Abstract:
A flat panel display includes a substrate, a front glass, a cathode, a gate electrode, a plurality of front ribs, a phosphor film and a metal-backed film, and a gate rib. The front glass is arranged to oppose the substrate and forms a vacuum envelope together with the substrate. The front glass is transparent at least partially. The cathode is arranged on the substrate. The gate electrode is arranged between the substrate and front glass and includes an electron-passing hole through which an electron emitted from the cathode passes. The front ribs extend vertically at a predetermined interval from the front glass toward the gate electrode. The phosphor film and metal-backed film are stacked on a region of the front glass which is sandwiched by the front ribs. The gate rib extends vertically from the gate electrode toward the front glass and is in contact with the front ribs. A gate electrode structure and a gate electrode structure manufacturing method are also disclosed.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a gate electrode structure which controls electron emission from a field emission type electron source, a method of manufacturing the same, and a flat panel display which has the gate electrode structure.  
         [0002]     In recent years, as a flat panel display such as an FED (Field Emission Display) or a flat vacuum fluorescent display in which electrons emitted from an electron-emitting source serving as a cathode bombard a light-emitting portion formed of phosphors on a counterelectrode to emit light, various types that use nanotube fibers, e.g., carbon nanotubes or carbon nanofibers, as the electron-emitting source have been proposed (for example, see Japanese Patent Laid-Open Nos. 2002-343281 and 2004-193038).  FIG. 15  shows an example of a conventional flat panel display which uses nanotube fibers as an electron-emitting source.  
         [0003]     This flat panel display has a cathode substrate  120  having a substrate  121  made of glass or the like, an anode substrate  130  having a front glass  131 , and a gate substrate  110  which is disposed substantially parallel to the substrate  121  and front glass  131 . The substrate  121  of the cathode substrate  120  and the front glass  131  of the anode substrate  130  form an envelope. The interior of the envelope is held in a vacuum state.  
         [0004]     The cathode substrate  120  further has a plurality of substrate ribs  122  which are formed parallel to each other on the substrate  121 , and cathodes  123  which are formed in regions sandwiched by the substrate ribs  122  on the substrate  121  and substantially form matrices when seen from the top. As the cathodes  123 , electron-emitting sources made of the nanotube fibers described above are used.  
         [0005]     The anode substrate  130  further has a plurality of black matrices  132  which are formed on the front glass  131  to be parallel to the substrate ribs  122 , phosphor films  133 R,  133 G, and  133 B which are formed on regions sandwiched by the black matrices  132  on the front glass  131 , metal-backed films  134  which are formed on the phosphor films  133 R,  133 G, and  133 B to serve as anodes, and a plurality of front ribs  135  which are formed on the black matrices  132 . The black matrices  132  serve to prevent leaking light emitted from adjacent phosphors so as to improve the contrast of the flat panel display. The black matrices  132  are desirably formed as thin as possible to prevent a decrease in luminance of the flat panel display. The front ribs  135  are also desirably formed thin.  
         [0006]     The gate substrate  110  comprises a glass plate  111 , a flat electrode  112  which is formed on the surface of the glass plate  111  on the anode substrate  130  side, band-like gate electrodes  113  formed on the surface of the glass plate  111  on the cathode substrate  120  side to correspond to the phosphor films  133 R,  133 G, and  133 B, and an insulating layer  114  which is formed on the gate electrodes  113 . The gate substrate  110  has electron-passing holes  115 , substantially circular when seen from the top, which are formed at regions where the band-like gate electrodes  113  and matrix-like cathodes  123  overlap, and extend through the flat electrode  112 , glass plate  111 , gate electrodes  113 , and insulating layer  114 . The gate substrate  110  is sandwiched by the substrate ribs  122  of the cathode substrate  120  and the front ribs  135  of the anode substrate  130 .  
