MXPA98009883A - Field emission device that has nanoconstrui emitters - Google Patents

Abstract

The present invention relates to an electric field emission device comprising an electrode including a layer comprising a dense array of solid, separate nanostructures placed on at least a portion of one or more surfaces of a substrate, the microstructures they have a density of area number greater than 107 / cm2, the microstructures are conformally coated individually with one or more layers of an electron-emitting material, the coated electron-emitting material is placed at least a portion of the microstructures and has a morphology of surface which is nanoscopically rough. A method for preparing the electrode used in the invention is described

Description

FIELD EMISSION DEVICE THAT TIEt FIELD OF INVENTION This invention relates to a field emission device that includes an electrode comprising a layer having a dense array of microstructures as electron emitters. The field emission devices can be emission flat panel displays. of electron field of two or more electrodes and flat panel screens of gaseous plasma, vacuum tubes for microwave devices or other electron beam or ionization source devices. _N? £££ Q £ X_m E L? INVENCIN Flat panel displays are known in the art for electronically presented graphics, symbols, alphanumeric signs and video images. They replace conventional cathode ray tubes, which have a large depth dimension, with a flat screen that includes both active light generation screens such as gas discharge (plasma), light emitting diode and cathode emission luminescence. field, and screens REP: 28947 passive light modulation such as liquid crystal devices. Flat panel displays are typically matrix addressed and constitute matrix addressing electrodes. The intersection of each row line and each column line in the matrix defines a pixel, the smallest element addressable on the electronic screen. The essence of electronic displays is the ability to turn on and off individual image elements (pixels). The high information content of a typical screen will have a quarter of a million pixels in an orthogonal array of 33 cm diagonal, each under individual control by the electronic system. The pixel resolution is usually just at or below the resolving power of the eye. Therefore, a good quality image can be created from a pattern of activated pixels. A means for generating arrays of cathode field emission structures is based on well-established semiconductor microfabrication techniques (U.S. Patent Nos. 3,812,559, 3,755,704, 3,665,241, CA Spindt, I. Brodie, L. Humphrey, and ER Westerberg, J. Appl. Phys 47, 5248 (1976) and 'CA Spindt, CE Holland and RD Stowell, Appl. Surf, Sci. 16, 268 (1983).) These techniques produce highly regular arrays of field emission tips. The lithography, generally used in these techniques, involves numerous processing steps, many of them wet, the number of tips per unit area, the size of the tips and their separations are determined by the available photoprotective layers and Exposure radiation The tips produced by the methods typically have the shape of with base diameters in the order of 0.5 to 1 μm, heights anywhere from 0.5 to 2 μm, tip radius of tenth of a nanometer and steps in the order of 0.5 to 1 points per micrometer. This size limits the number of possible points per pixel for high resolution screens, where large quantities (400-1000 emitters per pixel) are desirable for uniform emitter and provide adequate gray levels and to reduce the current density per tip, for stability and long duration. Maintaining a two-dimensional alignment of periodic spike arrays over large areas such as large-size television screens can also be a problem for gate-based field emission constructions, based on conventional means resulting in poor yields and High costs. U.S. Patent No. 4,338,164 describes a method for preparing flat surfaces having microstructured bumps thereon comprising a complicated series of steps involving irradiation of a soluble matrix (e.g. micas) with high energy ions, from a heavy ion accelerator, to provide traces similar to columns in the matrix that are subsequently eliminated by mordant to be later filled with an appropriate conductive, electron-emitting material. Subsequently, the original soluble matrix dissolves, followed by additional steps of metal deposition that provide a conductive substrate for the electron-emitting material. It is stated that the method produces up to 106 emitters per cm2, the emitters have diameters of approximately 1-2 μm. U.S. Patent No. 5,138,220 discloses a field-emitting cathode construction without gates comprising a metal-semiconductor eutectic composition such as silicon-tantalum-disilicide or a eutectic layer of germanium-titanium-digermanicide. The mordant treatment of most of the component, for example silicon, reveals rod-like protrusions or, for example, the tantalum disilicide having diameters of approximately 0.5 μm and an area density of 106 rods per cm 2. The tips of the rods are additionally coated with both conductive layers (for example gold) and semiconductors (for example amorphous silicon) in order to produce a field emitting cathode. US Patent No. 5,226,530 discloses a gate electron field emitter prepared by a complicated series of deposition and mordant treatment steps on a substrate, preferably crystalline, polycrystalline or amorphous silicon. In one example, 14 stages of deposition and mordant treatment are required to prepare an emitter material. It is stated that needle-like emitters are about 1 μm high, but the patent makes no mention of the diameter of the needle or its area density. Other approaches include Heer, et al., "A Carbon Nanotube Field-Emission Electron Source," Science 270. November 17, 1995, p. 1179; Kir patrick et al., "Demonstration of Vacuum Field Emission from a Self-Assembling Biomolecular Microstructure Composite", Appl. Phys Lett. 60 (13), March 30, 1992, pp. 1556-1558; and Technology News item in Solid State Technology. November 1995, p. 42, which are related to vertical thin film edge cylindrical field emitters. Composite microstructured articles have been described. See, for example, U.S. Patent Nos. 4,812,352, 5,039,561, 5,176,786, 5,336,558, 5,338,430 and 5,238,729.

BRIEF DESCRIPTION OF THE INVENTION Briefly, the present invention provides an electron field emission screen that includes an electrode comprising as a cathode a layer comprising a dense array of discrete solid microstructures placed on at least a portion of one or more surfaces of a substrate, the microstructures have a density of area number greater than 107 / cm2, preferably greater than 108 / cm2, and more preferably greater than 109 / cm2, at least a portion of the microstructures are overcoated conformally with one or more layers of electron-emitting material, the electron-emitting material overrides is placed over at least a portion of each of the microstructures and has a surface morphology that is nanoscopically rugged with multiple potential field emission sites per microstructure. Preferably, the microstructures have an average cross-sectional dimension less than 0.3 microns, preferably less than 0.1 microns, and average lengths less than 10 microns, preferably less than 3 microns. The screen includes an electric field producing structure comprising first and second conductive electrodes spaced in isolation and substantially parallel to each other, the first conductive electrode comprises a layer having a dense array of discrete solid microstructures placed over at least a portion of one or more surfaces of a substrate, the microstructures have a density of area number greater than 10 7 / cm 2, at least a portion of the microstructures is overcoated in a manner conforming to one or more nanolayers of an electron-emitting material, the Overcoated electron-emitting material is placed over at least a portion of each of the microstructures and has a surface morphology that is nanoscopically rugged to provide multiple sites of potential field emission by microstructure. In still another aspect, the present invention provides a method for preparing a field emission electrode, comprising the steps of: providing a substrate having on at least one surface thereof a microlayer comprising a dense array of solid microstructures and discrete, the microstructures have a density of area number greater than 107 / cm2, preferably greater than 108 / cm2, and more preferably greater than 109 / cm2, and individually over-coating at least a portion of the microstructures with one or more electronic emissive materials in an amount in the range of 10 to 1000 nm of planar equivalent thickness, preferably 30 to 500 nm, and more preferably 50 to 300 nm of planar equivalent thickness, by a process which produces a Conformal overcoat with a surface morphology that is nanoscopically rough. The process provides a plurality of potential electron emission sites on each overcoated microstructure and serves to decrease the effective working function of the electron emissive surface coating. The discrete microstructures comprising the dense array can be uniformly oriented, or preferably randomly oriented. The microstructures can be rigid and straight, curled, curved, bent or curvilinear. The spatial distribution can be a random or regular arrangement. The distribution of the microstructures does not need to be uniform (in other words, the distribution of the microstructures can be continuous or discontinuous). For example, the distribution of microstructures can form a pattern. The pattern can be repeated or not repeated and can be formed by deposition of microstructure precursors through a mask, or by physical removal of microstructures by mechanical means or by light or laser suppression, or by encapsulation followed by delamination, or by replication of a matrix with a pattern. Preferably, the microstructures have monocrystalline or polycrystalline regions.

