Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J9/00—Apparatus or processes specially adapted for the manufacture, installation, removal, maintenance of electric discharge tubes, discharge lamps, or parts thereof; Recovery of material from discharge tubes or lamps
  • H01J9/02—Manufacture of electrodes or electrode systems
  • H01J9/022—Manufacture of electrodes or electrode systems of cold cathodes

Definitions

• the present invention relates generally to the structures of individual or arrays of field emission cathodes and a process of fabricating the same. These individual or arrays of field emission cathodes can be made both with or without integrated extraction and/or control electrodes. More specifically, the present invention relates to field emission cathode structures and process for making the same.
• Electron sources or cathodes are essential to the functioning of all electron devices.
• cathodes for vacuum devices such as vacuum tubes and cathode ray tubes used thermionic emission to produce the required electrons. This required raising cathode materials to very high temperatures either by direct conduction of current or through the use of auxiliary heaters. The process is very inefficient, requiring relatively large currents and dissipating most of the energy as wasted heat.
• Field emission cathodes consists of very sharp points (typically less then 100 nm radius) of field emission materials. These sharp points when biased with a negative potential concentrate the electric field at the point. This high electric field allows the electrons to "tunnel" through the tip into surrounding space which is normally maintained under high vacuum conditions.
• the magnitude of the poten ⁇ tial required to produce sufficiently strong electric fields is proportional to the distance between the tip and the principal extraction electrode.
• This principal extraction electrode will be referred to as the extraction electrode. While this extraction electrode can be a physically separate structure, minimum extraction potentials can most conveniently be obtained by physically integrating the extraction electrode directly with the field emission cathode tips. This produces very small extraction electrode-cathode distances which are physically locked in proper alignment.
• Field emission cathode structures both with and with out integrated extraction electrodes are useful electron sources in a variety of current and potential applications such as displays, Vacuum Microelectronic Devices, and various electron microscopes.
• the field emission display elements that utilize these cathodes use the basic field emission structure and add additional structures, such as, an extension of the vacuum space, n phosphor surface opposite the cathode tip, and additional electrodes to collect and/or control the electron current.
• additional structures such as, an extension of the vacuum space, n phosphor surface opposite the cathode tip, and additional electrodes to collect and/or control the electron current.
• Groups of individual Vacuum Microelectronic Devices and/or display elements are electrically interconnected during fabrication to form integrated circuits and/or displays.
• Non-thermionic field emitters, field emission devices, and field emission displays are all known in the art.
• the fabrication of the field emission cathode structure is a critical element common to the devices mentioned.
• the material (insulators and conductors/field emitters) are all deposited and processed by relatively common deposition and lithographic processing techniques with the single exception of a special sharp edge (blade) or point
• the art of fabricating the sharp field emission tip or blade can be broadly classified into five categories. Methods of creating the extraction electrode are also noted in the examples within these categories.
• the first category is one of the earliest categories in which the cathode tip structure is formed by the direct deposition of the material. ⁇ n example of this type is exemplified in a paper by C. A. Spindt, "A Thin-Film Field-Emission Cathode", J. Appl. Phys., Vol. 39, No. 7, pages 3504-3505 (1968) , in which sharp molybdenum cone-shaped emitters are formed inside holes in a molybdenum anode layer and on a molybdenum cathode layer. The two layers are separated by an insulating layer which has been etched away in the areas of the holes in the anode layer down to the cathode layer.
• the cones are formed by simultaneous normal and steep angle depositions of the molybdenum and alumina, respectfully, onto the rotating substrate containing the anode and cathode layers.
• the newly deposited alumina is selectively removed. Similar work has also been disclosed in U. S. Patent No. 3,755,704.
• a second category is the use of orientation-dependent etching of single crystal materials such as silicon.
• the principle of the orientation-dependent etching is to preferentially attack a particular crystallographic face of a material.
• the anisotropically etched areas will be bounded by the slow etching faces which intersect at well defined edges and points of the material's basic crystallographic shape.
• a suitable combination of etch, material, and orientation can result in very sharply defined points that can be used as field emitters.
• 3,665,241 issued to Spindt, et al. is an example of this method in which an etch mask of one or more islands is placed over a single-crystal material which is then etched using an etchant which attacks some of the crystallographic planes of the material faster than the others creating etch profiles bounded by the slow etching planes (an orientation-dependent etch) .
