Patent Application
20050082964
The present invention relates to a cold cathode field emission display and, more specifically, to a cold cathode field emission display with a focus electrode in which an increase in potential in the focus electrode can be suppressed even if an abnormal discharge takes place.
In the fields of displays for use in television receivers and information terminals, studies have been made for replacing conventionally mainstream cathode ray tubes (CRT) with flat-panel displays that are to comply with demands for a decrease in thickness, a decrease in weight, a larger screen and a high fineness. Such flat panel displays include a liquid crystal display (LCD), an electroluminescence display (ELD), a plasma display panel (PDP) and a cold cathode field emission display (FED). Of these, a liquid crystal display is widely used as a display for an information terminal. For applying the liquid crystal display to a floor-type television receiver, however, it still has problems to be solved concerning a higher brightness and an increase in size. In contrast, a cold cathode field emission display uses cold cathode field emission devices (to be sometimes referred to as a “field emission device” hereinafter) capable of emitting electrons from a solid into a vacuum on the basis of a quantum tunnel effect without relying on thermal excitation, and it is of great interest from the viewpoints of a high brightness and a low power consumption.
The field emission device shown in
The anode panel AP comprises a substrate 30, a phosphor layer 31 (31R, 31B and 31G) which is formed on the substrate 30 and has a predetermined pattern, and an anode electrode 34 formed thereon. A black matrix 32 is formed on the substrate 30 between one phosphor layer 31 and another phosphor layer 31, and a separation wall 33 is formed on the black matrix 32.
Each pixel is constituted of a group of the field emission devices formed on the electron-emitting region EA which is an overlap region of the cathode electrode 11 and the gate electrode 13 of the cathode panel side and the phosphor layer 31 of the anode panel side arranged so as to face the electron-emitting region EA. In the effective field, such pixels are arranged on the order, for example, of hundreds of thousands to several millions.
The anode panel AP and the cathode panel CP are arranged such that the electron-emitting regions EA and the phosphor layers 31 are opposed to each other, and the anode panel AP and the cathode panel CP are bonded to each other in their circumferential portions through a frame 35, whereby the display is produced. In an ineffective field which surrounds the effective field and where a peripheral circuit for selecting pixels is formed, a through-hole (not shown) for vacuuming is provided, and a tip tube (not shown) is connected to the through-hole and sealed after vacuuming. That is, a space surrounded by the anode panel AP, the cathode panel CP and the frame 35 is in a vacuum state.
A relatively negative voltage is applied to the cathode electrode 11 from a cathode-electrode control circuit 40, a relatively positive voltage is applied to the gate electrode 13 from a gate-electrode control circuit 42, and a positive voltage having a higher level than the voltage applied to the gate electrode 13 is applied to the anode electrode 34 from an anode-electrode control circuit 43. Between the anode electrode control circuit 43 and the anode electrode 34 is generally provided a resistance member R0 (having a resistance value of 1 MΩ in a shown example) for preventing an over-current and discharging.
When such a display is used for displaying on its screen, a scanning signal is inputted to the cathode electrode 11 from the cathode-electrode control circuit 40, and a video signal is inputted to the gate electrode 13 from the gate-electrode control circuit 42. Due to an electric field generated when a voltage is applied between the cathode electrode 11 and the gate electrode 13, electrons are emitted from the electron-emitting portion 19 on the basis of a quantum tunnel effect, and the electrons are attracted toward the anode electrode 34 and collide with the phosphor layer 31. As a result, the phosphor layer 31 is excited to emit light, and a desired image can be obtained. That is, the working of the display is controlled, in principle, by a voltage applied to the gate electrode 13 and a voltage applied to the electron-emitting portion 19 through the cathode electrode 11.
In the field emission device having the above structure, electrons are emitted from the electron-emitting portion 19 with certain angles from the normal of the electron-emitting portion 19. As a result, electrons emitted from the electron-emitting portion 19 may not collide with the opposed phosphor layer 31 but collide with a phosphor layer 31 adjacent to the opposed phosphor layer 31. When such a phenomenon takes place, the brightness is decreased and an optical crosstalk occurs between contiguous pixels.
For preventing the occurrence of the above phenomenon, there has been proposed a field emission device provided with a focus electrode 215 as shown in the schematic partial end view of
Meanwhile, in the above display, the distance between the anode panel AP and the cathode panel CP is approximately 1 mm at the largest, so that an abnormal discharge (spark discharge) is liable to take place between the field emission device of the cathode panel (more specifically, the focus electrode 215) and the anode electrode 34 of the anode panel AP.
In a mechanism in which a discharge takes place in a vacuum space, first, electrons and ions that are emitted from the field emission device under a strong electric field work as a trigger to cause a small-scaled discharge. And, energy is supplied to the anode electrode 34 from the anode-electrode control circuit 43, the anode electrode 34 is locally temperature-increased, and an occluded gas inside the anode electrode 34 is released, or a material constituting the anode electrode 34 is caused to vaporize, so that the small-scaled discharge presumably grows to be an abnormal discharge. Besides the anode-electrode control circuit 43, energy accumulated in an electrostatic capacity formed between the anode electrode 34 and the field emission device may possibly work as a source for supplying energy that promotes the growth to the abnormal discharge.
When the above abnormal discharge takes place, not only the display quality is extremely impaired, but also the anode electrode 34 and the field emission device are damaged. That is, when the above abnormal discharge takes place, the potential in the focus electrode 215 comes close to the potential in the anode electrode 34, and the potential in the focus-electrode control circuit 41 connected to the focus electrode 215 is also increased, so that the focus-electrode control circuit 41 may be damaged. Further, as a result of the fact that the potential in the focus electrode 215 comes close to the potential in the anode electrode 34, the potential in the gate electrode 13 is also increased. As a result, the potential difference between the gate electrode 13 and the electron-emitting portion 19 is increased. Therefore, excess electrons may be emitted from the electron-emitting portion 19, the electron-emitting portion 19 may be damaged, or the gate-electrode control circuit 42 connected to the gate electrode 13 may be damaged. Further, the potential in the cathode electrode 11 is increased, and as a result, the cathode-electrode control circuit 40 connected to the cathode electrode 11 may be damaged.
For inhibiting the abnormal discharge (spark discharge), it is effective to control the emission of electrons and ions which trigger the discharge, while it is required to control the particles extremely strictly therefor. In a general production process of the cathode panels CP or the display panels using the cathode panels CP, practicing the above control involves great technical difficulties.
Therefore, it is an object of the present invention to provide a cold cathode field emission display in which an abnormal increase in potential in the focus electrode can be suppressed even when an abnormal discharge takes place.
The cold cathode field emission display according to a first aspect of the present invention for achieving the above object is a cold cathode field emission display comprising at least:
In the cold cathode field emission display according to the first aspect of the present invention, the capacitor (a capacitor part) and the resistance element may be arranged in an ineffective field which surrounds an effective field that works as an actual display portion and in which a peripheral circuit for selecting pixels is formed, or the capacitor and the resistance element may be arranged on that portion of the display panel that is outside a frame to be discussed later, or the capacitor and the resistance element may be arranged outside the display panel, or the capacitor and the resistance element may be arranged in the focus-electrode control circuit.