Suitable microstructure materials include those that are stable in air and that can be formed in microstructures and have low rates of outward bending under vacuum. Preferably, the microstructures comprise at least one of an inorganic material and an organic material. Preferably, the microstructures comprise an organic material. Preferably, the molecules of the organic material are planar and comprise chains or rings, preferably rings on which an electron density p (density of electron pi) is delocalized widely. Most preferred organic materials can be broadly classified as polynuclear aromatic hydrocarbons and heterocyclic aromatics. Particularly desirable are organic pigments, such as perylene dicarboximide compounds. A preferred method for manufacturing an electrode for a field emission display device of the present invention comprises the step of providing an addressable matrix substrate having a microstructured layer, wherein the microstructured layer comprises a dense array of overcoated microstructures, conformationally oriented uniformly or randomly, separately, solidly and preferably elongated. The discrete microstructures are each overcoated with at least one conformal coating of a material suitable for emission or field ionization such as the shaping coating of at least partial or individual overlays, each of a plurality of microstructures to provide the electrode useful in the present invention. More than one shaping coating may be present in each microstructure. Multiple conformal coatings which are electron emitting materials may have the same or different compositions. The multiple conformal coatings may comprise one or more layers which are not electron emitters and which are not surface layers. The multiple conformal coatings may comprise materials that are selected to have gas pumping properties by removal of waste gas. On each microstructure, a single conformal coating can be continuous or discontinuous. Preferably, a single conformal coating is continuous. If multiple shaping coating is applied, each individual shaping coating can be continuous or discontinuous. Preferably, the multiple shaping cores are collectively continuous. The surface of the shaping coating is nanoscopically rough. The coating comprises microcrystallites that substantially cover the surface of the microstructures. This large number of microcrystallites contribute to multiple emission sites due to their very large radius of curvature, large amounts and low work functions generally associated with the limits of crystalline grain, stages, facets, folds, protrusions and dissociations. The shaping coating may comprise crystalline and non-crystalline material. The surface morphology of the non-crystalline portions can also be nanoscopically rough. The roughness characteristics can be in the range from 0.3 nm to 300 nm in any single dimension, preferably from 3 to 100 nm. Preferred electron-emitting materials exhibit low electronic work functions, high thermal conductivity, high melting temperatures, negligible outward flexing and tend to form nanoscopically rough coatings. In this application: "nanostructured layer" or "nanocoating" means a nanometer-sized layer of average thickness which can be nanoscopically rough; "Nanoscopically rugged coating" means surface characteristics or film morphology (deviations from the flat part, including projections and depressions) that comprise heterogeneity of composition with a spatial scale in the order of nanometers in at least one dimension; "microstructures" or "microstructured element" refers to individual units that are straight, curved or curvilinear and include units such as, for example, filaments, rods, cones, pyramids, spheres, cylinders, rods and the like; "dense array" means microstructures in a closely spaced random or regular array, wherein the average separation is typically in the range of from about 1 nanometer to about 5000 nanometers, and preferably in the range of from about 10 to about 1000 nanometers, and where preferably the average separation is approximately equal to the average diameter of the microstructures; "discrete microstructures" are independent and are not fused together, although they may be in contact with each other in one or more areas along their lengths; "microstructures placed on a substrate" means: (a) fully exposed microstructures but adhered to a substrate and a material other than the substrate, (b) partially exposed and partially encapsulated micro-structures within a substrate and of a different material than the substrate, and / or (c) microstructures which are extensions of the substrate and the same material as that of the substrate; "microstructured layer" refers to a layer formed by all the microstructures taken together. An example of a microstructured surface region with spatial heterogeneity in two dimensions, in one consisting of elongated metallic coated elements (microstructured elements) uniformly or randomly oriented on the surface of the substrate, with or without touching each other, with a dimensional proportion and quantities per unit area to obtain the desired properties. A spatially heterogeneous two-dimensional microstructured surface region can be one that is translated through the region along any of two orthogonal directions, where two different materials will be observed, for example, the microstructured and hollow elements; "Composite microstructures" refers to conformationally coated microstructures; "conformationally coated" means a material that is deposited on at least a portion of at least one microstructure element and that conforms to the shape of at least a portion of the microstructure element; "uniformly oriented" means that at least 80 percent of the microstructures have angles between an imaginary line perpendicular to the surface of the substrate and the principal axis that varies no more than about + 15 ° from the average value of the angles mentioned above; "randomly oriented" means not uniformly oriented; "continuous" means that it covers a surface without interruption; "discontinuous" means covering a surface that is periodic or aperiodic (such coverage, for example, may involve individual microstructures, which have coated and uncoated regions of conformation, or more than one microstructure, wherein one or more microstructures are coated and one or more adjacent microstructures are not coated); "solid" means not hollow; "multiple" means at least two, preferably two or three; "flat equivalent thickness" means the thickness of the coating if it were coated on a plane instead of being distributed over the microstructures; "electronically emitting" means capable of emitting electrons by field or thermal emission; "uniform" with respect to the cross section means that the main dimension of the cross section of the individual microstructures varies no more than about 25 percent from the average value of the main dimensions, and that the smaller dimension of the cross section of the individual microstructures varies no more than about 25 percent of the average value of the smaller dimension; "uniform" with respect to length means that the individual microstructures vary no more than about 10 percent of the average value of their lengths; "hemostasically uniform" means randomly formed by a probability-dependent process but, due to the large amount of microstructures per unit area, a uniform property of the microstructured layer will be provided; "area density" means the number of microstructures per unit area; and "work function" of a uniform surface of an electronic conductor means the potential difference between the Fermi level (the electrochemical potential of the electrons within the solid) at the vacuum level near the surface defined as the potential at the point in which the image strength of an emitted electron becomes negligible; In this invention, work functions greater than zero and up to 6 eV may be desirable. Advantageously, the present invention provides a field emission screen that includes an electrode comprising very large amounts per unit area of extremely small microstructures, preferably elongated composite microstructures that can be applied to a wide variety of large area substrates by a process Simple deposition and that can form a pattern by efficient desiccated processing methods. The microstructured organic films of the present invention can be produced by a dry process and can be applied to any substrate of arbitrary size, capable of being heated in vacuum at about 260 ° C. The number of emitters per unit area can be as high as 30-40 per square micrometer, or more than 1000 microstructured per pixel of 6 μm x 6 μm. In the present invention, these high density densities of closely spaced, randomly arranged, nanoscopically rugged ultra-small particles provide spatially averaged emission levels which are consistently uniform from pixel to pixel at lower voltages compared to those of the prior art. Due to the large number of emitting sites per unit area, lower current densities per emission site are allowed. The microstructured electrodes of the present invention can be formed in patterns easily by laser suppression or by light suppression at arbitrary wavelengths. For example, with spot sizes of 17 micrometers, a pattern can easily be carried out using a YAG laser with 1.2 watts in the sample plane and 3200 cm / sec as the sweep speed. A brief article related to flat panel screen technology is presented in Encyclopedia of Applied Physics, Volume 5, VCH Publishers, Inc., New York, 1993, pp. 101-126. Electron field emission devices are known in the art. They are described, for example, in US Patent Nos. 3,812,559, 5,404,070, 5,507,676 and 5,508,584.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a scanning electron micrograph taken at 10, OOOX and 45 degrees of viewing angle of a microstructured layer of an electrode of the present invention showing a typical area, spacing and size density of the composite microstructures. Figures 2 (a-c) shows SEM micrographs at 150, OOOX of composite microstructures in electrodes of the invention, illustrating the variation of the nanoscopic roughness of the shaping coating and the size of the microstructures with the amount of metal coated on the microstructures.

Figure 3 (a) is a diagram showing the incorporation of microstructured layers in the electrodes in a vacuum directed matrix, gas plasma or a field emission device without gate, for example, as in Example 5-15. Figure 3 (b) is a diagram showing the incorporation of microstructured layers in electrodes in a directed array of a field display device with gate. Figure 4 shows a graph of ionization current versus voltage between separate electrodes, comprising coated microstructures on metallized silicon substrates, as in Examples 1-3. Figure 5 (a) shows a plot of the field emission current versus voltage between an electrode comprising a mis-structured layer and a phosphor screen, as in example 5. Figure 5 (b) shows a graph of Fowler- Nordheim of the data of Figure 5 (a). Figure 6 (a) shows the field emission current density versus the cell voltage of a microstructured layer to a phosphor screen for three electrodes comprising the microstructured layers, as in Example 6-8.

