Abstract:
A gas discharge type display apparatus includes a front substrate having a plurality of first electrodes and a back substrate having a plurality of second electrodes and at least ones of the first and second electrodes are made of the photosensitive material containing silver exposed by using the laser thereby, making a mask unnecessary.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a wiring board in which a wiring pattern is formed on a substrate and a gas discharge type display apparatus using such a wiring board. 
     2. Description of the Related Art 
     According to a gas discharge type display apparatus such as a plasma display or the like, since a display is performed by a self light emission, an angle of visibility is wide and a display can be easily seen. Such a display apparatus has features that a thin display apparatus can be manufactured and a large screen can be realized and the like. An application of such a display apparatus to a display apparatus of information terminal equipment or a high definition television receiver has been started. The plasma display is mainly classified into a DC driving type and an AC driving type. According to the plasma display of the AC driving type among them, a luminance is high owing to a memory function of a dielectric layer covering electrodes and a life enough to endure an actual use can be obtained due to the formation of a protecting layer or the like. Thus, the plasma display has been put into practical use as a multi-purpose video monitor. 
     FIG. 6 is a perspective view showing a structure of a plasma display panel which has been put into practical use. To make it easy to see, a front substrate  100  is illustrated in the diagram so as to be away from a back substrate  200  and a discharge space area  300 . 
     The front substrate  100  has a structure such that display electrodes  600  made of a transparent electrode material such as ITO (Indium Tin Oxide), tin oxide (SnO 2 ), or the like, bus electrodes  700  made of a low resistance material, a dielectric layer  800  made of a transparent insulating material, and a protecting layer  900  made of a material such as magnesium oxide (MgO) or the like are formed on a front glass substrate  400 . 
     The back substrate  200  has a structure such that address electrodes  1000 , barrier ribs  1100 , and a fluorescent layer  1200  are formed on a back glass substrate  500 . Although not shown, a dielectric layer is also formed on the address electrodes  1000 . 
     By adhering the front substrate  100  and back substrate  200  so that the display electrodes  600  and address electrodes  1000  almost perpendicularly cross, the discharge space area  300  is formed between the front substrate  100  and back substrate  200 . 
     In the gas discharge type display apparatus, an AC voltage is applied between a pair of display electrodes  600  formed on the front substrate  100  and a voltage is applied between the address electrodes  1000  formed on the back substrate  200  and the display electrodes  600 , thereby generating an address discharge and allowing predetermined discharge cells to generate a main discharge. By ultraviolet rays which are generated by the main discharge, the fluorescent materials  1200  of red, green, and blue separately coated on the discharge cells are allowed to emit light, thereby displaying. 
     A conventional technique of such a gas discharge type display apparatus has been disclosed in, for example, “Flat Panel Display 1996”, edited by Nikkei Microdevice, pages 208-215, 1995. 
     A method of forming the bus electrodes  700  provided for the front substrate  100  and the address electrodes  1000  provided for the back substrate  200  will be described further in detail. FIGS. 4 and 5 show an example of forming the address electrode  1000  onto the back glass substrate  500 . Since the bus electrodes  700  provided for the front substrate  100  are also formed by almost similar steps, its description is omitted here. 
     First referring now to FIG. 4, Cr/Cu/Cr layers ( 1000   a  to  1000   c ) serving as an address electrode  1000  and a resist  2500  to form a pattern of the address electrode  1000  are sequentially formed on the back glass substrate  500  so as to be laminated by using a film forming method such as sputtering method, evaporation deposition method, or the like and by using a resist forming method such as rotational coating, laminating, or the like (step (a): film forming step). Subsequently, the resist  2500  is exposed and developed so as to obtain a desired pattern of the address electrode  1000  (steps (b) and (c): photolithographic step). The Cr layer  1000   a  is etched in a desired pattern by using an etchant for Cr (step (d): etching step). Subsequently, the exposed and developed resist  2500  is removed and the resist  2500  is again formed (steps (e) and (f)). Subsequently, referring to FIG. 5, by repeating the above processes with respect to each of the Cu layer  1000   b  and Cr layer  1000   c  (steps (g) to (o)), the address electrode  1000  is formed on the back glass substrate  500 . 