The cold cathode field emission display according to a second aspect of the present invention for achieving the above object is a cold cathode field emission display comprising at least:
In the cold cathode field emission display according to the first or second aspect of the present invention, there may be employed a constitution in which a plurality of the first opening portions are formed through that portion of the focus electrode that is positioned in the overlap region of the cathode electrode and the gate electrode and through the insulating film positioned therebelow, and one second opening portion is communicating with one first opening portion. In other words, there may be employed a constitution in which a plurality of the focus electrodes are formed on the insulating film above the overlap region of the cathode electrode and the gate electrode, a plurality of the first opening portions are formed through the focus electrode and the insulating film above the overlap region of the cathode electrode and the gate electrode, and the second opening portion communicating with the first opening portion is formed. The above constitution will be referred to as the cold cathode field emission display according to the first-A aspect or second-A aspect of the present invention for convenience.
Alternatively, in the cold cathode field emission display according to the first or second aspect of the present invention, there may be employed a constitution in which one first opening portion is formed through that portion of the focus electrode that is positioned in the overlap region of the cathode electrode and the gate electrode and through the insulating film positioned therebelow, and a plurality of the second opening portions are communicating with the “one” first opening portion. The above constitution will be referred to as the cold cathode field emission display according to the first-B aspect or second-B aspect of the present invention for convenience. Preferably, the first opening portion is formed so as to surround a group of the cold cathode field emission devices formed in the overlap region of the cathode electrode and the gate electrode. In other words, there may be employed a constitution in which one focus electrode is formed on the insulating film so as to surround a group of the cold cathode field emission devices formed in the overlap region of the cathode electrode and the gate electrode, one first opening portion is formed through the focus electrode and the insulating film above a group of the cold cathode field emission devices formed in the overlap region of the cathode electrode and the gate electrode, and a plurality of the second opening portions communicating with the “one” first opening portion are formed.
Although differing depending upon the structure of the cold cathode field emission devices constituting the electron-emitting region, one electron-emitting portion may exist in one second opening portion and one third opening portion formed through the gate electrode and the insulating layer, or a plurality of the electron-emitting portions may exist in one second opening portion and one third opening portion formed through the gate electrode and the insulating layer, or there may be employed a constitution in which a plurality of the second opening portions are formed through the gate electrode, one third opening portion communicating with the second opening portions is formed through the insulating layer and one electron-emitting portion exists or a plurality of the electron-emitting portions exist in one third opening portion formed through the insulating layer.
In the cold cathode field emission display according to the second-B aspect of the present invention, there may be employed a constitution in which
Alternatively, there may be employed a constitution in which
Alternatively, in the cold cathode field emission display according to the second-B aspect of the present invention, there may be employed a constitution in which
Alternatively, there may be employed a constitution in which
Alternatively, in the cold cathode field emission display according to the second-B aspect of the present invention, there may be employed a constitution in which
Alternatively, in the cold cathode field emission display according to the second-B aspect of the present invention, there may be employed a constitution in which
Alternatively, in the cold cathode field emission display according to the second-B aspect of the present invention, there may be employed a constitution in which the focus electrode comprises a counterpart electrode formed on the insulating film, a dielectric material layer covering the top surface and side surface of the counterpart electrode, and a focus-electrode main portion formed on the dielectric material layer.
In the cold cathode field emission display according to the second aspect of the present invention, the resistance element may be arranged in the ineffective field which surrounds the effective field that works as an actual display portion and in which a peripheral circuit for selecting pixels is formed, or the resistance element may be arranged in that portion of the display panel that is outside a frame to be discussed later, or the resistance element may be arranged outside the display panel, or the resistance element may be arranged in the focus-electrode control circuit.
In the cold cathode field emission display according to the first aspect of the present invention, including the first-A aspect and the first-B aspect of the present invention, when the first voltage-output portion of the focus-electrode control circuit outputs a voltage V1 and when the second voltage-output portion of the focus-electrode control circuit outputs a voltage V2, preferably, V2<0 and |V1|−|V2|<0. More specifically, the value of |V1|−|V2 is preferably −1×10 volts to −1×103 volts, more preferably, −5×10 volts to −5×102 volts. When the capacity of the capacitor is Cc and when the electrostatic capacity based on the anode electrode and the focus electrode is CAF, preferably, Cc >20CAF is satisfied. Alternatively, the capacity Cc of the capacitor is preferably 2 nF to 1 μF.
In the cold cathode field emission display according to the second aspect of the present invention including the second-A aspect of the present invention, and the second-B aspect including the above various constitutions, when the first voltage-output portion of the focus-electrode control circuit outputs a voltage V1 and when the second voltage-output portion of the focus-electrode control circuit outputs a voltage V2, preferably, V2<0 and |V1|−|V2|<0. More specifically, the value of |V1|−|V2| is preferably −1×10 volts to −1×103 volts, more preferably, −5×10 volts to −5×102 volts. When the capacity of the capacitor formed by the focus-electrode main portion, the dielectric material layer and the counterpart electrode is Cc and when the electrostatic capacity based on the anode electrode and the focus electrode is CAF, preferably, Cc>20CAF is satisfied. Alternatively, the capacity Cc of the capacitor formed by focus-electrode main portion, the dielectric material layer and the counterpart electrode is preferably 2 nF to 1 μF.
In the cold cathode field emission display according to the first and second aspects of the present invention including the first-A aspect, first-B aspect, second-A aspect and second-B aspect of the present invention (these will be sometimes generally referred to as “the present invention” hereinafter), the focus electrode as a whole has the form of one sheet covering the entire effective field. The focus-electrode control circuit may have any known circuit constitution capable of outputting a predetermined DC voltage (including 0 volt) from the first voltage-output portion and the second voltage-output portion. The capacitor and the resistance element may be also constituted of any known capacitor and any known resistance element.
In the present invention, the cold cathode field emission device (to be abbreviated as “field emission device” hereinafter) can have a structure in which the electron-emitting portion is formed on the cathode electrode positioned in the bottom portion of the third opening portion and electrons are emitted from the electron-emitting portion exposed in the bottom portion of the third opening portion. The field emission device having the above first structure includes a Spindt-type (field emission device in which a conical electron-emitting portion is formed on the cathode electrode positioned in the bottom portion of the third opening portion) and a plane-type (field emission device in which an electron-emitting portion having the form of a nearly flat surface is formed on the cathode electrode positioned in the bottom portion of the third opening portion).
Specifically, the field emission device having the first structure comprises;
Alternatively, in the present invention, the field emission device can have a structure in which that portion of the cathode electrode that is exposed in the bottom portion of the third opening portion corresponds to the electron-emitting portion and electrons are emitted from that portion of the cathode electrode that is exposed in the bottom of the third opening portion. The field emission device having the above second structure includes a flat-type field emission device that is for emitting electrons from the surface of the flat cathode electrode.