         [0007]     The flat electrode  112  in contact with the front ribs  135  protects the cathodes  123  and gate electrodes  113  from the influence of an electric field generated by the anodes. This can prevent an electric field from being generated by a potential difference between the gate electrodes  113  and the metal-backed films  134  which serve as the anodes, and prevent abnormal discharge between the cathodes  123  and metal-backed films  134 , thus preventing leaking light.  
         [0008]     In this flat panel display, when a predetermined potential difference is applied between the gate substrate  110  and cathodes  123  such that the gate substrate  110  side has a positive potential, electrons extracted from those regions of the cathodes  123  which intersect the gate electrodes  113  are emitted from the electron-passing holes  115 .  
         [0009]     More specifically, first, a voltage is applied to the flat electrode  112  to set it to have a higher potential than that of the cathodes  123 , so as to form an electric field on the surfaces of the cathodes  123  in advance. When a voltage is further applied to the gate electrodes  113  to set it to have a higher potential than that of the cathodes  123 , an electric field is formed on the cathodes  123  to extend from the outer surfaces of the gate electrodes  113  which form the electron-passing holes  115 , to extract electrons from the electron-emitting sources on the surfaces of the cathodes  123 . The electrons are accelerated by the flat electrode  112  to which the voltage has been applied to set it to have a positive potential with respect to the gate electrodes  113 , and emitted from the electron-passing holes  115  toward the front glass  131 .  
         [0010]     If a positive potential (accelerating voltage) higher than that on the flat electrode  112  is applied to the metal-backed films  134 , the electrons emitted from the electron-passing holes  115  are accelerated toward the metal-backed films  134 , and penetrate through the metal-backed films  134  to bombard the phosphor films  133 R,  133 G, and  133 B. Thus, the phosphor films  133 G,  133 B, and  133 R emit light.  
         [0011]     A method of forming the respective constituent elements of the flat panel display shown in  FIG. 15  will be described.  
         [0012]     The cathode substrate  120  is formed in the following manner. First, an insulating paste such as a vitreous paste is printed on the substrate  121  with a known printing method such as screen printing to form the substrate ribs  122  on one surface of the substrate  121 . Subsequently, the cathodes  123  disposed with electron-emitting sources on their surfaces are disposed on those regions of the substrate  121  which are sandwiched by the substrate ribs  122 . This forms the cathode substrate  120 . The cathodes  123  described above can be formed by disposing the electron-emitting sources on their surfaces by CVD or the like.  
         [0013]     The anode substrate  130  is formed in the following manner. First, the front glass  131  is prepared. An insulating paste such as a vitreous paste is printed on the front glass  131  with a known printing method such as screen printing to form the black matrices  132  on one surface of the front glass  131 . Subsequently, a phosphor material is printed on those regions on the front glass  131  which are sandwiched by the black matrices  132  with a known printing method such as screen printing to form the phosphor films  133 R,  133 G, and  133 B. The metal-backed films  134  are formed on the phosphor films  133 R,  133 G, and  133 B with a known deposition method. Finally, a glass paste is repeatedly printed on the black matrices  132  with a known printing method such as screen printing to form the front ribs  135 . Alternatively, the front ribs  135  may be formed by fixing members, e.g., strip-like glass plates, made of glass or a ceramic material into predetermined shapes, on the black matrices  132  by adhesion using a frit paste, or by contact bonding using a metal film.  
         [0014]     The gate substrate  110  is formed in the following manner. First, the glass plate  111  is prepared, and the flat electrode  112  is formed on its one surface by printing or sputtering. Subsequently, the band-like gate electrodes  113  are formed on the other surface of the glass plate  111  by printing or sputtering. The insulating layer  114  is formed on the other surface of the glass plate  111  by printing or the like to cover the gate electrodes  113 . Finally, the electron-passing holes  115  which extend through the flat electrode  112 , glass plate  111 , gate electrodes  113 , and insulating layer  114  are formed by sandblasting.  
