Abstract:
A field emission display device includes: a first substrate; an electron emission assembly arranged on the first substrate; a second substrate arranged a predetermined distance from the first substrate, the first and second substrates forming a vacuum space; an illumination assembly arranged on the second substrate, the illumination assembly being illuminated by electrons emitted from the electron emission assembly; and a mesh grid and above the electron emission assembly.

Description:
CLAIM OF PRIORITY  
         [0001]    This application claims priority under 35 U.S.C. § 119 on an application entitled “FIELD EMISSION DISPLAY AND METHOD OF MANUFACTURING THE SAME”, filed in the Korean Intellectual Property Office on 21 Jan. 2003 and assigned Serial No. 2003-3982, the contents of which are hereby incorporated by reference and on an application filed in the Korean Intellectual Property Office on 2 Jul. 2003 and assigned Serial No. 2003-44534, the contents of which are also hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a field emission display and a method of manufacturing the same, and more particularly to a field emission display including a mesh grid and a focusing electrode and a method of manufacturing the same.  
           [0004]    2. Description of the Related Art  
           [0005]    Field emission displays (FEDs) are devices comprised of a front substrate and a rear substrate forming a vacuum chamber. The front substrate includes an anode and a phosphor on the inside thereof. The rear substrate includes a cathode and an emitter on the inside thereof. Electrons emitted from the emitter are directed toward the anode and then excite the phosphor, thereby emitting predetermined light. Field emission displays can be used in automobile dashboards.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides an improved field emission display.  
           [0007]    The present invention also provides a field emission display capable of preventing arc-discharge even when a high voltage is applied.  
           [0008]    The present invention also provides a method of manufacturing a field emission display capable of preventing arc-discharge even when a high voltage is applied.  
           [0009]    According to an aspect of the present invention, there is provided a field emission display comprising: a first substrate; an electron emission assembly arranged on said first substrate; a second substrate arranged a predetermined distance from said first substrate, said first and second substrates forming a vacuum space; an illumination assembly arranged on said second substrate, said illumination assembly being illuminated by electrons emitted from said electron emission assembly; and a mesh grid arranged above said electron emission assembly.  
           [0010]    According to another aspect of the present invention, said mesh grid comprises a metal.  
           [0011]    According to another aspect of the present invention, said mesh grid comprises one of stainless steel, invar, and an iron-nickel alloy.  
           [0012]    According to another aspect of the present invention, the iron-nickel alloy comprises 2.0 to 10.0 wt % of Cr.  
           [0013]    According to another aspect of the present invention, the iron-nickel alloy comprises 40.0 to 44.0 wt % of Ni.  
           [0014]    According to another aspect of the present invention, the iron-nickel alloy comprises 0.2 to 0.4 wt % of Mn, 0.7 wt % or less of C, and 0.3 wt % or less of Si.  
           [0015]    According to another aspect of the present invention, the thermal expansion coefficient of said mesh grid is in the range of 9.0×10 −6 /° C. to 10.0×10 −6 /° C.  
           [0016]    According to another aspect of the present invention, electron emission assembly comprises a cathode, a gate, and an electron emission source.  
           [0017]    According to another aspect of the present invention, the gate is arranged on the upper side of the cathode.  
           [0018]    According to another aspect of the present invention, the gate is arranged on the lower side of the cathode.  
           [0019]    According to another aspect of the present invention, an intermediate material is arranged between said electron emission assembly and said mesh grid.  
           [0020]    According to another aspect of the present invention, said intermediate material comprises an insulating material.  
           [0021]    According to another aspect of the present invention, wherein said intermediate material comprises a resistive material.  
           [0022]    According to another aspect of the invention, wherein a focusing electrode is further arranged on the mesh grid.  
           [0023]    According to another aspect of the present invention, there is provided a field emission display, comprising: a first substrate; an electron emission assembly arranged on said first substrate; a second substrate arranged at a predetermined distance from said first substrate, said first and second substrates forming a vaccum assembly; and an illumination assembly arranged on said second substrate, said illumination assembly being illuminated by electrons emitted from said electron emission assembly; and a mesh grid arranged above said electron emission assembly; wherein said mesh grid is bonded to said electron emission assembly by a frit.  