Figure 6 (b) is a Fowler-Nordheim plot of the data in Figure B in Figure 6 (a). Figure 7 shows a Fowler-Nordheim plot of the field emission stream from an electrode comprising a microstructured layer coated with cobalt, as in example 11. Figure 8 shows a SEM to 10, OOOX of the curvilinear • icrostructures with a diamond-like carbon coating used in example 12.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES It has been found that a significant low cold cathode vacuum tunnel field emission can be obtained from electrical fields applied from microstructured layers which comprise, in a preferred embodiment, organic pigment filaments coated with metal (eg. (red perylene)). The microstructured films comprise a dense two dimensional distribution of discrete, crystalline elongated filaments having substantially uniform cross sections, but not identical, and high proportions of length to width and, in additional contrast to the prior art, are not identical and may be arranged and randomly oriented. The filaments are conformationally coated with materials suitable for field emission or ionization, and which allow filaments with a nanoscopically fine surface structure to be able to act as multiple emission sites. It has been found that although the lengths, shapes, orientations, cross-sectional dimensions and conformal coating roughness of the individual emitters are not identical and can be arranged and randomly oriented according to a process of stochastic growth on a substrate, it can be obtain a uniform emission as that observed over dimensions of 'at least about 1-2 cm2 on a phosphor screen. It has also been observed that significant current densities can be obtained, which obey a Fowler-Nordheim ratio, with emission thresholds of 5 to 10 volts per μm and field improvement factors per unit of space distance greater than 106 / cm. It is considered that the extremely large numbers per unit area of non-identical microstructured, but extremely small, as well as the nanometer-scale roughness of the conformation field emission coating, are responsible for the low voltage threshold, and the large field improvements as well as the substantial uniformity of the spatially averaged emission. The microstructured layer can be deposited on a substrate of any desired size by a completely dry process, and a pattern can be formed conveniently and quickly using, for example, a high resolution (dry) laser suppression medium. The orientation of the microstructures is generally uniform in relation to the surface of the substrate. The microstructures are usually oriented normal to the surface of the original substrate, the normal direction of the substrate is defined as that direction of the line perpendicular to an imaginary plane that is tangent to the local substrate surface at the contact point of the base of the microstructure with the surface of the substrate. The normal surface direction is observed to follow the contours of the substrate surface. The major axes of the microstructures can be parallel or non-parallel with each other. Alternatively, the microstructures may be of non-uniform shape, size and orientation. For example, the upper parts of the microstructures may be bent, curled or curved, or the microstructures may be bent, curled or curved over their entire length. Preferably, the microstructures are of uniform length and shape and have uniform dimensions in terms of their cross section along their major axes. The preferred length of each microstructure is less than about 50 microns. More preferably, the length of each microstructure is in the range of from about 0.1 to 5 microns, more preferably from 0.1 to 3 microns. Within any microstructured layer, it is preferable that the microstructures be of uniform length. Preferably, the average cross-sectional dimension of each microstructured is less than about 1 micrometer, more preferably 0.01 to 0.5 micrometer. More preferably, the average cross-sectional dimension of each microstructured is in the range of 0.03 to 0.3 microns. Preferably, the microstructures have a density of area number in the range from about 107 to about 1011 microstructures per square centimeter. More preferably, the microstructures have an area density in the range from about 108 to about 10 10 microstructures per square centimeter. The microstructures may have various orientations and straight or curved shapes (for example filaments, rods, cones, pyramids, spheres, cylinders, rods and the like which may be twisted, curved or straight), and any layer may comprise a combination of orientations. and forms. The microstructures have a dimensional ratio (ie, a ratio of length to diameter) preferably in the range from about 1: 1 to about 100: 1). In US Patent Nos. 4,812,352 and No. 5,039,561 describes a preferred method for making a microstructured layer with an organic base. As described herein, a method for making a microstructured layer comprises the steps of: i) depositing a vapor of an organic material such as a thin, continuous or discontinuous layer on a substrate; and ii) annealing the organic layer under vacuum for a time and at a temperature sufficient to induce a physical change in the organic layer deposited to form a microstructured layer comprising a dense array of discrete microstructures, but insufficient to cause the organic layer to evaporate or sublime. Materials useful as a substrate include those which can maintain their integrity at temperature and vacuum and placed therein during the vapor deposition and annealing steps. The substrate may be flexible or rigid, flat or non-planar, convex, concave, textured or may be combinations thereof. Preferred substrate materials include organic materials and inorganic materials (including, for example, glasses, ceramics, semiconductor metals). The preferred substrate material is glass or metal. Representative organic substrates include those which are stable at the annealing temperature, for example, polymers such as polyimide film (commercially available, for example, under the trade designation "KAPTON" from Du Pont Electronics of Wilmington, DE), stable polyesters at high temperature, polyamides and polyaramides Useful metals as a substrate include, for example, aluminum, cobalt, copper, molybdenum, nickel, platinum, tantalum or combinations thereof. Ceramic materials useful as a substrate material include, for example, metal or non-metallic oxides such as alumina and silica. A particularly useful semiconductor is silicon. Preferred methods for preparing a metal substrate include, for example, vacuum vapor deposition or ion spray that deposits a metal layer on a polyimide sheet or network. Preferably, the thickness of the metal layer can be from about 10 to 100 nanometers. Although not necessarily harmful, the exposure of the metal surface to an oxidizing atmosphere (for example air) can cause an oxide layer to form on it. The organic material from which the microstructures can be formed can be coated on the substrate using techniques known in the art to apply a layer of an organic material on a substrate, including, for example, vapor phase deposition (e.g. vacuum evaporation, sublimation and vapor chemistry deposition) and solution or coating coating by dispersion (e.g. dip coating, spray coating, spin coating, knife or blade coating, stick coating, roll coating and coating by pouring (that is, pouring a liquid on a surface and allowing the liquid to flow over the surface)). Preferably, the organic layer is applied by physical vapor deposition under vacuum (i.e., sublimation of the organic material under applied vacuum). Organic materials useful for producing the microstructures, for example, by coating followed by plasma etch treatment, may include, for example, polymers or prepolymers thereof (e.g., thermoplastic polymers such as, for example, alkylaid materials, melamines , urea, formaldehydes, diallyl phthalates, epoxies, phenolic materials, polyesters and silicones, thermosetting polymers such as acrylonitrile-butadiene-styrenes, acetals, acrylics, cellulose materials, chlorinated polyethers, ethylene-vinyl acetates, fluorocarbons, ionomers, naylons , perylenes, phenoxy, polyanomers, polyethylenes, polypropylenes, polyamideimides, polyimides, polycarbonates, polyesters, polyphenylene oxides, polystyrenes, polysulfones and vinyls) and organometallic (for example bis (? s-cyclopentadienyl) iron (II), iron pentacarbonyl, ruthenium pentacarbonyl, osmium pentacarbonyl, chromium hexacarbonyl, molybdenum hexacarbonyl, tungsten hexacarbonyl, and tris (triphenylphosphine) rhodium chloride). Preferably, the chemical composition of the microstructured layer on an organic basis will be the same as that of the initial organic material. Useful organic materials for preparing the microstructured layer include, for example, planar molecules comprising chains or rings on which a p-electron density is extensively delocalized. These organic materials generally crystallize in a spike or herringbone configuration. Preferred organic materials can be broadly classified as polynuclear aromatic hydrocarbons and heterocyclic aromatics. Polynuclear aromatic hydrocarbons are described in Morrison and Boyd, Organic Chemistry. third edition, Allyn and Bacon, Inc. (Boston: 1974), chapter 30. Heterocyclic aromatic compounds are described in Morrison and Boyd, supra, chapter 31. Preferred polynuclear aromatic hydrocarbons, which are commercially available, include, for example , naphthalenes, phenanthrenes, perylenes, anthracenes, coronenes and pyrenes. A preferred polynuclear aromatic hydrocarbon is N, N '-di (3, 5-xylyl) perylene-3, 4, 9, 10 bis (dicarboxamide) (commercially available under the trade designation "Cl PIGMENT RED 149" from American Hoechst Corp. from Somerset, NJ), herein referred to as "perylene red". Preferred heterocyclic aromatic compounds, which are commercially available, include, for example, phthalocyanines, porphyrins, carbazoles, purines and terines. Representative examples of heterocyclic organic compounds include, for example, metal-free phthalocyanine (for example phthalocyanine dihydrogen) and their metal complexes (for example, copper phthalocyanine). The organic materials are preferably capable of forming a continuous layer when deposited on a substrate. Preferably, the thickness of this continuous layer is in the range from 1 nanometer to about 1000 nanometers. The orientation of the microstructures can be affected by the temperature of the substrate, the rate of deposition and the angle of incidence during the deposition of the organic layer. If the temperature of the substrate during the deposition of the organic material is sufficiently high (ie, above a critical substrate temperature which is associated with the technique with a value of one third the boiling point (K) of material organic), the organic material deposited will form randomly oriented microstructures either as they are deposited or when they are subsequently annealed. If the temperature of the substrate during deposition is relatively low (i.e., below the critical temperature of the substrate), the deposited organic materials tend to form uniformly oriented microstructures when annealing. For example, if uniformly oriented microstructures comprising perylene red are desired, the temperature of the substrate during the deposition of the perylene red is preferably from about 0 to about 30 ° C. Certain subsequent conformation coating processes, such as DC magnetron sputtering and cathodic arc vacuum processes, produce curvilinear microstructures. There can be a maximum optimum annealing temperature for different film thicknesses in order to completely convert the deposited layer to microstructures. When it is completely converted, the largest dimension of each microstructure is directly to provide the thickness of the organic layer initially deposited. Since the microstructures are discrete, they are separated by distances in the order of their dimensions in cross section, and preferably have uniform cross-sectional dimensions, and all the original organic film material is converted to microstructures, the conservation of mass implies that the lengths of the microstructures will provide to the thickness of the layer initially deposited. Due to this ratio of the thickness of the original organic layer to the lengths of the microstructures and the independence of the cross-sectional dimensions of the length, the lengths and bimensional proportions of the microstructures can vary independently of their cross-sectional dimensions and their area densities. For example, it has been found that the length of the microstructures is approximately ten times the thickness of the layer deposited perylene red, when the thickness varies from about 0.05 to about 0.2 microns. The surface area of the microstructured layer (ie, the sum of the surface areas of the individual microstructures) is much larger than that of the organic layer initially deposited on the substrate. Preferably, the thickness of the initially deposited layer is in the range of from about 0.05 to about 0.25 microns. Each individual microstructure can be microcrystalline or polycrystalline, instead of amorphous. The microstructured layer can have highly anisotropic properties due to the crystalline nature and the uniform orientation of the microstructures.