         [0015]     In the flat panel display, a high luminance can be realized by increasing the amount of current (anode current) flowing through the anodes or the voltage (anode voltage) to be applied to the anodes. If the anode current is increased, the phosphors will decompose. Hence, to realize a high luminance, it is effective to increase the anode voltage. When the anode voltage is increased, the gate electrodes  113  and cathodes  123  cannot be electrically shielded completely due to the influence of the electric field generated in the anodes by the flat electrode  112 , and abnormal discharge may occur between the anodes and the cathodes  123 . To prevent this, the front ribs  135  must be formed such that the distance between the anodes and the flat electrode  112  is sufficiently large. For example, when the anode voltage is 10 kV, the distance between the anodes and the gate electrodes  113  is desirably about 3.0 mm.  
         [0016]     As described above, the front ribs  135  form rods or plates which are very thin as compared to their lengths to prevent a decrease in luminance of the flat panel display. It is therefore difficult to form the front ribs  135  to predetermined heights with the conventional method of repeating printing. For example, when the front ribs  135  are to be formed with widths of about 200 μm, their heights are about 2.0 mm at most. When the front ribs  135  are to be formed with widths of about 50 μm, their heights are about 1.0 mm at most.  
         [0017]     When the strip-like glass plates are to be fixed on the black matrices  132  by adhesion or contact bonding to form the front ribs  135 , thin glass plates as thin as about 50 μm cannot be formed, and a high-resolution flat panel display cannot be obtained. Assume that comparatively thick glass plates are to be fixed by adhesion. Frit glass or a silver paste is used to fix the glass plates. Thus, even if the glass plates are arrayed on the black matrices  132  highly accurately, they are adversely affected by the thermal expansion of the front glass  131  or the like during annealing. Therefore, it is difficult to array the formed front ribs  135  highly accurately.  
       SUMMARY OF THE INVENTION  
       [0018]     The present invention has been made to solve the problems as described above, and has as its object to provide flat panel display that can realize a high luminance, a gate electrode structure, and a gate electrode structure manufacturing method.  
         [0019]     In order to achieve the above object, according to the present invention, there is provided a flat panel display comprising a substrate, a front glass which is arranged to oppose the substrate and forms a vacuum envelope together with the substrate, the front glass being transparent at least partially, a cathode which is arranged on the substrate, a gate electrode which is arranged between the substrate and front glass, the gate electrode comprising an electron-passing hole through which an electron emitted from the cathode passes, a plurality of front ribs which extend vertically from the front glass toward the gate electrode, the plurality of front ribs extending vertically at a predetermined interval, a phosphor film and an anode which are stacked on a region of the front glass which is sandwiched by the front ribs, and a support member which extends vertically from the gate electrode toward the front glass and is in contact with the front ribs.  
         [0020]     According to the present invention, there is also provided a gate electrode structure comprising a gate electrode and a support member which extends vertically on one surface of the gate electrode.  
         [0021]     According to the present invention, there is also provided a gate electrode structure manufacturing method comprising the steps of forming a plate-like body having a gate electrode, and forming a support member which extends vertically on one surface of the plate-like body. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]      FIG. 1  is a partially exploded sectional view showing the arrangement of a flat panel display according to an embodiment of the present invention;  
         [0023]      FIG. 2  is a perspective sectional view showing the arrangement of a gate substrate in  FIG. 1 ;  
         [0024]      FIGS. 3A, 4A ,  5 A,  6 A,  7 A, and  8 A are partial plan views showing the steps in manufacturing the gate substrate of  FIG. 1 , and  FIGS. 3B, 4B ,  5 B,  6 B,  7 B, and  8 B are sectional views taken along the lines I-I of  FIGS. 3A, 4A ,  5 A,  6 A,  7 A, and  8 A, respectively;  
         [0025]      FIG. 9  is a main part sectional view showing the arrangement of the flat panel display according to the embodiment shown in  FIG. 1  of the present invention;  
         [0026]      FIGS. 10, 11 ,  12 A, and  12 B are perspective sectional views showing modifications of the gate substrate;  
         [0027]      FIGS. 13 and 14  are partially exploded sectional views each showing an arrangement of a flat panel display provided with a focus substrate; and  
         [0028]      FIG. 15  is a partially exploded view showing an arrangement of a conventional flat panel display. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]     An embodiment of the present invention will be described in detail with reference to the accompanying drawings.  
