Patent Publication Number: US-7591700-B2

Title: Method of manufacturing a field emission display and process of welding a metal grid to a pair of blackened-treated fixing elements

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
   This application is a divisional of U.S. patent application Ser. No. 10/407,142, filed on Apr. 3, 2003 now U.S. Pat. No. 7,221,080, issued on May 22, 2007, and claims priority of Korean Patent Application No. 2002-0018209, filed on Apr. 3, 2002, the entire disclosure of which is incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   (a) Field of the Invention 
   The present invention relates to a field emission display. More particularly, the present invention relates to a field emission display that includes a mesh grid, and a manufacturing apparatus and a manufacturing method of the field emission display. 
   (b) Description of the Related Art 
   A field emission display (FED) is a flat panel display configuration that typically uses cold cathodes as electron emission sources to realize the display of images. FEDs generally employ a diode structure that includes cathode electrodes and anode electrodes, or a triode structure that includes cathode electrodes, anode electrodes, and gate electrodes. 
   A FED that employs a triode structure is described with reference to  FIG. 13 . The FED includes a rear substrate  1  and a front substrate  3  provided substantially in parallel with a predetermined gap therebetween. An emission structure for emitting electrons is formed on the rear substrate  1  and a phosphor structure that is excited by the emitted electrons is formed on the front substrate  3 . Spacers  5  are provided between the substrates  1  and  3  to maintain the gap therebetween. The rear substrate  1  and the front substrate  3  are sealed in a state where a vacuum is formed in the gap between these elements. 
   In more detail, electrons are emitted from electron emission sources  9  by a difference in voltage applied to cathode electrodes  7  and gate electrodes  15 . Also, a high voltage is applied to anode electrodes  11  such that the electrons are accelerated toward phosphor layers  13 . The electrons strike the phosphor layers  13  to excite the same. 
   During the above operation, it is possible for arc discharge to occur within the FED by the high voltage applied to the anode electrodes  11  and the small gap (i.e., cell gap) between the substrates  1  and  3 . If a short occurs between the gate electrodes  15  and the anode electrodes  11  as a result of such arc discharge, the high voltage of the anode electrodes  11  is applied to the gate electrodes  15  which may damage a drive circuit of the FED. 
   To prevent this problem, a grid substrate may be mounted between the rear substrate  1  and the front substrate  3 . The applicant discloses a metal grid as a grid substrate in Korean Laid-Open Patent Application No. 2001-0081496. The metal grid (indicated by reference numeral  17  in  FIG. 13 ) is a mesh grid electrode made of metal. 
   The metal grid  17  is low in cost (compared to other types of grid substrates that are made of photosensitive glass) and is easily made in large sizes. However, manipulation of the metal grid is difficult. For example, it is difficult to adhere the metal grid  17  to a glass substrate, that is, the rear substrate  1  and the front substrate  3 . 
   Further, to mount the metal grid  17  in a flat configuration to a substrate, it is necessary that the metal grid  17  be formed to a thickness that exceeds a predetermined amount. However, it is difficult to form the metal grid  17  to a thickness that is greater than or equal to 100 μm in order to allow for the formation of minute holes (of a diameter of less than or equal to 100 μm) by a chemical etching process. 
   The metal grid  17  is generally made of an alloy stainless steel sheet that contains chrome (for example, a 42-6 alloy—42% Ni, and 6% Cr, Fe, etc.). When attaching the metal grid  17  formed in this manner to a glass substrate, in order to securely and closely attach these elements, a blackening process is performed on the alloy stainless steel sheet to form an oxidation film on its surface, after which a crystallized glass (frit) is used as an adherent to attach the metal grid to the glass substrate through a baking process. 
   The two different types of oxidation materials used for the oxidation films include the spinel-type oxidation material (Mn,Fe)O.Cr 2 O 3  and the corundum-type oxidation material (Cr 2 O 3 ). With respect to the spinel-type oxidation material, part of the oxidation material frit is diffused to increase the chemical attraction between the oxidation film and the frit, and with respect to the corundum-type oxidation material, the airtight seal and contact strength between the parent metal and the oxidation film are increased. 
