Patent Application
20080169749
This application claims the benefit of Russian Patent Application No. 2006137605, filed on 24 Oct. 2006 in the Russian Patent Office, and Korean Patent Application No. 2006-126401, 126401, filed on 12 Dec. 2006 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.
1. Field of the Invention
Aspects of the present invention relate to carbide derived carbon, an emitter for cold cathodes including the carbide derived carbon and an electron emission device including the emitter; and more particularly, to carbide derived carbon that can be prepared using a more inexpensive method than that used to manufacture conventional carbon nanotubes where the nanotubes of the present invention have good uniformity and a long lifetime, an emitter for cold cathodes including the carbide derived carbon and an electron emission device including the emitter.
2. Description of the Related Art
In general, electron emission devices can be classified into electron emission devices using hot cathodes as an electron emission source and electron emission devices using cold cathodes as an electron emission source. Examples of electron emission devices using cold cathodes as an electron emission source include field emitter array (FEA) type electron emission devices, surface conduction emitter (SCE) type electron emission devices, metal insulator metal (MIM) type electron emission devices, metal insulator semiconductor (MIS) type electron emission devices, ballistic electron surface emitting (BSE) type electron emission devices, etc.
FEA type electron emission devices operate based on a principle that a low work function material or high beta function material as an electron emission source easily emits electrons because of an electric field formed between two or more electrodes under a vacuum condition. Recently, a tip-shaped structure mainly formed of Mo, Si, etc.; a carbonaceous material, such as graphite, diamond like carbon (DLC), or the like; and a nanomaterial, such as nanotubes, nano wires, or the like have been developed as electron emission sources for FEA type electron emission devices.
In an SCE type electron emission device, a first electrode on a first substrate faces a second electrode on the first substrate, and a conductive thin film having fine cracks is located between the first and second electrodes. These fine cracks are used as an electron emission source. In this structure, when a voltage is applied to the device, current flows in the surface of the conductive thin film and electrons are emitted through the fine cracks acting as an electron emission source.
MIM type electron emission devices and MIS type electron emission devices include an electron emission source having a metal-dielectric layer-metal (MIM) structure and an electron emission source having a metal-dielectric layer-semiconductor (MIS) structure, respectively. These devices operate based on a principle that when a voltage is applied between metals or between a metal and a semiconductor separated by a dielectric layer, electrons move, are accelerated and are emitted from the metal or semiconductor having higher electron electric charge to the metal having lower electron electric charge.
BSE type electron emission devices operate based on a principle that when a semiconductor is miniaturized to a dimension smaller than the mean free path of electrons of the semiconductor, electrons travel without being dispersed. In particular, an electron supply layer formed of a metal or semiconductor is formed on an ohmic electrode, an insulating layer and a thin metal film are formed on the electron supply layer, and a voltage is applied to the ohmic electrode and the thin metal film to emit electrons.
In addition, FEA type electron emission devices can be categorized into top gate type electron emission devices and under gate type electron emission devices according to the locations of cathodes and gate electrodes. Furthermore, according to the number of electrodes used, FEA type electron emission devices can be categorized into diode electron emission devices, triode electron emission devices, tetrode electron emission devices, etc.
In the electron emission devices described above, carbon-based materials included in an emitter, for example, carbon nanotubes, which have good conductivity, electric field concentration, electric emission properties and a low work function are commonly used.
However, the field enhancement factor, β, of the common fiber type carbon nanotube is great. Fiber type carbon nanotube materials have many problems such as bad uniformity, a short lifetime, and the like. When fiber type carbon nanotubes are manufactured using paste, ink, slurry, or the like, manufacturing problems occur compared with other materials in particle form. In addition, the raw materials are too expensive.
Recently, research has been conducted on materials substituted by carbon nanotubes from inexpensive carbide-based compounds in order to overcome these disadvantages. In particular, Korean Patent Publication No. 2001-13225 discloses a method of manufacturing a porous carbon product including forming a workpiece having a transport porosity using a carbon precursor, forming a nano-sized air gap in the workpiece by thermochemically treating the workpiece, and using the manufactured porous carbon product as electrode material for an electric layer capacitor. Meanwhile, Russia Patent Publication No. 2,249,876 discloses a method of applying nano porous carbon, in which nano porosities of predetermined size are distributed, to cold cathodes.
Aspects of the present invention provide carbide derived carbon that can be prepared using a more inexpensive method than that used to manufacture conventional carbon nanotubes where the nanotubes have good uniformity and a long lifetime, an emitter for cold cathodes including the carbide derived carbon and an electron emission device including the emitter.
