HK1140308A - Field emission device with anode coating - Google Patents

Description

Field emission device with anode coating

This patent application claims priority to U.S. provisional application 60/903,259 filed 24/2/2007, which is incorporated by reference herein in its entirety for all purposes.

Technical Field

The present invention relates to a field emission device in which a protective material for use in conjunction with an anode is provided.

Background

The field emission device may generate visible light for display or illumination applications or generate x-rays for analytical instruments. A typical field emission device includes an anode and a cathode, and the cathode generally comprises a material having a large electric field enhancement. The shape of the material may be, for example, conical or needle-like, to achieve the desired field enhancement when a voltage is applied to the cathode.

A commonly used acicular material in the cathode of a field emission device is carbon nanotubes ("CNTs"), which can be single-walled or multi-walled tubes. CNTs can be incorporated into a thick film paste which is then deposited onto a cathode structure to fabricate a field emission device. The field emission devices are typically around 1 x 10^-6The portions of the support operate in a vacuum, which causes electrons released by the emissive material to be transported from the cathode to the anode.

In this partial vacuum, sufficient oxygen or water vapor may be present to degrade the field emission of the electron emitting material. Degradation may result in lower emission current at a given voltage, or in the need to continually increase the applied voltage over time in order to keep the emission current constant. The deterioration is believed to be caused by the presence of ions and radicals formed by electron bombardment of the anode surface, and also by the presence of other free reactive gases. These ions, radicals and other reactive gases appear to cause degradation of the field emission of the cathode by reacting with the electron emitting material. It is believed that similar problems exist when metals, such as the so-called "sharp cathodes", are used as the needle-like emissive material in the cathode.

Carbon materials and polymers have previously been used for a variety of purposes in the manufacture of field emission devices. For example, U.S. patent 06/284,539 describes a diamond-like carbon coating on the anode of a field emission device to assist electron emission by virtue of the roughness of the diamond-like coating. Us patent 06/197,428 describes a carbon-containing black matrix that encapsulates a fluorescent material on the anode of a field emission device.

Polymers have previously been used to construct the anode of field emission devices, and these polymers are typically used for thick film printing of layers of phosphor material; a photoresist for patterning the anode; or for laminating an aluminum thin film on a fluorescent material. In such cases, however, all residues of these polymers are carefully removed from the anode, usually by baking and cleaning steps, before the field emission device is sealed.

Accordingly, there remains a need to select and utilize protective materials in field emission devices that can be used in conjunction with an anode with the goal of reducing degradation of the cathode.

Summary of The Invention

In one embodiment, the present invention provides a field emission device comprising an anode comprising one or more protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer and organic coating.

In another embodiment, the present invention provides a field emission device comprising an anode comprising (a) a layer of phosphor material, and (b) a layer of one or more protective materials disposed on the layer of phosphor material, the protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer and organic coating.

In another embodiment, the present invention provides a field emission device comprising an anode comprising a layer prepared from a mixture of (a) a fluorescent material and (b) one or more protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

In another embodiment, the present invention provides a display device comprising a field emission device as described above.

In another embodiment, the present invention provides a method of manufacturing a field emission device: the method comprises the following steps: (a) providing a substrate having an anode therein, and (b) coating a layer formed of a mixture of (i) a fluorescent material and (ii) one or more protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

In another embodiment, the present invention provides a method of manufacturing a field emission device: the method comprises the following steps: (a) providing a substrate as an anode therein, (b) coating a layer formed of a fluorescent material on the substrate, and (c) coating a layer formed of one or more protective materials on the layer of fluorescent material, the protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

Brief Description of Drawings

Fig. 1 shows a comparative graph of the applied voltage required to keep the emission current of the device tested in example 1 constant.

Fig. 2 shows a comparative graph of the applied voltages required to keep the emission current of the device tested in example 2 constant.

Fig. 3 shows a comparison of the applied voltages required to keep the emission current of the devices tested in examples 2 and 3 constant.

