Abstract:
Methods for sealing and fabricating a cap in an FED which is able to seal a cap in a vacuum space comprise: a step of fabricating a cap on which sealant is applied; a step of locating the cap with the sealant on a substrate of a panel on which a hole is formed in a vacuum chamber; a step of hardening the sealant by irradiating laser onto the sealant, in order to prevent oxygen from inducing into the panel, and to prevent electrodes formed on the panel from being contaminated.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a field emission display (FED), and particularly, to a method for sealing a cap and a method for fabricating the cap in a vacuumed space.  
           [0003]    2. Description of the Related Art  
           [0004]    Recently, interests and importance of display is increased as multimedia is developed. For example, a display having smaller weight, volume and power consumption is required in an environment where the mobility is an important feature such as portable information devices, and a display having larger screen and angular field is required when the display is used as a media for transmitting information to the masses. Therefore, in order to satisfy the above requires, light and thin flat panel display should be developed. Cathode ray tube (CRT) which is mainly used as the display device presently has superior function, however, volume and weight are increased as the screen is increased, and has some problems such as high voltage and high power consumption.  
           [0005]    Therefore, there are flat panel displays such as liquid crystal display (LCD), plasma display panel (PDP), electro-luminescence (EL) and field emission display (FED) for solving above problems.  
           [0006]    Especially, the FED is a triode like the conventional CRT, however, the FED uses an acute cathode, not using a hot cathode. That is, a cold cathode, which emits electrons by quantum mechanical tunnel effect after concentrating high electric field on an emitter, is used.  
           [0007]    Therefore, the electron emitted from the emitter is accelerated by voltage applied between the anode and the cathode, and crashed onto a phosphor formed on the anode to radiate the phosphor. Therefore, the FED has a relatively simple electrode structure, and can be operated with high speed by using phosphor radiation due to electron beam, and has advantages such as full-color, full-grayscale, high brightness and high videorate.  
           [0008]    [0008]FIG. 1 is a perspective view showing a conventional FED.  
           [0009]    [0009]FIG. 2 is a cross-sectional view showing the conventional FED.  
           [0010]    As shown in FIGS. 1 and 2, the conventional FED comprises an upper glass substrate  2  and a lower glass substrate  8 , a spacer  40  for supporting vacuum space between the upper and lower glass substrates  2  and  8 , and a field emission array  32  formed on the lower glass substrate  8 .  
           [0011]    The field emission array  32  comprises a cathode electrode  10  and a resistance layer  12  formed on the lower glass substrate  8 , a gate insulating layer  14  and an emitter  22  for emitting electrons formed on upper part of the resistance layer  12 , and a gate electrode  16  formed on the gate insulating layer  14 .  
           [0012]    The cathode electrode  10  supplies electric current to the emitter  22 , and the resistance layer  12  restricts overcurrent applied from the cathode electrode  10  toward the emitter  22  to supply even electric current to the emitter  22 .  
           [0013]    The gate insulating layer  14  insulates between the cathode electrode  10  and the gate electrode  16 . The gate electrode  16  is used as a fetch electrode for drawing electrons. The spacer  40  supports the upper and lower glass substrates  2  and  8  so as to maintain highly vacuumed status between the upper and lower glass substrates  2  and  8 .  
           [0014]    In order to display an image, cathode voltage of negative polarity (−) is applied to the cathode electrode  10 , and anode voltage of positive polarity (+) is applied to the anode electrode  4 . Therefore, when sufficient electric voltages are applied to the cathode electrode  10  and the gate electrode  16 , a strong electric field is generated, and electrons  30  are emitted from a tip of the emitter  22  due to the generated electric field in quantum mechanical tunneling effect. Then, the emitted electrons  30  pass a hall of the gate electrode, and crashed onto phosphors of red, green and blue colors to excite the phosphors  6 . At that time, visible ray of one of the red, green and blue colors is radiated according to the phosphor  6 .  
           [0015]    [0015]FIG. 3 is a cross-sectional view showing a conventional FED on which a focusing electrode is formed.  
           [0016]    As shown therein, a focusing electrode  20  is formed on the gate electrode  16  for focusing the electrons  30  emitted from the emitter  22 . The focusing electrode focuses the electrons  30  by being applied focusing voltage of negative polarity (−). Also, a focusing insulating layer  18  is formed between the focusing electrode  20  and the gate electrode  16 .  
