vacuum. At least one wall of the container 102 can be used as a light permeable portion 124. The light permeable portion 12 can have a planar surface, a spherical surface, or an aspheric surface. The sealed container 102 can be made of insulative material such as quartz or glass. The shape of the sealed container 102 can be a cube, polyhedron, cylinder, prism, hemisphere, or sphere. In one embodiment, the sealed container 102 has a substantially cylindrical shape and a side wall, a top wall, and a bottom wall. The top wall is used as the light permeable portion 124. The diameter of the sealed container 102 can be in a range from about 1 millimeter to about 10 millimeters. The length of the sealed container 102 can be in a range from about 2 millimeters to about 50 millimeters.
The anode 112 is located on an inner surface of the light permeable portion 124. The anode 112 can be a transparent conductive layer such as an indium tin oxide (ITO) film, a carbon nanotube film, or an aluminum film. The thickness and area of the anode 112 can be selected according to need. In one embodiment, the anode 112 is an aluminum film.
The phosphor layer 110 can be located on the anode 112 oriented to the cathode 104, or between the anode 112 and the light permeable portion 124. The phosphor layer 110 can be white phosphor or color phosphor such as red phosphor, green phosphor, or blue phosphor. The thickness and area of the phosphor layer 110 can be selected according to need. The phosphor layer 110 can be formed by deposition or coating. In one embodiment, the phosphor layer 110 is a white phosphor layer having thickness in a range from about 5 micrometers to about 50 micrometers.
The cathode 104 is located on the wall oriented to the light permeable portion 124. The cathode 104 is substantially perpendicular to the light permeable portion 124 and in alignment with an axis of the container 102. The cathode 104 includes a cathode support 106 and a cathode emitter 108 electrically connected to the cathode support 106. The cathode emitter 108 can be fixed on the cathode support 106 by a conductive paste, such as silver paste. The cathode emitter 108 includes an electron emission portion pointing to the light permeable portion 124. The cathode support 106 is electrically connected to the cathode terminal 116. The cathode support 106 can be an electrical and thermal conductor such as a metal wire. In one embodiment, the cathode support 106 is a copper wire or nickel wire. Furthermore, the cathode 104 can include a number of cathode emitters 108 electrically connected to the cathode support 106 and spaced from each other.
Referring to
Referring also to
Further referring to
Because the distance between the projecting carbon nanotubes is much greater than the diameter of the carbon nanotubes, the screening effect between the projecting carbon nanotubes is reduced.
The main body 109 of the carbon nanotube pipe can be formed by closely wrapping a carbon nanotube film or a carbon nanotube wire around the axis 111. The carbon nanotube film or carbon nanotube wire can be wrapped layer upon layer. The thickness of the wall of the main body 109 can be determined by the number of the layers. The inner diameter and outer diameter of the main body 109 can be selected according to need. The inner diameter of the carbon nanotube pipe can be in a range from about 10 micrometers to about 30 micrometers. The outer diameter of the carbon nanotube pipe can be in a range from about 15 micrometers to about 60 micrometers. In one embodiment, the inner diameter of the main body 109 is about 18 micrometers, and the outer diameter of the main body 109 is about 50 micrometers.
Referring to
A method for making the cathode emitter 108 is provided. The method can include:
In step (S10), the linear structure is configured to support the carbon nanotube film or wire and should have a certain strength and toughness. In addition, the linear structure should be easily removed by a chemical method, or a physical method. The material of the linear structure can be metal, alloy, or polymer. The metal can be gold, silver, copper, or aluminum. The alloy can be a copper-tin alloy. In one embodiment, the linear structure is a copper-tin alloy wire including about 97 wt. % copper and about 3 wt. % tin. Furthermore, the linear structure can be plated with a silver film.
In step (S20), the carbon nanotube film or wire can be made by following steps:
In step (S201), a method of forming the carbon nanotube array includes:
The carbon nanotube array can be approximately 200 to approximately 900 micrometers in height and includes a plurality of carbon nanotubes substantially parallel to each other and nearly perpendicular to the substrate. The carbon nanotubes can be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes. The carbon nanotube array formed under the above conditions is essentially free of impurities such as carbonaceous or residual catalyst particles. The carbon nanotubes in the carbon nanotube array are packed together closely by van der Waals force.
In step (S202), a carbon nanotube film or wire can be formed by the steps of:
In step (S2021), the carbon nanotube segment includes a plurality of parallel carbon nanotubes. The carbon nanotube segments can be selected by using an adhesive tape as the tool to contact the carbon nanotube array.
In step (S2022), the pulling direction is substantially perpendicular to the growing direction of the carbon nanotube array. 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 van der Waals force between ends of adjacent segments. This process of pulling produces a substantially continuous and uniform carbon nanotube film having a predetermined width can be formed. The width of the carbon nanotube film depends on a size of the carbon nanotube array. If the carbon nanotube film is very small, the carbon nanotube wire can be obtained. The length of the carbon nanotube film can be set as desired.