Fig. 4 shows a comparative graph of the applied voltages required to keep the emission current of the device tested in example 4 constant.

Detailed Description

The anode of the field emission device includes an electrical conductor to collect the emitted electrons for bombardment. If the device is a video display, the anode further comprises a layer of phosphor material that emits light when struck by emitted electrons. In the present invention, the anode of a field emission device is improved by providing a protective layer as part of the anode, the protective layer being made of one or more of the protective materials disclosed herein, or by mixing one or more of these protective materials with a phosphor material and incorporating into the phosphor layer.

While not limiting the present invention to any particular theory of operation, it is believed that the presence of the protective material extends the useful life of the electron emitting material, and thus ultimately the field emission device itself, by: when molecules on the surface of the anode are bombarded with electrons, the protective material reacts with radicals and ions generated at the anode. It is believed that the primary source of these ions and radicals includes surface adsorbed water. After the anode or the surface of the anode has reacted with the protective material, these ions and radicals are no longer free to react with the emissive material on the cathode, thus causing no degradation of its field emission. Localized heating of the anode can promote reaction of the protective material with ions and radicals derived from water and oxygen in the device, thereby consuming gases that can react with and cause degradation of the electron emitting material. Thus, a preferred embodiment involves facilitating the entry of reactive species into the protective material to facilitate reaction, such as may be achieved when the outer layer of the anode (i.e., the layer closest to the cathode) is a layer of protective material ("protective layer") located directly at the point of electron impact and having maximized surface area.

In one embodiment of the present invention, the protective layer may be formed by applying a protective material to the surface of the anode. Protective materials from which the protective layer may be made include one or more of the following: comprising amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer and organic coating compound. The preparation of the protective layer on the anode can be accomplished by any of a variety of coating techniques. The protective material to be coated can be suspended in a solvent, for example, and then spin coated, sprayed, printed, electrodeposited, or deposited with the suspension using thin film techniques such as sputter coating, electron beam or thermal evaporation, sublimation, or Chemical Vapor Deposition (CVD). To provide its protective function, it is not necessary to coat the protective layer uniformly, or to completely coat all layers thereunder.

In another embodiment of the invention, wherein for example the field emission device is a display and the anode thus comprises a layer of phosphor material, the above-mentioned protective material may be mixed with the phosphor and then applied to the anode as part of the layer of phosphor material. Alternatively, the phosphor layer may be applied using a conventional method, and then the protective layer may be disposed on the phosphor layer by coating the protective material on the phosphor layer.

As noted above, the protective material may include various forms of carbon or carbonaceous materials, such as amorphous carbon, graphite, diamond-like carbon, fullerenes, or carbon nanotubes. Amorphous carbon is carbon without any crystalline structure and generally has no long-range pattern of atomic positions, although some short-range order may be observed. However, amorphous carbon in many cases contains crystallites of graphite or diamond, which are bonded together by varying the amount of amorphous carbon, making it a technically polycrystalline or nanocrystalline material. Amorphous carbon as used herein also includes soot and carbon black. Graphite, one of the most common allotropes of carbon, is characterized by hexagonal layers of carbon atoms that typically adsorb air and water between the layers. This allows unstable interlayer connections between sheets in the structure due to delocalization of the pi-bonded electrons above and below the plane of the carbon atoms. In graphite, each carbon atom uses only 3 of its 4 external energy level electrons when covalently bonded to three other carbon atoms in the plane, and each carbon atom contributes one electron to an electron-displacing system, which is also part of the chemical bond.