           [0024]    According to another aspect of the present invention, there is provided a method of manufacturing a field emission display, the method comprising: providing a first substrate; arranging an electron emission assembly on said first substrate; arranging a second substrate a predetermined distance from said first substrate to form a vacuum space with said first and second substrates; arranging an illumination assembly on said second substrate, and illuminating said illumination assembly with electrons emitted from said electron emission assembly; and arranging a mesh grid above said electron emission assembly.  
           [0025]    According to another aspect of the present invention, there is provided a method of manufacturing a field emission display device, the method comprising: providing a first substrate; arranging an electron emission assembly on said first substrate; arranging a second substrate a predetermined distance from said first substrate to form a vaccum assembly with said first and second substrates; arranging an illumination assembly on said second substrate and illuminating said illumination assembly with electrons emitted from said electron emission assembly; arranging a mesh grid above said electron emission assembly; and bonding said mesh grid to said electron emission assembly with a frit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0027]    [0027]FIG. 1 is a schematic sectional view of a conventional field emission display;  
         [0028]    [0028]FIG. 2 is a schematic sectional view of another conventional field emission display;  
         [0029]    [0029]FIG. 3 is a partial perspective view of the field emission display of FIG. 2;  
         [0030]    [0030]FIG. 4 is a schematic sectional view of a field emission display according to an embodiment of the present invention;  
         [0031]    [0031]FIG. 5 is a partial perspective view of a mesh grid of the field emission display of FIG. 4;  
         [0032]    [0032]FIG. 6 is a partial perspective view that illustrates the insertion of a spacer in the field emission display of FIG. 4;  
         [0033]    [0033]FIG. 7 is a flowchart of a process of manufacturing a field emission display according to an embodiment of the present invention; and  
         [0034]    [0034]FIG. 8 is a schematic sectional view of a field emission display according to another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    [0035]FIG. 1 is a schematic sectional view of a conventional field emission display.  
         [0036]    Referring to FIG. 1, a conventional field emission display essentially includes a front substrate  5  and a rear substrate  1 , which are spaced a predetermined gap apart by a spacer  8  interposed therebetween. The rear substrate  1  has a stacked structure including a cathode  2 , an insulator  3 , and a gate  4  on the inside thereof. Holes are formed in the insulator  3  on the cathode  2 , and microtip emitters  2 ′ for electron emission are formed on the cathode  2  exposed through the holes. Openings  4 ′ corresponding to the holes are formed in the gate pattern to allows for the attraction of electrons emitted from the emitters  2 ′ toward an anode  6 . The front substrate  5  includes the anode  6  on the inside thereof opposite to the rear substrate. A phosphor  7  is coated on the anode  6 . The anode  6  can be formed either in a strip pattern or as a single unit to cover the whole inner surface of the front substrate. In such a display structure, the electrons emitted from the emitters  2 ′ excite the phosphor  7 , thereby emitting light.  
         [0037]    During the electron emission, arc-discharge can be caused in a space defined between the two substrates. Although an exact cause of the arc-discharge is not known, it is believed that the arc-discharge is caused by a discharge phenomenon through immediate ionization (avalanche phenomena) of a large number of gases when the gases generated inside the panel are outgassed.  
         [0038]    Arc-discharge can cause a short circuit between the anode and the gate. Therefore, a high voltage is applied to the gate, thereby causing damage to the gate oxide and resistive layer. This phenomenon becomes worse with increasing anode voltage. In particular, arc-discharge is more easily caused by application of an anode voltage of more than 1 kV. Therefore, it is impossible to obtain a high luminance field emission display stably driving at a high voltage in a conventional field emission display having a simple support structure of a cathode and an anode separated by a spacer.  
         [0039]    [0039]FIG. 2 shows a field emission display disclosed in Korean Patent Application No. 2001-0081496 arranged to prevent the above-described arc-discharge.  