Specifically, the field emission device having the second structure comprises;
In the Spindt-type field emission device, the material for constituting an electron-emitting portion may include at least one material selected from the group consisting of tungsten, a tungsten alloy, molybdenum, a molybdenum alloy, titanium, a titanium alloy, niobium, a niobium alloy, tantalum, a tantalum alloy, chromium, a chromium alloy and impurity-containing silicon (polysilicon or amorphous silicon). The electron-emitting portion of the Spindt-type field emission device can be formed by, for example, a vapor deposition method, a sputtering method and a CVD method.
In the plane-type field emission device, preferably, the electron-emitting portion is made of a material having a smaller work function Φ than a material for constituting a cathode electrode. The material for constituting an electron-emitting portion can be selected on the basis of the work function of a material for constituting a cathode electrode, a potential difference between the gate electrode and the cathode electrode, a required current density of emitted electrons, and the like. Typical examples of the material for constituting a cathode electrode of the field emission device include tungsten (Φ=4.55 eV), niobium (Φ=4.02-4.87 eV), molybdenum (Φ=4.53-4.95 eV), aluminum (Φ=4.28 eV), copper (Φ=4.6 eV), tantalum (Φ=4.3 eV), chromium (Φ=4.5 eV) and silicon (Φ=4.9 eV). The material for constituting an electron-emitting portion preferably has a smaller work function Φ than these materials, and the value of the work function thereof is preferably approximately 3 eV or smaller. Examples of such a material include carbon (Φ<1 eV), cesium (Φ=2.14 eV), LaB6 (Φ=2.66-2.76 eV), BaO (Φ=1.6-2.7 eV), SrO (Φ=1.25-1.6 eV), Y2O3 (Φ=2.0 eV), CaO (Φ=1.6-1.86 eV), BaS (Φ=2.05 eV), TiN (Φ=2.92 eV) and ZrN (Φ=2.92 eV). More preferably, the electron-emitting portion is made of a material having a work function Φ of 2 eV or smaller. The material for constituting an electron-emitting portion is not necessarily required to have electric conductivity.
Otherwise, in the plane-type field emission device, the material for constituting an electron-emitting portion can be selected from materials having a secondary electron gain δ greater than the secondary electron gain δ of the electrically conductive material for constituting a cathode electrode. That is, the above material can be properly selected from metals such as silver (Ag), aluminum (Al), gold (Au), cobalt (Co), copper (Cu), molybdenum (Mo), niobium (Nb), nickel (Ni), platinum (Pt), tantalum (Ta), tungsten (W) and zirconium (Zr); semiconductors such as silicon (Si) and germanium (Ge); inorganic simple substances such as carbon and diamond; and compounds such as aluminum oxide (Al2O3) barium oxide (Bao), beryllium oxide (BeO), calcium oxide (CaO), magnesium oxide (MgO), tin oxide (SnO2), barium fluoride (BaF2) and calcium fluoride (CaF2). The material for constituting an electron-emitting portion is not necessarily required to have electric conductivity.
In the plane-type field emission device, carbon is preferred as a material for constituting an electron-emitting portion. More specifically, diamond, graphite and a carbon-nanotube structure are preferred. When the electron-emitting portion is made of diamond, graphite or the carbon-nanotube structure, an emitted-electron current density necessary for the cold cathode field emission display can be obtained at an electric field intensity of 5×107 V/m or lower. Further, since diamond is an electric resister, emitted-electron currents obtained from the electron-emitting portions can be brought into uniform currents, and the fluctuation of luminescence efficiency can be suppressed when such field emission devices are incorporated into the display. Further, since the above materials exhibit remarkably high durability against sputtering by ions of residual gas in the cold cathode field emission display, field emission devices having a longer lifetime can be attained.
Specifically, the carbon-nanotube structure includes a carbon-nanotube and a carbon-nanofiber. More specifically, the electron-emitting portion may be constituted of a carbon-nanotube, it may be constituted of a carbon-nanofiber, or it may be constituted of a mixture of a carbon-nanotube with a carbon-nanofiber. Macroscopically, the carbon-nanotube and carbon-nanofiber may have the form of a powder or a thin film. The carbon-nanotube structure may have the form of a cone in some cases. The carbon-nanotube and carbon-nanofiber can be produced or formed by a known PVD method as an arc discharge method and a laser abrasion method; and any one of various CVD methods such as a plasma CVD method, a laser CVD method, a thermal CVD method, a gaseous phase synthetic method and a gaseous phase growth method.
The plane-type field emission device can be produced by a method in which a dispersion of a carbon-nanotube structure in a binder material is, for example, applied onto a desired region of the cathode electrode and the binder material is fired or cured. More specifically, the plane-type field emission device can be produced by a method in which the carbon-nanotube structure is dispersed in an organic binder material, such as an epoxy resin or an acrylic resin, or an inorganic binder material, such as water glass or silver paste and the like, the dispersion is, for example, applied onto a desired region of the cathode electrode, then, the solvent is removed and the binder material is fired and cured. The above method will be referred to as a “first forming method of a carbon-nanotube structure”. The application method includes, for example, a screen printing method.
Alternatively, the plane-type field emission device can be produced by a method in which a dispersion of the carbon-nanotube structure in a metal compound solution is applied onto the cathode electrode and then, the metal compound is fired, whereby the carbon-nanotube structure is fixed to the surface of the cathode electrode with a matrix containing metal atoms derived from the metal compound. The above method will be referred to as a “second forming method of a carbon-nanotube structure”. The matrix is preferably made of an electrically conductive metal oxide. More specifically, it is preferably made of tin oxide, indium oxide, indium-tin oxide, zinc oxide, antimony oxide or antimony-tin oxide. After the firing, there can be obtained a state where part of each carbon-nanotube structure is embedded in the matrix, or there can be obtained a state where the entire portion of each carbon-nanotube is embedded in the matrix. The matrix preferably has a volume resistivity of 1×10−9 Ω·m to 5×10−6 Ω·m.
The metal compound for constituting the metal compound solution includes, for example, an organometal compound, an organic acid metal compound and metal salts (for example, chloride, nitrate and acetate). The organic acid metal compound solution is, for example, a solution prepared by dissolving an organic tin compound, an organic indium compound, an organic zinc compound or an organic antimony compound in an acid (for example, hydrochloric acid, nitric acid or sulfuric acid) and diluting the resultant solution with an organic solvent (for example, toluene, butyl acetate or isopropyl alcohol). Further, the organic metal compound solution is, for example, a solution prepared by dissolving an organic tin compound, an organic indium compound, an organic zinc compound or an organic antimony compound in an organic solvent (for example, toluene, butyl acetate or isopropyl alcohol). When the amount of the solution is 100 parts by weight, the solution preferably has a composition containing 0.001 to 20 parts by weight of the carbon-nanotube structure and 0.1 to 10 parts by weight of the metal compound. The solution may contain a dispersing agent and a surfactant. From the viewpoint of increasing the thickness of the matrix, an additive such as carbon black or the like may be added to the metal compound solution. In some cases, the organic solvent may be replaced with water.
The method for applying onto the cathode electrode the metal compound solution in which the carbon-nanotube structure is dispersed includes a spray method, a spin coating method, a dipping method, a die quarter method and a screen printing method. Of these, a spray method is preferred in view of its easiness in application.