   Accordingly, when the metal grid is heat-treated or is otherwise manipulated (e.g., attached to other elements), there is a high possibility that the metal grid will be deformed. Therefore, in the prior art FED described above, the metal grid is securely mounted, then spacers are provided in the FED to maintain the cell gap between the substrates. 
   However, since the spacers are mounted passing through the metal grid, it is possible for the spacers to be misplaced by the different degrees of thermal expansion between the glass substrate and metal grid or by shock given to the FED during assembly. This may result in the metal grid sagging or otherwise becoming deformed. 
   SUMMARY OF THE INVENTION 
   In one embodiment, the present invention is a field emission display, in which a metal grid is stably provided between two substrates. 
   Other embodiments of the present invention include a field emission display, a manufacturing apparatus, and a manufacturing method of the field emission display, in which deformation of a metal grid is prevented during assembly of the field emission display. 
   In one embodiment, the present invention is a field emission display including first and second substrates opposing one another with a predetermined gap therebetween; cathode electrodes formed on the first substrate; gate electrodes formed on the first substrate and insulated from the cathode electrodes by an insulating layer; anode electrodes formed on a surface of the second substrate opposing the first substrate, and including phosphor layers formed thereon; at least a pair of fixing rails formed along one of opposing edges of the first and second substrates, the fixing rails having undergone a blackening process; and a metal grid provided between the first and second substrates and welded to an upper surface of the fixing rails. 
   The present invention also provides a field emission display including first and second substrates provided opposing one another with a predetermined gap therebetween; cathode electrodes formed on the first substrate; gate electrodes formed on the first substrate and insulated from the cathode electrodes by an insulating layer; anode electrodes formed on a surface of the second substrate opposing the first substrate, and including phosphor layers formed thereon; at least a pair of grid holders formed along one of opposing edges of the first and second substrates; a plurality of fixing brackets formed on the grid holders, the fixing brackets having undergone a blackening process; and a metal grid provided between the first and second substrates and welded to an upper surface of the fixing brackets. 
   In one embodiment, the present invention is an apparatus for manufacturing a field emission display including a metal grid and a plurality of fixing elements. The apparatus includes a plurality of magnetic elements provided to an upper surface of the metal grid before performing welding to secure the metal grid to the fixing elements using magnetic force; and a support assembly for securing the magnetic elements. 
   In one embodiment, the present invention is a method for manufacturing a field emission display including providing a plurality of fixing rails on one of two opposing surfaces of first and second substrates, the fixing rails having undergone a blackening process; placing a metal grid on the a plurality of fixing rails, and positioning magnetic elements on the metal grid such that the metal grid is secured on the a plurality of fixing rails by a magnetic force of the magnetic elements; welding the metal grid to the a plurality of fixing rails; and cutting the metal grid at areas not corresponding to a pixel region. 
   In one embodiment, the present invention is a method for manufacturing a field emission display includes providing a plurality of grid holders on one of two opposing surfaces of first and second substrates, and attaching fixing brackets that have undergone a blackening process to an upper surface of the a plurality of grid holders; placing a metal grid on the fixing brackets, and positioning magnetic elements on the metal grid such that the metal grid is secured on the fixing brackets by a magnetic force of the magnetic elements; welding the metal grid to the fixing brackets; and cutting the metal grid at areas not corresponding to a pixel region. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate various embodiments of the invention, and, together with the description, serve to explain the principles of the invention. 
       FIG. 1  is a sectional view of a field emission display according to a first embodiment of the present invention. 
       FIG. 2  is a sectional view of a field emission display according to a second embodiment of the present invention. 
       FIG. 3  is a perspective view of a manufacturing apparatus for a field emission display according to a first embodiment of the present invention. 
       FIG. 4  is a side view of the manufacturing apparatus of  FIG. 3 . 