         [0040]    Referring to FIG. 2, like in FIG. 1, a field emission display includes a front substrate  15  and a rear substrate  11 , a spacer  18  interposed between the two substrates, a strip-patterned cathode  12 , an insulator  13 , a strip-patterned gate  14 , and emitters  12 ′ exposed through holes formed in the insulator  13 . The front substrate  15  includes an anode  16  and a phosphor  17  on the inside thereof. As mentioned above, the anode  16  can be formed either in a strip pattern, or as a single layer pattern formed over the whole inner surface of the front substrate.  
         [0041]    The field emission display further includes as arcing prevention means comprising a mesh grid  19  formed between the gate and the anode to control electrons emitted from the emitters  12 ′.  
         [0042]    In such a field emission display structure, even when a voltage of −100 to 300 V is applied, an electric field at the gate edges decreases, thereby preventing arc-discharge. Furthermore, even when arcing is caused, arc ions are trapped in the mesh grid prior to causing damage to the cathode and then flow through a ground outlet, thereby preventing mechanical and electrical damages.  
         [0043]    [0043]FIG. 3 is a schematic sectional view that illustrates a process of forming the mesh grid of FIG. 2.  
         [0044]    Referring to FIG. 3, a mesh grid  19  is installed adjacent to a front substrate  15 . A spacer  28  serves to maintain a gap between the mesh grid  19  and the front substrate  15 . Protrusions of the spacer  28  are inserted into through-holes formed in the mesh grid  19 . A glass holder  23  serves to support both ends of the spacer  28 . An electrode  22  and the mesh grid  19  are interconnected through a conductive paste  24 . Therefore, a voltage can be applied to the electrode  22  and the mesh grid  19 .  
         [0045]    In the field emission display described with reference to FIGS. 2 and 3, a mesh grid is aligned with respect to an anode of a front substrate and fixed in position through firing. The resultant structure thus obtained is then aligned with respect to a cathode of the rear substrate. However, due to the difference in thermal expansion coefficient between metal and glass materials during the firing process, it is difficult to perform an appropriate alignment between the mesh grid and the cathode of the rear substrate. Therefore, electrons emitted from the emitters collide with a phosphor adjacent to a desired emission region, thereby decreasing color purity. Also, when a pulse voltage and a DC voltage are respectively applied to the gate electrode and the mesh grid, a noise phenomenon due to vibration of the mesh grid can be caused in a display structure in which only the edges of the mesh grid are fixed by the spacer.  
         [0046]    Hereinafter, a field emission display including a mesh grid and a method of manufacturing the same according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.  
         [0047]    [0047]FIG. 4 is a schematic sectional view of a field emission display according to an embodiment of the present invention.  
         [0048]    Referring to FIG. 4, a field emission display according to this embodiment has a joined structure of a front substrate  41  and a rear substrate  42 , which are separated from each other by a predetermined gap, and thus, a vacuum space is formed between the two substrates. A spacer  43  is installed to maintain the gap between the front substrate  41  and the rear substrate  42 . A cathode  55  is formed on the inside of the rear substrate  42 . An insulator  45  is formed on the cathode  55 . The insulator  45  has holes therein. Emitters  46  serving as an electron emission source are exposed through the holes.  
         [0049]    A gate  47  is formed on the insulator  45 . The gate  47  has openings corresponding to the holes of the insulator  45  to allow for attraction of electrons emitted from the emitters  46  toward an anode  53 . The cathode  55 , the emitter and the gate  47  serve as an electron emission assembly. In the illustrated embodiment, it is appreciated that the gate  46  is disposed on the upper side of the cathode  55 .  
         [0050]    On the other hand, in another embodiment not shown in the drawings, the gate is disposed on the lower side of the cathode. In this case, insulation between the gate and the cathode  55  must be ensured. However, there is no need to form openings in the gate. An example of a field emission display having a gate formed on the lower side of a cathode is disclosed in Korean Patent Application No. 2002-16804.  
         [0051]    The front substrate  41  includes the anode  53  on the inside thereof. The anode  53  can formed either in a strip pattern or as a single layer formed over the whole inner surface of the front substrate  41 . When the anode  53  is formed in a strip pattern, the cathode  55  and the anode  53  intersect each other perpendicularly as viewed from top. A phosphor  54  is coated on the anode  53 . The phosphor  54  can be red, green, or blue.  