           [0017]    As described above, the conventional FED requires highly vacuumed status in the panel greater than 10 −6  Torr due to the operational properties. For example, a distance about sub-micron is maintained between the gate electrode  16  and the emitter  22  and high electric field of 10 7 V/cm is applied therebetween. If the highly vacuumed status is not maintained between the upper and lower glass substrates  2  and  8 , the insulation between the gate electrode  16  and the emitter  22  may be broken. That is, neutral particles in the panel are crashed into the electron beam and positive ions are generated. The positive ions are sputtered on the tip of the emitter  22  to degrade the device. Also, the electrons  30  crashed with the neutral particles lose their energies, and therefore, the electrons  30  can not sufficiently excite the phosphor  6 , and thereby to lower the brightness.  
           [0018]    Packaging processes of the conventional FED according to above structure will be described as follows.  
           [0019]    [0019]FIG. 4 is a flow chart showing processing orders of vacuum packaging the conventional FED using a vacuum pump in atmosphere.  
           [0020]    [0020]FIG. 5 is an exemplary view showing process of installing a tube and process of applying sealant for the conventional FED.  
           [0021]    As shown in FIGS. 4 and 5, in the tube installing process, a frit glass is applied on the lower glass substrate  8  as a first sealant  52 , and after that, a tube  50  is installed (ST 2 ). At that time, the tube  50  is installed on a hall  51  of the lower glass substrate  8 .  
           [0022]    After that, a spacer  40  is formed on the upper glass substrate  2 , and the frit glass is dispensed and dried around the spacer as a second sealant  54  (ST 4 ). Herein, the second sealant  54  is installed to be higher than the spacer  40  as much as a predetermined distance (H1; usually 1 mm-2 mm), because the height of the frit glass is reduced about 30-40% in preform sintering.  
           [0023]    After the second sealant  54  is dispensed on the glass substrate  2 , the second sealant  54  is pre-sintered (ST 6 ).  
           [0024]    [0024]FIG. 6 is an exemplary view showing a process of preform sintering the sealant conventionally.  
           [0025]    The preform sintering process has different sintering temperature curves according to frit materials in order to completely burn out a binder of organic material included in the frit glass. Generally, in the above preform sintering process, a standard process is to hold the second sealant  54  for 30 minutes˜1 hour at about 300° C. temperature. After the second sealant  54  is preform sintered, the upper glass substrate  2  and the lower glass substrate  8  are compressed and aligned to adhere the substrates.  
           [0026]    After that, the upper and lower glass substrates  2  and  8  are moved to a heating chamber to sinter the first and second sealant  52  and  54  (ST 6 ).  
           [0027]    [0027]FIG. 7 is an exemplary view showing a sealant sintering process in the conventional art.  
           [0028]    As shown therein, the sintering process is performed at the temperature of 400° C.˜450° C. which is higher than that of the preform sintering after moving the panel into the heating chamber  70 . At that time, when the sintering process is performed under atmosphere environment, the cathode electrode  10 , the gate insulating layer  14 , the gate electrode  16 , the emitter  22 , the focusing insulation layer  18  and the focusing electrode  20 , which emit the electrons in the FED, may be damaged by reacting with oxygen or carbon in the atmosphere. Especially, the metal material such as the emitter  22  can be oxidated easily, and therefore, the luminous characteristic is lowered greatly.  
           [0029]    In order to prevent the damage as above, inert gas  58  such as nitrogen and/or argon is supplied into the panel using a tube  56  extended from the heating chamber  70 , and therefore, devices of the field emitting array are not reacted with the oxygen.  
           [0030]    On the other hand, FIG. 8 is an exemplary view showing sealant sintering process according to the conventional art.  
           [0031]    As shown therein, a gas inlet port  60  is formed on a lower end portion of the heating chamber  70  and a gas outlet port  62  is formed on an upper end portion of the heating chamber  70  to flow the inert gas such as the nitrogen and/or the argon into the entire heating chamber  70 , and therefore, the materials for emitting the electrons can not be reacted with the oxygen in a high temperature process. Herein, the inducing of the inert gas is made by opening the inlet port for 10˜20 minutes in the state that a valve out of the outlet port is closed to make the inside of heating chamber  70  be the nitrogen and/or argon inert gas atmosphere, and after that, the outer valve is opened to flow the gas continuously.  
           [0032]    Under above atmosphere, when the temperature of the panel is maintained as 400˜450° C. temperature for 30 minutes˜1 hour, the first and the second sealants are sintered and the panel sealing is completed. The above conventional sintering method is defined as a atmosphere sealing method. At that time, the height of the second sealant  54  is extracted during the sintering process, and therefore, the height of the frit glass is coincided with that of the spacer  40 .  