         [0030]     As shown in  FIG. 1 , a flat panel display  1  according to this embodiment has a cathode substrate  20  having a substrate  21  made of glass or the like, an anode substrate  30  having an at least partially transparent front glass  31 , and a gate substrate (gate electrode structure)  10  which is disposed to be substantially parallel to the substrate  21  and front glass  31 . The substrate  21  of the cathode substrate  20  and the front glass  31  of the anode substrate  30  are arranged to oppose each other through a frame-like spacer glass and are adhered to the spacer glass with low-melting frit glass to form an envelope. The interior of the envelope is maintained at a vacuum degree on the order of 10 −5  Pa.  
         [0031]     The cathode substrate  20  has the substrate  21  described above, a plurality of substrate ribs  22 , and cathodes  23 . The substrate ribs  22  vertically extend on that surface of the substrate  21  which opposes the gate substrate  10  at a predetermined interval to be parallel to each other. The cathodes  23  are disposed on those regions of the substrate  21  which are sandwiched by the substrate ribs  22  to substantially form matrices when seen from the top. As the cathodes  23 , those obtained by fixing electron-emitting sources made of nanotube fibers such as carbon nanotubes or carbon nanofibers to the surfaces of metal members such as 42-6 alloy members can be used. The upper surfaces of the cathodes  23  have the same heights as those of the upper surfaces of the substrate ribs  22 .  
         [0032]     The anode substrate  30  has the front glass  31  described above, a plurality of black matrices  32  having rectangular sections, red-, green-, and blue-emitting phosphor films  33 R,  33 G, and  33 B, metal-backed films  34  serving as anodes, and a plurality of front ribs  35  having rectangular sections. The black matrices  32  are formed on that surface of the front glass  31  which opposes the gate substrate  10  to form stripes at a predetermined interval in a direction parallel to the substrate ribs  22  of the cathode substrate  20 . The phosphor films  33 R,  33 G, and  33 B are formed on those regions of the front glass  31  which are sandwiched by the black matrices  32 . The metal-backed films  34  are formed on those regions of the front glass  31  which are sandwiched by the phosphor films  33 R,  33 G, and  33 B. The front ribs  35  vertically extend on the black matrices  32  at a predetermined interval toward the gate substrate  10 .  
         [0033]     The front ribs  35  form rods or plates which are very thin as compared to their lengths. The front ribs  35  are made of a material having a small secondary electron emission ratio in consideration of secondary electron emission from the front ribs  35 , or a slightly conductive material so the front ribs  35  will not accumulate electrons. For example, a glass paste containing chromium oxide or the like, more specifically, one of NP-7800 series (manufactured by Noritake Kizai K.K.) such as NP-7833, can be used.  
         [0034]     The gate substrate  10  is sandwiched in the envelope by the substrate ribs  22  of the cathode substrate  20  and the front ribs  35  of the anode substrate  30 . The gate substrate  10  has a second insulating layer  11  which is arranged to oppose the cathode substrate  20 , a plurality of parallel ribs  12  which are formed on the anode substrate  30 -side surface of the second insulating layer  11  to be spaced apart from each other at a predetermined interval, gate electrodes  13  which are disposed between the ribs  12 , a first insulating layer  14  which is formed on the ribs  12  and gate electrodes  13 , a flat electrode  15  which is disposed on the first insulating layer  14  to serve as a field control electrode, and a plurality of gate ribs  16  which extend vertically on the flat electrode  15  at a predetermined interval toward the front glass  31 , run in a direction perpendicular to the front ribs  35 , and each have a rectangular section. The gate substrate  10  has electron-passing holes  17  which are formed at regions where the gate electrodes  13  and cathodes  23  intersect, and extend through the second insulating layer  11 , gate electrodes  13 , first insulating layer  14 , and flat electrode  15 . The gate substrate  10  excluding the gate ribs  16  will be referred to as a “plate-like body”.  