Diamond-like carbon ("DLC") is a form of amorphous carbon that has some of the unique properties of natural diamond. DLC contains a significant amount of sp³Carbon atoms are hybridized and can be found in two crystalline polymorphs. One common type of crystalline polymorph arranges carbon atoms in a cubic lattice, while one rare type of crystalline polymorph (hexagonal carbon) has a hexagonal lattice. By mixing these polymorphs in various ways in a nanoscale structure, DLC coatings can be produced that are simultaneously amorphous, flexible and composed of pure sp³Bonded "diamond". The usual method for preparing DLC is: high energy precursor carbons (e.g., in plasma form, sputter deposition form, and ion beam deposition form) are rapidly cooled or quenched on a relatively cool surface. In these cases, the cubic and hexagonal lattices can be randomly mixed on an atomic layer by atomic layer basis because there is no time for one of the crystalline geometries to grow against the other before the carbon atoms are properly "frozen" in the material. sp³Bonds can form not only in crystals (i.e., in long range ordered solids), but also in amorphous solids with random atomic arrangements. In this case, the bonding is only present between a few individual atoms and is not distributed in a long-range order over a large number of atoms. If it is predominantly sp²Type, the film will be softer, if sp is predominant³Type, the membrane will be stiffer.

Fullerenes are allotropes of carbon in which the molecules are composed entirely of carbon and are in the form of hollow spheres, ellipsoids, or tubes. Fullerenes are similar in structure to graphite, consisting of linked hexagonal ring sheets, but they contain pentagonal (and sometimes heptagonal) rings that prevent the sheets from becoming planar. Carbon nanotubes are cylindrical carbon molecules that can be considered as cylinders formed by rolling up a graphite sheet and are typically terminated at least one end by a hemisphere of a fullerene-type structure. Nanotubes are on the order of nanometers in diameter and up to several centimeters in length. Nanotubes are mainly of two types: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Carbon nanotubes may also have fullerene-like "buds" covalently attached to the outer sidewall of the tube. Fullerenes and carbon nanotubes are also described in U.S. patent application 11/205,452, which is incorporated by reference herein in its entirety as part of this document for all purposes.

The (co) polymers (i.e., polymers or copolymers) useful herein as protective materials can include, for example, one or more of the following: polyvinyl alcohol, ethyl cellulose, polyacrylonitrile, polyvinyl chloride, polyvinyl pyrrolidone, polypropylene, polyolefins (including polyethylene), polyesters (including polyethylene terephthalate), acrylic/acrylate polymers (including polymethyl methacrylate), polyamides, polycarbonates, polystyrene, parylene, polysaccharides. Suitable (co) polymers also include other polymers that are solid at room temperature, have primarily a carbon backbone, and react with various degradation species present in the field emission device (e.g., species derived from water). When the (co) polymer is applied as a protective material to the anode, the application can be spin coating, spray coating, various printing techniques, and slot-die coating. Various (co) polymers may also be deposited using thin film techniques, including sublimation and Chemical Vapor Deposition (CVD).

The organic coating material used herein as a protective material may include, for example, a material that is solid at room temperature and has a vapor pressure low enough that it does not completely evaporate in a vacuum present in the field emission device. Suitable organic coating materials may, for example, have a temperature of less than about 10 ℃ at 25 ℃^-6The vapor pressure of torr. Examples of organic coating materials suitable for use as the material protected herein include polycyclic aromatic hydrocarbons (e.g., perylenes or pyrenes), polycyclic heteroaromatic compounds, porphyrins, phthalocyanines, and carbohydrates. Such materials may be suspended in a solvent and then spin-coated or spray-coated on the anode. Some of these materials may also be deposited using thin film techniquesIncluding sublimation and Chemical Vapor Deposition (CVD).

Protective materials and phosphors suitable for use in the present invention may be made by methods known in the art or may be obtained commercially from suppliers such as Alfa Aesar (Ward Hill, Massachusetts), city chemical (West Haven, Connecticut), Fisher Scientific (Fairlawn, New Jersey), Sigma-Aldrich (st. louis, Missouri), or stanford materials (alio Viejo, California).

