A method of manufacturing a flat panel display apparatus

Abstract: The method of manufacturing a flat panel after forming the plurality of cathodes (104) on a conductive substrate (101), provides for a field evaporation caused from tips of the plurality of cathodes (104) by applying a predetermined voltage to said plurality of cathodes.

Description: BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a method of manufacturing a flat panel display apparatus; this method is particularly suitable when it is applied to a flat panel display using a field emission type cathode array. Description of the Prior Art Hitherto, as a method of manufacturing a flat panel display using a field emission type cathode array by microtips of the size of a micrometer order a method as shown in Figs. 1A to 1E is known. According to the manufacturing method, as shown in Fig. 1A, an SiO 2 film 102 is first formed on a conductive Si substrate 101 by, for instance, a thermal oxidation method, a CVD method or a sputtering method. After that, a metal film 107 made of, for example, Mo film, a Nb film, or the like to form gate electrodes is formed onto the SiO 2 film 102 by, e. g. a sputtering method or an electron beam evaporation depositing method. Subsequently, a resist pattern 104 having shapes corresponding to the gate electrodes to be formed are formed onto the metal film 107 by a lithography. The metal film 107 is subsequently etched by a wet etching method or a dry etching method by using the resist pattern 104 as a mask, thereby forming gate electrodes 103 as shown in Fig. 1B. After that, the SiO 2 film 102 is etched by a wet etching method or a dry etching method by using the resist pattern 104 and the gate electrodes 105 as masks, thereby forming cavities 102a. After the resist pattern 104 was removed, as shown in Fig. 1C, an oblique evaporation deposition is executed to the substrate surface by an electron beam evaporation depositing method from the direction which is inclined by a predetermined angle to the substrate surface, thereby forming a peeling-off layer 109 made of, e.g., aluminium (Aℓ) or nickel (Ni) onto the gate electrodes 103. After that, for instance, Mo as a material to form cathodes is evaporation deposited onto the substrate surface by an electron beam evaporation depositing method from the direction perpendicular to the substrate surface. Thus, cathodes (emitters) 104 comprising microtips are formed onto the Si substrates 101 in the cavities 102a. Reference numeral 110 denotes a metal film which has been evaporation deposited onto the peeling-off layer 109. The peeling-off layer 109 is subsequently removed by a lift-off method together with the metal film 110 formed on the peeling-off layer 109, so that a state shown in Fig. 1D is obtained. After that, as shown in Fig. 1E, a screen in which a fluorescent material 106 is formed on a glass plate 105 serving as a display screen is arranged so as to face the Si substrate 101 on which the cathode array is formed in a manner such that the fluorescent material 106 is positioned on the inside. The space between such a screen and the Si substrate 101 is sealed in a state in which it is held in vacuum. A desired flat panel display is consequently completed. Upon operation of the flat panel display, a negative voltage of, e.g., about -50V is applied to each cathode 104. In the foregoing conventional manufacturing method of the flat panel display, it is extremely difficult to align all of radii of curvatures of the tips of a number of (for instance, tens of thousand) cathodes 104 which are simultaneously formed by an evaporation depositing method and the occurrence of a slight variation in the radii of curvatures of the tips of the cathodes 104 can hardly be avoided. On the other hand, as shown in Fig. 2, there is generally a correlation between the radius of curvature of the tip of the cathode and an allowable applied voltage to the cathode. In Fig. 2, Vmin denotes a minimum voltage (absolute value) at which a current emission can be performed and Vmax indicates a maximum voltage (absolute value) at which a current emission can be executed without causing a discharge. As will be understood from Fig. 2, as a radius of curvature of the tip of the cathode increases, a voltage at which the current emission can be performed rises. Therefore, if only one cathode whose radius of curvature of the tip is smaller than those of the other cathodes exists, for instance, among tens of thousand cathodes when a negative voltage is gradually applied to those cathodes whose radius of curvature of the tip is smaller than those of the other cathodes, there is a problem such that when the current emission starts from the other cathodes, the voltage exceeds the allowable applied voltage, those cathodes discharge, the tips are rounded, and the current emission stops. To solve the above problem, a method whereby a resistor is provided between each cathode and a power source to thereby prevent the occurrence of the emission of a predetermined current or higher has also been proposed. There is a problem such that the above method is extremely difficult from a viewpoint of the manufacturing process. Prior art document INSTRUMENTS AND EXPERIMENTAL, no. 1, January 1969, pages 213-215, XP002021146 R. I.Garber et al.: "current field emission cathode", describes a method wherein the field intensity over emitters in a packet is equalized, and pulses lasting 2 • 10 -7 s with voltages up to 200 kV are applied. Further, prior art document US-A-4,908,539 discloses a display unit which comprises a plurality of elementary patterns, each having a cathode able to emit electrons. The cathode comprises a plurality of electrically interconnected micropoints subject to electron emission by field effect, when the cathode is negatively polarized compared with a corresponding anode. The micropoints are located in the same region on a conductive coating which is itself deposited on an insulating substrate. An insulating coating is deposited on the conductive coating, and the micropoints are separated from each other. A grid coating having holes corresponding to the micropoints is deposited on the insulating coating, and a phosphor coating is deposited on the grid coating, except above the region in which the