         [0035]     The second insulating layer  11  is made of, e.g., frit glass or PPSQ (PolyPhenyl SilsesQuioxane), and has a plurality of openings  11   a  (see  FIGS. 7A and 7B  to be described later) which are spaced apart from each other at predetermined intervals in the widthwise and longitudinal directions of the front ribs  35 . The openings  11   a , together with the openings of the gate electrodes  13 , first insulating layer  14 , and flat electrode  15  to be described later, form part of the electron-passing holes  17 .  
         [0036]     The ribs  12  are made of a vitreous insulating paste into rods or plates each having a rectangular section. The ribs  12  are formed on the second insulating layer  11  at the intermediate portions of the openings  11   a  that are adjacent in either the widthwise or longitudinal direction. Hence, the ribs  12  line up to be spaced apart from the adjacent ones at predetermined intervals. Such ribs  12  serve as a guide to dispose the gate electrodes  13  to be spaced apart from each other at predetermined intervals.  
         [0037]     The gate electrodes  13  are formed of strip-like flat plates, e.g., flat plates made of a conductor such as a 42-6 alloy. The gate electrodes  13  have openings  13   a  (see  FIGS. 6A and 6B  to be described later) at a predetermined interval in the longitudinal direction to form part of the electron-passing holes  17 .  
         [0038]     The first insulating layer  14  is made of, e.g., frit glass. The first insulating layer  14  has openings  14   a  (see  FIGS. 4A and 4B  to be described hereinafter), which are substantially rectangular when seen from the top, at the equal interval to that of the openings  11   a  of the second insulating layer  11 . The openings  14   a  form part of the electron-passing holes  17 .  
         [0039]     The flat electrode  15  is formed of flat plates made of a conductor such as a 42-6 alloy. The flat electrode  15  has openings  15   a , which are substantially rectangular when seen from the top, at the equal interval to that of the openings  11   a  of the second insulating layer  11  and that of the openings  14   a  of the first insulating layer  14 . The openings  15   a  form part of the electron-passing holes  17 . The flat electrode  15  not only accelerates electrons extracted from the electron-emitting sources of the cathodes  23  but also shields the electric field of the metal-backed films  34  serving as the anodes to prevent leaking light.  
         [0040]     The gate ribs  16  form rods or plates each having a rectangular section. The gate ribs  16  are formed on the flat electrode  15  at the intermediate portions of the electron-passing holes  17  that are adjacent in either the widthwise or longitudinal direction. For example, the gate ribs  16  are formed immediately on the ribs  12 . Hence, the gate ribs  16  line up to be spaced apart from the adjacent ones at predetermined intervals. In the case of  FIG. 1 , the gate ribs  16  are formed in a direction perpendicular to the front ribs  35 . Such gate ribs  16  are made of a material having a small secondary emission ratio in consideration of secondary emission from the gate ribs  16 , or a slightly conductive material so the gate ribs  16  will not accumulate electrons. For example, a glass paste containing chromium oxide or the like, more specifically, one of NP-7800 series (manufactured by Noritake Kizai K.K.) such as NP-7833, can be used.  
         [0041]     A method of forming the gate substrate  10  will be described with reference to  FIGS. 3A and 3B  to  FIGS. 8A and 8B . First, the flat electrode  15  is prepared as shown in  FIGS. 3A and 3B . The plurality of openings  15   a  which are substantially rectangular when seen from the top are formed in the flat electrode  15  in advance with a known etching method such as wet etching, dry etching, or electric field etching, such that they are spaced apart from each other by predetermined intervals.  
         [0042]     Using a predetermined mask pattern, frit glass is printed and calcined on the flat electrode  15  with a known printing method such as screen printing. As shown in  FIGS. 4A and 4B , this forms the first insulating layer  14  having the openings  14   a , which form the electron-passing holes  17 , at positions corresponding to the openings  15   a  of the flat electrode  15 .  
