Abstract:
The present invention provides a method for manufacturing a triode field emission display (FED) that can accommodate a large screen size and that has holes that are minutely and uniformly formed. The method includes forming cathode electrodes on a first substrate; depositing a photosensitive material on the first substrate covering the cathode electrodes; patterning the photosensitive material in a predetermined pattern to form guide supports for the formation of insulation layer holes at locations where an electron emitting layer will be formed on the cathode electrodes; forming a preliminary insulation layer on the first substrate covering the guide supports; removing the guide supports from the cathode electrodes to form holes at the locations of the guide supports, thereby realizing a completed insulation layer from the preliminary insulation layer; forming gate electrodes on the insulation layer, the gate electrodes having holes corresponding to the holes of the insulation layer; forming an electron emitting layer on the cathode electrodes; providing a second substrate with anode electrodes and a phosphor layer formed thereon, substantially in parallel to the first substrate, and connecting and sealing the first and second substrates to realize a sealed assembly; and exhausting air from within the sealed assembly.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a manufacturing method for a triode field emission display, and more particularly, to a manufacturing method for a triode field emission display, in which the field emission display provides a large screen size and has holes that are minutely and uniformly formed.  
         BACKGROUND OF THE INVENTION  
         [0002]    In the first field emission displays (FEDs), conical metal microtips were formed on cathode electrodes, and gate electrodes were formed in peripheries of the metal microtips. With such a structure, electrons emitted from the metal microtips are accelerated toward a phosphor layer provided on anode electrodes to thereby realize images. However, a drawback of this configuration is that expensive semiconductor equipment is needed to form the metal microtips (i.e., an electron-emitting layer). This increases overall manufacturing costs and makes the production of display devices of a large screen size difficult.  
           [0003]    To remedy this problem, there has been disclosed an FED with a surface electron source structure, in which the electron emitting layer is formed as a film. Such a surface-type electron emitting layer is realized using a conventional carbon-based material. In recent times, much attention has been given to a carbon nanotube structure. Carbon nanotubes have the advantages of a minute curvature radius at their tips of approximately 100. and are capable of realizing smooth electron emission at driving voltages of approximately 10.50V. Accordingly, carbon nanotubes enable operation at low voltages, and are an ideal electron emitting source for FEDs with large screen sizes.  
           [0004]    FEDs that use carbon nanotubes as the electron emitting source generally employ a triode structure having gate electrodes. In such FEDs, an insulation layer and gate electrodes are provided on cathode electrodes, holes are formed to expose the cathode electrodes through the insulation layer and gate electrodes, then a carbon nanotube electron emitting layer is formed within the holes and on the cathode electrodes.  
           [0005]    In the above processes, the insulation layer having the holes may be formed by a thin film process such as the PECVD (plasma enhanced chemical vapor deposition) process or by a thick film process using paste printing. However, problems result in either of the two types of processes that interfere with the manufacture of the triode FED.  
           [0006]    In particular, when forming the insulation layer using the thin film process, although it is possible to obtain a film having superior insulating characteristics, it is difficult to realize a sufficient thickness for the film, that is, a thickness at least matching that of the electron emitting layer. Further, even if an adequate thickness for the insulation layer is realized using the thin film process, the time required for the process is long, it is necessary to control the stresses within the film, and a complicated etching process is required to make the thick film uniform when forming the holes.  
           [0007]    In the case where the insulation layer is formed using the thick film printing process, although it is easy to realize a desired thickness, there are difficulties in making the holes uniform and adequately minute as a result of the inherent characteristics of the printing method. When forming the holes in the insulation layer using the printing process, it is possible to realize an insulation layer having holes using only the printing process, and also to form the holes by an etching process after the insulation layer is printed and sintered. However, in either of the two printing processes to form the holes in the insulting layer, again it is possible to realize a desired thickness for the insulating but difficult to form the holes to a minute size.  
         SUMMARY OF THE INVENTION  
         [0008]    It is one object of the present invention to provide a manufacturing method for a triode FED that enables the formation of an insulation layer provided between cathode electrodes and gate electrodes to a desired thickness, as well as the formation of holes in the insulation layer that are both uniform and minute.  