There may be employed a constitution in which the metal compound solution in which the carbon-nanotube structure is dispersed is applied onto the cathode electrode, the metal compound solution is dried to form a metal compound layer, then, an unnecessary portion of the metal compound layer on the cathode electrode is removed, and then the metal compound is fired. Alternatively, an unnecessary portion of the metal compound layer on the cathode electrode may be removed after the metal compound is fired. Alternatively, the metal compound solution may be applied only onto a desired region of the cathode electrode.
The temperature for firing the metal compound is preferably, for example, a temperature at which the metal salt is oxidized to form a metal oxide having electric conductivity, or a temperature at which the organometal compound or an organic acid metal compound is decomposed to form a matrix (for example, a metal oxide having electric conductivity) containing metal atoms derived from the organometal compound or the organic acid metal compound. For example, the above temperature is preferably at least 300° C. The upper limit of the firing temperature can be a temperature at which elements constituting the field emission device or the cathode panel do not suffer any thermal damage and the like.
In the first forming method or the second forming method of a carbon-nanotube structure, it is preferred to carry out a kind of an activation treatment (washing treatment) of the surface of the electron-emitting portion after the formation of the electron-emitting portion, since the efficiency of emission of electrons from the electron-emitting portion is further improved. The above activation treatment includes a plasma treatment in an atmosphere containing a gas such as hydrogen gas, ammonia gas, helium gas, argon gas, neon gas, methane gas, ethylene gas, acetylene gas or nitrogen gas.
In the first forming method or the second forming method of a carbon-nanotube structure, the electron-emitting portion may be formed in that portion of the cathode electrode that is positioned in the bottom portion of the third opening portion, or the electron-emitting portion may be also formed so as to extend from that portion of the cathode electrode that is positioned in the bottom portion of the third opening portion to the surface of that portion of the cathode electrode that is different from the portion of the cathode electrode in the bottom portion of the third opening portion. Further, the electron-emitting portion may be formed on the entire surface or part of the surface of that portion of the cathode electrode that is positioned in the bottom portion of the third opening portion.
In the plane-type field emission device, a convexoconcave shape may be formed in the surface of the cathode electrode. As a result, the probability that top portions of a material (specifically, for example, a carbon-nanotube structure) having the function of electron emission projected from the matrix face the anode electrode is increased, and the efficiency of electron emission can be further improved. The convexoconcave shape can be formed, for example, by dry-etching the cathode electrode, by subjecting the cathode electrode to anodic oxidation, or by a method in which spheres are sprayed on to the supporting member, the cathode electrode is formed on the spheres and then, for example, the spheres are combusted.
In the field emission device having the first structure, a resistance layer may be formed between the cathode electrode and the electron-emitting portion. Otherwise, when the surface of the cathode electrode corresponds to the electron-emitting portion, that is, in the field emission device having the second structure, the cathode electrode may have a three-layered structure constituted of an electrically conductive material layer, a resistance layer and an electron-emitting layer corresponding to the electron-emitting portion. The resistance layer can stabilize performances of the field emission device and can attain uniform electron-emitting properties. The material for constituting a resistance layer includes carbon-containing materials such as silicon carbide (SiC) and SiCN; SiN; semiconductor materials such as amorphous silicon and the like; and refractory metal oxides such as ruthenium oxide (RuO2), tantalum oxide and tantalum nitride. The resistance layer can be formed by a sputtering method, a CVD method or a screen-printing method. The resistance value of the resistance layer is approximately 1×105 to 1×107 Ω, preferably several MΩ.
In the various field emission devices, the material for constituting a cathode electrode can be selected from metals such as tungsten (W), niobium (Nb), tantalum (Ta), titanium (Ti), molybdenum (Mo), chromium (Cr), aluminum (Al) and copper (Cu), gold (Au), silver (Ag) and the like; alloys and compounds containing these metal elements (for example, nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2 and TaSi2); semiconductors such as silicon (Si); carbon thin film such as diamond; and indium-tin oxide (ITO). Although not specially limited thereto, the thickness of the cathode electrode is approximately 0.05 to 0.5 μm, and preferably 0.1 to 0.3 μm.
In the various field emission devices, the material for constituting the gate electrode includes at least one metal selected from the group consisting of tungsten (W), niobium (Nb), tantalum (Ta), titanium (Ti), molybdenum (Mo), chromium (Cr), aluminum (Al), copper (Cu), gold (Au), silver (Ag), nickel (Ni), cobalt (Co), zirconium (Zr), iron (Fe), platinum (Pt) and zinc (Zn); alloys or compounds containing these metal elements (for example, nitrides such as TiN and silicides such as WSi2, MoSi2, TiSi2 and TaSi2); semiconductors such as silicon (Si); and electrically conductive metal oxides such as indium-tin oxide (ITO), indium oxide and zinc oxide.
The method for forming the cathode electrode and the gate electrode includes deposition methods such as an electron beam deposition method and a hot filament deposition method, a sputtering method, a combination of a CVD method or an ion plating method with an etching method, a screen-printing method, a plating method and a lift-off method. When a screen-printing method or a plating method is employed, the cathode electrodes in the form of a stripe can be directly formed.
The method of forming the focus electrode in the cold cathode field emission display according to the first-A aspect or second-A aspect of the present invention includes, for example, vapor deposition methods such as an electron beam vapor deposition method and a hot filament vapor deposition method, a sputtering method, a CVD method, an ion plating method, a screen printing method, a plating method and a lift-off method. Generally, patterning is not required in any case except for the formation of the first opening portion and the removal of unnecessary portions. Further, the focus electrode in the cold cathode field emission display according to the first-B aspect of the present invention can be formed by a similar method, or it can be formed by a method in which a sheet-shaped focus electrode is prepared in advance and such a sheet-shaped focus electrode is stacked on the gate electrode and the insulating layer. Further, the focus electrode in the cold cathode field emission display according to the second-B aspect of the present invention can be also formed by a similar method, or it can be formed by a method in which a sheet-shaped stacked structure is formed in advance and such a sheet-shaped stacked structure can be stacked on the insulating film or the metal layer.
The plan form of the first, second or third opening portion (form obtained by cutting the first, second or third opening portion with an imaginary plane in parallel with the surface of the supporting member) may be any form such as a circle, an oval, a rectangle, a polygon, a rounded rectangle or a rounded polygon. These opening portions can be formed, for example, by isotropic etching or by a combination of anisotropic etching and isotropic etching. In the cold cathode field emission display according to the first-B or the second-B aspect of the present invention, the first opening portion can be formed by a mechanical method (for example, punching) or a chemical method (for example, etching).
As an electrically conductive material for constituting the focus electrode, an electrically conductive material for constituting the focus-electrode main portion and a material for constituting the metal layer, for example, the materials can be selected from the above electrically conductive materials used for constituting the cathode electrode or the gate electrode, or can be also selected from other materials such as sheets and foils made of metals or alloys.
As a material for constituting the dielectric material layer, for example, the material can be selected from SiO2, SiN, SiON, Ta2O5, SiC, glass and an alumina.