         [0043]     Subsequently, using a predetermined mask pattern, a vitreous insulating paste is printed on the first insulating layer  14  with a known printing method such as screen printing. This forms the ribs  12  on the first insulating layer  14 , as shown in  FIGS. 5A and 5B . With the ribs  12 , the gate electrodes  13  can be positioned accurately.  
         [0044]     As shown in  FIGS. 6A and 6B , the gate electrodes  13 , in which the openings  13   a  are formed in advance with a known etching method such as wet etching, dry etching, or electric field etching, are disposed at those regions on the first insulating layer  14  which are sandwiched by the ribs  12 . The surfaces of the gate electrodes  13  on the first insulating layer  14  side are entirely fixed to the first insulating layer  14  by adhesion with frit glass or the like such that the openings  13   a  overlap the openings  14   a  of the first insulating layer  14 .  
         [0045]     Using a predetermined mask pattern, frit glass is printed and calcined on the ribs  12  and gate electrodes  13  with a known printing method such as screen printing. As shown in  FIGS. 7A and 7B , this forms the second insulating layer  11  having the openings  11   a , which form the electron-passing holes  17 , at positions corresponding to the openings  15   a  of the gate electrodes  13 .  
         [0046]     Subsequently, using a predetermined mask pattern, frit glass is repeatedly printed and calcined on that surface of the flat electrode  15  which is opposite to the surface where the first insulating layer  14  has been formed, with a known printing method such as screen printing. As shown in  FIGS. 8A and 8B , this forms the gate ribs  16  on the flat electrode  15 .  
         [0047]     Alternatively, the gate ribs  16  can be formed in the following manner. First, a vitreous paste mixed with a resin that is cured by ultraviolet radiation is prepared. This paste is discharged from a tapered nozzle onto that surface of the flat electrode  15  which is opposite to the surface where the first insulating layer  14  has been formed. The paste is irradiated with ultraviolet rays so its surface is cured. In this state, the paste is calcined so it is cured to its interior. Hence, for example, the gate ribs  16  having widths of 50 μm to 200 μm and heights of 1 mm to 2 mm can be formed. The gate ribs  16  having the above heights can be formed by conducting only once the series of steps of discharging the paste, ultraviolet radiation, and calcination. Alternatively, the series of steps may be performed a plurality of number of times to form the gate ribs  16  to desired heights.  
         [0048]     In the above description, after the ribs  12  are formed, the gate electrodes  13  are disposed on the first insulating layer  14 . Alternatively, the gate electrodes  13  may be disposed on the first insulating layer  14  after the gate ribs  16  are formed. This case will be described hereinafter.  
         [0049]     First, as shown in  FIGS. 5A and 5B , the ribs  12  are formed on the first insulating layer  14 , and thereafter the gate ribs  16  are formed on the flat electrode  15 . The second insulating layer  11  is formed on one surface of the gate electrodes  13 . The ribs  12  are formed to have substantially the same thicknesses as those of the gate electrodes  13 .  
         [0050]     Then, the gate electrodes  13  on which the second insulating layer  11  is formed are fitted on those regions of the first insulating layer  14  which are sandwiched by the ribs  12 , from the surface where the second insulating layer  11  is not formed. At this time, the gate electrodes  13  may be positioned by adhering one end in the longitudinal direction of each gate electrode  13  on the first insulating layer  14  with frit glass or the like.  
         [0051]     The gate substrate  10  can be formed in this manner as well. In this case, the second insulating layer  11  is not formed on the ribs  12 . The second insulating layer  11  need not be formed on the ribs  12  as far as the gate electrodes  13  are not in direct contact with the cathodes  23 .  
         [0052]     The method of forming the gate substrate  10  has been described so far. The cathode substrate  20  and anode substrate  30  can be formed in the same manner as in the conventional case. The substrate ribs  22  of the cathode substrate  20  and the front ribs  35  of the anode substrate  30  can be formed by employing the method including ultraviolet radiation and calcination of the paste which has been described regarding the gate ribs  16 .  