• an etchant which attacks some of the crystallographic planes of the material faster than the others creating etch profiles bounded by the slow etching planes (an orientation-dependent etch) .
• the slow etching planes converge under the center of the mask, multifaceted geometric forms with sharp edges and points are formed whose shape is determined by the etchant, orientation of the crystal, and shape of the mask.
• a third category uses isotropic etches to form the structure. Isotropic etches etch uniformly in all directions. When masked, the mask edge becomes the center point of an arc which outlines the classic isotropic etch profile under the masking material.
• the radius of the arc is equal to the etch depth.
• Etching around an isolated masked island allows the etch profile to converge on the center of the mask leaving a sharp tip of the unetched material which can be used as a field emitter.
• An example of this is exemplified in U. S. Patent No. 3,998,678, issued to
• an emitter material is masked using islands of a lithographically formed and etch resistant material.
• the emitter material is etched with an isotropic etchant which forms an isotropic etch profile
• a fourth category uses oxidation processes, which form a tip by oxidizing the emitter material.
• Oxidation profiles under oxidation masks are vir ⁇ tually identical to isotropic etch profiles under masks and form the same tip structure as the profiles converge under a circular mask.
• the oxidized material is removed the unoxidized tip can function as a field emitter.
• U. S. Patent No. 3,970,887 issued to Smith et al. exemplifies this process.
• the process of this category is very similar to the isotropic etch category.
• a substrate of electron emission material such as silicon is used.
• a thermally grown oxide layer is grown on the substrate and is then lithographically featured and etched to result in one or more islands of silicon dioxide.
• the substrate is then reoxidized during which the islands of previously formed oxide act to sig- nificantly retard the oxidation of the silicon under them.
• the resulting oxidation profile is very similar to the isotropic etch profile and similarly converges under the islands leaving a sharp point profile in the silicon which can be exposed by removing the oxide.
• extraction electrodes are added to the structure after the tip has been formed.
• Other masking material such as silicon nitride can be used to similarly retard the oxidation and produce the desired sharp tip profile.
• a fifth category etches a pit which is the inverse of the desired sharply pointed shape in an expendable material which is used as a mold for the emitter material and then removed by etching.
• Orientation-dependent etching requires the use of a substrate of single crystal emitter material. Most all of them require the substrate to be made of or coated with the emitter material. Most all of them form the emitter first which complicates the fabrication of the subsequent electrode layers.
• S. Patent No. 3,921,022 also discloses a novel method of providing multiple tips or tiplets at the tip of a conical or pyramidical shaped field emitter.
• a typical field emission cathode structure is made up of a sharply pointed tip or blade.
• the cathode tip or blade could also be surrounded by a control and/or extraction electrode.
• cathode tip which has preferably a radius on the order of 10 - 100 nm.
• the most common methods of -9- formation include orientation-dependent etching, isotropic etching, and thermal oxidation.
• step (c) depositing at least one layer of a material which is capable of emitting electrons under the influence of an electrical field, over the insulative material of step (c) , and filling at least a portion of -the tip of the cusp, and
• step (c) depositing at least one layer of a material -11- which is capable of emitting electrons under the influence of an electrical field, over the insulative material of step (c) , and filling at least a portion of the tip of the cusp, and
• Still another aspect of this invention comprises of a field emission cathode structure comprising a layer of material which is capable of emitting electrons under the influence of an electrical field, and having at least one tip formed by the process of this invention for the emission of electrons.
• the field emission cathode structure of this invention further comprises on the tip side of the electron-emitting layer at least one electrically conductive material which is separated from the layer by at least one insulative material such that the emitter tip is exposed.
• the field emission cathode structure of this invention still further comprises on the tip side of the electron-emitting layer a plurality of electrically conductive material, each of which is separated from each other and the electron-emitting layer by at least one insulative material such that the emitter tip is exposed.
• the field emission cathode structure of this invention could further comprise on the tip side of the electron-emitting layer at least one barrier layer, which is selectively removed to expose the tip.
• a product can also be made by any of the process -12- of this invention.