         [0052]    A mesh grid  50  is formed between the gate  47  and the anode  53  to control electrons emitted from the emitters  46 . The mesh grid  50  is disposed on the gate  47 . That is, the mesh gird  50  includes lower and upper insulators  49  and  51 , which are respectively formed on lower and upper surfaces of the mesh grid  50 , and then the mesh grid  50  is disposed on the gate  47 . The lower insulator  49  can be replaced with a resistive layer comprising of a resistive material. Further, both the lower and upper insulators  49  and  50  are replaced with the resistive layer. As shown in the drawing, the mesh grid  50  is fixed in such a way that it is bonded to the gate  47  by a frit. The mesh grid  50  serves to block the action of the electric field of the anode  53  on the electron emission of the cathode  55  and to accelerate the emitted electrons. In another embodiment (not shown) in which the cathode is disposed on the upper side of the gate, the mesh grid is disposed upper side of the cathode.  
         [0053]    A focusing electrode  52  is formed on the upper insulator  51 , which is in turn formed on the upper surface of the mesh grid  50 . The focusing electrode  52  serves to enhance the focusing performance of electron beam. That is, the focusing electrode  52  prevents the dispersion of electrons accelerated by the mesh grid  50  and focuses the accelerated electrons on the anode  53  of interest for collision of them with the anode  53 .  
         [0054]    [0054]FIG. 5 is a schematic exploded perspective view that illustrates an arrangement of the mesh grid  50  and the focusing electrode  52 .  
         [0055]    Referring to FIG. 5, the upper and lower insulators  51  and  49  are respectively formed on the upper and lower surfaces of the mesh grid  50 . The frit  48  is disposed on the lower surface of the lower insulator  49  and the focusing electrode  52  is disposed on the upper surface of the upper insulator  51 .  
         [0056]    The mesh grid  50  is formed in a mesh shape and made of stainless steel or invar or SUS. Since invar and SUS have the thermal expansion coefficient smaller than normal stainless steel, it is advantageous in decreasing a thermal stress generated during a firing process. The mesh grid  50  can also be made of an iron-nickel alloy. Since the iron-nickel alloy has the thermal expansion coefficient much smaller than normal stainless steel, it is very advantageous in decreasing a thermal stress generated during a firing process. Further, since the iron-nickel alloy has the thermal expansion coefficient similar to glass, when the mesh grid made of the iron-nickel alloy is fixed to the rear substrate, the thermal expansion coefficient of the mesh grid advantageously affects the alignment with the cathode.  
         [0057]    Meanwhile, openings  56  are formed in the mesh grid  50 . Each of the openings  56  corresponds to one of red, blue, and green phosphors that make one pixel. That is, as shown in FIG. 4, each of the openings  56  corresponds to only one phosphor  54 . In detail, the openings  56  are formed correspondingly to intersections of the cathode  55  and the anode  53 . Electrons emitted from the emitters  46  pass through the openings  56 .  
         [0058]    The lower and upper insulators  49  and  51  are respectively formed on the lower and upper surfaces of the mesh grid  50  in such a way not to be overlapped with the openings  56 , as shown in FIG. 5. As illustrated in FIG. 5, the upper and lower insulators  49  and  51  have openings. The openings are extended in the longitudinal direction of the cathode  55 . The focusing electrode  52  is formed on the upper surface of the upper insulator  51  in the same shape as the upper insulator  51 . The frit  48  is formed on the lower surface of the lower insulator  49  in the same shape as the lower insulator  49 . The frit  48  serves to maintain the mesh grid  50  in position.  
         [0059]    Through-holes  59  are also formed in the mesh grid  50 . The spacer  43  of FIG. 4 is inserted into the through-holes  59  and maintains a gap between the front substrate  41  and the rear substrate  42 .  
         [0060]    [0060]FIG. 6 is a schematic partial exploded perspective view of the field emission display of FIG. 4.  