     Although such a process is usually called a photolithograph-etching process, such a process has difficulties that the number of steps is large and costs are high because the resist formation and the like are included. Although the forming method of the Cr/Cu/Cr wirings has been described here, there are similar difficulties so long as a resist is used even if wirings are formed by using another single material. Although a mask to expose and form the resist pattern is necessary to form a resist, according to the gas discharge type display apparatus, since it ordinarily has a large screen, a positional deviation occurs more easily as a position of the mask approaches a periphery and it is difficult to accurately form wirings. It is also difficult to realize a highly accurate position matching itself of the mask. The mask is expensive. 
     As a wiring forming method in which the resist is made unnecessary, there is a method whereby a photosensitive material (for example, silver material having photosensitivity) is used and the photosensitive material is exposed and developed by a light source such as a mercury lamp or the like, thereby forming wirings. 
     In this case as well, however, in case of exposing the photosensitive material, a mask on which a desired wiring pattern has been formed is necessary and the difficulties in case of using the mask as mentioned above still remain. That is, there are the difficulties of the positional deviation at the time of formation of the wirings, the positional mismatching of the mask, and the costs of the mask. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an exactly novel process which makes a mask unnecessary. That is, an object of the invention is to provide a gas discharge type display apparatus in which wirings are formed by exactly novel processes without needing a mask. 
     According to the invention, when wirings are formed by using a photosensitive material, a wiring pattern is directly drawn by a laser and the photosensitive material is exposed by the laser drawing, thereby making the conventional mask unnecessary. That is, according to the invention, to accomplish the above object, a front substrate having a plurality of first electrodes and a back substrate having a plurality of second electrodes are provided, and at least ones of the first and second electrodes are made of a photosensitive material containing silver exposed by using the laser. 
     As mentioned above, by directly drawing and exposing the photosensitive material with the laser, the conventional exposing process using the mask is unnecessary, so that the difficulties of the positional deviation at the time of the formation of the wirings due to the mask, the positional mismatching of the mask, and the costs of the mask can be solved. Therefore, according to the gas discharge type display apparatus of the invention, there is no positional mismatching of the mask and high positioning precision of the wirings can be easily assured, namely, the wirings can be formed at a desired position as compared with the conventional apparatus, so that uniform discharging characteristics can be obtained on the whole panel surface. 
     The wirings can be also formed at low costs. 
     Silver is preferable as a photosensitive material because of a wiring resistance or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view showing an embodiment of the invention; 
     FIG. 2 is a cross sectional view showing the embodiment of the invention; 
     FIG. 3 is a cross sectional view showing the embodiment of the invention; 
     FIGS. 4 and 5 are conventional process diagrams; and 
     FIG. 6 is a cross sectional view showing a conventional gas discharge type display apparatus. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the invention will now be described hereinbelow with reference to the drawings. 
     FIG. 1 shows an example of processes to form address electrodes onto a back glass substrate. 
     FIG,  1 ( a ) shows a state where a material  1000  having photosensitivity containing silver is coated onto the glass substrate  500  by a dichoter and is pre-dried. 
     FIG.  1 ( b ) shows a state where a desired pattern is drawn in the material  1000  containing silver by using a YAG (Yttrium Aluminum Garnet) laser having an exposing apparatus (not shown). A beam irradiated from the YAG laser uses a wavelength of a third harmonic so that the material containing silver can be photosensed. 
     FIG.  1 ( c ) relates to a developing step and shows a state where a non-drawing portion which is not drawn by the laser is removed by a developing liquid. After that, a heat treatment is performed to improve the reliability of the wirings. 