           [0009]    In one embodiment, the present invention provides a method for manufacturing a triode FED comprising forming cathode electrodes on a first substrate; depositing a photosensitive material on the first substrate covering the cathode electrodes; patterning the photosensitive material in a predetermined pattern to form guide supports for the formation of insulation layer holes at locations where an electron emitting layer will be formed on the cathode electrodes; forming a preliminary insulation layer on the first substrate covering the guide supports; removing the guide supports from the cathode electrodes to form holes at the locations of the guide supports, thereby realizing a completed insulation layer from the preliminary insulation layer; forming gate electrodes on the insulation layer, the gate electrodes having holes corresponding to the holes of the insulation layer; forming an electron emitting layer on the cathode electrodes; providing a second substrate with anode electrodes and a phosphor layer formed thereon, substantially in parallel to the first substrate, and connecting and sealing the first and second substrates to realize a sealed assembly; and exhausting air from within the sealed assembly.  
           [0010]    According to a feature of an embodiment of the present invention, the photosensitive material is selected from the group consisting of a DFR (dry film resist) film, polyimide, an emulsion, and a photoresist.  
           [0011]    According to another feature of an embodiment of the present invention, the preliminary insulation layer is formed by using a printing process to deposit and dry an insulation paste on the first substrate covering the guide supports.  
           [0012]    According to yet another feature of an embodiment of the present invention, the guide supports for the formation of insulation layer holes are formed by forming holes in the photosensitive material in a predetermined pattern using a photolithography process, and performing a plating process within the holes to form a plating layer therein, then removing the photosensitive material from the first substrate to thereby realize metal supports by the plating layer.  
           [0013]    According to still yet another feature of an embodiment of the present invention, the removal of the guide supports is realized by removing an upper portion of the preliminary insulation layer to expose an upper end of the guide supports, and removing the guide supports by using one of a chemical etching process and an electrolysis process.  
           [0014]    According to still yet another feature of an embodiment of the present invention, the guide supports for the formation of insulation layer holes are formed by patterning the photosensitive material using a photolithography process to thereby realize photosensitive supports obtained by the photosensitive material at locations where an electron emitting layer will be formed.  
           [0015]    According to still yet another feature of an embodiment of the present invention, the exposure performed by the photolithography process is effected from a side of the first substrate opposite that on which the cathode electrodes are formed.  
           [0016]    According to still yet another feature of an embodiment of the present invention, the removal of the guide supports is realized by sintering the preliminary insulation layer and removing portions of the preliminary insulation layer corresponding to positions of the guide supports.  
           [0017]    According to still yet another feature of an embodiment of the present invention, the sintering is performed by maintaining a temperature that exceeds a softening point of an insulation frit by 20-30. for 5-60 minutes.  
           [0018]    According to still yet another feature of an embodiment of the present invention, the preliminary insulation layer is formed by a process selected from the group consisting of a printing process, a cataphoresis process, a doctor blade process, and a spray process. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention, in which:  
         [0020]    FIGS.  1 A- 1 J show partially enlarged sectional views of a FED as it undergoes sequential processes in a manufacturing method according to a first preferred embodiment of the present invention;  
         [0021]    FIGS.  2 A- 2 H show partially enlarged sectional views of a FED as it undergoes sequential processes in a manufacturing method according to a second preferred embodiment of the present invention; and  
         [0022]    FIGS.  3 A- 3 L show partially enlarged sectional views of a FED as it undergoes sequential processes in a manufacturing method according to a third preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.  
         [0024]    [0024]FIGS. 1A through 1J are partially enlarged sectional views of a triode FED as it undergoes sequential processes in a manufacturing method according to a first preferred embodiment of the present invention. The drawings show the FED cut along a long axis direction.  
         [0025]    First, with reference to FIG. 1A, a plurality of cathode electrodes  4  are formed in a stripe pattern on a first substrate (hereinafter referred to as a lower substrate)  2 . The cathode electrodes  4  are typically made of a metal such as chrome, silver, or nickel, but may also be made of a clear material such as ITO (indium tin oxide). It is preferable that the cathode electrodes  4  are maintained at a thickness of between  1000  and  3000 . The cathode electrodes  4  are formed using a thin film formation process such as sputtering or a thick film formation process such as printing, depending on the material used for the cathode electrodes  4 .  