As a material for constituting the insulating layer and the insulating film, SiO2-containing material such as SiO2, BPSG, PSG, BSG, AsSG, PbSG, SiN, SiON and spin on glass (SOG), low-melting-point glass and a glass paste, SiN, an insulating resin such as polyimide and the like can be used alone or in combination. The insulating layer and the insulating film can be constituted of the same material or different materials. The insulating layer and the insulating film can be formed by a known method such as a CVD method, an application method, a sputtering method or a screen printing method.
The supporting member for constituting the cathode panel in the present invention includes a glass substrate, a glass substrate having an insulating film formed on its surface, a quartz substrate, a quartz substrate having an insulating film formed on its surface and a semiconductor substrate having an insulating film formed on its surface. From the viewpoint that the production cost is decreased, it is preferred to use a glass substrate or a glass substrate having an insulating film formed on its surface. Examples of the glass substrate include high-distortion glass, soda glass (Na2O.CaO.SiO2), borosilicate glass (Na2O.B2O3.SiO2), forsterite (2MgO.SiO2) and lead glass (Na2O.PbO.SiO2). A substrate for constituting the anode panel can have the same constitution as that of the above supporting member.
In the present invention, the anode panel comprises a substrate, a phosphor layer and an anode electrode. The surface to be irradiated with electrons is constituted of the phosphor layer or the anode electrode depending upon the structure of the anode panel.
Examples of the constitution of the anode electrode and the phosphor layer include a constitution (1) in which the anode electrode is formed on the substrate and the phosphor layer is formed on the anode electrode, and a constitution (2) in which the phosphor layer is formed on the substrate and the anode electrode is formed on the phosphor layer. In the constitution (1), a so-called metal back film may be formed on the phosphor layer. In the constitution (2), a metal back layer may be formed on the anode electrode.
The material for constituting the anode electrode can be selected depending upon the constitution of the cold cathode field emission display. That is, when the cold cathode field emission display is a transmission type (the substrate corresponds to a display screen), and when the anode electrode and the phosphor layer are stacked on the substrate in this order, not only the substrate on which the anode electrode is to be formed but also the anode electrode itself is required to be transparent, and a transparent electrically conductive material such as indium-tin oxide (ITO) is used. When the cold cathode field emission display is a reflection type (the supporting member corresponds to a display screen), or when the cold cathode field emission display is a transmission type and the phosphor layer and the anode electrode are stacked on the substrate in this order (the anode electrode also works as the metal back film), ITO can be used, and besides ITO, the material for the anode electrode can be properly selected from the above materials with respect of the cathode electrode, the gate electrode or the focus electrode. More preferably, aluminum (Al) or chromium (Cr) is used for constituting the anode electrode. When the anode electrode is made of aluminum (Al) or chromium (Cr), for example, the specific thickness of the anode electrode is 3×10−8 m (30 nm) to 1.5×10−7 m (150 nm), preferably 5×10−8 m (50 nm) to 1×10−7 m (100 nm). The anode electrode can be formed by a vapor deposition method or a sputtering method.
The phosphor material for constituting the phosphor layer can be selected from a fast-electron-excitation type phosphor material or a slow-electron-excitation type phosphor material. When the cold cathode field emission display is a monochrome display, it is not required to pattern the phosphor layer. When the cold cathode field emission display is a color display, preferably, the phosphor layers corresponding to three primary colors of red (R), green (G) and blue (B) patterned in the form of stripes or dots are alternately arranged. A black matrix may be filled in a gap between one patterned phosphor layer and another phosphor layer for improving the contrast of a display screen.
Further, the anode panel is preferably provided with a plurality of separation walls for preventing the occurrence of so-called optical crosstalk (color mixing) that is caused when electrons recoiling from the phosphor layer or secondary electrons emitted from the phosphor layer enter another phosphor layer, or for preventing the collision of electrons with other phosphor layer when electrons recoiling from the phosphor layer or secondary electrons emitted from the phosphor layer enter other phosphor layer over the separation wall.
The form of the separation walls includes the form of a lattice (grilles), that is, a form in which the separation wall surrounds the phosphor layer corresponding to one pixel and having a plan form being nearly rectangular (or dot-shaped), and a stripe or band-like form that extends in parallel with opposite two sides of a rectangular or stripe-shaped phosphor layer. When the separation wall(s) has (have) the form of a lattice, the separation wall may have a form in which the separation wall continuously or discontinuously surrounds four sides of one phosphor layer. When the separation wall(s) has (have) the form of a stripe, the stripe may be continuous or discontinuous. The formed separation walls may be polished to flatten the top surface of each separation wall.
For improving the contrast of display images, preferably, a black matrix that absorbs light from the phosphor layer is formed between one phosphor layer and another adjacent phosphor layer and between the separation wall and the substrate. As a material for constituting the black matrix, it is preferred to select a material that absorbs at least 99% of light from the phosphor layer. The above material includes carbon, a thin metal film (made, for example, of chromium, nickel, aluminum, molybdenum and an alloy of these), a metal oxide (for example, chromium oxide), metal nitride (for example, chromium nitride), a heat-resistant organic resin, glass paste, and glass paste containing a black pigment or electrically conductive particles of silver or the like. Specific examples thereof include a photosensitive polyimide resin, chromium oxide, and a chromium oxide/chromium stacked film. Concerning the chromium oxide/chromium stacked film, the chromium film is to be in contact with the substrate.
When the cathode panel and the anode panel are bonded in their circumferential portions, the bonding may be carried out with an adhesive layer or with a frame made of an insulating rigid material such as glass or ceramic and an adhesive layer. When the frame and the adhesive layer are used in combination, the facing distance between the cathode panel and the anode panel can be adjusted to be longer by properly determining the height of the frame than that obtained when the adhesive layer alone is used. While a frit glass is generally used as a material for the adhesive layer, a so-called low-melting-point metal material having a melting point of approximately 120 to 400° C. may be used. The low-melting-point metal material includes In (indium; melting point 157° C.); an indium-gold low-melting-point alloy; tin (Sn)-containing high-temperature solders such as Sn80Ag20 (melting point 220 to 370° C.) and Sn95Cu5 (melting point 227 to 370° C.); lead (Pb)-containing high-temperature solders such as Pb97.5Ag2.5 (melting point 304° C.), Pb94.5Ag5.5 (melting point 304-365° C.) and Pb97.5Ag1.5Sn1.0 (melting point 309° C.); zinc (Zn)-containing high-temperature solders such as Zn95Al5 (melting point 380° C.); tin-lead-containing standard solders such as Sn5Pb95 (melting point 300-314° C.) and Sn2Pb98 (melting point 316-322° C.); and brazing materials such as Au88Ga12 (melting point 381° C.) (all of the above parenthesized values show atomic %).
When three members of the cathode panel, the anode panel and the frame are bonded, these three members may be bonded at the same time, or one of the cathode panel and the anode panel may be bonded to the frame at a first stage, and then the other of the cathode panel and the anode panel may be bonded to the frame at a second stage. When bonding of the three members or bonding at the second stage is carried out in a high-vacuum atmosphere, a space surrounded by the cathode panel, the anode panel, the frame and the adhesive layer comes to be a vacuum space upon bonding. Otherwise, after the three members are bonded, the space surrounded by the cathode panel, the anode panel, the frame and the adhesive layer may be vacuumed to obtain a vacuum space. When the vacuuming is carried out after the bonding, the pressure in an atmosphere during the bonding may be any one of atmospheric pressure and reduced pressure, and the gas constituting the atmosphere may be ambient atmosphere or an inert gas containing nitrogen gas or a gas (for example, Ar gas) coming under the group 0 of the periodic table.