If a discontinuous distribution of the microstructures is desired, masks may be used in the organic layer deposition step to selectively coat specific areas or regions of the substrate. A discontinuous distribution of the microstructures can also be obtained by coating (for example spray coating, vapor coating or chemical vapor deposition) of a metal layer (for example Au, Ag and Pt) on the organic layer before the step of annealing. The areas of the organic layer having the metallic coating thereon are generally not converted to microstructures during the annealing step. Preferably, the flat equivalent thickness of the metallic coating, which may be discontinuous, is in the range of from about 0.01 to about 500 nanometers. Other techniques known in the art may also be useful to selectively deposit an organic layer over specific areas or regions of a substrate. In the annealing step, the substrate having an organic layer coating thereon is heated under vacuum for a time and at a temperature sufficient for the coated organic layer to undergo a physical change, wherein the organic layer grows to form a layer microstructured that comprises a dense array of monocrystalline or polycrystalline microstructures, oriented and discrete. The uniform orientation of the microstructures is an inherent consequence of the annealing process when the temperature of the substrate during deposition is sufficiently low. The exposure of the coated substrate to the atmosphere prior to the annealing step is not considered to be harmful to a subsequent formation of microstructures. For example, if the coated organic material is copper perylene or copper phthalocyanine, the annealing is preferably carried out under vacuum (i.e., less than about 1 x 10"3 Torr) at a temperature in the range from about 160. to about 270 ° C. The annealing time necessary to convert the original organic layer to the microstructured layer depends on the annealing temperature Typically, an annealing time in the range of about 10 minutes to about 6 hours is sufficient. the annealing time is in the range from about 20 minutes to about 4 hours.Also, for perylene red, the optimum annealing temperature to convert the entire original organic layer to a microstructured layer, but not to be removed by sublimated, it is observed that it varies with the thickness of the deposited layer, typically for an original organic layer thickness from 0.05 to 0.15 micrometers, the temperature is in the range of 245 to 270 ° C.

The time interval between the vapor deposition step and the annealing step can vary from several minutes to several months, without significant adverse effect, with the condition that the coated composite is stored in a covered container to minimize contamination ( for example the dust). As the microstructures grow, the organic infrared band intensities change and the laser specular reflectivity decreases, which allows the conversion to be accurately monitored, for example, in situ by infrared surface spectroscopy. After the microstructures have grown to the desired dimensions, the resulting stratified structure, which comprises the substrate and the microstructures, is allowed to cool before being brought to atmospheric pressure. If a patterned distribution of the microstructures is desired, the microstructures can be removed selectively from the substrate, for example, by mechanical means, vacuum process means, chemical means, gas pressure or fluid medium, radiation medium and combinations of the same. Useful mechanical means include, for example, scraping microstructures to remove the substrate with a cutting instrument (for example with a razor) and encapsulation with a polymer followed by delamination. Useful radiation means include laser or light suppression.

Such suppression can result in a cathode with a pattern. A useful chemical means includes, for example, acid etch treatment of selected areas or regions of the microstructured layer. A useful vacuum medium includes, for example, ion spray and ionic reactive mordant treatment. Useful air pressure means includes, for example, blowing the microstructures to remove the substrate with a gas (for example air) or a fluid stream. Combinations of the above are also possible, such as the use of photoprotective layers and photolithography. The microstructures can be partially exposed and partially encapsulated within a final substrate, and of a material different from that of the final substrate, by first forming the microstructures in a temporary substrate, and then pressing the microstructures partially into the surface of the final substrate ( example by tiling with hot rollers, as described in U.S. Patent No. 5,352,651, example 34) and removing the temporary substrate. The microstructures can be extensions of the substrate and the same material as the substrate by, for example, vapor deposition of a mask of discontinuous metallic micro-beads on the surface of a polymer, then the material is eliminated by treatment with ionic mordant of plasma or reactant. of polymer not masked by the metal micro-strands, to leave polymer substrate poles protruding from the surface. Other methods for making microstructured layers are known in the art. For example, to elaborate layers organic microstructures that is described in Materials Science and Engine ring, A158 (1992), pp. 1-6; J. Vac. Sci. Technol. .5., (4), July / August 1987, pp. 1914-16; .1. Vac, T_.c_.nol A.6. (3), May / August, 1988, pp. 1907-11; Thin Solid Films. 186. 1990, pp. 327-47; J, Mat, Sci 25, 1990, pp. 5257-68; Rapidly Ouenched Metals, Proc. of the Fifth Int. Conf. on Rapidly Quenched Metals, Wurzburg Germany (Sept. 3-7, 1984), S. Steeb et al., eds. Elsevier Science Publishers B.V., New York, (1985), pp. 1117-24; Photo Sci. And Ens. 24. (4), July / August 1980, pp. 211-16; and US Patent Documents Nos. 4,568,598 and 4,340,276. Methods for making inorganic based microstructured layers in filaments are described, for example, in J. Vac. Sci. Tech. A. 1 (3), July / Sept., 1983, pp. 1398-1402 and in U.S. Patent No. 3,969,545; US Patents Nos. 4,252,865, 4,396,643, 4,148,294, 4,252,843, 4,155,781, 4,209,008 and 5,138,220. Inorganic materials useful for producing the microstructures include, for example, carbon, diamond-like carbon, ceramics (for example metal or non-metallic oxides such as alumina, silica, iron oxide and copper oxide; metallic or non-metallic nitrides such as nitride) of silicon and titanium nitride, and metal or non-metal carbides such as silicon carbide, metal or non-metallic borides such as titanium boride); metal or non-metallic sulfides such as cadmium sulfide and zinc sulphide; metal silicides such as magnesium silicide, aluminum silicide, and iron silicide; metals (for example noble metals such as gold, silver, platinum, osmium, iridium, palladium, ruthenium, rhodium and combinations thereof, transition metals such as scandium, vanadium, chromium, manganese, cobalt, nickel, copper, zirconium and combinations thereof; metals with low melting point such as bismuth, lead, indium, antimony, tin, zinc and aluminum; refractory metals such as tungsten, remio, tantalum, molybdenum and combinations thereof); and semiconductor materials (e.g. diamond, germanium, selenium, arcenic, silicon, tellurium, gallium arsenide, gallium antimonide, gallium phosphide, aluminum antimonide, indium antimonide, indium tin oxide, zinc antimonide, indium phosphide, aluminum and gallium arsenide, zinc terlurium and combinations thereof). The microstructures of the preferred embodiment can be made to have random orientations by controlling the temperature of the substrate during the deposition of the initial layer PR 149, as described above. They can also be processed to have curvilinear shapes by conditions of the conformation coating process. As discussed in Figure 6 of L. Aleksandrov, "GROWTH OF CRYSTALLINE SEMICONDUCTOR MATERIALS ON CRYSTAL SURFACES", Chapter 1, Elsevier, New York, 1984, energies of incoming atoms applied by different coating methods, for example deposition of thermal evaporation, ion deposition, spraying in plantation, can vary of more than 5 orders of magnitude. The higher energy process can cause the PR 149 filaments to be deformed during the forming coating process, as shown in Figure 8 of the drawing of the invention. This effect can be an advantage for the emission of fields from the microstructures that have multiple potential emission sites on their surfaces in the form of nanoscopic rugose characteristics, since as the tips curl over the potential emission sites are placed properly for field emission towards a cathode. It is within the scope of the present invention to modify the methods for making a microstructured layer to manufacture a discontinuous distribution of microstructures. Preferably, if one or more layers of conformal coating material are applied they serve as a functional layer imparting desirable electronic properties such as conductivity and electronic work function, and also properties such as thermal properties, optical properties, for example absorption of light for suppression, mechanical properties (for example increased resistance of the microstructures comprising the microstructured layer), chemical properties (for example providing a protective layer) and low vapor pressure properties. An additional function of the shaping coating may be to provide a high surface area to the vacuum that removes the residual gas in the material for continuous pumping away from gases which may be produced by outward fractionation and permeation to degrade the vacuum quality within the device. flat panel screen. Examples of coating materials with vacuum residual gas removal properties include Zr-V-Fe and Ti. Preferably, the shaping coating material can be an inorganic material or it can be an organic material that includes a polymeric material. Useful inorganic and organic conformal coating materials include, for example, those described above in the description of the microstructures. Useful organic materials also include, for example, conductive polymers (e.g., polyacetylene), polymers derived from poly-p-xylylene and materials capable of forming self-assembled layers.