         [0026]    Next, with reference to FIG. 1B, a photosensitive material  6  is first deposited on the lower substrate  2  covering the cathode electrodes  4 , then formed in a predetermined pattern. For the photosensitive material  6 , it is possible to use a DFR (dry film resist) film, polyimide, an emulsion, or a photoresist. In the first preferred embodiment of the present invention, a DFR film is used for the photosensitive material  6 .  
         [0027]    In the first embodiment of the present invention, the photosensitive material  6  is provided on the cathode electrodes  4  then patterned thereon before the formation of an insulation layer (as with conventional FED manufacturing methods) in order to form guide supports. The guide supports enable the formation of insulation layer holes on top of the cathode electrodes  4 , that is, at locations corresponding to an electron emitting layer. The guide supports are formed in the first preferred embodiment of the present invention according to the following processes.  
         [0028]    First, in a state where the photosensitive material  6  is provided at a predetermined thickness as shown in FIG. 1B, the photosensitive material  6  is exposed and developed using a photolithography process such that holes  6   a  are formed in the photosensitive material  6  in a predetermined pattern as shown in FIG. 1C.  
         [0029]    Next, a plating layer  7 ′ is formed in the holes  6   a  using a plating process such as an electrolytic plating process or a non-electrolytic plating process as shown in FIG. 1D. After the plating layer  7 ′ is formed, the photosensitive material  6  is removed from the lower substrate  2  such that the plating layer  7 ′ is exposed. With the removal of the photosensitive material  6 , the plating layer  7 ′ becomes the guide supports, hereinafter indicated by reference numeral  7 . The completed guide supports  7  are shown in FIG. 1E. Therefore, the guide supports  7  in the first preferred embodiment of the present invention are metal guide supports realized through a plating process.  
         [0030]    Subsequently, a preliminary insulation layer  8  is formed on the lower substrate  2  at a thickness sufficient to completely cover the guide supports  7 . In the first preferred embodiment of the present invention, the preliminary insulation layer  8  is formed by a printing process. That is, an insulation paste is printed on the lower substrate  2  covering the guide supports  7 , then the printed insulation paste is dried at a temperature between 90 and 120. to thereby form the preliminary insulation layer  8  as shown in FIG. 1F.  
         [0031]    Next, an upper portion of the preliminary insulation layer  8  is removed by a grinding, sandblasting, or etching process such that upper ends of the guide supports  7  are exposed as shown in FIG. 1G. After the upper portion of the preliminary insulation layer  8  is removed, it is preferable that a thickness (t) of the preliminary insulation layer  8  and a height (h) of the guide supports  7  are identical. However, it is also possible for the thickness (t) of the preliminary insulation layer  8  and the height (h) of the guide supports  7  to be somewhat different. Sintering is then performed on the elements shown in FIG. 1G at a temperature between 400 and 550. to thereby prepare an insulating layer having a required layer quality.  
         [0032]    Following the above, the guide supports  7  are removed using a solution for this purpose, or through electrolysis. With the removal of the guide supports  7  from the lower substrate  2 , a plurality of holes  10   a  is formed in the preliminary insulation layer  8  to thereby realize a completed insulation layer  10  as shown in FIG. 1H.  
         [0033]    After the insulation layer  10  is prepared through the processes described above, gate electrodes  12  are formed on an upper end of the insulation layer  10  using the same process as when forming the cathode electrodes  4 . Also, a paste is printed on the cathode electrodes  4  within the holes  10   a  of the insulation layer  10  to thereby form an electron emitting layer  14  having a predetermined pattern as shown in FIG. 11. The paste includes a carbon-based material such as carbon nanotubes, graphite, diamond, diamond-like carbon, etc.  
         [0034]    After the printing process to form the electron emitting layer  14  as shown in FIG. 11, anode electrodes  18  and a phosphor layer  20  are formed on a second substrate (hereinafter referred to as an upper substrate)  16 . A side glass  22  is then interposed between the upper substrate  16  and the lower substrate  2  so as to place the upper substrate  16  and the lower substrate  2  substantially in parallel, after which a sealant  24  is used to fuse the lower substrate  2 , the upper substrate  16 , and the side glass  22 . As a result, a sealed assembly for the FED is realized. Finally, an exhaust unit is used to remove the air from between the substrates  2  and  16  to thereby complete the triode FED as shown in FIG. 1J.  