When the vacuuming is carried out after the bonding, the vacuuming can be carried out through a tip tube pre-connected to the cathode panel and/or the anode panel. Typically, the tip tube is made of a glass tube and is bonded to a circumference of a through-hole formed in the ineffective field of the cathode panel and/or the anode panel (i.e., the field other than the effective field which works as a display portion) with a frit glass or the above low-melting-point metal material. After the space reaches a predetermined vacuum degree, the tip tube is sealed by thermal fusion. It is preferred to heat and then temperature-decrease the cold cathode field emission display as a whole before the sealing, since residual gas can be released into the space, and the residual gas can be removed out of the space by vacuuming.
In the present invention, the gate electrode in the form of a stripe and the cathode electrode in the form of a stripe extend in the direction in which the projection images thereof cross each other at right angles, which is preferred for the simplification of structure of the cold cathode field emission display. A plurality of the field emission devices are provided in the overlap region of projection images of the cathode electrode in the form of a stripe and the gate electrode in the form of a stripe (the overlap region being an electron-emitting region and corresponding to a region forming one pixel or one sub-pixel). Such overlap regions are arranged, generally in the form of a two-dimensional matrix, in the effective field of the cathode panel. A relatively negative voltage is applied to the cathode electrode, the focus electrode or the focus-electrode main portion, a relatively positive voltage is applied to the gate electrode, and a positive voltage higher than the voltage (to be) applied to the gate electrode is applied to the anode electrode. Electrons are emitted into the vacuum space selectively from the electron-emitting portions positioned in the electron-emitting region which is an overlap region of a row-selected cathode electrode and a column-selected gate electrode (or a column-selected cathode electrode and a row-selected gate electrode), and such electrons are drawn toward the anode electrode and collide with the phosphor layer constituting the anode panel, to excite and cause the phosphor layer to emit light.
In the present invention, the capacitor is provided between the focus electrode and the focus-electrode control circuit, or the focus electrode per se works as a capacitor. When a discharge takes place between the anode electrode and the focus electrode, therefore, a current caused by the discharge flows in the capacitor, so that an abnormal increase in potential in the focus electrode can be reliably suppressed.
The present invention will be explained on the basis of Examples and with reference to drawings hereinafter.
Example 1 is concerned with the cold cathode field emission display (to be abbreviated as “display” hereinafter) according to the first-A aspect of the present invention.
The above display comprises at least;
Each electron-emitting region EA comprises;
In Example 1, the cold cathode field emission device (to be abbreviated as “field emission device” hereinafter) may have a structure in which the electron-emitting portion 19 is formed on the cathode electrode 11 positioned in the bottom portion of the third opening portion 18 and electrons are emitted from the electron-emitting portion 19 exposed in the bottom portion of the third opening portion 18. The field emission device having such a first structure includes a Spindt-type field emission device.
That is, the field emission device in Example 1 is a Spindt-type field emission device having the first structure and comprises;
The focus electrode 15 as a whole has the form of one sheet covering the entire effective field. A plurality of the first opening portions 16 are formed through that portion of the focus electrode 15 that is positioned in the overlap region of the cathode electrode 11 and the gate electrode 13 and through the insulating film 14 positioned therebelow, and one second opening portion 17 communicates with one first opening portion 16.
The focus electrode 15 is connected to a first voltage-output portion 41A of the focus-electrode control circuit 41 through the resistance element R, and further, the focus electrode 15 is connected to a second voltage-output portion 41B of the focus-electrode control circuit 41 through the capacitor C. The capacitor C and the resistance element R are attached, for example, to a printed circuit board provided with the focus-electrode control circuit 41, the capacitor C and the focus-electrode control circuit 41 are connected to each other through a wiring, the capacitor C and the focus electrode 15 are connected to each other through a wiring, the resistance element R and the focus-electrode control circuit 41 are connected to each other through a wiring, and the resistance element R and the focus electrode 15 are connected to each other through a wiring. A voltage V1 (for example, 0 volt) is outputted from the first voltage-output portion 41A of the focus-electrode control circuit 41, and a voltage V2 (for example, −100 volts) is outputted from the second voltage-output portion 41B of the focus-electrode control circuit 41.
The display panel in Example 1 comprises a cathode panel CP and an anode panel AP and has a plurality of pixels. In the cathode panel CP, a great number of the above electron-emitting regions EA provided with the above field emission devices are formed in the effective field in a manner in which they form a two-dimensional matrix. The anode panel. AP comprises a substrate 30, phosphor layers 31 (a phosphor layer 31R for emitting light in red, a phosphor layer 31G for emitting light in green and a phosphor layer 31B for emitting light in blue) formed on the substrate 30 and an anode electrode 34 that is in the form of one sheet covering the entire effective field and which is made, for example, of an aluminum thin film. A black matrix 32 is formed on the substrate 30 between the phosphor layer 31 and the phosphor layer 31, and a separation wall 33 is formed on the black matrix 32. The black matrix 32 and the separation wall 33 may be omitted. Further, when a monochromatic display is assumed, it is not required to form the phosphor layer 31 according to a predetermined pattern. Further, an anode electrode made of a transparent electrically conductive film of ITO or the like may be formed between the substrate 30 and the phosphor layer 31. Alternatively, the anode panel may comprise the anode electrode 34 made of a transparent electrically conductive film formed on the substrate 30, the phosphor layer 31 and the black matrix 32 formed on the anode electrode 34, and a light-reflecting electrically conductive film which is made of aluminum, is formed on the phosphor layer 31 and the black matrix 32 and is electrically connected to the anode electrode 34.
The display has a structure in which the substrate 30 having the anode electrode 34 and the phosphor layers 31 (31R, 31G and 31B) and the supporting member 10 having the electron-emitting regions EA are arranged in a manner in which the phosphor layers 31 and the electron-emitting regions EA are opposed and the substrate 30 and the supporting member 10 are bonded to each other in their circumferential portions. Specifically, the cathode panel CP and the anode panel AP are bonded to each other through a frame 35 in their circumferential portions. Further, the ineffective field of the cathode panel CP is provided with a through-hole (not shown) for vacuuming, and a tip tube to be used for sealing therewith after vacuuming is connected to the through-hole. The frame 35 is made of ceramic or glass and has a height, for example, of 1.0 mm. In some cases, an adhesive layer alone may be provided in place of the frame 35.
One pixel is constituted of the electron-emitting region EA and the phosphor layer 31 that is arranged in the effective field of the anode panel AP so as to face the electron-emitting region EA. In the effective filed, such pixels are arranged, for example, on the order of several hundreds of thousand to several millions.