• Another object of this invention is to eliminate the dependence on single crystal materials while maintaining a high degree of flexibility in the choice of field emission materials.
• Another object is to fabricate an integrated extraction electrode which is both self-aligned and formed as part of the tip formation process rather than added as a subsequent operation thus greatly simplifying the total fabrication process.
• Yet another objective is to provide a means of isolating and interconnecting multiple field emitters, extraction electrodes, and other electrodes in useful electrical configurations.
• the objects of the present invention are achieved by using the cusp that is formed when a hole in an substrate is filled usinq a conformal layer deposition or formation technique.
• the cusp serves as a mold that can be filled with any material that is capable of emitting electrons under the influence of an electric field (emitter layer) . Once the mold is removed either by some common release mechanism or by selectively etching both the substrate and the cusp forming layer, a sharp tip which is the replica of the cusp is freed.
• This tip is expected to have a small enough radius as formed to act as a field emission cathode.
• tips may bo sharpened using procedures already known in the art, such as slow isotropic tip etching, or the -13- oxidation and subsequent removal of the oxide.
• the process is not limited to any particular material. Many materials and material combinations can be used for substrate, conformal layer, and emitter material.
• An extraction electrode can be added to the basic structure by first depositing a conductive electrode layer on the base substrate.
• the hole that is to be later used to form the cusp is etched through the conductive electrode layer and to or into the substrate.
• the conformal cusp forming layer is deposited or formed followed by the deposition of the emitter layer.
• the substrate is released or etched away selectively with an etchant that does not attack the conductive electrode.
• the conformal . layer is then removed selectively by an etchant that does not attack either the conductive electrode (extraction electrode) or the emitter material, until the tip is freed to the desired degree.
• the process further allows the addition of more electrodes which can be used for extraction, control, or the selection of particular emitter structures within an array of such structures. These additional electrodes are added starting with the electrode covered substrate. An layer of an insulator is deposited followed by the deposition of an additional electrode layer. Each repetitive deposition of this new pair of layers will create an additional -14- electrode. The hole that will be later used to form the cusp is now etched through all of the electrode and insulator layers down to or into the base layer itself. The process then proceeds just as it would be performed for the single extraction electrode structure.
• Multi-electrode structures open the possibility of nonproductive undercut etching of the insulators between electrodes. This occurs if isotropic etches which attack both the conformal cusp forming material and the electrode insulators is used. This can be minimized or eliminated by using an anisotropic etch which does not significantly attack the material of the first electrode, which is nearest the substrate, or the emitter layer.
• Release or barrier layers can be used at various steps in the process to provide for easy release of molds or substrates from the complete or partially complete structure, or as etch stops, or as protective layers to aid in controlling the process.
• the silicon-silicon interface would not allow the selective removal of the cusp to free the tip.
• This impediment can be eliminated by the addition of a very thin film of silicon nitride onto the cusp layer, followed by the silicon deposition to fill the cusp.
• This additional layer will now allow the cusp silicon etch to be stopped by the silicon nitride.
• the nitride can subsequently be removed with an etchant such as boiling phosphoric acid that does not attack the remaining silicon thus freeing the tip.
• the electrode layers including the emitter layer are typically good conductors and as such they can be -15- lithographically patterned before the next layer is added to form isolations and interconnections between emitter structures.
• the associated insulators can be lithographically featured to provide via openings for vertical interconnections.
• One use of such patterning is the formation of X and Y addressing lines which can be used to selectively activate individual or groups of emitters for display applications.
• Figure IA is a cross-sectional view of a single layered substrate having at least one hole for the subsequent formation of the emitter tip.
• Figure IB is a cross-sectional view showing the deposition of a cusp forming layer and an emitter layer over the substrate.
• -16- Figure 1C shows a cross-sectional view of a free standing emitter layer after the emitter tip has been freed.
• Figure ID shows a cross-sectional view of a free standing emitter layer after the emitter tip has been cladded and the emitter layer has been provided with a support layer.
• Figure 2A is a cross-sectional view of another embodiment of the invention showing a substrate comprising of one expendable layer under an electrode layer and having at least one hole.
• Figure 2B is a cross-sectional view showing the structure of Figure 2A, covered with a cusp forming layer and the emitter material layer.