         [0035]    In the FED manufactured as in the above, it is unnecessary to undergo a complicated and difficult process of etching to control the formation of the holes or thick layer printing to control the hole pattern. Instead, the guide supports that correspond to the formation of the holes are formed by simple processes and an easy plating process for pattern control such that the holes of the insulation layer may be realized to minute sizes and having a suitable aspect ratio. Therefore, an FED of an improved quality may be realized.  
         [0036]    [0036]FIGS. 2A through 2H are partially enlarged sectional views of a triode FED as it undergoes sequential processes in a manufacturing method according to a second preferred embodiment of the present invention. The drawings show the FED cut along a long axis direction. The second preferred embodiment differs from the first preferred embodiment of the present invention mainly in the formation of guide supports.  
         [0037]    First, with reference to FIG. 2A, a plurality of cathode electrodes  32  are formed in a stripe pattern on a first substrate (hereinafter referred to as a lower substrate)  30 . In the second preferred embodiment of the present invention, the cathode electrodes  32  are realized by sequentially depositing an ITO layer  32   a  and chrome elements  32   b  in a predetermined pattern.  
         [0038]    Next, to form guide supports, a photosensitive material  34  is deposited on the lower substrate  30  covering the cathode electrodes  32  (as in the first preferred embodiment) as shown in FIG. 2B. It is preferable that the materials are as described with reference to the first preferred embodiment. A DFR film is also used for the photosensitive material  34  in the second preferred embodiment of the present invention. A thickness of the photosensitive material  34  is either the same as or greater than a thickness of an insulation layer  40  (see FIG. 2F), which will be described below.  
         [0039]    In this state, the photosensitive material  34  is patterned to form guide supports. In the second preferred embodiment of the present invention, a photolithography process is used for the purpose of forming the guide supports. That is, the photosensitive material  34  is exposed and developed to realized a predetermined pattern of the photosensitive material  34 . At this time, exposure is performed by irradiating a predetermined light from a light source onto the photosensitive material  34  toward either a front surface of the lower substrate  30  on which the cathode electrodes  32  are formed or a rear surface of the lower substrate  30  opposite the surface on which the cathode electrodes  32  are formed. In the second preferred embodiment of the present invention, exposure is performed by irradiating the light to the rear of the lower substrate  30  as shown by the arrows in FIG. 2B. During exposure, the chrome elements  32   b  of the cathode electrodes  32  act as a mask for patterning the photosensitive material  34 .  
         [0040]    After exposure, developing of the photosensitive material  34  is performed such that guide supports  36  of a predetermined height and width for the formation of insulation layer holes are formed between the chrome elements  32   b  of the cathode electrodes  32 , that is, in the area where an electron emitting layer is provided. The end result of this process is shown in FIG. 2C.  
         [0041]    Next, as in the first preferred embodiment of the present invention, a preliminary insulation layer  38  is formed on the lower substrate  30  as shown in FIG. 2D, an upper portion of the preliminary insulation layer  30  is removed such that upper ends of the guide supports  36  are exposed as shown in FIG. 2E, then the guide supports  36  are removed from the lower substrate  30  such that a plurality of holes  40   a  are formed in the preliminary insulation layer  38  to thereby realize a completed insulation layer  40  having the holes  40   a  as shown in FIG. 2F.  
         [0042]    Since the formation of the preliminary insulation layer  38 , removal of the upper portion of the preliminary insulation layer  38 , and removal of the guide supports  36  are realized by processes identical to those used in the first preferred embodiment of the present invention, a detailed description will not be provided. However, it should be noted that that since the guide supports  36  are formed using photosensitive material in the second preferred embodiment of the present invention, a solution used for this purpose is such that it is suitable for the photosensitive material.  