A relatively negative voltage is applied to the cathode electrode 11 from the cathode-electrode control circuit 40, a relatively negative voltage (for example, 0 volt) is applied to the focus electrode 15 from the first voltage-output portion 41A of the focus-electrode control circuit 41, a positive voltage is applied to the gate electrode 13 from the gate-electrode control circuit 42, and a positive voltage higher than that applied to the gate electrode 13 is applied to the anode electrode 34 from the anode-electrode control circuit 43. Generally, a resistance member Ro (a resistance value of 1 MΩ in an example shown) for preventing over-current and electrical discharge is provided between the anode-electrode control circuit 43 and the anode electrode 34.
Further, a voltage V1 (for example, 0 volt) is applied to one end of the capacitor C (focus electrode side), and V2 (for example, −100 volts) is applied to the other end of the capacitor C (the second voltage-output portion side of the focus-electrode control circuit 41) from the second voltage-output portion 41B.
When display is performed with the above display, for example, a scanning signal is inputted to the cathode electrode 11 from the cathode-electrode control circuit 40, and a video signal is inputted to the gate electrode 13 from the gate-electrode control circuit 42. Alternatively, a video signal may be inputted to the cathode electrode 11 from the cathode-electrode control circuit 40, and a scanning signal may be inputted to the gate electrode 13 from the gate-electrode control circuit 42. Due to an electric field generated when a voltage is applied between the cathode electrode 11 and the gate electrode 13, electrons are emitted from the electron-emitting portion 19 on the basis of a quantum tunnel effect, and the electrons are drawn toward the anode electrode 34 to collide with the phosphor layers 31. As a result, the phosphor layers 31 are excited, whereby a desired image can be obtained.
Further,
As is clear from FIGS. 3 to 5, the potential at the point “A” is approximately 30 volts or less when the capacitor C had a capacity of 10 nF or more. Further, it is seen that when Cc>20CAF is satisfied in which Cc is a capacity of the capacitor C and CAF is an electrostatic capacity based on the anode electrode 34 and the focus electrode 15, it is made possible to fully inhibit an increase in potential in the focus electrode 15.
Even when a discharge takes place between the anode electrode 34 and the focus electrode 15, the capacitor C can reliably serve to inhibit an increase in potential in the focus electrode 15. Further, when simulations were carried out by changing the voltage (VA) applied to the anode electrode 34, similar results were obtained.
The method of manufacturing a Spindt-type field emission device having the focus electrode 15 and the method of manufacturing of a display panel in Example 1 will be explained with reference to
The Spindt-type field emission device can be obtained in principle by a method of forming the circular-cone-shaped electron-emitting portion 19 by vertical vapor deposition of a metal material. That is, vaporized particles perpendicularly enter the first opening portion 16 formed through the focus electrode 15. The amount of the vaporized particles which reach the bottom portion of the third opening portion 18 is gradually decreased by utilizing the shielding effect of an overhanging deposit formed around an opening edge portion of the first opening portion 16, so that the electron-emitting portion 19 as a circular-cone-shaped deposit is formed in a self-aligned manner. The method will be explained in which a peeling-off layer 50 is formed in advance on the focus electrode 15 for easing removal of an unnecessary overhanging deposit.
[Step-100]
A conductive material layer composed, for example, of polysilicon for a cathode electrode is formed on a supporting member 10 composed, for example, of a glass substrate by a plasma-enhanced CVD method. Then, the conductive material layer for a cathode electrode is patterned by a lithograph method and a dry etching method, to form the cathode electrode 11 having a stripe form. Thereafter, the insulating layer 12 composed of SiO2 is formed on the entire surface by a CVD method.
[Step-110]
Then, the conductive material layer (for example, TiN layer) for a gate electrode is formed on the insulating layer 12 by a sputtering method. Then, the conductive material layer for a gate electrode is patterned by a lithograph method and a dry etching method to form the stripe-shaped gate electrode 13. The cathode electrode 11 in the form of a stripe extends in a direction rightward and leftward to the paper surface of the drawing and the gate electrode 13 in the form of a stripe extends in a direction perpendicular to the paper surface of the drawing.
The gate electrode 13 can be formed by a known thin film forming method such as a PVD method including a vapor deposition method and the like, a CVD method, a plating method including an electroplating method and an electroless plating method, a screen printing method, a laser abrasion method, a sol-gel method, a lift-off method and the like, or a combination of one of them with an etching method as required. For example, a stripe-shaped gate electrode can be directly formed when a screen-printing method or a plating method is employed.
Thereafter, an insulating film 14 composed of SiO2 is formed on the entire surface (specifically, on the insulating layer 12 and the gate electrode 13) by a CVD method.
[Step-130]
Then, the focus electrode 15 composed of aluminum (Al) is formed on the insulating film 14 by a vapor deposition method, and the first opening portion 16 is formed through the focus electrode 15 and the insulating film 14 by a lithograph method and a dry etching method using a resist layer. Further, the second opening portion 17 communicating with the first opening portion 16 is formed through the gate electrode 13, the third opening portion 18 communicating with the second opening portion 17 is formed through the insulating layer 12 so as to expose the cathode electrode 11 in the bottom portion of the third opening portion 18, and then, the resist layer is removed.
[Step-140]
As shown in
[Step-150]
Then, an electrically conductive material such as molybdenum (Mo) is deposited on the entire surface by vertical vapor deposition (incidence angle 3° to 10°). During the above vapor deposition, as shown in
[Step-160]
Then, the peeling-off layer 50 is peeled off from the surface of the focus electrode 15 by a lift-off method, and the conductive material layer 51 above the focus electrode 15 is selectively removed. In this manner, the cathode panel CP having a plurality of the Spindt-type field emission devices can be obtained. Then, the side wall surface of the first opening portion 16 formed through the insulating film 14 and the side wall surface of the third opening portion 18 formed through the insulating layer 12 are allowed to recede by isotropic etching, which is preferred from the viewpoint of exposing the opening end portion of the gate electrode 13. The isotropic etching can be carried out by dry etching using radicals as main etching species like chemical dry etching, or by wet etching using an etching solution. As an etching solution, for example, a mixture containing a 49% hydrofluoric acid aqueous solution and pure water in a hydrofluoric acid aqueous solution: pure water volume ratio of 1:100 can be used. In the above manner, the field emission device shown in
[Step-170]
On the other hand, the anode panel AP is prepared. Then, the display is assembled. Specifically, the anode panel AP and the cathode panel CP are arranged such that the phosphor layer 31 and the electron-emitting region EA face each other, and the anode panel AP and the cathode panel CP (more specifically, the substrate 30 and the supporting member 10) are bonded to each other in their circumferential portions through the frame 35. In the bonding, a frit glass is applied to bonding portions of the frame 35 and the anode panel AP and bonding portions of the frame 35 and the cathode panel CP. Then, the anode panel AP, the cathode panel CP and the frame 35 are attached. The frit glass is pre-calcined or pre-sintered to be dried, and then fully calcined or sintered at approximately 450° C. for 10 to 30 minutes. Then, a space surrounded by the anode panel AP, the cathode panel CP, the frame 35 and the frit glass is vacuumed through a through-hole (not shown) and a tip tube (not shown), and when the space comes to have a pressure of approximately 10−4 Pa, the tip tube is sealed by thermal fusion. In the above manner, the space surrounded by the anode panel AP, the cathode panel CP and the frame 35 can be vacuumed, whereby the display panel can be obtained. Then, wiring to external circuits is carried out to complete the so-called three-electrode-type display.