         [0061]    Referring to FIG. 6, the front substrate  41  is positioned in an upside-down state unlike in FIG. 4. The front substrate  41  includes, on the inside thereof, the anode  53  and the phosphor  54 , which form an illumination assembly. The illumination assembly is lighted by electrons emitted from the electron emission assembly. As described above, the anode can be formed either in a strip pattern or as a single layer formed over the whole inner surface of the front substrate. In this case, it is preferable to form the phosphor  54  in a strip pattern perpendicular to the cathode. The openings  56  corresponding to the phosphor  43  are formed in the mesh grid  50 . The mesh grid  50  also has the through-holes  59  for the insertion of the spacer  43 . As shown in FIG. 6, the spacer  43  comprises a horizontal portion  43   a  extended in the longitudinal direction of the anode  53  and a vertical portion  43   b  extended perpendicularly to the horizontal portion  43   a . The vertical portion  43   b  is inserted into the through-holes  59  of the mesh grid  50 . Both ends of the vertical portion  43   b  are contacted with the inner surfaces of the front substrate  41  and the rear substrate  42 . Accordingly, a gap between the two substrates is maintained.  
         [0062]    [0062]FIG. 7 is a schematic flowchart of a process of manufacturing a field emission display having the above-described structure. The process of manufacturing a field emission display will now be described in detail with reference to FIGS. 4 through 7.  
         [0063]    First, the cathode  55 , the emitters  46 , the insulator  45 , and the gate  47  are formed on the rear substrate  42  (step  71 ). The cathode, the emitters, the insulator, and the gate are formed in a conventional method.  
         [0064]    Next, the mesh grid  50  is formed (step  72 ). The mesh grid can be made of stainless steel or invar as described above. The mesh grid is processed to a predetermined shape as described above with reference to FIG. 5. The mesh grid can be made of an iron-nickel alloy to minimize thermal expansion-related problems. Preferably, 2.0 to 10.0 wt % of chromium is added to the iron-nickel alloy. Preferably, the thermal expansion coefficient of the mesh grid is in the range of 9.0×10 −6 /° C. to 10.0×10 −6 /° C., which is more similar to the thermal expansion coefficient of the substrate than that of invar, a conventional mesh grid material, i.e., about 1.2×10 −6 /° C. In particular, the mesh grid  50  made of an iron-nickel alloy has a thermal expansion coefficient similar to substrates made of a glass.  
         [0065]    In more detail, the mesh grid  50  can be made of a iron-nickel alloy which contains 40.0 to 44.0 wt % of Ni, 49.38 to 53.38 wt % of Fe, 2.0 to 10.0 wt % of Cr, 0.2 to 0.4 wt % of Mn, 0.07 wt % or less of C, 0.3 wt % or less of Si, and an impurity.  
         [0066]    Meanwhile, as shown in FIG. 6, the through-holes for insertion of the vertical portion  43   b  of the spacer  43  are formed in the mesh grid.  
         [0067]    The mesh grid is subjected to pretreatment such as pre-firing to prevent the deformation of the mesh grid in subsequent processes (step  73 ). An object of the pre-firing is to prevent the generation of a residual stress during processing the mesh grid. The mesh grid with a residual stress can be distorted in a subsequent firing process. During the pre-firing process, the mesh grid  50  is coated with an oxide film. The oxide film increases an adhesion between the mesh grid and the insulators formed on the mesh grid. The pre-firing can be carried out at a temperature of 800 to 1,000° C.  
         [0068]    Subsequent to the completion of the pre-firing, an insulating material is coated on the upper and lower surfaces of the mesh grid using, for example, a thick film technology such as screen printing. The coated insulating material can be fired at a temperature of 400 to 600° C. and crystallized to form the upper and lower insulators  49  and  51  (step  74 ).  
         [0069]    The mesh grid having the insulators on the upper and lower surfaces thereof is arranged on the rear substrate with respect to the emitters exposed through the openings of the gate. The mesh grid is completely bonded to the rear substrate using the frit. The bonding of the mesh grid to the rear substrate can be accomplished by firing the frit at a temperature of 400 to 500° C. (step  75 ). In another embodiment, the mesh grid is not bonded using the frit. In other words, the mesh grid can be supported above the electron emission assembly to maintain relative position thereto.  