micropoints are concentrated. OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to provide a method of manufacturing a flat panel display apparatus in which radii of curvatures of the tips of all of cathodes constructing the cathode array can be easily made equal at a high accuracy. To solve this object the present invention provides a method as specified in the claim. According to this manufacturing method of a flat panel display apparatus as mentioned above, in the case where radii of curvatures of the tips of a plurality of cathodes constructing the cathode array are not aligned, when a predetermined voltage is applied to the cathodes, a field evaporation first occurs from the tip of the cathode whose radius of curvature of the tip is smallest. That is, atoms on the surface of the tip of such a cathode are eliminated as ions. Due to the field evaporation, the radius of curvature of the tip of the cathode gradually increases. When the radius of curvature of the tip of the cathode coincides with the radius of curvature of the cathode whose radius of curvature of the tip is small as a second smallest value, the field evaporation occurs from those cathodes. As mentioned above, the field evaporation sequentially occurs from the cathode whose radius of curvature of the tips is small. After the elapse of a predetermined time, the radii of curvatures of the tips of all of the cathodes constructing the cathode array are equalized. Due to this, the radii of curvatures of the tips of all of the cathodes constructing the cathode array can be easily aligned at a high precision. The field emission from each cathode can be uniformed. The above, and other, objects, features and advantages of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross sectional view for explaining a conventional manufacturing method of a flat panel display; Fig. 2 is a graph showing the relation between the radius of curvature of the tip of the cathode and the allowable applied voltage to the cathode; Fig. 3 is a cross sectional view showing a flat panel display; and Fig. 4 is a cross sectional view for explaining a manufacturing method of a flat panel display according to the second embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described hereinbelow with reference to the drawings. Fig. 3 is a cross sectional view showing a flat panel display. As shown in Fig. 3, in a flat panel display an insulating film 202 such as an SiO 2 film having cavities 202a is formed on, for instance, a conductive flat Si substrate 201. A gate electrode 203 made of, for example, Mo or Nb is formed on the insulating film 202 in the peripheral portion of the cavity 202a. A cathod 204 made of a microtip is formed on the Si substrate 201 in the cavity 202a. A manufacturing method of the flat panel display will now be described. As shown in Fig. 3, the insulating film 202 such as an SiO 2 film is first formed onto the Si substrate 201 by, for instance, a thermal oxidation method, a CVD method, or a sputtering method. After that, a metal film made of, for example, Mo, Nb, or the like to form gate electrodes is formed onto the insulating film 202, by, e.g., a sputtering method or an electron beam evaporation depositing method. Subsequently, a resist pattern (not shown) having a shape corresponding to the gate electrodes to be formed is formed onto the metal film by a lithography. By subsequently etching the metal film by a wet etching method or a dry etching method by using the resist pattern as a mask, the gate electrodes 203 are formed. After that, the insulating film 202 is etched by a wet etching method or a dry etching method by using the resist pattern and the gate electrodes 203 as masks, thereby forming the cavities 202a. After the resist pattern was removed, an oblique evaporation deposition is performed onto the substrate surface from the direction which is inclined by a predetermined angle for the substrate surface by an electrode beam evaporation depositing method, thereby forming a peeling-off layer made of, for example, Aℓ or Ni onto the gate electrodes. After that, for instance, Mo as a material to form the cathodes is evaporation deposited onto the substrate surface from the direction perpendicular thereto by an electron beam evaporation depositing method. The cathodes 204, thus, are formed on the Si substrate 201 in the cavities 202a. The peeling-off layer is subsequently removed together with the metal film formed thereon by a lift-off method. The fluorescent screen in which the fluorescent material 206 is formed on the glass plate 205 is arranged so as to face the Si substrate 201 on which the cathode array is formed. Further, the spherical glass plate 207 serving as a screen is arranged on the outside of the fluorescent screen. The space between the fluorescent screen and the galss plate 207 is sealed in a state in which it is held in vacuum, thereby completing a desired flat panel display. According to the first embodiment as mentioned above, since the screen is formed by the spherical glass plate 207, the flat panel display can be formed as a large screen. Moreover, since both of the spaces on both sides of the fluorescent screen are vacuum, there is hardly a differential pressure between both sides of the fluorescent screen, so that a situation such that a force is applied to the fluorescent screen due to the differential pressure actually does not occur. Thus, even when an area of the fluorescent screen is enlarged to realize a large screen of the flat panel display, no problem occurs with respect to the strength. In the first embodiment, the screen is formed by the spherical glass plate 207. However, the screen is not always necessary to be formed in a spherical shape. For example, it can be also formed in a cylindrical or other convex curved shape. The second embodiment of the invention will be described hereinbelow with reference to the drawings. Figs. 4A to 4C are cross sectional views showing a manufacturing method of a flat panel display according to the second embodiment of the invention. In the second embodiment, as shown in Fig. 4A, an insulating film 302 such as an SiO 2 film having cavities 302a, gate electrodes 303, and cathodes 304 comprising microtips are formed on, for example, a conductive substrate 301 in a manner