         [0053]     The positional relationship between the gate substrate  10  and anode substrate  30  (both are described above) in the flat panel display according to this embodiment will be described with reference to  FIG. 9 . According to this embodiment, the front ribs  35  are formed on the front glass  31  of the anode substrate  30 , and the gate ribs  16  are formed on the flat electrode  15  of the gate substrate  10 . The gate ribs  16  are in contact with the front ribs  35  to support the anode substrate  30 . Namely, the gate ribs  16  serve as a support member. In this manner, in the flat panel display of this embodiment, not only the front ribs  35  but also the gate ribs  16  are provided between the anode substrate  30  and gate substrate  10 . Thus, the distance between the gate substrate  10  and anode substrate  30  can be increased to be larger than in a case wherein only the front ribs  135  are provided as in the conventional flat panel display.  
         [0054]     Conventionally, the gate ribs cannot be formed on the gate substrate  110 . This is because of the following reason. The glass plate  111  having a thickness of about 0.1 mm is used as the insulating layer that separates the gate electrodes  113  from the flat electrode  112 . If the gate electrodes  113  and flat electrode  112  are respectively printed on the two surfaces of the glass plate  111  and the gate ribs are formed on the flat electrode  112  by repeating printing, the glass plate  111  may be broken. In view of this, according to this embodiment, the flat electrode  15  is formed of a conductive plate. Then, even if the gate ribs  16  are printed on the flat electrode  15  by repeating printing, the first insulating layer  14  will not be broken, so the gate ribs  16  can be formed on the gate substrate  10 .  
         [0055]     In this manner, according to this embodiment, the gate ribs  16  can be formed on the gate substrate  10 . Thus, the distance between the gate substrate  10  and anode substrate  30  can be increased to such a degree that even when a high voltage is applied to the metal-backed films  34 , abnormal discharge will not occur between the cathodes  23  and metal-backed films  34 .  
         [0056]     Therefore, as shown in, e.g.,  FIG. 9 , if the gate ribs  16  and front ribs  35  are formed to have heights of 1.5 mm, the distance between the gate substrate  10  and anode substrate  30  becomes 3.0 mm. A high voltage of about 10 kV can be applied to the metal-backed films  34 , so that a high luminance can be realized. At this time, while the gate ribs  16  and front ribs  35  are formed to have widths of, e.g., 0.2 mm in  FIG. 9 , they can be formed to have widths of about 0.05 mm to 0.2 mm. As a result, micropatterning can also be realized simultaneously.  
         [0057]     Modifications of the gate substrate  10  will be described. The direction in which the gate ribs  16  are to be formed is not limited to the direction perpendicular to the front ribs  35 , as shown in  FIG. 1 , but may be a direction merely intersecting the front ribs  35 . The gate ribs  16  may be formed in a direction parallel to the front ribs  35 , like gate ribs  16   a  of a gate substrate  10   a  shown in  FIG. 10 . In this case, regarding the gate ribs  16   a  and front ribs  35 , the gate ribs  16   a  and front ribs  35  at opposing positions are in contact with each other.  
         [0058]     The gate ribs are not limited to the rods as shown in  FIGS. 1 and 10 , but may substantially form matrices when seen from the top, which extend vertically on the flat electrode  15 , like gate ribs  16   b  of a gate substrate  10   b  shown in  FIG. 11 . In this case, the gate ribs  16   b  are formed by repeatedly printing and calcining frit glass on the flat electrode  15  to a predetermined height using a predetermined mask pattern, with a known printing method such as screen printing. With the matrix shape, the gate ribs  16   b  can improve the resistance against the pressures from the cathode substrate  20  and anode substrate  30  which result from the atmospheric pressure or the like.  