       FIG. 5  is a perspective view of a manufacturing apparatus for a field emission display according to a second embodiment of the present invention. 
       FIG. 6  is a side view of the manufacturing apparatus of  FIG. 5 . 
       FIGS. 7 to 12  are perspective views showing sequential steps in manufacturing a field emission display according to a one embodiment of the present invention. 
       FIG. 13  is a sectional view of a conventional field emission display. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 1  is a sectional view of a field emission display according to a first embodiment of the present invention. 
   With reference to the drawings, the field emission display (FED) includes a first substrate  21  of predetermined dimensions (hereinafter referred to as a rear substrate) and a second substrate  23  of predetermined dimensions (hereinafter referred to as a front substrate). The front substrate  23  is provided substantially in parallel with the rear substrate  21  with a predetermined gap therebetween. The front substrate  23  and the rear substrate  21  are connected in this configuration to define an exterior of the FED and to form a vacuum assembly. 
   An emission structure to enable the emission of electrons by an electric field is formed on the rear substrate  21 , and an illumination structure to enable the realization of predetermined images by interaction with electrons is formed on the front substrate  23 . 
   In more detail, for the emission structure, cathode electrodes  25 , one at each gate electrode  29 , are formed in a stripe pattern, and an insulation layer  27  is formed over an entire surface of the rear substrate  21  covering the cathode electrodes  25 . Further, gate electrodes  29  are formed on the insulation layer  27 . Holes  29   a  are formed in the gate electrodes  29  and the insulation layer  27 , and electron emission sources  31  are formed on the cathode electrodes  25  on the same areas being exposed through the holes  29   a.    
   With respect to the illumination structure for realizing predetermined images, anode electrodes  33  are formed on a surface of the front substrate  23  opposing the rear substrate  21 . Also, phosphor layers  35  are formed on the anode electrodes  33 . The phosphor layers  35  are illuminated by electrons emitted from the electron sources  31  of the rear substrate  21 . 
   With this structure, if electrons are emitted from the electron emission sources  31  by the voltage difference between the cathode electrodes  25  and the gate electrodes  29 , the electrons are attracted by a high voltage applied to the anode electrodes  33  to strike the phosphor layers  35  and excite the same. 
   A metal grid  37  is mounted between the front substrate  23  and the rear substrate  21  to prevent arc discharge between these elements and to aid in focusing the emitted electrons. Preferably, the metal grid  37  includes a plurality of apertures  37   a,  each aperture  37   a  corresponding to one electron emission source  31 . 
   To mount the metal grid  37 , fixing elements, such as fixing rails  38  that have already undergone a blackening process are secured to a surface of the rear substrate  21  opposing the front substrate  23 . Each of the fixing rails  38  is formed in a shape of a rod having a predetermined height, and the fixing rails  38  are attached to the rear substrate  21  using frit along at least two opposing edges of the rear substrate  21 . The metal grid  37  is then fixed to an upper surface (in the drawing) of the fixing rails  38 . 
   The fixing rails  38  and the metal grid  37  are made of an alloy stainless steel sheet that has undergone a blackening process (e.g., a 42-6 alloy) as described with reference to the prior art. 
     FIG. 2  is a sectional view of a field emission display according to a second embodiment of the present invention. The second embodiment has the below-mentioned modified structures on the basis of the first embodiment. 
   In this embodiment, to mount the metal grid  37 , grid holders  39  made of glass are secured to a surface of the rear substrate  21  opposing the front substrate  23 . Fixing elements, such as fixing brackets  41 , which have already undergone a blackening process, are attached to the grid holder  39  using frit, after which baking is performed. The metal grid  37  is then fixed to an upper surface of the fixing brackets  41  by welding such that the fixing brackets  41  can withstand a horizontal stress of the metal grid  37 , which is mounted in a tensed state. In this configuration, each of the fixing brackets  41  is bent at a substantially right angle and fixed to the grid holder  39 . 
   The fixing brackets  41  are made of an alloy stainless steel sheet that has undergone a blackening process (e.g., a 42-6 alloy) as described with reference to the prior art. 