           [0033]    [0033]FIG. 9 is an exemplary view showing a getter inserted into the conventional tube.  
           [0034]    [0034]FIG. 10 is an exemplary view showing a cutting process of the conventional tube.  
           [0035]    As shown in FIGS. 9 and 10, after the upper glass substrate  9  and the lower glass substrate  8  are attached, a getter  66  is inserted into the panel through the tube  50  and the pumping process is performed (ST 8 ). That is, as the panel, on which the upper glass substrate  2 n and the lower glass substrate  8  are attached, is heated in the heating chamber  70 , and at the same time, the inside of the panel is pumped by a vacuum pump  72 . Therefore, when the inside of the panel reaches to a desired vacuumed degree, middle portion of the tube  50  is heated by a local heating device  68  to cut off the tube  50 , and therefore, the panel is separated from the heating chamber  70 .  
           [0036]    On the other hand, in a pinch-off process for cutting off the tube  50 , the tube  50  which is exposed in atmosphere is cut, and therefore, the vacuumed degree of the panel is lowered. In order to increase the vacuumed degree of the panel having lowered vacuumed degree, high temperature is compressed to the getter  66  located in the panel to activate the getter  66  (S 12 ). When the getter  66  is activated, the vacuumed degree of the panel is increased more than a predetermined level, and therefore, the final panel is completed.  
           [0037]    However, the pinch-off process of the FED as described above is performed under the atmosphere, the oxygen is induced through the hole  51 . Accordingly, when the oxygen is induced into the panel, the metal material such as the emitter is easily oxidated, and thereby, the life span of the FED is reduced and the luminous characteristic is lowered greatly. Also, color purities are different from respective points due to the oxygen in displaying. Also, since the conventional panel sealing method is performed at high temperature, it takes a lot of times to process. Also, in the process of installing the tube, the tube is attached on the lower glass substrate  8  by the first sealant  52 . At that time, the electrodes formed on the lower glass substrate  8  may be contaminated by the organic binder of the first sealant  52 .  
         SUMMARY OF THE INVENTION  
         [0038]    Therefore, an object of the present invention is to provide a method for sealing a cap in a field emission display (FED) which is able to prevent oxygen from being induced into a panel by sealing a cap in a vacuumed space.  
           [0039]    Another object of the present invention is to provide a method for fabricating a cap of an FED which is able to prevent electrodes formed on a panel from being contaminated by removing an organic binder included in a sealant applied on a cap through a sintering process when the cap is fabricated.  
           [0040]    To achieve the objects of the present invention, as embodied and broadly described herein, there is provided a method for sealing a cap in an FED comprising: a step of locating a cap, on which a sealant is applied, on a substrate of a panel on which a hole is formed in a vacuum chamber; and a step of hardening the sealant by irradiating laser in order to cover the hole.  
           [0041]    Also, to achieve the objects of the present invention, there is provided a method for fabricating a cap in an FED comprising: a step of applying a sealant on a substrate of glass material; a step of sintering the glass substrate on which the sealant is applied; and a step of cutting the glass substrate on which the sealant is applied.  
           [0042]    The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0043]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.  
         [0044]    In the drawings:  
         [0045]    [0045]FIG. 1 is a perspective view showing a conventional field emission display (FED) device;  
         [0046]    [0046]FIG. 2 is a cross-sectional view showing the conventional FED;  
         [0047]    [0047]FIG. 3 is a cross-sectional view showing a conventional FED on which a focusing electrode is formed;  
         [0048]    [0048]FIG. 4 is a flow chart illustrating process orders of vacuum packaging for the conventional FED using a vacuum pump in atmosphere;  
         [0049]    [0049]FIG. 5 is an exemplary view showing a process of installing tube and a process of applying sealant for the conventional FED;  
         [0050]    [0050]FIG. 6 is an exemplary view showing a conventional sealant preform sintering process;  
         [0051]    [0051]FIG. 7 is an exemplary view showing a conventional sealant sintering process;  
         [0052]    [0052]FIG. 8 is an another exemplary view showing a conventional sealant sintering process;  
         [0053]    [0053]FIG. 9 is an exemplary view showing a getter inserted into a conventional tube;  
         [0054]    [0054]FIG. 10 is an exemplary view showing a processing of cutting tube;  
         [0055]    [0055]FIGS. 11 through 13 are exemplary views showing a vacuum sealing method for an FED panel according to the present invention;  
         [0056]    [0056]FIG. 14 is an exemplary view showing a method for sealing a cap in an FED according to an embodiment of the present invention;  
         [0057]    [0057]FIGS. 15A and 15B are exemplary views showing laser radiated onto a sealant of the cap;  
         [0058]    [0058]FIG. 16 is an exemplary view showing hardening process of the sealant when the laser is radiated between the sealant of the cap and a lower substrate according to the present invention; and  
         [0059]    [0059]FIG. 17 is a view illustrating a method for fabricating the cap in the FED according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0060]    Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0061]    [0061]FIGS. 11 through 13 are exemplary views showing a vacuum sealing method for a field emission display (FED) panel according to the present invention.  