• Figure 2C is a cross-sectional view showing the structure of Figure 2B, after the expendable layer has been removed.
• Figure 2D is a cross-sectional view of the emitter tip being exposed after the partial removal of the cusp forming layer within an integrated extraction electrode.
• Figure 3A shows a cross-sectional view of still another embodiment of the invention showing a substrate comprising two electrode layers separated by an insulator layer over a base layer, and having at least one hole.
• Figure 3B is a cross-sectional view showing the structure of Figure 3A, after the emitter tip has been exposed.
• Figure 4A is a cross-sectional view showing yet another embodiment of this invention where the emitter layer has a barrier layer along with multiple electrodes separated by insulating material.
• Figure 4B shows a cross-sectional view of the structure of Figure 4A, where the barrier material at -17- and around the emitter tip has been exposed.
• Figure 4C shows a cross-sectional view of the structure of Figure 4B, where the barrier material at and around the emitter tip has been removed and the emitter tip has been exposed.
• Figure 5A is a cross-sectional view showing a cusp that results from conformally filling a hole whose dimensions do not change with depth.
• Figure 5B shows a cross-sectional view of another method of making a cusp from an opening having a different profile so that the location of the cusp could be adjusted.
• Figure 5C shows a cross-sectional view of still another method of making a cusp from an opening having still a different profile.
• Figure 6 shows a cross-sectional view of a cusp made by a marginally conformal process in a hole whose dimensions are constant with depth.
• Figures 7A, 7B and 7C illustrate a cross-sectional view of a field emission cathode that had a blunt tip that was sharpened.
• Figure 8 illustrates a perspective and a partial cut-away view of a field emission cathode that has been interconnected.
• This invention describes a novel new technique and structure for the integrated fabrication of both field emission cathodes, and field emission cathodes with integral single or multiple extraction and/or control electrodes. Both of these structures may be made as individuals or groups.
• the field emission cathode of this invention may be used as an electron source in a Vacuum
• VMD Vacuum
• Microelectronic Device as used herein, means not only a diode but a triode, tetrode, pentode or any other device that is made using this process, including the interconnection thereof.
• a VMD is any device with at least a sharp emitter (cathode) tip, and a collector (anode) with an insulator separating the emitter from the anode and there is preferably a straight-line or direct transmission of electrons from the emitter to the collector (anode) .
• this layer is exposed patternwise to the appropriate actinic radiation and developed to selectively remove the masking layer and expose the underlying surface in the patterns required.
• Third the exposed surface is etched to remove all or part of the underlying material as required.
• the remaining areas of the masking layer are removed.
• the term "lithographically defined" can refer to following "liftoff process.”
• a masking layer that is sensitive in a positive or negative sense to some actinic radiation, for example, light, e-beams, and/or X-rays, is deposited on the surface.
• this layer is exposed patternwise to the appropriate actinic radiation and developed to selectively remove the masking layer and expose the underlying surface in patterns where the desired material layer is to remain.
• the deposition, exposure, and development process is controlled in such a way that the edges of the remaining mask image has a negative or undercut profile.
• the desired material is deposited over both the open and mask covered areas by a line of sight deposition process such as evaporation.
• the mask material is removed, for example, by dissolution and freeing any material over it and allowing it to be washed away.
• conductive material or “conductor layer” or “conductive substrate” refers to any of a wide variety of materials which are electrical conductors. Typical examples include the elements
• insulative material or "insulator layer” or “insulative substrate” refers to a wide variety of materials that are electrical insulators especially glasses, and ceramics. Typical examples include elements such as carbon in a diamond form (crystalline or amorphous) , single crystal compounds -20- such as sapphire, glasses and polycrystalline or amorphous compounds such as some oxides of Si, Al, Mg, and Ce, some fluorides of Ca, and Mg, some carbides and nitrides of silicon, and ceramics such as alumina or glass ceramic.
• electron-emitting material or “emitter layer” or “emitter material” refers to any material capable of emitting electrons under the influence of an electric field. Typical examples include any of the electrical conductors, such as in the examples listed above, and borides of the rare earth elements, solid solutions consisting of 1) a boride of a rare earth or an alkaline earth (such as Ca, Sr, or Ba) , and 2) a boride of a transition metal (such as Hf or Zr) .