The carbon nanotube film or wire includes a plurality of successively oriented carbon nanotube segments joined end-to-end by van der Waals force therebetween. Each carbon nanotube segment includes a plurality of carbon nanotubes substantially parallel to each other, and combined by van der Waals force therebetween. Some variations can occur in the drawn carbon nanotube film or wire. The carbon nanotubes in the drawn carbon nanotube film or wire are oriented along a preferred orientation.
Furthermore, the carbon nanotube film can be treated by applying organic solvent to the carbon nanotube film or twisting to form a carbon nanotube wire.
The step (S30) can include the following steps:
In step (S302), the extending direction of the carbon nanotubes in the film or wire and the axial direction of the linear structure can be greater than 0 degrees and less than 90 degrees.
The step (S40) can be performed by a chemical method, or a physical method, such as a mechanical method. If the linear structure is made of an active metal or an alloy composed of active metals, such as iron, aluminum, or an alloy thereof, the step (S40) can be performed by reacting with an acid liquid. If the material of the linear structure is an inactive metal or an alloy including inactive metals, such as gold, silver, or an alloy thereof; the step (S40) can be performed by heating to evaporate. If the material of the linear structure is a polymer material, the step (S40) can be performed by pulling the linear structure out using a stretching device along the axial direction of the linear structure. Therefore, the shape and the effective diameter of the linear structure can decide the figure and effective inner diameter of the carbon nanotube hollow cylinder. In one embodiment, the linear structure is an aluminum wire and removed by dissolving in a solution of about 0.5 mol/L hydrochloric acid.
Referring to
In step (S50), the carbon nanotube hollow cylinder can be cut by laser scanning, electron beam irradiation, ion beam irradiation, heating by supplying a current, and/or laser-assisted fusing after supplying current.
In one embodiment, step (S50) includes
In step (S501), the chamber can be a vacuum or filled with an inert gas. The vacuum can be less than 1×10−3 Pascal (Pa). In one embodiment, the vacuum of the chamber is about 2×10−5 Pa. The chamber includes an anode and a cathode therein, which lead from inside to outside of the chamber. One end of the carbon nanotube hollow cylinder is electrically connected to the anode, and the other one end is electrically connected to the cathode.
In step (S502), a voltage is supplied between the anode and the cathode to heat the carbon nanotube hollow cylinder. The voltage depends on the inner diameter, outer diameter, and the length of the carbon nanotube hollow cylinder. In one embodiment, the carbon nanotube hollow cylinder is about 2 centimeters in length, about 25 micrometers in the inner diameter, and about 40 micrometers in the outer diameter, and a 40 V direct current (DC) voltage applied. After a while, the carbon nanotube hollow cylinder snaps at a certain point to form two carbon nanotube pipes. Each carbon nanotube pipe has broken end.
When the voltage is applied to the carbon nanotube hollow cylinder, a current flows through the carbon nanotube hollow cylinder. Consequently, the carbon nanotube hollow cylinder is heated by Joule-heating. The temperature of the carbon nanotube hollow cylinder can reach a range from about 2000 Kelvin (K) to about 2400 K. The resistance at different points along the axial direction of the carbon nanotube hollow cylinder is different, and thus the temperature distribution along the axial direction of the carbon nanotube hollow cylinder is different. The greater the resistance, the higher the temperature, and the easier it snaps. The carbon nanotube hollow cylinder is snapped at a point having the greatest resistance. The heating time is less than 1 hour.
During snapping, some carbon atoms vaporize from the snapping portion of the carbon nanotube hollow cylinder. After snapping, a micro-fissure is formed between the two broken ends, arc discharge may occur between the micro-fissure, and the carbon atoms are transformed into carbon ions due to ionization. These carbon ions bombard or etch the broken ends to form a number of carbon nanotube peaks 101. A wall by wall breakdown of carbon nanotubes is caused by the Joule-heating at a temperature higher than 2000K. The carbon nanotubes at the broken ends have smaller diameters and a fewer number of graphite layers.
In one embodiment, a step (S503) of irradiating the carbon nanotube hollow cylinder by an electron beam can be performed after step (S502). With electron beam bombarding, a temperature of the predetermined point is enhanced, and thus the temperature thereof is higher than the other points. Thus, the carbon nanotube hollow cylinder can be snapped quickly at a predetermined point. In step (S503), an electron emitter can be used to produce an electron beam and bombard a predetermined point of the carbon nanotube hollow cylinder. When step (S503) is performed, the vacuum of the chamber can be less than 1×10−4 Pa.