similar to the conventional manufacturing method of the flat panel display shown in Figs. 1A to 1E. Among a number of cathodes 304 formed as mentioned above, it is now assumed that a radius of curvature of the tip of the central cathode in Fig. 4A is set to, e.g., 180 Å (10 Å = 1 nm) and radii of curvatures of the tips of the other cathodes are set to, e.g., 200Å and the radius of curvature of the tip of only the central cathode is smaller than those of the other cathodes. In the second embodiment, a voltage V of a polarity opposite to that of the voltage (negative voltage) which is applied to the cathodes 304 upon operation of the flat panel display, that is, the positive voltage V is first applied to the conductive Si substrate 301 which is electrically connected to all of the cathodes 304. The voltage V is gradually increased to a voltage, e.g., 500 V corresponding to the radius of curvature of the tip of the central cathode from 0 V. Voltage applying means for applying the voltage V is preferably provided in the flat panel display. When the positive voltage V is gradually applied to the cathode array as mentioned above, in Fig. 4A, a field evaporation preferentially starts to occur from the tip of the central cathode whose radius of curvature of the tip is smaller than those of the other cathodes. The radius of curvature of the tip of such a central cathode gradually increases in association with the field evaporation. As shown in Fig. 4B, the radius of curvature of the tip of the central cathode is equal to those of the tips of the other cathodes. That is, the radii of curvatures of the tips of all of the cathodes 304 are aligned to, e.g., 200 Å. After that, when the voltage V is increased to, for instance, 600 V, the current emission starts to occur from all of the cathodes 304. Therefore, the apply of the voltage V is stopped at this time point. After that, as shown in Fig. 4C, a screen in which a fluorescent material 306 is formed on a glass plate 305 serving as a display screen is arranged so as to face the foregoing Si substrate 301 on which the cathode array is formed in a manner such that the fluorescent material 306 is located on the inside. The space between the screen and the Si substrate 301 is sealed in a state in which it is held in vacuum. Due to this, a desired flat panel display is completed. The above second embodiment relates to the case where only one cathode whose radius of curvature of the tip is small exists among a number of cathodes 304. However, the similar method can be applied to all of the cases where the radii of curvatures of the tips of the cathodes constructing the cathode array are not equal. In such a case as well, in a manner similar to the above, when the voltage V is applied to the cathode array, the field evaporation sequentially starts to occur from the cathode whose radius of curvature of the tip is small. Finally, the radii of curvatures of the tips of all of the cathodes are made equal. As mentioned above, according to the second embodiment, by applying the positive voltage V to the cathode array, the field evaporation is preferentially caused from the cathode 304 whose radius of curvature of the tip is small. Therefore, the radii of curvatures of the tips of all of the cathodes 304 constructing the cathode array can be easily made equal at a high accuracy. Thus, unevenness of the luminances of the flat panel display can be eliminated and a flat panel display of a high quality can be realized. Further, since the field evaporation is caused by applying the positive voltage V to each cathode 304, a contaminant adhered on the surface of the cathode 304 can be eliminated. Thus, a good current emission can be executed from the cathode 304. Each of the numerical values mentioned in the above second embodiment is merely nothing but an example. Those numerical values can be obviously changed as necessary. The cathode array of the flat panel display according to the second embodiment can be also formed by a method different from that mentioned above. The cathode array may also have a structure different from that in the second embodiment. In the second embodiment, the Si substrate 301 is used as a substrate of the flat panel display. However, various kinds of conductive substrates other than the Si substrate 301 can be used. For instance, a substrate in which a conductive film such as a metal film is formed on the whole surface of an insulating substrate such as glass substrate or ceramics substrate or is selectively formed on such an insulating substrate can be also used. According to the method of manufacturing a flat panel display apparatus of the invention, since the field evaporation is caused from the tips of a plurality of cathodes, the radii of curvatures of the tips of all of the cathodes constructing the cathode array can be easily made equal at a high accuracy. As a result, the luminances of the flat panel display can be uniformed.

Claims: A method of manufacturing a flat panel display apparatus in which a plurality of cone-shaped cathodes (204; 304) having rounded tips of differing radius of curvature (r) are formed on a conductive substrate (201; 301) opposite a fluorescent screen (205, 206), an improvement comprising the steps of: applying a predetermined voltage (V) to said plurality of cathodes (204; 304) after the plurality of cathodes (204; 304) are formed, said predetermined voltage (V) having a polarity opposite to that which is applied for operation of the flat panel display, and a magnitude such that a cathode (204; 304) having a smallest radius of curvature (r) begins the field evaporation before field evaporation occurs at the other tips, increasing gradually the magnitude of said predetermined voltage until current emission starts to occur from all the plurality of cathodes (204; 304) thereby causing a field evaporation from tips of the plurality of cathodes (204; 304) until all the rounded tips of the cathodes (204; 304) have a substantially same radius of curvature (r), and stopping the application of voltage, when current emission occurs from all the plurality of cathodes (204; 304).

Inventors: KONISHI MORIKAZU, KONISHI, MORIKAZU, Konishi, Morikazu, Sony Corp.
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H01J9
IPC codes: H01J9