In the present invention, the protective material can be utilized as follows: or by providing a protective layer on the surface of the anode, including over any other layer previously applied to the anode; or by mixing a protective material with a phosphor, and applying the coating formulation as a mixture of such components to the anode to become the surface of the anode. In addition to (or instead of) the phosphor, a coating mixture may be formed from a protective material and a material to be applied to the anode. After the protective material is mixed with the fluorescent material and/or other components to form a mixture and the mixture is then applied as a coating formulation to the surface of the anode, the protective material may comprise from about 5 to about 50 wt%, or from about 10 to about 40 wt%, or from about 15 to about 20 wt% of the mixture, relative to the weight of the entire mixture.

The protective layer, or the layer in which the protective material is mixed as a component, will preferably be located on the surface of the anode and directly on the path of the electrons emitted from the cathode, while the surface of such a layer will preferably be smooth, rather than rough or uneven. It is believed that the protective material extends the useful life of the cathode and thus the device by preferentially reacting with the degradation species and thereby inhibiting degradation of the electron emissive material.

Generally, the effect of the protective material in reducing the rate of emitter degradation in a field emission device can be enhanced by, for example: providing a greater component of protective material to mix with the phosphor to form a mixed phosphor layer, operating the device at a lower vacuum, operating the device with a lower level of emission, and employing a greater spacing between the cathode and anode in the construction of the vacuum chamber of the device.

In a field emission device, an electron emissive material is disposed on a cathode, which, when excited, bombards an anode with electrons. The electron emitting material may be an acicular substance such as carbon, a semiconductor, a metal, or a mixture thereof. As used herein, "acicular" refers to particles having an aspect ratio of 10 or greater. The electron emitting material is typically attached to a substrate in the cathode assembly using glass frit, metal powder or metal paint or mixtures thereof.

Acicular carbon used as an electron emitting material may be of various types, but carbon nanotubes are the preferred acicular carbon, with single-walled carbon nanotubes being particularly preferred. Carbon fibers obtained by catalytic decomposition of carbon-containing gases on small metal particles may also be used as acicular carbon, other examples of which are polyacrylonitrile-based (PAN-based) carbon fibers and pitch-based carbon fibers.

Various methods may be used to bond the electron emissive material to the substrate. The bonding method must be able to withstand the conditions of the fabrication equipment in which the field emission cathode is placed, as well as the conditions of its use and maintain its integrity, e.g., typical vacuum conditions and temperature conditions of up to about 450 ℃. A preferred method is to screen print a paste of the electron emissive material and a glass frit, metal powder or metal paint or mixture thereof onto a substrate in the desired pattern and then bake the dried patterned paste. For a wider variety of applications, such as those requiring finer resolution, the preferred method involves screen printing a paste further comprising a photoinitiator and a photocurable monomer, photopatterning the dried paste, and then baking the patterned paste.

The substrate may be any material as long as the paste composition can be adhered thereto. If the paste is non-conductive and a non-conductive substrate is used, a thin film of electrical conductor is required, which serves as a cathode electrode and provides a means of applying a voltage to the electron emitting material. Silicon, glass, metal, or refractory materials (e.g., alumina) may be used as the substrate. For display applications, the preferred substrate is glass, and soda lime glass is particularly preferred. To achieve the best conductivity on the glass, the silver paste can be pre-baked onto the glass in air or nitrogen, preferably in air, at 500-. The emitter paste can then be printed on the conductive layer so formed.

Pastes for screen printing typically comprise an electron emitting material, an organic medium, a solvent, a surfactant, and a low softening point frit, metal powder or metal paint or mixtures thereof. The function of the medium and solvent is to suspend and disperse the particulate components, i.e., the solids, in the paste with the appropriate rheology for typical patterning processes, such as screen printing. There are numerous organic media known for this purpose, including cellulosic resins, such as ethyl cellulose and alkyd resins of various molecular weights. Examples of useful solvents are butyl carbitol ester, butyl carbitol acetate, dibutyl carbitol, dibutyl phthalate and terpineol. These and other solvents are formulated to achieve the desired viscosity and volatility requirements.