The preferred thickness of the shaping coating is typically in the range of from about 0.2 to about 50 nm, based on the application of electron emission. The shaping coating can be deposited on the microstructure layer using conventional techniques including, for example, those described in U.S. Patent Nos. 4,812,352 and 5,039,561. Any method that prevents alteration of the microstructured layer by mechanical forces to deposit the conformal coating can be used. Suitable methods include, for example, vapor phase deposition (eg vacuum evaporation, spray coating and chemical vapor deposition), solution coating or dispersion coating (eg dip coating, spray coating, powder coating). centrifugation, pour coating (ie pouring a liquid over a surface and allowing the liquid to flow over the microstructured layer followed by removal of solvents)), immersion coating (i.e. immersing the microstructured layer in a solution for a period of time) sufficient to allow the layer to absorb molecules from the solution, or colloidal substances or other particles of a dispersion), electrodeposition and deposition without electrons. More preferably, the forming coating is deposited by vapor phase deposition methods such as, for example, ion spray deposition, cathode arc deposition, vapor condensation, vacuum sublimation, physical vapor transport, transport chemical vapor and chemical methane organic vapor deposition. Preferably, the shaping coating material is a metal of a low working melting material such as diamond-like carbon. For the deposition of a conformal coating with a pattern, the deposition techniques are modified as are known in the art to produce such discontinuous coatings. Known modifications include, for example, the use of masks, formwork elements, directed ion beams and deposition source beams. The nanometer-scale roughness of the electron-emissive-forming coating on the microstructure element is an important aspect of the present invention. The morphology of this coating is generally determined by the coating process and the surface characteristics of the microstructure elements. For example, for the preferred process of metal vacuum deposition coating on the microstructure PR 149, the morphology of conformation coating is first determined by means of nucleations of specific coating material on islands of the largest scale-average dimension of nanometers on the sides of the crystalline filaments, and subsequently the manner in which the coating develops from these initial nucleation sites. This nucleation and growth can be determined by the choice of the vacuum coating method, for example, physical vapor deposition or spray deposition, the deposition rates and incidence angles chosen for any process, the substrate temperature and the pressures of background gas during the deposition and the like. H.J. Leamy et al., "The Microstructure of Vapor Deposited Thin Films," CURRENT TOPICS IN MATERIALS SCIENCE, vol. 6, chapter 4, North-Holland Publishing Company, 1980, J.P. Hirth et al. "Nucleation Processes in Thin Film Formation", PHYSICS OF THIN FILMS, vol. 4, Academic Press, New York, 1967; and L. Aleksandrov, GROWTH OF CRYSTALLINE SEMICONDUCTOR MATERIALS ON CRYSTAL SURFACES, chapter 1, Elsevier, New York, 1984, describes such mechanisms of nucleation and growth in greater detail. The roughness at the nanoscale can also be affected by the presence of impurities or intentional additives added to the surfaces of the microstructure elements, and by preprocessing steps such as plasma etching treatment of the microstructure elements before deposition of the shaping coating. The morphology can also be affected when the conditions for epitaxial growth of the coating material on the crystalline microstructures are satisfied. See, for example, U.S. Patent No. 5,176,786, which is incorporated herein by reference for these teachings, and J.H. van der Merwe, "Recent Developments in the Theory of Epitaxy", CHEMISTRY AND PHYSICS OF SOLID SURFACES, Springer-Verlag, New York, 1984. The shading, by the microstructures themselves, of the vapor deposition material will also include in the roughness of the conformal coating and its distribution along the lengths of the microstructures. The effect will generally be to cause the tops of the oriented microstructures to be preferentially coated at the expense of their bases, as illustrated in Figure 2 (a) through 2 (c) and as discussed in A.G. Dirks et al., "Columnar Microstructure in Vapor-Deposited Thin Films", THIN SOLID FILMS, 47, pp. 219-233. The final size of the roughness characteristics derive from this nucleation and growth can be determined more accurately by the total amounts of the applied conformation coating material. This is illustrated in Figures 2 (a-c).