In one embodiment, a step (S504) of irradiating the carbon nanotube hollow cylinder by a laser can be performed before step (S501), after step (S501) or step (S502). With the laser irradiating, a defect can be introduced at a predetermined point of the carbon nanotube hollow cylinder. The temperature of the predetermined point having the defect increases faster than the other points. Thus, the carbon nanotube hollow cylinder can be snapped quickly at a predetermined point. The power of the laser can be in a range from about 1 W to about 60 W, and the speed of the laser movement can be in a range from about 100 millimeters per second to about 2000 millimeters per second.
If the material of the linear structure is an inactive metal or an alloy including inactive metals, the step (S40) can be omitted, and step (S50) can be performed directly after step (S30). During snapping, the linear structure near the snapping point is heated to vaporize. Thus, the cathode emitter 108 of
Referring to
Furthermore, the pixel tube 100 can include a getter 118 configured for absorbing residual gas inside the sealed container 102 and maintaining the vacuum in the inner space of the sealed container 102. The getter 118 can be arranged on an inner surface of the sealed container 102. The getter 118 can be an evaporable getter formed on the inner surface of the sealed container 102 using high frequency heating or a non-evaporable getter attached on the inner surface of the sealed container 102 directly. The non-evaporable getter can be made of titanium, zirconium, hafnium, thorium, rare earth metals, or alloys thereof.
In use, a high voltage is supplied to the anode 112, a low voltage is supplied to the gate electrode 113, and the cathode 104 is grounded. The cathode emitter 108 can emit electrons under the electric field force of the gate electrode 113. The electrons can strike the phosphor layer 110 to luminesce under the electric field force of the anode 112.
Thus, the pixel tube 100 lights. A number of the pixel tubes 100 can be arranged in an array to form a field emission display.
Referring to
The cathode 204, the phosphor layer 210, the anode 212, the cathode terminal 216, and the anode terminal 214 can be used as a field emission unit 203. In one embodiment, the anode 212 and the cathode support 206 each have a post configuration and are located substantially parallel to each other. The cathode emitter 208 is electrically connected to the cathode support 206 and extends from the cathode support 206 to the phosphor layer 210. The cathode emitter 208 includes an electron emission portion 222 located adjacent to spaced from and oriented to the phosphor layer 210. Referring to
The anode 212 can be an electrical and thermal conductor such as a metal post. The shape of the anode 212 can be selected according to need. In one embodiment, the anode 212 is a copper post having a diameter in a range from about 100 micrometers to about 3 millimeters. The end surface 220 can be a polished metal surface or a plated metal surface that can reflect the light beams emitted from the phosphor layer 210 to the light permeable portion 214 to enhance the brightness of the pixel tube 200. The end surface 220 can be a planar or curved surface such as a hemispherical, spherical, or conical surface. In one embodiment, the end surface 220 is a polished plane at the end of the copper post.
Referring to
The field emission units 303 can be arranged to form a line or an array. In one embodiment, the sealed container 302 is a hollow cylinder, and the field emission units 303 are substantially equidistantly arranged along a lengthwise direction of the sealed container 302. A drive circuit independently controls the field emission units 303. The pixel tube 300 can be used as a field emission display or to assemble a large screen field emission display. Because a number of field emission units 303 are disposed in the sealed container 302, the manufacturing process is simple and the cost is low.
Referring to
In one embodiment, the pixel tube 400 includes only one field emission unit 403. The field emission unit 403 includes a cathode 404 including a cathode support 406 and three cathode emitters 408, a cathode terminal 416, three anodes 412, three phosphor layers 410, and three anode terminals 414. The three anodes 412 are located around the cathode support 406 so that the orthographic projection of the three anodes 412 forms a triangle. In one embodiment, the triangle is an equilateral triangle, and the orthographic projection of the cathode support 406 is at a center of the equilateral triangle.
Each of the three phosphor layers 410 is located on the end surface 420 of the corresponding anode 412. The three phosphor layers 410 are different colors such as a red phosphor layer, a green phosphor layer, and a blue phosphor layer. Each of the three cathode emitters 408 is electrically connected to the cathode support 406, and extends from the cathode support 406 to the corresponding phosphor layer 410. Each of the three cathode emitters 408 has an electron emission portion 422 adjacent to the corresponding phosphor layer 410.
In use, the pixel tube 400 can produce different color lights by controlling the different color phosphor layers 410 to luminesce. The pixel tube 400 can be used to assemble a color field emission display.
It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Any elements described in accordance with any embodiments is understood that they can be used in addition or substituted in other embodiments. Embodiments can also be used together. Variations may be made to the embodiments without departing from the spirit of the disclosure. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.
Depending on the embodiment, certain of the steps of methods described may be removed, others may be added, and the sequence of steps may be altered. It is also to be understood that the description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201010564731.0 | Nov 2010 | CN | national |