• the emitter material can be a single layered, a composite or a multilayered structure.
• a multilayered emitter might include the addition of one or more of the following; a work function enhancement layer, a robust emitter layer, a high performance electrically conductive layer, a thermally conductive layer, a physically strengthening layer or a stiffening layer.
• This multilayered composite may contain both emitter and non-emitter materials, which can all act ⁇ ynergistically together to optimize emitter performance.
• An example of this is discussed in Busta, H. H. et al. "Field Emission from Tungsten-Clad Silicon Pyramids" , IEEE Transactions on Electron Devices, Vol. 36, No. 11, pages 2679-2685 (November 1989) , where they show the use of coating or cladding on these cathode tips or pyramids to enhance or modify the cathode tip properties.
• This coating or cladding can also be used in situations where one cannot form the desired tip structure or it is difficult to form the desired tip 0/0596
• deposited refers to any method of layer formation that is suitable to the material as are generally practiced throughout the semiconductor industry.
• deposition techniques can be used with the previously mentioned materials, such as, sputtering, chemical vapor deposition, electro or electroless plating, oxidation, evaporation, sublimation, plasma deposi- tion, anodization, anodic deposition, molecular beam deposition or photodeposition.
• tip means not only a pointed projection but also a blade.
• Field emitter shapes other than points are sometimes used, such as blades. Blades are formed using the same methods except that the hole is a narrow elongated segment.
• the shape of the sharp edge of the blade can be linear or circular or a linear segment or a curve segment to name a few.
• the hole to make the field emission cathode structure of this invention is preferably formed by a process selected from a group comprising, ablation, drilling, etching, ion milling or molding.
• the hole can also be etched, using etching techniques selected from a group comprising anisotropic etching, ion beam etching, isotropic etching, reactive ion etching, plasma etching or wet etching.
• the hole profile or dimensions could be constant with depth or vary with depth.
• the material underneath the tip in the cusp forming layer or material is removed preferably by a process selected from the group comprising, dissolution, etching, evaporation, melting or subliming. As discussed elsewhere the entire substrate underneath
• the layer of electron-emitting material could also b completely removed. In some situations the entir material underneath the electron-emitting materia can be completely removed. ⁇ barrier layer or material could also be forme prior to the deposition of the electron-emitting material. The barrier layer subsequently can be selectively removed.
• the field emission cathode structure of this invention can be used as an electron source. As discussed elsewhere at least one tip of this cathode structure could be electrically isolated from another tip, or at least one tip could be electrically connected to another electronic component. Of course the field emission cathode structure of this invention could be used in or be a part of an electronic display device.
• Figures IA through 1C demonstrate the fabrication of the simplest field emission structure 35, having the field emission tip 31, on a field emission layer 30.
• a hole or opening 15 is formed, as for example by lithographical techniques.
• the substrate or base 5, could be a single-layered or a multilayered structure.
• the shape of the hole 15, can be square, round, oval, etc., and the hole 15, can be formed by any method known to a person skilled in the art, for example, hole 15, can be etched by reactive ion -23- etching (RIE) which typically results in the profile shown in Figure IA.
• RIE reactive ion -23- etching
• the depth of the hole 15, should be greater than half of its diameter. Therefore, the base or substrate 5, should be of sufficient thickness to allow for the proper formation of hole 15. The effects of hole profile variations will be discussed later.
• a layer of a second expendable material 20, is conformally deposited on the- substrate 5, until the growing thickness on the sidewalls of the hole 15, converge in the center of hole 15, to form a cusp 21.
• An emitter layer 30, is deposited to fill cusp 21, as well as other desired areas as shown in Figure IB.
• Substrate 5 is now selectively etched away.
• the top of emitter layer 30, or the surface 32, away from the emitter tip 31, may be protected if necessary by mechanical means or by the temporary deposition of a masking or backing layer which is subsequently removed.
• Layer 20 is then selectively removed freeing tip 31, as shown in Figure 1C.
• release agent or the thin release layer that is used between layers 20 and 30, will depend upon the material that is used to make layers 20 and 30.
• the field emission cathode 35 can also be coated or clad with a layer 29, as illustrated in
• the layer 29, must be of a material which is capable of emitting electrons under
• the basic process can be expanded to creat cathode 40, by forming an emitter tip 41, which i self-aligned inside an integral extraction electrod ⁇ o.