         [0043]    Following the formation of the insulation layer  40  through the processes described above, gate electrodes  42  are formed on the insulation layer  40  using a conventional process, and an electron emitting layer  44  is formed on the cathode electrodes  32  within the holes  40   a  of the insulation layer  40  as shown in FIG. 2G. Next, anode electrodes  48  and a phosphor layer  50  are formed on a second substrate (hereinafter referred to as an upper substrate)  46 . A side glass  52  is then interposed between the upper substrate  46  and the lower substrate  30  so as to place the upper substrate  46  and the lower substrate  30  substantially in parallel, after which a sealant  54  is used to fuse the lower substrate  30 , the upper substrate  46 , and the side glass  52 . As a result, a sealed assembly for the FED is realized. Finally, an exhaust unit is used to remove the air from between the substrates  30  and  46  to thereby complete the triode FED as shown in FIG. 2H.  
         [0044]    Since the above processes are also identical to those of the first preferred embodiment of the present invention, a detailed description thereof will not be provided. FIGS. 3A through 3L are partially enlarged sectional views of a triode FED as it undergoes sequential processes in a manufacturing method according to a third preferred embodiment of the present invention. The drawings show the FED cut along a long axis direction.  
         [0045]    First, with reference to FIG. 3A, a plurality of cathode electrodes  62  are formed in a stripe pattern on a first substrate (hereinafter referred to as a lower substrate)  60 .  
         [0046]    The cathode electrodes  62  are formed to a thickness of between  1000  and  3000 ., and are typically made of a metal such as chrome, silver, or nickel, but may also be made of a clear material such as ITO (indium tin oxide). The cathode electrodes  62  are formed using a photolithography process or a thick layer printing process, depending on the material used for the cathode electrodes  62 .  
         [0047]    Next, a photosensitive material  64  is deposited on the lower substrate  60  covering the cathode electrodes  62  as shown in FIG. 3B, exposed using a conventional photolithography process and a mask  66  of a predetermined pattern as shown in FIG. 3C, then developed to form photosensitive supports  68  for the formation of holes (this will be described in more detail below) as shown in FIG. 3D.  
         [0048]    Exposure of the photosensitive material  64  may be performed by irradiating a predetermined light from a light source onto the photosensitive material  64  toward either a front surface of the lower substrate  60  on which the cathode electrodes  62  are formed as shown by the arrows in FIG. 3C, or a rear surface of the lower substrate  60  opposite the surface on which the cathode electrodes  62  are formed. Also, as shown in FIG. 3D, it is preferable that a height (h) of the photosensitive supports  68  is within the range of 1. m to 20. m, and less than a height of a preliminary insulation layer to be formed hereinafter. It is also preferable for a width of the photosensitive supports  68  to be less than a size of holes to be formed hereinafter.  
         [0049]    After the formation of the photosensitive supports  68 , a preliminary insulation layer  70  is formed on the lower substrate  60  at a thickness sufficient to completely cover the photosensitive supports  68  as shown in FIG. 3E. The preliminary insulation layer  70  may be formed by a conventional printing process, a cataphoresis process, a doctor blade process, or a spray process. The case where the printing process is used to form the preliminary insulation layer  70  will be described as an example.  
         [0050]    To form the preliminary insulation layer  70  by a printing process, an insulation paste is first produced. This is accomplished by completely producing a solid vehicle using a solvent such as terpineol, butyl carbitol (BC), and butyl carbitol acetate (BCA) and a binder such as ethyl cellulose (EC) and nitro cellulose (NC). A solvent in which frit and an insulating powder are uniformly mixed is then mixed with the vehicle to complete the insulation paste.  
         [0051]    After producing the insulation paste, the paste is provided over an entire upper surface (in the drawing) of the lower substrate  60 . It is preferable that the preliminary insulation layer  70  has a height that is approximately double the height (h) of the photosensitive supports  68 . This enables the full removal of the insulation material even to a center portion thereof after sintering such that under-cutting is minimized in consideration of etching isotropy.  
         [0052]    Next, the preliminary insulation layer  70  is dried for 5-30 minutes at a temperature between 90 and 120. Following the drying of the preliminary insulation layer  70 , a temperature between 350 and 450. is maintained for 10-60 minutes to remove the solvent and binder, after which a temperature that exceeds a softening point of the insulation frit (450-550.) by 20-30. is maintained for 5-60 minutes to sinter the preliminary insulation layer  70 . A feature of the third preferred embodiment of the present invention is the automatic removal of the photosensitive supports  68  during the sintering of the preliminary insulation layer  70 .  