A frit is also used that softens sufficiently at the firing temperature to adhere to the substrate and to the electron emissive material. Lead or bismuth frits may be used, as well as other glasses with low softening points, such as calcium and zinc borosilicates. The paste may also contain a metal, such as silver or gold, if a screen-printable composition with higher conductivity is desired. The paste typically comprises from about 40 wt% to about 80 wt% solids, based on the total weight of the paste. These solids include an electron emitting material and a glass frit and/or a metal component. Variations in the composition can be used to adjust the viscosity and the final thickness of the printed material.

Emitter pastes are typically prepared by three-roll milling a mixture of: electron emitting materials, organic media, surfactants, solvents, and low softening point frits, metal powders or metal coatings or mixtures thereof. The paste mixture may be screen printed using, for example, a 165-400 mesh stainless steel screen. The paste may be deposited in the form of a continuous film or desired pattern. If the substrate is glass, the paste is baked at a temperature of about 350 deg.C to about 550 deg.C, preferably about 450 deg.C to about 525 deg.C, under nitrogen for about 10 minutes. Higher baking temperatures that the substrate can withstand can be used, provided that the baking environment does not contain oxygen. However, the organic components in the paste are effectively volatilized at 350-450 ℃ leaving a composite layer of the electron-emitting material and the glass and/or metal conductor. During baking under nitrogen, the electron emitting material appeared to undergo no observable oxidation or other chemical or physical changes.

If the screen-printed paste is to be photopatterned, the paste may also contain a photoinitiator, a ductile binder, and a photocurable monomer containing, for example, at least one addition polymerizable ethylenically unsaturated compound having at least one polymerizable vinyl group. Typically, a paste prepared from electron emitting materials (e.g., carbon nanotubes, silver, and glass frit) will contain about 0.01 to 6.0 weight percent nanotubes, about 40 to 75 weight percent silver (in the form of fine silver particles), and about 3 to 15 weight percent glass frit, based on the total weight of the paste.

The anode of the device is an electrode coated with a conductive layer. When a field emission device is used in a display device, where the cathode has an array of pixels of thick film paste deposited as described above, the anode in the display device may comprise a fluorescent material that converts incident electrons to light. The substrate of the anode may also be selected to be a transparent substrate so that the resulting light can be transmitted. The cathode assembly and the anode constitute a sealed unit, wherein the cathode assembly and the anode are separated by a separator and an evacuated space is present between the anode and the cathode. The evacuated space needs to be partially evacuated so that electrons emitted from the cathode can be transported to the anode with only a small number of collisions with gas molecules. Typically, the evacuated space is pumped to less than 10^-5The pressure of the tray.

Such field emission devices are useful in a variety of electronic applications such as vacuum electronics, flat panel computer and television displays, backlights for liquid crystal displays, emission gate amplifiers, klystrons, and lighting devices. For example, flat panel displays have been proposed having a cathode employing a field emission electron source, i.e., a field emission material or field emitter, and a phosphor material capable of emitting light upon bombardment by electrons emitted by the field emitter. This type of display screen has both the visual display advantages of conventional cathode ray tubes and the depth, weight and power consumption advantages of other flat panel displays. The flat panel display may be planar or curved. U.S. Pat. Nos. 4,857,799 and 5,015,912 disclose matrix-addressed flat panel displays using microtip cathodes constructed of tungsten, molybdenum or silicon. WO 94-15352, WO 94-15350 and WO 94-28571 disclose flat panel displays in which the cathode has a relatively flat emission surface. These devices are also described in U.S. patent 2002/0074932, which is incorporated by reference herein in its entirety as part of the present disclosure for all purposes.

Advantageous properties and effects of the present invention can be seen in a series of examples (examples 1 to 4) described below. The embodiments on which the examples are based are representative only, and the selection of those embodiments to illustrate the invention does not indicate that materials, arrangements, components, ingredients or configurations not described in the examples are not suitable for practicing the invention, nor does it indicate that subject matter not described in the examples is excluded from the scope of the appended claims and equivalents thereof.