One aspect of the present invention provides carbide derived carbon prepared by first thermochemically reacting carbide compounds with a gas containing a halogen group element (Group VII) and then extracting all atoms of the carbide compounds except carbon atoms, wherein the intensity ratios of a graphite G band at 1590 cm−1 to a disordered-induced D band at 1350 cm−1 are in the range of 0.3 through 5 when the carbon produced is analyzed using Raman peak analysis.
Another aspect of the present invention provides carbide derived carbon prepared by first thermochemically reacting carbide compounds with a gas containing a halogen group element and then extracting all atoms of the carbide compounds except carbon atoms, wherein the BET surface area of the carbon produced is 1000 m2/g or more.
Another aspect of the present invention provides carbide derived carbon prepared by first thermochemically reacting carbide compounds with a gas containing a halogen element and then extracting all atoms of the carbide compounds except carbon atoms, wherein a weak peak or wide single peak of a graphite (002) surface is seen at 2θ=25° when the carbon produced is analyzed using X-ray diffractometry.
Another aspect of the present invention provides carbide derived carbon prepared by first thermochemically reacting carbide compounds and a gas containing a halogen element and then extracting all atoms of the carbide compounds except carbon atoms, wherein the electron diffraction pattern of the carbide derived carbon is the halo pattern typical of amorphous carbon when the carbon produced is analyzed using electron microscopy.
Another aspect of the present invention provides an emitter for cold cathodes comprising the carbide derived carbon.
Another aspect of the present invention provides an electron emission device comprising the emitter.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
According to embodiments of the present invention, carbide derived carbon having reduced manufacturing costs and good electron emission properties, an emitter prepared using the carbide derived carbon, and an electron emission device including the emitter are provided.
According to one embodiment of the present invention, carbide derived carbon may be prepared using a method in which carbide compounds are thermochemically reacted with halogen containing gases to extract all atoms of the carbide compounds except carbon atoms. As disclosed in Korean Patent Publication No. 2001-13225, the carbide derived carbon may be prepared using a method including: i) forming workpieces comprised of particles of carbide compounds having a predetermined transport porosity, and ii) thermochemically treating the workpieces with halogen containing gases at a temperature in the range of 350 through 1200° C. to extract all atoms of the workpieces except carbon atoms. Thus the carbide derived carbon has a nano porosity throughout the workpieces.
For example, when the carbide derived carbon prepared using the above method is analyzed using Raman peaks, it has intensity ratios of a graphite G band of 1590 cm−1 to a disordered-induced D band at 1350 cm−1 in the range of 0.3 through 5, or a BET surface area of 1000 m2/g or more. Second, when the carbide derived carbon is analyzed using X-ray diffractometry, a weak or wide peak of a graphite (002) surface can be seen at 2θ=25°. Third, when the carbide derived carbon is analyzed using electron microscopy, the electron diffraction pattern is the halo pattern typical of amorphous carbon.
Generally, results of analysis of the Raman peaks, X-ray diffractometry and electron microscopy are commonly used as criteria of degrees of crystallinity. It can be seen that carbide derived carbon according to these embodiments of the present invention has a structure that has a degree of crystallinity within the short ranges relevant to these embodiments that are similar to those of amorphous carbon analyzed by the same techniques. It has been documented that amorphous carbon having a degree of crystallinity in short range order has a structure where bent graphite sheets and open pores that are not in the shape of the 6-membered rings that surround the pores are mixed (Enn Lust, et al., J. Electroanalytical Chem., vol. 586, p 247, 2006).
A composition for preparing an emitter according to an embodiment of the present invention may be a carbon compound which is reacted with Group II, III, IV, V, or VI elements, respectively, and preferably, may be diamond type carbides such as silicon carbide or boron carbide; metal type carbides such as titanium carbide or zirconium carbide; alkaline metal type carbides such as aluminum carbide or calcium carbide; complex carbides such as titanium tantalum carbide or molybdenum tungsten carbide; carbonitrides such as titanium nitride carbide or zirconium nitride carbide; or compounds thereof. The halogen containing gas may be Cl2, TiCl4 or F2.
In addition, the present invention provides an emitter for cold cathodes prepared using the method of preparing the carbide derived carbon according to another embodiment of the present invention.
An emitter according to this embodiment of the present invention is an emitter for cold cathodes. The emitter emits electrons by photoelectric emission, electric field emission, or the like where the electrons are generated by secondary electron emission and ion recombination subsequent to ion bombardment, rather than the electrons being generated through heating. In this embodiment, the emitter includes the carbide derived carbon according to other embodiments of the present invention where the carbide derived carbon has good electron emission properties. Accordingly, the emitter has good electron emission efficiency.