• electrode laye To fabricate the electrode 40, electrode laye
• Hole 15, having a mouth or opening 38, is lithographically featured typically using RI through electrode layer 10, into the substrate 5, t a depth which is greater than half the diameter o the hole 15, as shown in Figure 2A.
• th substrate 5, should be thick enough to allow for th proper formation of hole 15.
• An insulator layer 25, is conformally deposite on the electrode layer 10, and fills the hole 15, i the base layer or substrate 5, to form the cusp 26.
• Emitter layer 30 is then deposited to fill cusp 26, as shown in Figure 2B.
• the expendable base layer or substrate 5 is selectively etched away leaving behind the structure as shown in Figure 2C.
• Insulator 25 is then selectively etched through the mouth or opening 38, in electrode 10.
• Figure 2D shows the resulting cathode structure 40, having a cathode tip 41, that is self-aligned inside an -25- integral extraction electrode 10.
• the etch profile for an isotropic etch 32 is shown in Figure 2D, while phantom lines 34, depict an etch profile that would result if a selective anisotropic etch was used instead to etch insulator layer 25.
• a further expansion of the basic process allows the formation of an emitter tip that is self-aligned in several electrodes which can be used for extraction and control of the electron current.
• the structure 45 illustrates a cathode with two extraction/control electrodes. As shown in Figure
• the structure can be made starting again by depositing electrode layer 10, on expendable substrate 5, depositing insulator layer 12, on the already deposited electrode layer 10, and then depositing electrode layer 14, on the insulator layer 12.
• the hole or opening 15, is lithographically formed etching through layers 14, 12 and 10, to or into expendable substrate 5.
• the process then proceeds as before, by conformally depositing insulator 25, to form a cusp (not shown) , depositing emitter layer 30, to fill the cusp, removing the expendable substrate 5, by peeling or etching, and then selectively etching insulator 25, from the bottom to expose emitter tip 51, as shown in Figure 3B.
• the degree of exposure can be varied as desired, by altering the etch time.
• Figure 3B shows the etch profiles 32, that results from etching layer 25, that had filled the hole 15, with an isotropic etch.
• the evident undercut serves no useful purpose and may actually be detrimental by weakening the structure and occupying more spatial area then needed. This undercut can be eliminated by using an anisotropic -26- etch such as RIE.
• the phantom lines 34 depict the etch profile that would result if an anisotropic etch had instead been used to etch layer 25.
• RIE etches are favored for their anisotropy and all dry processing but they are often not totally selective but rely on significant differences in the etch rates between different materials.
• some desirable RIE processes such as that suggested in the fabrication of structure 45, ( Figure 3B) to remove insulator 25, and expose emitter tip 51, without undercut, may actually attack the emitter material very slowly but enough to undesirably reduce the radius of tip 51.
• One method of correcting such a problem, if it occurs, is to sharpen the tip as as been described elsewhere.
• Figures 4 through 4C show how such damage can be avoided and also represent an example how barrier layers can be used.
• the two electrode, (plus emitter) field emission cathode of structure 45 is used for illustration. All of the steps up to the formation of the cusp are identical to those of the preceding paragraphs.
• a very thin barrier layer 28, which preserves the cusp profile is deposited to cover layer 25.
• the barrier can be any material that forms a film, that preserves the cusp structure, thajt is selectively removable without damage to the other cathode substructures, and is stable enough to remain with the finished structure.
• silicon nitride which is selectively soluble in hot phosphoric acid.
• the emitter layer 30, is deposited over the barrier layer 28, to fill the cusp as shown in Figure 4A.
• the substrate 5, is then removed by peeling or etching.
• the insulator layer 25, is then etched using the RIE process to expose barrier 28, without undercutting electrodes 10 or 14, as shown in Figure 4B.
• the barrier layer 28, can now be selectively etched exposing emitter tip 51, and completing the structure 55, as shown in Figure AC .
• Figure 5A illustrates a typical cusp forming hole profile
• Figures 5B and 5C illustrate some of the alternative cusp forming hole profiles.
• Holes 15, 16 and 17 are shown as being in simple solid substrates, but they are not limited in any way to these examples and may be usefully created in the previously discussed multielectrode or multilayered substrate or composites as well.