Examples

The samples of the field emitters were tested in a vacuum chamber having a pressure range of about 1X 10^-6To about 1X 10^-8And (4) supporting. The cathode therein is made using a thick film paste containing carbon nanotubes. The thick film paste was patterned on the cathode using the typical pattern of interest. The patterned cathode was then baked at about 420 ℃ for about 30 minutes in a nitrogen atmosphere. After the baking, the mixture is baked,the patterned electron emission film is broken by laminating an adhesive tape on the panel and then removing the adhesive tape to expose the electron emission material. A separator having a thickness d of 640 μm was then placed on the cathode surface, and the anode of interest was then placed on the separator to form a diode field emission device.

Each sample field emission device is then placed in a vacuum system where electrical contacts are made to the anode and cathode of each device. Applying a high voltage pulsed square wave (V) to the cathode of the sample_C) To form an emission current. To maintain a constant current, a DC bias (V) is applied to the anode_A). Degradation of the emission current directly corresponds to the total applied field [ (V)_A-V_C)/d]The rate of increase of (c). As the emitter degrades, a larger electric field is required to compensate for its degradation, so the rate of increase of the total applied field corresponds directly to the degradation rate. A lower rate of increase of the applied electric field indicates a lower degradation rate and thus is advantageous for the lifetime or service life of the field emission device.

Example 1

Fig. 1 shows the electric field that needs to be applied when two different samples of field emission devices operating simultaneously in the same vacuum chamber maintain the emission current constant. The curve consisting of solid black squares corresponds to the sample with the phosphor layer that has not been baked, while the curve consisting of hollow circles corresponds to the sample with the phosphor layer that has been baked. The main differences between the phosphor layers that were baked and not baked are: the green phosphor layer contains phosphor still mixed with binder material (typically a polymer, in this case ethyl cellulose) because the device is not subjected to a typical firing process, during which the binder is volatilized. In the sample having the baked phosphor layer, the phosphor layer does not contain residual binder due to the volatilization described above.

Initially, the degradation rate of the sample with the unbaked phosphor layer (i.e., the rate of increase of the applied voltage required to keep the present emission current constant) was lower than that of the sample with the baked phosphor layer. This difference in degradation rate is due to the residual binder contained in the unbaked phosphor layer. However, during use, the binder is volatilized and the rate of degradation begins to increase, consistent with the rate of degradation of a device that has not contained binder in a layer of phosphor material that has been baked since the beginning of use. In this embodiment, the addition of the protective material for mixing with the phosphor powder in the phosphor layer can be achieved by a technique of leaving the residual binder material in the phosphor layer by omitting the baking step of the phosphor layer.

Example 2

Carbon as a protective material was sputter deposited onto an anode made of ITO (indium tin oxide, transparent conductive material). The carbon coating was 22nm thick and amorphous in nature. The carbon coated anode was mounted in a field emission device and the degradation rate of the emitter in the device was compared to that of a device in which the anode was made of ITO and without any coating. In the anode coated device, the degradation rate was significantly lower than in the anode uncoated device, as shown in fig. 2. However, after about 75 hours, the degradation rate started to increase due to the consumption of the carbon layer. This can be observed if the anode is placed under an optical microscope for inspection. Between 50-70 hours, the lower curve of the anode made of ITO only slightly decreased because the dc bias applied to the anode had a voltage limit.

Example 3

The protective carbon on the anode need not be amorphous or sputter deposited. In this example, an ITO anode was coated by spin coating using a commercially available graphite coating (Neolube No.2, Huron Industries inc., Port Huron, MI 48061) comprising a mixture of graphitic carbon and amorphous carbon in isopropanol. Figure 3 shows that the degradation rate of the emitter in a field emission device fitted with such an anode is similar to that of the device with a carbon coated anode in example 2. While running an ITO anode uncoated device, it exhibited a much greater degradation rate, which is comparable to the performance of the anode uncoated device in example 2.