         [0053]    For this purpose, the photosensitive material  64  forming the photosensitive supports  68  may be realized using the materials described in the above preferred embodiments. These photosensitive materials experience abrupt vaporization at a temperature less than or equal to a sintering temperature of the preliminary insulation layer  70 , for example, at approximately 350.  
         [0054]    Accordingly, with the vaporization of the photosensitive supports  68 , empty spaces  72  are left remaining within the preliminary insulation layer  70  where the photosensitive supports  68  were located as shown in FIG. 3F, or areas of the preliminary insulation layer  70  over where the photosensitive supports  68  were located are depressed toward the empty spaces  72  as shown in FIG. 3G. The latter case of depressions being formed in the preliminary insulation layer  70  will be assumed for the following processes.  
         [0055]    With areas of the preliminary insulation layer  70  depressed as described above, a mask  74  is used and areas of the preliminary insulation layer  70  corresponding to the depressions of the same (shown by the dotted lines in FIG. 3H) are etched to complete the removal of the photosensitive supports  68 . As a result, an insulation layer  71  having holes  71   a  where the photosensitive supports  68  were located is realized as shown in FIG. 31. HF may be used to etch the areas corresponding to the depressions of the preliminary insulation layer  70 .  
         [0056]    Accordingly, since the holes  71   a  of the insulation layer  71  are formed by etching either portions of the preliminary insulation layer  70  above the empty spaces  72  or areas of the preliminary insulation layer  72  corresponding to the depressions, undercutting of the holes  71   a  is minimized as a result of etching isotropy. Therefore, a cross-section of the holes  71   a  that is nearly vertical (a width of the holes over an entire length from top to bottom) is realized. This enables the formation of the holes  71   a  to a minute size.  
         [0057]    Subsequently, with reference to FIG. 3J, gate electrodes  78  are formed in a stripe pattern on the insulation layer  71  using a conventional thin layer or thick layer process, and gate holes  78   a  are formed in the gate electrodes  78  at areas corresponding to the holes  71   a  of the insulation layer  71  using an etching process. The gate electrodes  78  are provided perpendicularly intersecting the cathode electrodes  62  such that pixel regions are defined by the gate electrodes  78  and the cathode electrodes  62 .  
         [0058]    After the formation of the gate electrodes  78 , an electron emitting layer  80  is formed on the cathode electrodes  62  within the holes  71   a  of the insulation layer  71  as shown in FIG. 3K. The electron emitting layer  80  may be formed by printing carbonbased material such as carbon nanotubes, graphite, carbon fiber, and diamond-like carbon, and it may also be formed using conical metal tips.  
         [0059]    Next, a second substrate (hereinafter referred to as an upper substrate)  84  having anode electrodes  80  and a phosphor layer  82  formed thereon is provided substantially in parallel to the lower substrate  60 , then a side glass  86  is interposed between the upper substrate  84  and the lower substrate  60 , after which a sealant  88  is used to fuse the lower substrate  60 , the upper substrate  84 , and the side glass  86 . As a result, a sealed assembly for the FED is realized. Finally, an exhaust unit is used to remove the air from between the substrates  60  and  84  to thereby complete the triode FED as shown in FIG. 3L.  
         [0060]    In the FED of the present invention manufactured as described above, guide supports are formed using photosensitive material or a plating layer, and the holes of the insulation layer are formed using the guide holes. As a result, the holes are uniformly formed to minute sizes and having a large aspect ratio without having to undergo complicated etching process.  
         [0061]    Further, since the holes of the insulation layer are uniform, minute, and have a large aspect ratio, when the electrons are accelerated from the electron emitting layer toward the phosphor layer and through the holes, the amount of electrons leaking between the gate electrodes and the phosphor layer is reduced and the electrons are better accelerated. This results in an exceptional picture quality with high contrast and sharp color separation.  
         [0062]    Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught, which may appear to those skilled in the present art, will still fall within the spirit and scope of the present invention, as defined in the appended claims.