An electron emission device according to an embodiment of the present invention is manufactured using a method, which is not limited, including preparing a composition for forming an emitter and applying and calcinating the compositions on a substrate, or the like as follows.
First a composition for forming an emitter including the carbide derived carbon of an aspect of the present invention as well as a vehicle is prepared. The vehicle adjusts printability and viscosity of the composition for forming the emitter, and includes a resin and a solvent component. In addition, the composition for forming the emitter may further comprise a photosensitive resin, a photoinitiator, an adhesive component, a filler, etc.
Next, the composition for forming the emitter is applied to a substrate. The substrate on which the emitter is formed may vary according to the type of electron emission device to be formed, where the substrate to be selected should be obvious to one of ordinary skill in the art. For example, when manufacturing an electron emission device with gate electrodes between a cathode and an anode, the substrate may be the cathode.
The application of the composition for forming the emitter to the substrate may vary according to whether or not photosensitive resins are included in the composition for forming the emitter. First, additional photoresist patterns are unnecessary when the composition for forming the emitter includes photosensitive resins. That is, after coating the composition for forming the emitter including photosensitive resins on the substrate, the composition for forming the emitter is exposed and developed according to the desired emitter forming region. A photolithography process using additional photoresist patterns is required when the composition for forming the emitter does not include photosensitive resins. That is, after photoresist patterns are formed on the substrate using a photoresist film, the composition for forming the emitter is applied to the substrate on which the photoresist patterns have been formed.
The composition for forming the emitter applied to the substrate is calcinated as described above. The adhesion between the carbon-based material in the composition for forming the emitter and the substrate is increased due to the calcination. Many vehicles are volatilized, and other inorganic binders, etc. are melted and solidified to enhance the durability of the emitter. The calcination temperature should be determined according to the volatilization temperature and volatilization time of the vehicle included in the composition for forming the emitter. The calcination may be performed in an inert gas atmosphere in order to inhibit degradation of the carbon-based material. The inert gas may be, for example, nitrogen gas, argon gas, neon gas, xenon gas or a mixture of at least two of the aforementioned gases.
An activation process is alternatively performed for the vertical alignment and exposing of the surface of the carbon-based material, etc. According to an embodiment of the present invention, an electron emission source surface treatment material including a solution, which can be cured using heat treatment, for example, polyimide group polymer, is coated on the heat-treated resultant material described above, and the combination is then heat treated. Subsequently, the heat-treated film is delaminated. According to another embodiment of the present invention, the adhesive component is formed on the surface of a roller driven by a predetermined driving source, and the activation process is performed by applying a predetermined pressure to the surface of the heat-treated resultant material. Through this activation process, the carbide derived carbon can be exposed on the surface of the emitter or aligned vertically.
In addition, the present invention provides en electron emission device including the emitter according to the current embodiment of the present invention.
An electron emission device according to an embodiment of the present invention includes a first substrate, a cathode and an emitter formed on the first substrate, a gate electrode arranged so as to be insulated electrically from the cathode, and an insulating layer arranged between the cathode and the gate electrode to insulate the cathode from the gate electrode. Here, the emitter includes carbide derived carbon as described above.
The electron emission device may further include a second insulating layer formed on an upper surface of the gate electrode to insulate the gate electrode. In addition, various changes can be made. For example, as the gate electrode is insulated by the second insulating layer, the electron emission device may further include a focusing electrode arranged to be parallel with the gate electrode.
The emitter can be used in a vacuum electric device such as a flat display, a television, an X-ray tube, an emission gate amplifier, or the like.
Referring to
The lower plate 202 includes a lower substrate 110 formed opposite the upper substrate 190 and parallel to the upper substrate 190 so that a predetermined interval or an emission space 210 is formed between the lower substrate 110 and the upper substrate 190, an elongated form cathode electrode 120 formed on the lower substrate 110, an elongated form gate electrode 140 formed to overlap the cathode electrode 120, an insulating layer 130 formed between the gate electrode 140 and the cathode electrode 120, emitter holes 169 formed next to the insulating layer 130 and gate electrode 140, and emitters 160 which are formed in the emitter holes 169 to have a height lower than that of the gate electrode 140. An electric current is supplied to the cathode electrode 120.