Example 4

In a field emission display device, the anode is typically an ITO glass substrate coated with a fluorescent material and then with an aluminum layer. The function of the aluminum layer is to maximize the amount of light emitted from the front of the anode and to increase the conductivity of the anode. It was found that the conventional device employing this structure performed the worst in terms of degradation rate.

Fig. 4 shows the results for two device samples run simultaneously, the curve consisting of a solid square corresponding to the sample with an ITO anode coated with a fluorescent material that is then baked and with 100nm thick aluminum deposited by electron beam deposition. The anode in the device represented by the curve formed by the open circles corresponds to the former except that a 100nm thick carbon layer was sputter coated on top of the aluminum layer. It can be seen that this final carbon coating greatly reduces the rate of degradation of the emitter in the carbon coated anode device. The device with the anode uncoated with carbon degrades rapidly until the voltage limit is reached, whereas the device with the anode coated with carbon degrades at a much lower rate.

Features of certain devices of the invention are described herein in the context of one or more specific embodiments that combine various such features. The scope of the invention, however, is not limited to the description of only a few of the features in any particular embodiment, and the invention also includes (1) subcombinations of less than all of the features of any of the described embodiments, where such subcombinations are characterized by the absence of features omitted from forming such subcombinations; (2) each feature independently included in any combination of the embodiments; and (3) combinations of other features formed by merely categorizing selected features of two or more of the described embodiments, optionally together with other features disclosed elsewhere herein.

In this specification, unless explicitly stated otherwise or indicated to the contrary by the context of usage, where an embodiment of the subject matter hereof is stated or described as comprising, including, containing, having, being composed of or being constituted by or of certain features or elements, one or more features or elements in addition to those explicitly stated or described may also be present in the embodiment. However, an alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, wherein embodiment features or elements that would materially alter the principle of operation or the distinguishing characteristics of the embodiment are not present herein. Another alternative embodiment of the inventive subject matter may be discussed or described as consisting essentially of certain features or elements, in which embodiment, or in insubstantial variations thereof, only the features or elements specifically discussed or described are present.

Claims (18)

1. A field emission device comprising an anode comprising (a) a layer of phosphor material, and (b) a layer of one or more protective materials disposed on the layer of phosphor material, the protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

2. The apparatus of claim 1, wherein the layer formed of the protective material forms a surface of the anode.

3. The device of claim 1, comprising a cathode comprising carbon nanotubes.

4. The device of claim 1, wherein the protective material comprises carbon.

5. The device of claim 1, wherein the protective material comprises a (co) polymer.

6. Display device comprising a field emission device according to claim 1.

7. A field emission device comprising an anode comprising a layer prepared from a mixture of (a) a fluorescent material and (b) one or more protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

8. The apparatus of claim 7, wherein the layer formed from the mixture forms a surface of the anode.

9. The device of claim 7, comprising a cathode comprising carbon nanotubes.

10. The apparatus of claim 7, wherein the protective material comprises carbon.

11. The device of claim 7, wherein the protective material comprises a (co) polymer.

12. Display device comprising a field emission device according to claim 7.

13. A method of manufacturing a field emission device, the method comprising: (a) providing a substrate having an anode therein, and (b) coating a layer formed of a mixture of (i) a fluorescent material and (ii) one or more protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

14. The method of claim 13, wherein the protective material comprises carbon.

15. The method of claim 13, wherein the protective material comprises a (co) polymer.

16. A method of manufacturing a field emission device, the method comprising: (a) providing a substrate as an anode therein, (b) coating a layer formed of a fluorescent material on the substrate, and (c) coating a layer formed of one or more protective materials on the layer of fluorescent material, the protective materials consisting of: amorphous carbon, graphite, diamond-like carbon, fullerene, carbon nanotube, (co) polymer, and organic coating compound.

17. The method of claim 16, wherein the protective material comprises carbon.

18. The method of claim 16, wherein the protective material comprises a (co) polymer.