         [0062]    As shown therein, a sealing application unit  110  comprises a frame  100 , and a first and a second sealants  102  and  104  applied on upper/lower parts of the frame. Also, an upper glass substrate  106  and a lower glass substrate  108  are aligned as taking the sealing application unit  110  therebetween. At that time, a getter  122  for maintaining a highly vacuumed status by absorbing gas remained in a panel is inserted between the upper glass substrate  106  and the lower glass substrate  108 .  
         [0063]    The vacuum sealing method for the FED panel according to above construction will be described in detail as follows.  
         [0064]    The frame  100  is made by a material having same thermal expansion coefficient as those of the upper and lower glass substrates  106  and  108 . For example, the frame  100  can be made using glass material.  
         [0065]    It is desirable that the first and second sealants  102  and  104  are applied in a screen printing method rather than the conventional dispensing method, because frit glass of lower viscosity flows down in dispensing since the frit glass of paste type has the viscosity.  
         [0066]    After that, the upper glass substrate  106 , the lower glass substrate  108  and the sealing application unit  110  are moved to a vacuum chamber  120 .  
         [0067]    On the other hand, a plurality of auxiliary jigs, desirably,  4  or more auxiliary jigs  112  are installed between the upper glass substrate  106  and the lower glass substrate  108 . The auxiliary jigs  112  maintain a distance between the upper glass substrate  106  and the lower glass substrate  108 . After that, the upper and lower glass substrates  106  and  108  are adhered by applying a predetermined load on the lower glass substrate  108 . On the other hand, the above sealing method is defined as a vacuum sealing method.  
         [0068]    [0068]FIG. 14 is an exemplary view showing a method for sealing a cap in the FED device according to an embodiment of the present invention.  
         [0069]    As shown in FIG. 14, the FED device of the present invention undergoes cap sealing after the lower glass substrate  108  and the upper glass substrate  106  are adhered by the vacuum sealing method. That is, in the cap sealing method according to the present invention, a cap  136  of glass material is disposed, and the cap  136 , on which the sealant is applied, is located on the substrate of the panel on which the hole is formed in the vacuum chamber. After that, the laser is radiated to the sealant  138  of the cap  136  to harden the sealant, in order to cover the hole.  
         [0070]    On the other hand, as an another embodiment of the cap sealing method according to the present invention, the method of the present invention can be applied after attaching the lower glass substrate  8  and the upper glass substrate  2  by the conventional atmosphere sealing method. At that time, there is no need to install the tube  50  as in the conventional atmosphere sealing method.  
         [0071]    The cap sealing method for the FED according to the present invention will be described more specifically.  
         [0072]    A plurality of spacers  144  for supporting the upper glass substrate  140  and the lower glass substrate  130  are installed in the upper and lower glass substrates  140  and  130  attached by the atmosphere sealing method or by the vacuum sealing method. Also, the sealing application unit  110  is installed to attach the upper and lower glass substrate  140  and  130 .  
         [0073]    After that, the attached upper and lower glass substrates  140  and  130  (hereinafter, referred to as “panel”) is moved to the vacuum chamber  142 . The vacuum chamber is exhausted to be vacuumed status of a predetermined Torr (desirably, 10 −7  Torr) by a vacuum pump which is not shown, after the panel is moved therein. At that time, the inside of the panel is also exhausted to be the vacuumed status.  
         [0074]    After that, the cap  136  is aligned so as to cover the hole  132  of the lower glass substrate. That is, when the cap  136  is located on the hole  132  of the lower glass substrate by a robot arm (not shown) in the panel of vacuum status, the hole  132  of the lower glass substrate and the cap  136  are attached by the sealant of the cap.  