In [Step-130], there may be employed a constitution in which one first opening portion 16A is formed through the focus electrode 15 and the insulating film 14 so as to surround a group of the cold cathode field emission devices formed in the overlap region of the cathode electrode 11 and the gate electrode 13, a plurality of the second opening portion 17A communicating one first opening portion 16A are formed through the gate electrode 13, and the third opening portion 18A communicating with each second opening portion 17A is formed through the insulating layer 12. In this case, in [Step-140], the peel-off layer 50 is also formed on the gate electrode 13 exposed in the bottom portion of the first opening portion 16A. In the above manner, there can be obtained a structure in which the focus electrode 15 is formed on the insulating film 14 so as to surround a group of the cold cathode field emission devices formed in the overlap region of the cathode electrode 11 and the gate electrode 13, one first opening portion 16A is formed through that portion of the focus electrode 15 that is positioned in the overlap region of the cathode electrode 11 and the gate electrode 13 and through the insulating film 14 positioned therebelow, and a plurality of the second opening portions 17A communicate with one first opening portion 16A, that is, there can be obtained the display according to the first-B aspect of the present invention.
Example 2 is a variant of Example 1. Example 1 used the Spindt-type as a field emission device. In Example 2, the field emission device is a plane-type (a field emission device in which an electron-emitting portion having the form of a nearly flat plane is formed on the cathode electrode positioned in the bottom portion of the third opening portion).
An electron-emitting portion 19A constituting the plane-type field emission device in Example 2 comprises a matrix 52 and a carbon-nanotube structure (specifically, a carbon-nanotube 53) embedded in the matrix 52 in a state where the top portion of the carbon-nanotube structure is projected, and the matrix 52 is formed from an electrically conductive metal oxide (specifically, oxide-tin oxide, ITO) as shown in a schematic partial end view of
The production method of the field emission device will be explained with reference to
[Step-200]
First, a stripe-shaped cathode electrode 11 made of an approximately 0.2 μm thick chromium (Cr) layer is formed on a supporting member 10 made, for example, of a glass substrate, for example, by a sputtering method and an etching technique.
[Step-210]
Then, a metal compound solution consisting of an organic acid metal compound solution in which the carbon-nanotube structure is dispersed is applied onto the cathode electrode 11, for example, by a spray method. Specifically, a metal compound solution shown in Table 1 is used. In the metal compound solution, the organic tin compound and the organic indium compound are in a state where they are dissolved in an acid (for example, hydrochloric acid, nitric acid or sulfuric acid). The carbon-nanotube is produced by an arc discharge method and has an average diameter of 30 nm and an average length of 1 μm. In the application, the supporting member 10 is heated to 70-150° C. Atmospheric atmosphere is employed as an application atmosphere. After the application, the supporting member 10 is heated for 5 to 30 minutes to fully evaporate butyl acetate off. When the supporting member 10 is heated during the application as described above, the applied solution begins to dry before the carbon-nanotube is self-leveled toward the horizontal direction of the surface of the cathode electrode 11. As a result, the carbon-nanotube can be arranged on the surface of the cathode electrode 11 in a state where the carbon-nanotube is not in a level position. That is, the carbon-nanotube can be aligned in the direction in which the top portion of the carbon-nanotube faces the anode electrode 34, in other words, the carbon-nanotube comes close to the normal direction of the supporting member 10. The metal compound solution having a composition shown in Table 1 may be prepared beforehand, or a metal compound solution containing no carbon-nanotube may be prepared beforehand and the carbon-nanotube and the metal compound solution may be mixed before the application. For improving dispersibility of the carbon-nanotube, ultrasonic wave may be applied when the metal compound solution is prepared.
When a solution of an organic indium compound dissolved in an acid is used, indium oxide is obtained as a matrix. When a solution of an organic zinc compound dissolved in an acid is used, zinc oxide is obtained as a matrix. When a solution of an organic antimony compound dissolved in an acid is used, antimony oxide is obtained as a matrix. When a solution of an organic antimony compound and an organic tin compound dissolved in an acid is used, antimony-tin oxide is obtained as a matrix. Further, when an organic tin compound is used as an organic metal compound solution, tin oxide is obtained as a matrix. When an organic indium compound is used, indium oxide is obtained as a matrix. When an organic zinc compound is used, zinc oxide is obtained as a matrix. When an organic antimony compound is used, antimony oxide is obtained as a matrix. When an organic antimony compound and an organic tin compound are used, antimony-tin oxide is obtained as a matrix. Alternatively, a solution of metal chloride (for example, tin chloride or indium chloride) may be used.
After the metal compound solution is dried, salient convexo-concave shapes may be formed in the surface of the metal compound layer in some cases. In such cases, it is desirable to apply the metal compound solution again on the metal compound layer without heating the supporting member 10.
[Step-220]
Then, the metal compound composed of the organic acid metal compound is fired, to give an electron-emitting portion 19A having the carbon-nanotubes 53 fixed onto the surface of the cathode electrode 11 with a matrix 52 (which is specifically a metal oxide, and more specifically, ITO) containing metal atoms (specifically, In and Sn) derived from the organic acid metal compound. The firing is carried out in an atmospheric atmosphere at 350° C. for 20 minutes. The thus-obtained matrix 52 had a volume resistivity of 5×10−7Ω·m. When the organic acid metal compound is used as a starting material, the matrix 52 made of ITO can be formed at a low firing temperature of as low as 350° C. The organic acid metal compound solution may be replaced with an organic metal compound solution. When a solution of metal chloride (for example, tin chloride and indium chloride) is used, the matrix 52 made of ITO is formed while the tin chloride and indium chloride are oxidized by the firing.
[Step-230]
Then, a resist layer is formed on the entire surface, and the circular resist layer having a diameter, for example, of 10 μm is retained above a desired region of the cathode electrode 11. The matrix 52 is etched with hydrochloric acid having a temperature of 10 to 60° C. for 1 to 30 minutes, to remove an unnecessary portion of the electron-emitting portion. Further, when the carbon-nanotubes still remain in a region different from the desired region, the carbon-nanotubes are etched by an oxygen plasma etching treatment under a condition shown in Table 2. A bias power may be 0 W, i.e., direct current, while it is desirable to apply the bias power. The supporting member 10 may be heated, for example, to approximately 80° C.
Alternatively, the carbon-nanotubes can be etched by a wet etching treatment under a condition shown in Table 3.
Then, the resist layer is removed, whereby a structure shown in
The process may be carried out in the order of [Step-210], [Step-230] and [Step-220].
[Step-240]
An insulating layer 12 is formed on the electron-emitting portion 19A, the supporting member 10 and the cathode electrode 11. Specifically, an approximately 1 μm thick insulating layer 12 is formed on the entire surface by a CVD method using, for example, tetraethoxysilane (TEOS) as a source gas.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-129606 | May 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP03/03800 | 3/27/2003 | WO |