   The FED, structured as in the above, is realized using a manufacturing apparatus as described below. 
   With reference to  FIG. 3 , a manufacturing apparatus according to a first embodiment of the present invention includes magnetic elements, a support assembly  43  for securing the magnetic elements, and a power supply  45  for supplying power to the magnetic elements. Permanent magnets or electromagnets may be used for the magnetic elements. In the following description, it is assumed that the magnetic elements are electromagnets  47 , which operate by power supplied from the power supply  45 . 
   With reference to  FIG. 4 , each of the electromagnets  47  is formed by surrounding a core  51  with an insulator  51 , then winding an electric wire  53  around an exterior of the insulator  51  a number of times to form a coil. The core  49  is made of a material with a high magnetic susceptibility that is magnetized by an external magnetic field. 
   With the electromagnets  47  structured in this manner, if power is applied to the electric wire  53  to form a closed circuit, a magnetic field is generated in the electromagnet  47  because of the wound electric wire  53 , while current is flowing. If a direction of the current is reversed, the direction of the magnetic field is reversed. 
   The strength of the magnetic field at a center of the core  49  is proportional to the number of coil windings, the amount of current, and the magnetic susceptibility of the material of the electromagnet  47 . 
   A plurality of the electromagnets  47  structured as in the above are interconnected for use as an electromagnet assembly. For such interconnections, input terminals and output terminals of the coil are connected respectively to an input bus electrode  54  and an output bus electrode  55 . The bus electrodes  54  and  55  are connected to opposite ends of the power supply  45 . Also, a switch  57  is provided between one of the two bus electrodes  53  and  55  and the power supply  55 . 
   The support assembly  43  that secures the electromagnets  47  includes support bars  61  provided to opposite sides of a support plate  59  located between the two rows of the electromagnets  47 ; and fixing rods  63  provided at predetermined intervals on an upper surface of the support plate  59  and substantially perpendicular to a long axis direction of the support plate  59 . An electromagnet  47  is secured to each end of each of the fixing rods  63 . 
   The above manufacturing apparatus is used when welding points occur between the electromagnets  47 . However, when welding points correspond to a center of the cores, a manufacturing apparatus according to a second embodiment of the present invention may be used. This manufacturing apparatus is shown in  FIGS. 5 and 6 . The second embodiment of the present invention is used when areas of the metal grid  37  corresponding to between electromagnets  65  are bent. That is, the second embodiment enables welding where the electromagnets  65  are located so that the bent areas may be avoided. 
   Insulators  69  and electric wires  71  of the electromagnets  65  of the second embodiment are formed identically as the same elements of the electromagnets  47  of the first embodiment therefore, a detailed explanation of the insulators  69  and the electric wires  71  will not be provided in the following. However, cores  67  of the electromagnets  65  are formed differently from the same element of the electromagnets  47  of the first embodiment of the present invention. 
   The cores  67  include passage holes  67   a  formed in a center of the cores  67 . The passage holes  67   a  allow laser beams to be passed through the electromagnets  65  to perform welding. 
   A plurality of the electromagnets  65  structured as in the above are interconnected for use as an electromagnet assembly. To realize such a configuration, a connecting rod  73  is secured to upper ends of the cores  67  of the electromagnets  65  forming each row of the same. Then, ends of the resulting two connecting rods  73  are connected through support bars  75 . Further, the structure of input bus electrodes  77 , output bus electrodes  79 , a power source  81 , and a switch  83  is identical to that described with reference to the first embodiment of the present invention. 
   A method of manufacturing a field emission display according to the first embodiment of the present invention  1  is now described. 
   Referring first to  FIG. 7 , the fixing rails  38  are secured on a substrate, which then becomes the rear substrate  21 . The fixing rails  38  are magnetized after undergoing a blackening process, and are secured to the rear substrate  21  using frit. 