         [0075]    [0075]FIGS. 15A and 15B are exemplary views showing radiation of the laser onto the sealant of the cap.  
         [0076]    As shown in therein, when the laser is radiated onto the sealant  138  of the cap  136 , the sealant  138  is hardened and the cap  136  is attached on the lower glass substrate  130 .  
         [0077]    For example, since the sealant  138  applied on the cap  136  surrounds the cap  136  as a circular shape, the laser  146  is irradiated on the sealant  138  as making a concentric circle. At that time, if a diameter of the sealant  138  applied on the cap  136  is small, most of the sealant is melted when the center part of the sealant is sintered. On the contrary, if the diameter of the sealant  138  applied on the cap  136 , the laser  146  is irradiated onto the sealant  138  once more to attach the cap  136  on the lower glass substrate  130  completely. At that time, in order to prevent the cap  136  or the upper and lower glass substrates  140  and  130  from being damaged by local high temperature energy of the laser  146 , 200˜350° C. reference temperature is made. Accordingly, the damages of the devices due to the oxidation or other thermal processes in sintering for the cap sealing can be minimized, and also, the processing time can be reduced as much as the difference of sintering temperature.  
         [0078]    [0078]FIG. 16 is an exemplary view showing a process of hardening the sealant when the laser is radiated between the sealant and the lower substrate according to the present invention.  
         [0079]    As shown therein, a first sealant portion  152  from the point where the laser is radiated at first to the present point is a part that is solidificated after melted by the energy, and a second sealant portion  154  on which the laser  146  is located is under process of melting. In addition, a third sealant portion  150  besides the above portions is under pre-sintered status which is not yet sintered by the laser  146 . Herein, the first sealant portion  152  is melted in a state that the height is maintained as it is, and solidificated, and therefore, the first sealant portion  152  maintains same height as that of the third sealant portion  150  which is in preform-sintered status. In addition, even though the second sealant portion  154  is under the process of laser irradiation, the height of the second sealant portion  154  is not affected because the first and third sealant portions support the second sealant portion  154 .  
         [0080]    However, if the laser irradiation speed is high, the first sealant portion  152  on which the laser is irradiated may be distributed widely,iated may be distributed widely,ction may be generated. At that time, the laser  146  is irradiated as compressing the upper part of the cap  136  with a predetermined pressure by using a gap reference frame, and thereby, the height change of the cap  136  can be prevented.  
         [0081]    [0081]FIG. 17 is a view showing a method for fabricating the cap in the FED device according to an embodiment of the present invention.  
         [0082]    Referring to FIG. 17, a substrate  160  of glass material is disposed. The substrate  160  of glass substrate is the same material as those of the upper glass substrate  140  and the lower glass substrate  130 .  
         [0083]    After that, a lot of sealant  138  is applied on the glass substrate  160  using a screen printing method as a circular shape. At that time, a center of circular sealant  138  is empty so that the sealant  138  is not overlapped with the hole  132 . Also, the sealant  138  of the cap is printed to be a few μm˜hundreds of μm thickness so as to absorb incident energy of the laser  146  easily and to maintain the vacuumed state in the panel. Also, the frit glass is used as the sealant, and the frit glass is formed by mixing glass powder and binder with more than 10:1 mass ratio.  
         [0084]    After the sealant  138  is printed on the glass substrate  160 , the glass substrate  160  is sintered under 300˜400° C. At that time, the organic binder component included in the sealant  138  is completely burnt out and removed.  
         [0085]    Finally, the glass substrate  160  is cut into predetermined sizes to complete the cap  136  on which the sealant is printed.  
         [0086]    As described above, according to the method for sealing and fabricating the cap of the FED device of the present invention, the cap is sealed in the vacuum space to prevent the oxygen from inducing into the panel during the cap sealing process. Therefore, damages of the devices due to the oxidation and other thermal processes can be minimized, and color purity can be maintained constantly on respective points of the panel in displaying. Also, the processing time can be reduced less than that of the conventional sintering process as much as the difference of sintering temperatures. Also, there is no need to install the tube on the panel as in the conventional sintering method, and therefore, the process becomes simple and the processing time can be reduced. In addition, the organic binder included in the sealant applied on the cap is removed through the sintering process when the cap is fabricated, and therefore, the contamination of the electrodes formed on the lower glass substrate can be prevented.  
         [0087]    As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalence of such metes and bounds are therefore intended to be embraced by the appended claims.