         [0070]    Next, the focusing electrode is formed on the upper surface of the upper insulator of the mesh grid (step  76 ). The focusing electrode can be formed using an electrode material by thick film technology such as screen printing, or thin film technology such as sputtering, chemical vapor deposition, and an e-beam method.  
         [0071]    Next, the spacer  43  is installed on the rear substrate (step  77 ). The spacer  43  is installed to maintain a gap between the rear substrate  42  and the front substrate  41 . The spacer  43  is inserted into the through-holes  59  formed in the mesh grid  50 .  
         [0072]    Next, the front substrate  41  having the anode  53  and the phosphor  54  is joined to the rear substrate  42  (step  78 ). The anode  53  and the phosphor  54  can be formed on the front substrate  41  using a conventional method. Even though not shown in drawings, a black matrix can be patterned between the phosphor  54 . The phosphor and the black matrix can be formed by electro-phoresis, screen printing, or a slurry method. When the front substrate and the rear substrate are joined to each other, an assembly can be fired at a temperature of 400 to 500° C. (step  79 ). Accordingly, a field emission display is obtained as a final product.  
         [0073]    When the fabrication of a field emission display is completed, a voltage applied to the mesh grid for optimal electron acceleration and a voltage applied to the focusing electrode for optimal focusing are selected as follows.  
         [0074]    First, a common voltage is applied to the gate and the anode. The voltage applied to the gate is about 70 to 120 V and the voltage applied to the anode is about 1 kV or more. Then, a voltage applied to the mesh grid is selected within a range of 30 to 300 V in order to find out an optimal voltage condition for acceleration of electrons emitted from the emitter. Also, a voltage applied to focusing electrode is selected within a range of −100 to 0 V in order to find out an optimal voltage condition for focusing the accelerated electrons.  
         [0075]    [0075]FIG. 8 is a schematic sectional view of a field emission display according to another embodiment of the present invention.  
         [0076]    Referring to FIG. 8, the field emission display of this embodiment has a structure similar to that as shown in FIG. 4. The same constitutional elements have been represented by the same reference numerals. The focusing electrode formed on the upper side of the mesh grid  50  is omitted in the field emission display of FIG. 8.  
         [0077]    As described above, the mesh grid  50  can be made of an iron-nickel alloy which contains 2.0 to 10.0 wt % of Cr. In more detail, the mesh grid  50  can be made of an iron-nickel alloy which contains 40.0 to 44.0 wt % of Ni, 49.38 to 53.38 wt % of Fe, 2.0 to 10.0 wt % of Cr, 0.2 to 0.4 wt % of Mn, 0.07 wt % or less of C, 0.3 wt % or less of Si, and an impurity. In this way, when the mesh grid  50  is made of an iron-nickel alloy which contains chromium, the thermal expansion coefficient of the mesh grid becomes approximate to those of the substrates. Therefore, a mis-alignment between the mesh grid and the substrates can be prevented.  
         [0078]    The present invention provides a field emission display including a mesh grid and a focusing electrode that enable the prevention of display damage due to arcing and to acceleration and focusing of emitted electrons. The mesh grid is formed in a space defined between a gate and an anode so that electrons emitted from emitters pass through openings of the mesh grid corresponding to the intersections of the anode and the cathode. Insulators are formed on the upper and lower surfaces of the mesh grid. The mesh grid thus formed is fixed on the rear substrate by a frit. Therefore, an adjustment of alignment between the mesh grid and the rear substrate is simplified and a noise by vibration of the mesh grid that can be caused upon display driving can be minimized. Also, arc-discharge is decreased, thereby enabling to application of a high voltage. Even when an arc-discharge occurs, no damage to a cathode is caused. Furthermore, the acceleration performance of emitted electrons is enhanced, thereby increasing the luminance of the field emission display. Still furthermore, an e-beam can be focused by adjusting a voltage applied to a focusing electrode, thereby producing a high luminance and high resolution field emission display.  
         [0079]    While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present invention as defined by the following claims.