The emission space 210 between the upper plate 201 and the lower plate 202 is maintained in position at a pressure lower than ambient air pressure, and a spacer 192 is formed between the upper plate 201 and the lower plate 202 so as to sustain the vacuum pressure between the upper plate 201 and the lower plate 202, as well as to maintain the emission space 210.
A high voltage is applied to the anode electrode 180 to accelerate electrons emitted from the emitters 160 so that they collide with the phosphor layer 170 at high speed. The phosphor layer 170 is excited by the electrons and the phosphor layer 170 emits visible rays whereby the electrons drop from a high energy level to a low energy level. When the electron emission device 200 is a color electron emission device, phosphor layers, which emit red, green and blue light into the plurality of emission spaces 210 constituting a unit pixel, are formed on the lower surface 180a of the anode electrode 180.
The gate electrode 140 causes electrons to be easily emitted from the emitters 160. The insulating layer 130 insures the spacing of the emitter holes 169, and insulates the emitters 160 from the gate electrodes 140.
As described above, the emitters 160 include carbide derived carbon which emits electrons by forming an electric field.
Aspects of the present invention will now be described in further detail with reference to the following examples. These examples are for illustrative purposes only, and are not intended to limit the scope of the present invention.
First, as a carbon precursor, 100 g of particulate α-SiC with the particles having a mean diameter of 0.7 μm were prepared in a high temperature furnace composed of a graphite reaction chamber, a transformer, and the like. 0.5 l per minute of Cl2 gas were applied to the high temperature furnace held at 1000° C. for 7 hours. Then, 30 g of carbide derived carbon were prepared by extracting Si from the carbon precursor using a thermochemical reaction.
The carbide derived carbon was analyzed using Raman peak analysis, X-ray diffractometry and an electron microscope. The IG/ID ratio ranged from 0.5 through 1. A weak peak of the graphite (002) surface could be seen at 2θ=25°. The electron diffraction pattern was a halo-pattern typical of amorphous carbon. In addition, the specific surface area of the carbide derived carbon synthesized by this method ranged from 1000 through 1100 m2/g according to the method of Brunauer, Emmett and Teller (BET method).
13 g of carbide derived carbon were prepared in the same manner as in Example 1 except that 100 g of particulate ZrC, with the particles having a mean diameter of 3 μm, were used as a starting carbide compound and were heat treated at 600° C. for 5 hours. The carbide derived carbon was analyzed using Raman peak analysis. The IG/ID ratio ranged from 1 through 1.3. A weak single peak of the graphite (002) surface could be seen at 2θ=25° using the X-ray diffractometry. In addition, the specific surface area of the carbide derived carbon synthesized by this method was 1200 m2/g according to the BET method.
25 g of carbide derived carbon were prepared in the same manner as in Example 1 except that 100 g of particulate Al4C3, with the particles having a mean diameter of 3 μm, were used as a starting carbide compound and were heat treated at 700° C. for 5 hours. The carbide derived carbon was analyzed using Raman peak analysis and X-ray diffractometry. The IG/ID ratio ranged from 1 through 3.2. A weak single peak of the graphite (002) surface was seen at 2θ=25°. The carbide derived carbon was analyzed using high resolution TEM. Many graphite fringes could be seen, as illustrated in
Carbide derived carbon was prepared in the same manner as in Example 1 except that 100 g of particulate B4C, with the particles having a mean diameter of 0.8 μm, were used as a starting carbide compound and were heat treated at 1000° C. for 3 hours. The carbide derived carbon was analyzed using Raman peak analysis and X-ray diffractometry. The IG/ID ratio ranged from 0.4 through 1. A weak peak of the graphite (002) surface could be seen at 2θ=25°. The carbide derived carbon was analyzed using high resolution TEM. It could be seen that an amorphous open pore was changed to a graphite fringe, as illustrated in
Carbide derived carbon was prepared in the same manner as in Example 1 except that particles of β-SiC having a fiber shape were used as a starting carbide compound. The carbide derived carbon was analyzed using Raman peak analysis. The IG/ID ratio ranged from 0.5 through 0.8. The diameter of the carbide derived carbon particles was about 200 nm or more. Here, the carbide derived carbon particles were not vertically aligned because of the large diameter. As a result, an electric field emission measurement of the carbide derived carbon could not be obtained.
5.5 g of carbide derived carbon were prepared in the same manner as in Example 1 except that 100 g of particulate MoC, with the particles having a mean diameter of 40 μm, were used as the starting carbide compound. The carbide derived carbon was analyzed using Raman peak analysis. The IG/ID ratio ranged from 0.3 through 0.8. The surface area of the carbide derived carbon was 800 m2/g according to the BET method, that is, less than the range of 1000 to 1310 m2/g as found in Examples 1-4.