     After that, although not shown, a dielectric layer, a barrier, and a fluorescent layer are sequentially formed and a back substrate is completed. 
     By using the processes as mentioned above, since the wiring pattern is directly exposed by the laser, the conventional mask is unnecessary and the reduction of costs can be realized. Since the area exposed by the laser becomes the wiring pattern, the conventional etching process using the resist is also unnecessary and a defective disconnection or the like based on the etching process is eliminated. Since the wiring pattern is directly drawn, the electrodes can be formed at high positioning precision and desired discharging characteristics can be realized on the whole panel surface. 
     Although the embodiment has been described with respect to the example of the material containing silver, there is no problem even if a photosensitive material containing another metal is used. The invention is not limited to the YAG laser but there is no problem even if another laser such as excimer laser, argon ion laser, or the like is used. 
     The same shall also similarly apply to the following embodiments. 
     FIG. 2 is a whole diagram of the back substrate shown in FIG.  1 . 
     As will be understood from the diagram, when address electrodes are formed on the back substrate, a plurality of electrodes are formed in parallel by using a plurality of beams. By adjusting a spot diameter (energy) of the laser, one wiring is exposed by one laser scan. 
     Generally, the address electrode has external connecting terminals  1010 , leading wirings  1020 , and wirings  1030  and a wiring width of each external connecting terminal  1010  is wider than that of each of the other wirings  1020  and  1030 . Therefore, the external connecting terminals  1010  are exposed by beam scans of a plural number of times and, after that, the leading wirings  1020  and wirings  1030  are exposed by one successive beam scan, thereby improving a throughput. 
     On the other hand, among the lasers, there is a laser like a pulse laser in which an irradiating area is controlled on a dot unit basis. In this case, it is sufficient to control such that the beam is scanned in a predetermined direction and the laser is irradiated to an area to be exposed and the laser is not irradiated to an area which is not exposed. 
     An example of the process of forming bus electrodes onto the front glass substrate will now be described with reference to FIG.  3 . 
     First, materials forming the display electrodes  600  and bus electrodes  700  are sequentially formed as films onto the glass substrate  400  (step (a)). In this case, ITO serving as transparent electrodes is used as display electrodes  600  and a photosensitive silver material is used as bus electrodes  700 . The ITO material is formed as a film by a film forming method such as sputtering method, evaporation deposition method, or the like. The silver material is coated by the dichoter and is formed as a film. 
     An exposing laser is subsequently irradiated to an area serving as a wiring pattern in the material layer containing silver (step (b)) and the irradiated area is developed, thereby forming the bus electrode  700  (step (c)) in a manner similar to the foregoing embodiment. 
     The area is worked so as to remove a predetermined area in the ITO layer by using a working laser (step (d)), thereby forming the display electrode  600  (step (e)). 
     After that, although not shown, the front substrate is completed by forming a dielectric layer and a protecting layer of MgO or the like. An insulating layer can be also formed between the glass substrate  400  and display electrode  600 . 
     The bus electrode  700  is formed by the exposing and developing processes using the laser and the display electrode  600  is formed by the laser working process as mentioned above. Therefore, the conventional resist is unnecessary and the mask to form the resist is also unnecessary, so that the large reduction of the costs can be realized. Since the conventional etching process using the resist is not used as well, the defective disconnection or the like based on the etching process is eliminated. Since the electrodes can be formed at high positional precision, desired discharge characteristics can be realized on the whole panel surface. 
     Even if the display electrodes  600  are formed by etching or abrasive blasting using the resist, an advantage that is obtained by exposing and developing the bus electrodes  700  by using the laser is not lost. 
     According to the invention, processes of low costs in which the mask is unnecessary can be realized by working the material having photosensitivity by the directly drawing by the laser. 
     Since the electrodes can be formed at a desired position at high precision, a gas discharge type display apparatus of a high quality in which desired discharge characteristics are realized on the whole panel surface can be provided.