         [0059]     As in a gate substrate  10   c  shown in  FIG. 12A , focus electrodes  18  may be formed on the distal end faces of the gate ribs  16  which oppose the front ribs  35 . A positive potential equal to that applied to the flat electrode  15  is applied to the focus electrodes  18 . It was confirmed that with the focus electrodes  18 , electrons extracted from the cathodes  23  and emitted from the electron-passing holes  17  converge toward the centers of the phosphor films  33 R,  33 G, and  33 B from the side surfaces of the front ribs  35 . This may be because the strength of the electric field generated by the metal-backed films  34  which serve as the anodes is changed by the electric field generated by the focus electrodes  18 .  
         [0060]     The focus electrodes  18  can shield the cathodes  23  and gate electrodes  13  from the influence of the electric field generated by the metal-backed films  34 , so an electric field will not be generated by the potential difference between the gate electrodes  13  and the metal-backed films  34  which serve as the anodes. Thus, abnormal discharge between the cathodes  23  and metal-backed films  34 , and leaking light can be prevented.  
         [0061]     The focus electrodes  18  can be formed by printing, e.g., silver paste on the gate ribs  16  with a known printing method such as screen printing. The positions to form the focus electrodes  18  are not limited to on the gate ribs  16  shown in  FIG. 12A  which are perpendicular to the front ribs  35 . As in a gate substrate  10   d  shown in  FIG. 12B , focus electrodes  18   a  can be formed on gate ribs  16   a  which are parallel to the front ribs  35 . Alternatively, the focus electrodes may be formed on gate ribs  16   b  shown in  FIG. 11  which substantially form matrices when seen from the top. The focus electrodes may also be formed on those surfaces of the front ribs  35  which oppose the gate ribs  16 ,  16   a , or  16   b.    
         [0062]     In place of the focus electrodes  18  described above, as shown in  FIG. 13 , a focus substrate (focus electrode)  40  may be arranged between the gate ribs  16  and front ribs  35  to be sandwiched by them. The focus substrate  40  is formed of a conductive plate made of, e.g., a 42-6 alloy, and openings  40   a  are formed in it, at positions corresponding to the electron-passing holes  17  of the gate substrate  10 , with a known etching method such as wet etching, dry etching, or field etching. With the focus substrate  40 , in the same manner as in the case provided with the focus electrodes  18 , the gate electrodes  13  can be electrically shielded so as to prevent an electric field from being generated by the potential difference between the gate electrodes  13  and the metal-backed films  34  which serve as anodes. Consequently, abnormal discharge between the cathodes  23  and metal-backed films  34 , and leaking light can be prevented. The focus substrate  40  can be formed not only when the gate ribs  16  of the gate substrate  10  are perpendicular to the front ribs  35 , as shown in  FIG. 13 , but also when the gate ribs  16  of the gate substrate  10  are parallel to the front ribs  35 , as shown in  FIG. 14 .  
         [0063]     According to this embodiment, the electron-passing holes  17  form substantially matrices when seen from the top. The shapes of the electron-passing holes  17  are not limited to this, but can be set arbitrarily and freely, e.g., substantially circular when seen from the top.  
         [0064]     According to this embodiment, one end in the longitudinal direction of each gate electrode  13  is adhered on the first insulating layer  14  with frit glass. Alternatively, an adhesion layer made of frit glass or the like may be formed on the first insulating layer  14 , and the gate electrodes  13  may be disposed on the adhesion layer. In this case, the ribs  12  are formed on the adhesion layer as well.  
         [0065]     As has been described above, according to the present invention, the gate ribs  16 ,  16   a , or  16   b  are formed on one surface of the gate substrate  10 ,  10   a ,  10   b ,  10   c , or  10   d . Thus, the distance between the gate substrate  10 ,  10   a ,  10   b ,  10   c , or  10   d  and the metal-backed films  34  serving as the anodes can be increased. Even when a high voltage is applied to the anodes, the cathodes  23  and gate electrodes  13  can be protected from the influence of the electric field generated by the anodes. Thus, discharge between the cathodes  23  and the anodes can be prevented. As a result, a high luminance can be realized.