21 g of carbide derived carbon were prepared in the same manner as in Example 1 except that B4C, that is, the starting material used in Example 4, was used as the starting carbide compound, and the synthesizing temperature and reaction time were 1300° C. and 12 hours, respectively. The carbide derived carbon was analyzed using Raman peak analysis and X-ray diffractometry. The IG/ID ratio ranged from 6 through 7. A narrow peak of the graphite (002) surface was seen at 2θ=25°. In addition, the specific surface area of the carbide derived carbon was 400 m2/g, markedly less than that of Examples 1 through 4.
Table 1 shows the main properties of the carbide derived carbon of Examples 1 through 4 and Comparative Examples 1 through 3.
1)property of the starting carbide compound and the carbide derived carbon(the diameter of a particle of the starting carbide compound does not change after preparation of the carbide derived carbon)
2)synthesizing condition for the carbide derived carbon
3)type where adsorption occurs regardless of the pressure of the nitrogen. The adsorption is great and adsorption occurs at a specific point
4)type where the capillary phenomenon at the middle opening and the separation curve is higher than the adsorption curve regardless of the relative pressure
5)Electrons are not emitted at a 1/500 duty ratio, but are emitted at a 1/140 duty ratio
If one analyzes the physical properties and electric field emission properties of the carbide derived carbon of Examples 1 through 4 and Comparative Examples 1 through 3, one sees similar Raman IG/ID ratios, XRD patterns and TEM morphologies, but differences in electron emission performance. Although carbide derived carbon is synthesized under similar synthesizing conditions, differing only according to the kinds of starting materials, since the distances between carbon and carbon, the distribution of crystalloids, and the diameters and volumes of openings of the amorphous material resulting from the synthesized carbide derived carbon, different electric field emission properties can be seen. However, carbide derive carbon materials in which electric field emission can occur at a greater than 1/140 duty ratio include carbide derived carbon whose intensity ratios of the graphite G band at 1590 cm−1 to a disordered-induced D band at 1350 cm−1 are in the range of 0.3 through 5 when the carbide derived carbon is analyzed using Raman peak analysis, where the carbon has a specific surface area of 1000 m2/g and more, where the carbide derived carbon exhibits a weak or wide single peak of the graphite (002) surface at 2θ=25° when analyzing the carbide derived carbon using X-ray diffractometry and where the electron diffraction pattern of the carbide derived carbon exhibits the halo-pattern typical of amorphous carbon when the carbide derived carbon is analyzed using electron microscopy.
Compositions containing 1 g each respectively of the carbide derived carbon prepared in Examples 1 through 4 and Comparative Examples 1 through 3 were mixed with 6.5 g of an acryl ate binder, 5.5 g of ethoxylate trimethylolpropane triacrylate, 5.5 g of TEXANOL® (Eastman Chemical Co.), 1 g of a photoinitiator and 1 g of di-octylphthalate as a plasticizer. The mixtures were then dispersed using a 3-roll mill until a well-mixed composition for forming an emitter was obtained (for example, the milling was repeated 8 times). Screen printing was used to apply the obtained compositions to a transparent glass substrate on which an indium-tin oxide (ITO) electrode (10×10 mm) was coated on top of the mixture, and the compositions were exposed to UV (at 500 mJ) and developed. Next, the resulting products were first calcinated under a nitrogen atmosphere at 450° C., and were then activated to form cold cathodes for measuring IV. The electron emission devices were manufactured using the emitters as cold cathodes, polyethylene terephthalate film having a thickness of 100 μm as spacers and copper plates as anode plates.
The emission current densities of the manufactured electron emission devices were measured by applying a pulse voltage at a duty ratio having a pulse width of 20 μs and a frequency of 100 Hz (duty ratio of 1/500). For Example 1, the electron emission device turned on at a field ranging from 5.8 through 7.5 V/μm and demonstrated superior electron emission performance by reaching a current density of 100 μA/cm2 at a field of about 11.2 V/μm, as illustrated in
Similar measurements of performance were obtained with respect to the other carbide derived carbon samples and are summarized in Table 1
As described above, an emitter according to aspects of the present invention has good uniformity and a long lifetime. An emitter can be prepared using a more inexpensive method than that used to manufacture conventional carbon nanotubes.
While aspects of the present invention have been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006137605 | Oct 2006 | RU | national |
| 2006-126401 | Dec 2006 | KR | national |