Figure 2 (a) shows microstructures that have been coated with 0.054 mg / cm2 of Pt, Figure 2 (b) with 0.22 mg / cm2 of Pt, and Figure 2 (c) with 0.86 mg / cm2 of Pt. Figure 2 (b) shows the sides of the microstructures that are densely covered with sharp angular crystallites, with total dimensions of 20 mm or smaller. The near-normal incidence view of the upper portions of the heavily coated microstructures in Figure 2 (c) shows the Pt nanometer-sized crystalline flakes. The tip widths in Figure 2 (c) are much larger. larger than its bases as a result of the shading effect described above. The nanoscopic crystallites in Figures 2 (ac) are characterized by edges having atomic scale radii of curvature, and multiple facets and grain boundaries and other potentially low work function sites, all characteristics leading to a field emission of improved electrons. Figure 3 (a) shows a schematic (cross-sectional view) of a portion of the components of a gas plasma directional matrix or a field emission screen device without gate that includes a cathode 20, for a mode of the invention. The patterned microstructured layer 12 shown in the row conductors 16 which are supported by the substrate 14 provide the cathode 20. The transparent column conductors 18, generally indium tin oxide (ITO), are placed on the substrate 22, preferably glass, which supports a continuous or discontinuous phosphor material layer 23 and which comprises an anode 24 of the invention. The phosphor material 23 is capable of excitation by electrons. Applying a voltage from the voltage source 26 results in a high electric field being applied to the emission sites of the microstructured layer 12. This causes a flow of electrons through the low pressure gas or vacuum space 28 between the column conductors 18 and the row conductors 16. The space 28, which is the space between the phosphorus 23 and the cathode 20, can have a vertical dimension of about 1 μm to several mm. Electrons accelerated by voltage across space 28 impinge on phosphorus-containing layer 23, resulting in light emission, as is known in the art. Figure 3 (b) shows a schematic (cross sectional view) of a portion of the components for a directed array mode of a gate field emission display device 30. The device includes a gate cathode 32 which includes conductive gate columns 34, insulated spacers 36 having a height in the range of 0.5 to 20 μm, a layer 38 microstructured with a pattern, deposited on and in electrical contact with the conductors 40 of row which are supported on the substrate 41, generally glass. The cathode 32 is separated from the anode 42 by a low pressure gas or preferably a vacuum space 44, the space between the phosphor 50 and the cathode 32 which may have a vertical dimension in the range from about 1 μm to 5 mm. The anode 42 comprises a substrate 46, generally glass, on which is located an ITO layer, continuous or discontinuous, transparent, which supports a phosphorus-containing layer 50, continuous or discontinuous, as is known in the art. In the operational mode, a voltage is applied from the voltage source 52 between the conductive gate columns 34 and the row conductors 40 which results in a high electric field being applied to the microstructure layer 38, and subsequently the field emission Subsequent electrons within the space 44. The voltage from the voltage source 54 accelerates the electrons emitted in the field through the space 44, resulting in light emission after the collision of the electrons with the phosphor layer 50 . Preferably, the height of the layers 38 microstructures is the same or smaller than the height of the cathode 32. In a second operational mode, the voltage of the source 54 can provide the emitting field and the source 52 can serve to focus or modulate the current that reaches the anode 42. With reference to FIGS. 3 (a) and 3 (b), in other embodiments, it may be desirable to include a resistive layer between the cathode spinneret conductors (16, 40) and the microstructure layers (12, 38). Such resistive layers are known in the art, see, for example, U.S. Patent Nos. 4,940,916 and 5,507,676. Further, in Figures 3 (a) and 3 (b), it is not shown but it is understood by those familiar with the art that the circuit includes suitable ballast resistors to feed the emission current so as not to ignite the tips of the circuit. microstructure The electrodes of the invention find utility in the technology of flat panel display, specifically of gas plasma and in field emission types, in vacuum tubes for microwave devices, and in other electron beam or electron beam source devices. ionization The objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof mentioned in these examples, as well as other conditions and details, should not be considered as undue constraints of this invention.

EXAMPLES Vacuum Field Emission Quantum field emission from a one-dimensional cold cathode emitter is described by the Fowler-Nordheim equation as originally discussed in R.B. Fowler, et al., Proc. R. Soc. London, Ser. A, lli (1928) 173. where J is in Amp / cm2, E is the electric field strength in volts / cm, A = 1.54 x 10"6, B = 6.87 x 107, y = 3.79 x 10" 4 (ßE) 12 / F, t2 (y) ~ 1.1 yv (y) ~ 0.95 - y2, ß is the field improvement factor due to the local geometry and F the work function in electron volts of the emitter material. Suppose that the current I = Ja, where a is the emission area, in cm2, and we define ßE = ß'V, equation (I) can be rewritten as: ln = ln to 1 4 (ß ') + 2m. . e, 52 x1Q7 3/2 (2) M f 10 € F, / 2 ß 'V When graphing In (I / V2) vs I / V, a graph of Fowler-Nordheim, a straight line with a negative slope is produced which provides the field improvement factor, ß ~ ß'd, at the tip or field emission site, since V ~ Ed, where d is the space between the electrodes, ß 'is the field improvement factor per unit of space distance. The microstructure layers used in the following examples were produced in a three-step process, as described in U.S. Patent Nos. 4,812,352 and 5,039,561. First, an organic pigment, C.l. Pigment Red 149 (N, N '-di (3,5-xylyl) perylene-3, 4, 9, 10-bis (dicarboximide)), available from American Hoechst-Celanese, Somerset, NJ, is deposited as vapor under vacuum to a thickness of approximately 0.15 micrometers on a suitable substrate, usually a metallized polyamide film of 50 μm (2 mils) thick, at a pressure of 2 x 10"6 Torr.Secondly, the polyimide coated with red Perylene is vacuum annealed at 240-260 ° C for approximately 30 minutes.The vacuum level during annealing is not critical and can vary up to 5 x 10 ~ 2 Torr.This annealing process causes the original regular layer of red of perylene undergo a phase transition to form a layer of crystalline, oriented, discrete filaments, each having approximately 0.05 x approximately 0.03 micrometers in its cross sections, lengths of approximately 2 micrometers, and densities of approximate area number. 30 filaments per square micrometer. (The filament growth mechanism and physical structure characteristics have been detailed in MK Debe and RJ Poirier, J. Vac. Sci. Technol. A 12 (4) (1994) 2017-2022, and MK Debe and AR Drube, J. Vac. Sci. Technol. B 13 (3) (1995) 1236-1241). As the third stage, the microstructure layer is vacuum-coated by evaporation, spraying or by another similar process which applies a conformal coating of metal or other suitable electron-emitting material around each individual filament. The geometric surface area of the filaments is 10 to 15 times the flat area of the substrate, so that the thickness of flat equivalent metal deposited is 10 to 15 times greater than the thickness of conformation on the sides of each nanostructure element ( coated filament). Instead of the perylene red microstructures, other inorganic and organic compounds can be substituted as described in U.S. Patent No. 5,336,558, which is incorporated herein by reference. Particularly useful are polynuclear aromatic hydrocarbons, for example naphthalenes, phenanthrenes, perylenes, phenyls, anthracenes, coronenes and pyrenes. The microstructured samples used in the following examples are not cleaned or pretreated in any way prior to the evaluations described. Examples 5-15 use a phosphor / space / electrode construction similar to that of Figure 3 (a).

Ejespío 1 A microstructured layer of perylene red is deposited on Si polished standard 7.6 cm (3") diameter wafers coated with 70 nm (700 μl) of Pt. The filaments, nominally 1.5 micrometers high with dimensions in cross section and numerical densities described above, are coated in conformation with a flat equivalent of 340 nm (3400 Á) de Pt. The microstructured side is spray coated with several sprays of about 1 second of a 1 percent by weight dispersion of 20 micrometer diameter glass fibers in isopropanol. The function of the fibers is to act as a separator to hold two pieces that are not joined, separated from the wafers by the diameters of the fibers. Two pieces of 6.5 mm wafer width are interposed perpendicular to each other with the filaments oriented towards the 20 μm space. In air at ambient temperature and pressure, a voltage is applied to the Pt coated sides of each piece of wafer and the current through the space is measured with a 1000 ohm ballast resistor in place to avoid excessive current levels. The voltage is varied between 0 and 2.0 volts, and the current is recorded. Figure 4, graphs A and B show the result for two sequential runs. The current densities are extremely large for such low voltages. These runs were typical of many numerous measurements, which were generally observed to finally end short between the wafers when the voltages are applied for prolonged periods. Then the current was limited by the ballast resistor. Evidence was obtained that the short produced by the "growth" of filaments or groups of filaments that formed a bridge in space. Graphs A and B in Figure 4 are therefore not representative of large area emission, but rather of local emission for small numbers of microstructured elements. Applying the voltage without the resistor would often burn out the short circuit and the process would be repeated.

Example 2 Two pieces of the Si wafers covered with microstructures, coated with Pt, described in Example 1, each 1 cm wide of approximately 2 cm long, placed perpendicularly to each other so as to interpose a 0.02 piece were placed. mm (0.001 inches) thick polyimide at its intersection. The polyimide has an aperture cut of 6.5mm x 9.5mm therein, to expose the microstructures of each piece of the wafer to the opposite piece at the intersection. Thin wires were attached by Ag paint to the microstructured side of each piece of wafer, and the sample cell was connected in series with a 103 K ohm ballast resistor and a direct current power supply. The sample was placed in a vacuum chamber and evacuated to approximately 35 mTorr. Voltage was applied to the Pt-coated sides of each piece of wafer and the voltage developed by the emission of current through the ballast resistor was measured with a digital voltmeter, and was considered as the voltage developed just across the cell. In Figure 4, the measured current density amps / cm2 is shown as graph C. The next day a second measurement was made, at a slightly lower pressure of 16 mTorr, and graph in figure 4 as the graph B.

