A flat panel display apparatus

Abstract: The flat panel display using a field emission type cathode array (204), comprises a flat fluorescent screen (205, 206) arranged between the cathode array (204) formed on a flat substrate (201) and a screen comprising a glass plate (207) having a convex curved shape in parallel with the substrate (201). The space between the fluorescent screen (205, 206) and the cathode array (204) and the space between the fluorescent screen (205, 206) and the substrate (201) are set to be vacuum. The method of manufacturing said flat panel after forming the plurality of cathodes (204) on a conductive substrate (201), provides for a field evaporation caused from tips of the plurality of cathodes (204) by applying a predetermined voltage to said plurality of cathodes.

Description: BACKGROUND OF THE INVENTION Field of the Invention The invention relates to a flat panel display apparatus and, more particularly the invention is 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 flat panel displav using a field emission type cathode array comprising microtips of the size of a micron order, a display as shown in Fig. 1 is known. As shown in Fig. 1, in the conventional flat panel display, a silicon dioxide (SiO 2 ) film 102 having cavities 102a is formed on a conductive flat silicon (Si) substrate 101. Gate electrodes 103 made of molybdenum (Mo), niobium (Nb), or the like are formed on the SiO 2 film 102 in the peripheral portions of the cavities 102a. A cathode 104 made of Mo or the like is formed on the Si substrate 101 in the cavity 102a. A fluorescent screen in which a fluorescent material 106 is formed on the flat glass plate 105 is arranged so as to face in parallel with the Si substrate 101 on which the cathode array is formed. The space between the fluorescent screen and the Si substrate 101 is sealed in a state in which it is held in vacuum. In recent years, a request to realize a large screen of the flat panel display is becoming strong. The above conventional flat panel display, however, has a structure in which a differential pressure between the atmospheric pressure and the vacuum is held by only the glass plate 105 on which the fluorescent material 106 is formed. It is, accordingly, difficult to simply enlarge the screen from a viewpoint of the strength of the glass plate 105. To solve the above problem, there is considered a method of realizing a large screen by forming the screen into a spherical shape as shown in Fig. 2 as in the case of the cathode ray tube of an ordinary television receiver. When such a structure is used, however, the formation of a portion in which a distance between the cathode array and the fluorescent screen is large cannot be avoided. In the above conventional flat panel display, however, it is necessary to closely arrange the cathode array and the fluorescent screen in terms of the operation principle. Therefore, when the screen is simply formed in a spherical shape as mentioned above, a trouble occurs in the operation of the flat panel display. To prevent it, there is also considered a method whereby the Si substrate is also formed in a spherical shape and the cathode array is formed on the Si substrate. It is, however, extremely difficult to realize such a structure from a viewpoint of the manufacturing processes. Therefore, in the flat panel display shown in Fig. 1, there is considered a method whereby pillars are formed at regular intervals between the glass plate 105 and the Si substrate 101 and the differential of pressure between the atmospheric pressure and the vacuum is held by the pillars. When such a structure is used, however, there are problems such that not only the manufacturing processes become complicated but also the cathode 104 cannot be formed on the Si substrate 101 in the portion of the pillar. From the above reasons, it is so far difficult to realize a large screen of the flat panel display using the field emission type cathode array. Document US-PS-2,760,119 discloses a plasma display apparatus whose pressure in a tube is greater than 1 torr. Document EP-0,404,022 discloses the use of a plurality of cathodes formed on a substrate within a flat configuration image display apparatus. On the other hand, as shown in Fig. 3, 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. 3, 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. 3 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 cathode 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. OBJECTS AND SUMMARY OF THE INVENTION It is, therefore, an object of the invention to provide a flat panel display apparatus which can realize a large screen. According to the invention, this object is achieved by the features as indicated in the claim 1. According to the flat panel display apparatus of the invention as claimed and constructed as mentioned above, since the screen is formed by the glass plate of the convex curved shape, a large screen of the flat panel display can be realized. Moreover, since the space between the fluorescent screen and the screen and the space between the fluorescent screen and the substrate are vacuum, a differential pressure does not substantially exist on both sides of the fluorescent screen. Thus, even when the area of the fluorescent screen is increased in order to realize a large screen, no problem occurs with respect to the strength. 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 showing a conventional flat panel display; Fig. 2 is a cross sectional view showing an example in which the screen is formed in a spherical shape in a conventional flat panel display; Fig. 3 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. 4 is a cross sectional view showing a flat panel display according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the invention will be described hereinbelow with reference to the drawings. Fig. 4 is a cross sectional view showing a flat panel display according to the invention. As shown in Fig. 4, in a flat panel display according to the invention, 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 cathode 204 made of a microtip is formed on the Si substrate 201 in the cavity 202a. The cathode array is formed by a number of cathodes 204. A fluorescent screen in which a fluorescent material 206 is formed on a glass plate 205 is arranged so as to face the Si substrate 201 on which the cathode array is formed. Further, a spherical glass plate 207 serving as a screen is provided on the outside of the fluorescent screen. The space between the fluorescent screen and the Si substrate 201 on which the cathode array is formed and the space between the fluorescent screen and the spherical glass plate 207 serving as a screen are held in vacuum. In the above case, a degree of vacuum of the space between the fluorescent screen and the Si substrate 201 and a degree of vacuum of the space between the fluorescent screen and the spherical glass plate 207 can be set to be either equal or different. As shown in Fig. 4, 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 glass plate 207 is sealed in a state in which it is held in vacuum, thereby completing a desired flat panel display. According to the invention 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. 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. According to the 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 flat panel display apparatus for cold field emission having a cathode array on a flat substrate, said cathode comprising tens of thousand of individual cathode tips with cone shape in the order of µm on the substrate which tips project through apertures in an insulating layer on the substrate, a gate electrode being formed on a surface of the insulating layer, and a fluorescent screen comprising a fluorescent material layer on a glass plate being arranged opposite the cathode array with the fluorescent layer facing the cathode array, comprising: a spherical glass plate screen which is formed by a convex glass plate having spherical inner and outer surfaces, the fluorescent screen being positioned between the spherical glass plate screen and cathode array; said fluorescent screen being flat; and a space between the flat fluorescent screen and the spherical glass plate screen and a space between the fluorescent screen and the substrate comprising a vacuum. An apparatus according to claim 1, wherein the vacuum between the flat fluorescent screen and the spherical glass plate is the same as the vacuum in the space between the fluorescent screen and the substrate. An apparatus according to claim 1, wherein the vacuum in the space between the flat fluorescent screen and the spherical glass plate is different than the vacuum in the space between the flat fluorescent screen and the substrate.

Inventors: KONISHI MONISHI, KONISHI, MONISHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1991
Main classification: H01J31
IPC codes: H01J9, H01J31, H01J29