• Figure 5A shows the vertical sidewall hole 15, which has been used in the previous descriptions of the process. It has the advantage of occupying the smallest spatial area.
• One of its characteristics is that the tip 21, of the cusp initially forms at the level of the substrate surface 62, and if the conformal deposition is continued will move vertically upwards as shown by phantom line 22, to a position above the surface whose height is controlled by the amount of additional deposition. Under some deposition conditions one or more voids 23, may form in the hole 15. Since the material 20, in the hole -28- 15, will be removed later to free the emitter tip
• the location of the emitter tip 31 may be of little or no consequence, but in applications using additional electrodes, a more optimum placement of the emitter tip is desired.
• Some field models suggest that the optimum placement of the emitter tip is at a height between the heights of the top and bottom of the electrode layer nearest to the emitter layer.
• One method of adjusting this placement is to adjust the profile of the vacuum space hole.
• An example of such a profile is shown in Figure 5B, where the dimensions of the hole profile varies or changes with depth.
• Hole 16 has sloped sidewalls so that the conformal film 20, grows perpendicular to the sloped side wall which forces initial convergence at a point equidistant from the sides and bottom which is well below the top surface 62, of the substrate 5.
• Additional deposition as shown by phantom lines 22 moves the cusp upward and the location of the cusp can be selected to nominally place the cusp vertically where desired. This allows a process variations to move the cusp up or down through desired range. With proper choice of the nominal position and the vacuum space hole wall angle, the accumulated process tolerances can be absorbed and the cusp will stay within its optimal placement range.
• Figure 5C shows that complex hole profiles can be used to produce useful cusp structures.
• electrode layer 10 on substrate 5 was lithographically featured with hole 17, first by -29- anisotropically etching into electrode 10, followed by the selective isotropic etching of the substrate
• the deposition of conformal layer 20, produces the cusp 21, and may produce void 23. It should be noted that void 23, does not affect the successful use of this structure for the formation of the emitter tip (not shown) because it will be subsequently removed to expose the emitter tip.
• Figure 6 is an example of how even marginally conformal processes can be used to form useful cusp structures.
• nominally vertical walled hole 15, in substrate 5, is sputter coated with layer 27.
• the cusps produced should have the following attributes. First, it should be open and should thus be easier to fill. Secondly, it should naturally form below the surface of the electrode without requiring special vacuum space hole profiles.
• the emitter material 30 has the approximate shape of a tip 72, which is more like a blunt tip, as shown in
• Means of isolating and interconnecting multiple field emitters, extraction electrodes, and other electrodes in useful electrical configurations can also be provided. This can be done because, the electrode layers including the emitter layer are typically good conductors and as such they can be lithographically patterned before the next layer is added to form isolations and interconnections between emitter structures. Similarly the associated insulators can be lithographically featured to provide via openings for vertical interconnections.
• Y addressing lines which can be used to selectively activate individual or groups of emitters for display applications.
• Microelectronic Devices and/or display elements are electrically interconnected during fabrication to form integrated circuits and/or displays.
• FIG 8. An example of an interconnection of the field emission cathodes is shown in Figure 8.
• the emitter layer has been lithographically featured into lines which interconnect individual emitters 84, in the "X” direction and form “X” emitter lines 94.
• the space 88 isolates one "X” emitter line 94, from another -31- "X” emitter line 94.
• the extraction electrode layer is lithographically featured into "Y" electrode line 92, with spaces 87, that isolate one
• Insulating or cusp forming layer 85 separates the individual extraction electrode 82 or "Y” electrode line 92, from the individual emitter electrode 84 or the "X" emitter line 94. Also, shown is the secondary cusp

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  • 1991-06-18 KR KR91010044A patent/KR950001485B1/ko not_active IP Right Cessation
  • 1991-06-18 NZ NZ238590A patent/NZ238590A/xx unknown
  • 1991-06-18 MY MYPI91001091A patent/MY106537A/en unknown
  • 1991-06-18 AU AU78494/91A patent/AU639342B2/en not_active Ceased
  • 1991-06-18 CN CN91104165.6A patent/CN1021389C/zh not_active Expired - Lifetime

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