Example 3 A second interposition of Pt-coated filaments was prepared on pieces of silicon wafers as in Example 2, except that the opening in the 25 μm thick polyimide separator is 5.2 mm x 6.5 mm. In figure 4 the graph of E is shown as the emission current density, measured as in example 2, at a pressure of 6 mTorr, in a first run. The sample was then brought to ambient pressure and the graph F was generated in figure 4 from the data taken. Then the sample cell was left overnight with one volt applied to it (approximately 16 hours), during which time the current was stable. After this the graph G is obtained in figure 4. At a maximum of 17 volts (6,800 volts / cm), the cell made a short one. At ambient pressure, the mean free path of air molecules is 6.7 x 10"6 cm, or 0.067 micrometers, considerably smaller than the 20-25 μm spaces used in examples 1-4., D and E in Figure 4 taken at 35 mTorr or less for which the mean free path is 0.15 cm or greater and much greater than the space, the pressure appears to be too low to sustain a gas discharge into the space. The graphs in Figure 4 of current versus voltage (below 10 volts at least) are not similar to those of Fowler-Nordheim, but rather are characterized by the fact that J varies in proportion to V3, and most likely do not represent vacuum field emission. Graphing again the data of the graph D as In J / V2 versus l / V suggests a relation of Fowler-Nordheim for V >; 10 volts. The data of figure 4 below 10 volts (4000 volts / cm) show a gas phase ionization mechanism which is absent when the microstructures are excluded, as in comparative example 4.

Example 4. Ccoparative Two pieces of Si wafer coated with Pt were formed, without microstructure coating on both pieces, in an interposition otherwise identical to that of Example 3. It was mounted identically in the vacuum chamber and tested at 27 mTorr of the same way as the samples in examples 2 and 3. The applied voltage varied from 0 to 10, 15 and 20 volts, with no detectable current above about 5 x 10"11 ampere deviation of the electrometer, the chamber was then re-pulsed until ambient pressure and the measurements were repeated, up to a maximum applied voltage of 50 volts Again, there was no detectable current above the noise level through the ballast resistor In Examples 5-15, the vacuum field emission for samples for microstructured layers on polyimide substrates were imaged on a phosphor screen, in correlation with current / volta emission curve measurements je.

Example 5 In this example, the filaments coated with Pt / Ni (300 nm (3000 μ) Ni, followed by 100 nm (1000 Á) of e-beam of Pt deposited on filaments PR 149 of 1.5 μm high as described in the example 1) formed a microstructured layer on a 50 μm thick polyimide substrate pre-coated with 70 nm (700 μl) Ni. A sample piece of the microstructured film was placed on a 12 mm x 12 mm opening in a 50 μm thick polyimide film separator in contact with the phosphor of a commercial electronic diffraction screen. The screen was a high-energy electron diffraction model 425-24 (HEED) assembly, purchased from SPTC, Inc. Van Nuys, CA. Phosphorus is type P43, coated at 10 mg / cm2 with an average particle size of 7-8 μm. The total space of the microstructure from the transparent conductive coating between the phosphor and glass substrate is the thickness of the phosphorus plus the polyimide separator. The phosphorus thickness is approximately 65 μm. The screen and cell assembly were placed in a vacuum chamber and evacuated to less than 10 mTorr. A voltage A (-V) was applied to the microstructured film side of the sample with respect to the ground potential. A ballast resistor Rb = 103K ohms was between the ground and the metal flange of the HEED screen. As the voltage applied to the microstructure exceeds approximately 600 volts, flashes of significant points and discharges occur in the exposed area of microstructure, mainly due to residual gas ionizations. Many of the local emission points were very stable, which provided the opening of a "night with lightning" appearance. The brightness points, many bright enough to be observed even with normal lights, were superimposed over a matte but even phosphor background illumination that could be observed in a well-darkened room. The intensity of the background illumination varies directly with the applied voltage between 500 and 800 volts, being barely detectable 500 volts. The illuminated aperture area is observed for 15 minutes and then the current through Rb is measured as a function of V. Figure 5 (a) shows a graph of this current measured as a function of the cell voltage, and the figure 5 (b) shows a graph of the same data on a Fowler-Nordheim chart as defined in equation (2). The line continues through the plotted points of Figure 5 (b) is a linear curve fit of equation (2) with respect to the data with the work function F = 5.6 eV for Pt. The slope of the linear curve fit graph in Figure 5 (b) provides a value for ß ', defined in equation (2) of 5 x 105 cm "1. The field improvement factor, β, is related to with ß ', and the distance of space d over which the electric field is applied, as ß «ß'd, as discussed following equation (2). Based on the electrical properties of phosphorus, this distance of space it can vary from a minimum equal to the thickness of the polyimide separator, up to a maximum of the thickness of the separator plus phosphor.In this example, this range is 15 μm <; d < 114 μm. This indicates that the range for the field improvement factor is approximately 2500 < ß < 5700. The threshold voltage, Vth, that is, where the emission current first begins to become rapidly measurable, and the space separation, d, defines the emission threshold, g = Vth / d. From Figure 5 (a), Vth is ~ 325 volts, which, with the internal range for d implies an emission threshold in the range of 2.85 volts / μm < g < 6.5 volts / μm. The polarity of the voltage applied between the microstructured layer and the phosphor is subsequently reversed, that is, up to (+), 800 volts and applied to the microstructured layer with respect to the phosphor screen. No emission of current or emission of light from the screen is observed, consistent with the diode behavior of the electron field emission.

Example 6 A test cell similar to that of Example 5 was assembled using a 25 μm thick polyimide separator and a microstructured film of the same perylene red filament sizes but having a base equivalent to 440 nm (4400 A) of Pt coated on the filaments. The current density voltage was measured at a pressure of 6 mTorr, and is shown in Figure 6 (a) as Figure A. A similar emission pattern is observed on the phosphor screen somo in Example 5.

Example 7 A cell test similar to that of Example 6 was assembled, they are a polyimide film separator of 25 μm in thickness and 340 nm (3400 μl) of Pt coated on the perylene filaments of approximately 2 μm in length, compared to the filaments of approximately 1.5 μm from the previous examples. It was evaluated at 2 x 10"s Torr.This sample also produces a visible illumination of the screen in the nanostructure opening area.As with the previous samples, at higher pressures, the cell current fructuates due to the flashes However, it is sufficiently stable that even the heights of the emission current can be taken, provided that the flashes are absent, which correspond to the minimum value observed at any applied volt- age.It is considered that this current is representative of the uniform illumination of the screen over approximately 1 cm2 of exposed area Graph I in Figure 6 (a) shows the measured current density, and Figure 6 (b) is a Fowler-Nordheim plot of the same data The slope of the linear curve fit graph in Figure 6 (b) gives a value for ß 'defined in equation (2) of 9.2 x 105 cm "1. As in the above, the field improvement factor, ß, is related to ß1, and the distance of space d over which the electric field is applied, such as ß ~ ß'd. Again, this distance of space varies from a minimum equal to the thickness of the polyimide separator, to a maximum of the thickness of the separator plus the phosphor, of 25 μm < d < 89 μm. This shows the range for the field enhancement factor which is about 2300 < ß < 8100. The threshold voltage, Vth, that is, where the emission current first begins to become rapidly measurable, appears for graph B in Fig. 6 (a), Vth is ~ 200 volts, which is the interval interior for d shows an emission threshold in the range of 2.25 volts / μm < g < 8.0 volts / μm.

Example 8 A test similar to that of Example 6 is assembled with a 50 μm thick polyimide separator and an 8.5 mm x 8.5 mm opening to expose the microstructured layer to the HEED screen. The sample of misroestrust in this example has 150 nm (1500 A) of gold coated in filaments of 1.5 μm high, as shown by misographies by SEM. The current measured per unit area of opening as a function of the voltage applied in Fig. 6 (a) is shown as graph C.