   Next, with reference to  FIG. 8 , the metal grid  37  is positioned on the fixing rails  38 . That is, the apertures  37   a  of the metal grid  37  are precisely positioned directly over the electron emission sources  31 . So that the metal grid  37  does not move from this aligned position. The electromagnets  47  are positioned on the metal grid  37 , then the metal grid  37  is secured to the fixing rails  38  in this state. 
   Subsequently, with reference to  FIG. 9 , welding is performed using a laser beam. In the case where the welding points are between the electromagnets, the manufacturing apparatus as described with reference to  FIG. 4  is used, that is, the manufacturing apparatus including the electromagnets  47  is used. On the other hand, if the metal grid  37  becomes bent between the electromagnets to prevent welding from being performed in a satisfactory manner, the manufacturing apparatus as described with reference to  FIG. 5  is used, that is, the manufacturing apparatus including the electromagnets  65  that have the cores  67  with the passages holes  67   a  formed therethrough is used. 
   The order in which welding is performed along the fixing rails  38  is shown in  FIG. 9 . Welding is first performed at a center area of the fixing rails  38 , then at predetermined intervals in one direction from the center weld then in the opposite direction from the center weld. It is preferred that the center welds for both the fixing rails  38  be made simultaneously so that the metal grid  37  is maintained in precise alignment. 
   Referring now to  FIG. 10 , cutting is performed following the completion of welding. That is, the metal grid  37  is cut at areas outside the fixing rails  38  that do not correspond to a display or pixel region. Cutting is performed using lasers to prevent deformation of the metal grid  37  and so that an equal amount of tension is given to both sides of the metal grid  37  (i.e., to both welding areas of the metal grid  37 ). That is, a laser apparatus  85  that has a significantly greater output than the laser equipment used for welding is used to cut the metal grid  37 . 
   If cutting is performed using the laser apparatus  85 , the metal grid  37  is cut only at areas outside the pixel region by focus control of the laser optical system, cutoff control of the laser beam, and movement control of the substrate. Shock given to the substrate and other structural elements is also minimized through such control. The cutting of the metal grid  37  proceeds in the same sequence as the welding of the metal grid  37 . In particular, the metal grid  37  is first cut at an area corresponding to a center of the fixing rails  38 , then cutting is continued along one direction from this location then along the opposite direction. 
   With reference to  FIG. 11 , after completing the cutting of the metal grid  37 , as shown in  FIG. 1 , side glass elements  20 , which are formed to a height extending past the metal grid  37 , are mounted to the outside of the fixing rails  38 . Then, the front substrate  23  having formed thereon the anode electrodes  33  and the phosphor layers  35  is provided on the side glass elements  20 , as shown in  FIG. 1 . The front substrate  23  and the rear substrate  21  are sealed using the side glass elements  20  to thereby complete the FED. 
   A method of manufacturing a field emission display according to the second embodiment of the present invention now described. This method modifies only the fixing process of the above-mentioned manufacturing method. 
   Referring first to  FIG. 12 , the grid holders  39  are secured on a substrate, which then becomes the rear substrate  21 , then the fixing brackets  41  are mounted on the grid holders  39 . The fixing brackets  41  are magnetized after undergoing a blackening process, and are secured to the holders  39  using frit. Also, the fixing brackets  41  are bent at a substantially right angle so that they may endure the horizontal stress of the metal grid  37 . The following processes are the same as the above-mentioned manufacturing method. 
   With the FED of the present invention structured as in the above, when the metal grid is secured to the rear substrate on which the fixing rails or the fixing brackets are mounted, the metal grid may be uniformly fixed in its position regardless of the size of the substrate, since the electromagnets contact only an upper surface of the metal grid. 
   Further, the metal grid is firmly secured to the fixing rails or the fixing brackets by a plurality of the electromagnets such that exceptional precision in welding is ensured and the quality of the welding itself is enhanced. Also, by cutting the metal grid using lasers, the possibility of damage to the rear substrate and other structural elements is minimized. Finally, sagging or other deformation of the metal grid is prevented by the manufacturing apparatus and method used in the present invention. 
   Although 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.