Example 9. Tip Conditioning This example shows how emission over a large area can be stabilized by "conditioning" the microstructure emission sites by an operation initially at a higher pressure. It is observed for many samples. A test cell, with a 4 mm x 14 mm opening in a 25 μm polyimide separator, is assembled between the phosphor of the HEED screen and a sample of Pt / Ni coated filaments used in Example 5. The application of voltages between 500-1000 volts at pressures below 10"5 Torr produces flashes of multiple localized high intensity points above the aperture area, most of which are transient, there is no significant uniform background illumination of the opening area, because the emission current is emitted preferentially from localized points.The intensity from the brightest points is suitable to be observed on the screen under usual lighting conditions.This behavior is stable over prolonged periods (for example, 30 minutes) . The pressure is increased to 3 mTorr with 900 volts applied. Localized transient flashes are replaced with an aperture area with a uniform brightness, visible in a well-darkened room. The pressure decreases again to less than 10"5 Torr and the image remains stable Occasionally a localized emission point of sustained brightness is present, which has the effect of reducing the background brightness of the total aperture area as the emission is Presented preferentially from the localized point, by reducing the voltage and reapplying rapidly, the localized dot emission is broken and the intensity is returned to the entire phosphor screen aperture area at 1000 volts applied to the cell, the uniform background illumination corresponds to a total current of 10"8 amp. Operation at high pressures, for example at 1 mTorr for a sufficient time (for example several minutes) resulted in a superfisie with uniform electron emission.

Example 10. Comparative A sample of electrodes without a microstructure, a 50 μm thick polyimide piece coated with Cu spray, is colosed on the same 25 μm polyimide separator used in example 9, oriented to the HEED screen. It is evaluated in the same way as the previous samples. No sustained emission of points or uniform background illumination of the opening area is observed. With 1000 volts applied through space, the current through the ballast resistor is in the order of the base line noise level 10"10 amp.

Example 11 A test cell similar to the one in the example was valued 7, with a 25 μm polyimide separator using a sample of PR149 micro-stringed filaments of the same size as in Example 1, but having a mass of 200 nm, of equivalent thickness of the cobalt deposited spray applied as a shaping coating. The particularly stable emissions sorptive with a very low threshold voltage of approximately 100 volts. In figure 7 the graph of Fswler-Nordheim is shown for this emission stream. The slope of the adjusted graph of the linear surva in Figure 7 uses a work function for sobalto F = 4.18 eV, which provides a value for ß 'defined in equation (2) of 4.3 x 105 cm "1. in the above, the field improvement factor, ß, is related to ß 'and the distance of space d over which the electric field is applied, such as ß * ß'd, again, this separation distance varies from a minimum equal to the thickness of the polyimide separator, up to a maximum of the thickness of the separator plus phosphor, or 25 μm <d> 89 μm This shows that the range for the field improvement factor is approximately 11,000 < < 38,000. The emission threshold range is approximately 1.13 volts / μm <g < 4.0 volts / μm.

Example 12 A test cell similar to that of Example 7 was evaluated with a 25 μm polyimide separator using a sample of microstructured PR149 filaments of the same size as in Example 1, except that PR149 has been deposited on a polyimide substrate coated with Ag and a diamond-like saucer-forming (DLC) coating is applied to a sanding vessel, as described in U.S. Patent No. 5,401,543, example 1. The efestos thermuses of the coating process are DLC provided. PR149 misroestrusting becomes survilineous, as shown in Figure 8, in an Elestronean scanning misrography of 10, OOOX of a coated misroestrust sapa are DLC. The exlusive flat equivalent thickness of the DLC coating was not measured, but was considered from the cross-sectional thickness of the misestruments in Figure 8 and based on larger amplifisasiones, and an approximate flat equivalent thickness of 400-500 nm was estimated. . It was observed that the vacuum field emission is similar to the metallic coated filaments of Examples 5-9 and 11, which produces, for example, current densities in the order of 1 micro-perior / cm 2 with a potential of 1000 volts applied between the sample and the phosphor screen. The DLC-coated microstructures tend to be more robust and are not damaged by residual gas treatments, as are the metal-coated filaments. It is considered that the carbon coating facilitates or improves the adhesion of the microstructured elements to the substrate and renders them less susceptible to removal by force elestrostátisa.

Examples 13-15 Sections similar to those in the examples were evaluated -12 with the phosphor screen, polyimide separators μm and microstructured films coated according to the process of example 1 are Pd, Ag and Cu. Similar results were observed as in the previous examples. Various modifications and alterations of this invention will become evident to those familiar with the art without departing from the scope and spirit of this invention., and it should be understood that this invention is not unduly limited by the illustrative embodiments set forth therein. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (11)

1. An electrode in an electron field emission device or a directed matrix of a gas plasma display device, the electrode is characterized in that it includes as a cathode a layer comprising a dense array of discrete solid microstructures placed over at least one portion of one or more surfaces of a substrate, the microstructures have a density of area number of more than 107 / cm2, at least a portion of the microstructures is covered conformationally with one or more layers of an electron-emitting material, the Overcoated electron-emitting material is placed on at least a portion of each of the microstructures and has a surface morphology that is nanoscopically rough and which provides multiple field emission sites by microstrust.

The electrode according to claim 1, characterized in that the dense array of microstructures of the electrode are randomly oriented or the dense array of microstructures of the electrode is oriented such that the major axes are parallel to each other.

3. The electrode according to claim 1 or 2, characterized in that the microstructures of the electrode satisfy at least one of i) or ii) following: i) a dimension in average transverse sessión in the range from 0.01 to 0.5 micrometers and a average length of 0.1 to 5 micrometers, or ii) a sural dimensional propulsion varies from about 1: 1 to about 100: 1.

4. The electrode according to any of claims 1 to 3, sarasterized because the misroestrustures of the elestrode somprende an organism material that somes flat molleulas and sadenas or rings on the suals dislosaliza the density of electrons pi, the organic material opsionally is a polymer, a polynuclear aromatic hydrosarbide or a heterocyclic aromatic compound, in which the polynuclear aromatic hydrocarbons are selected from the group consisting of naphthalenes, phenanthrenes, perylenes, anthracenes, soronens and pyrenes, and in which the heterocyclic aromatic solos are separated from the group that of phthalocyanines, porphyrins, carbazoles, purines and terines.

5. The electrode according to any of claims 1 to 3, characterized. because the microstructures are semiconductors made of a material that is selected from the group consisting of diamond, germanium, selenium, arsenic, silicon, tellurium, gallium arsenide, gallium antimonide, gallium phosphide, aluminum antimony, indium antimonide, oxide of indium and tin, zinc antimonide, indium phosphide, aluminum and gallium arsenide, zinc tellurium, and combinations thereof.

6. The electrode according to any of claims 1 to 5, characterized in that the microstructures of the elestrode include at least one of a repeated or non-repeated pattern, the pattern is opsionally produced by means that are selected from the group consisting of suppression. by • radiation, photolithography, mechanical process, vacuum process, chemical process and gas or fluid pressure process.

7. The compliance electrode is any of claims 1 to 6, characterized in that the coating of the deformation of the crotch of the elestrode includes a material that is separated from the group consisting of an organic material and an inorganic material, the organic material being optionally The group consists of metals, carbon, metal oxides, metal sulphides, metal slurries, metal carbides, metal borides, metal nitrides, metal silicides and a vacuum gas removal material.

The electrode according to any of claims 1 to 7, characterized in that the over-coated microstructures have low electronic work functions in the range of more than zero and up to 6 eV.

9. The electrode according to any of claims 1 to 8, characterized in that the substrate (14, 41) are selected from the group consisting of organic and inorganic materials, which are optionally selected from the group consisting of polymers, glass, ceramic materials , metals and semiconductors.

A method for preparing an electrode, according to any of claims 1 to 9, characterized in that it comprises the steps of: providing a substrate having on one or more surface thereof a microlayer comprising a dense array of solid microstructures and discrete, the microstructures have a density of area number of more than 107 / cm2, and. individually overwrapping, shaping, at least a portion of the microstructures with one or more electron emitting materials in an amount in the range of 10 to 1000 nm of flat equivalent thickness, the overcoating layer has a surface morphology that is nanoscopically rugose, optionally the method further comprises the step of conditioning the electrode by subjecting it to high pressure for a sufficient time to produce a uniform electron emitting surface.

11. A structure that produces an electric field, characterized in that a first and second conductive electrodes separated in an insulating manner from, and substantially parallel to one another, the first conductive electrode is the electrode prepared according to the method according to claim 10. , the structure that produces an electric field is optionally useful in a microwave device.