Patent Publication Number: US-7714496-B2

Title: Field emission display device and field emission type backlight device having a sealing structure for vacuum exhaust

Description:
CLAIM OF PRIORITY 
   This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for FIELD EMISSION DISPLAY DEVICE AND FIELD EMISSION TYPE BACKLIGHT DEVICE HAVING A SEALING STRUCTURE FOR VACUUM EXHAUST earlier filed in the Korean Intellectual Property Office on 31 Mar. 2006 and there duly assigned Serial No. 10-2006-00029806. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a field emission display device and a field emission type backlight device, and more particularly, to a field emission display device and a field emission type backlight device in which a sealing structure for hermetically sealing a vacuum-exhausted panel space is provided as an exhaust path for an impure gas in the panel space. 
   2. Description of the Related Art 
   A field emission display device is a self-luminous display device that directly reproduces a full color image by concentrating a high electric field on an emitter that is an electron emission source to induce an emission of cold electrons and directing the electrons accelerated by a voltage difference between a cathode electrode and an anode electrode to collide with red, green, and blue phosphors. A field emission type backlight device is a backlight device that uses the aforementioned field emission, and does not form an image by itself but is mounted on a rear surface of a separate image-forming device, such as a liquid crystal display panel to supply a uniform surface light to the image-forming device. 
   In the field emission display device and the field emission type backlight device, a cathode substrate and an anode substrate are disposed facing each other and spaced apart from each other. A cathode electrode and a gate electrode crossing the cathode electrode are disposed on the cathode substrate, and the emitter, which is the electron emission source, is disposed at a crossing portion of the cathode electrode and the gate electrode. An anode electrode and a phosphor emitting a light by colliding with the electrons emitted from the electron emission source and accelerated by the anode electrode, are disposed on the anode substrate. The cathode substrate and the anode substrate are attached to each other by a sealant sealing a panel space therebetween. The panel space should be kept in a high vacuum state so as not to disturb the movement of the emitted electrons, and particularly to prevent charged particles from being generated by collision between an impure gas in the panel space and the accelerated electrons. Accordingly, a method for manufacturing the foregoing devices necessarily includes a vacuum exhaust process for sucking an impure gas, such as vapor, from the panel space with a vacuum pump and discharging the impure gas to the outside. According to the related art, an exhaust hole is perforated in a portion adjacent to an edge of the cathode substrate deviating from a display region, and an exhaust pipe is attached to a rear surface of the cathode substrate so as to communicate with the exhaust hole, and then the exhaust pipe is connected to the vacuum pump so that the impure gas in the panel is pumped out until the inside of the panel reaches a vacuum. In attaching the exhaust pipe, a frit paste is coated around the exhaust pipe located at the rear surface of the cathode substrate, and then the cathode substrate is heated to about the melting temperature of the frit paste in a heating chamber. 
   According to the related art, since the exhaust hole is perforated and the exhaust pipe is attached prior to the exhaust process, the number of processes increases. Also, when fine particles generated during the perforation of the exhaust hole through the panel, the particles may obstruct normal operation and result in a defective product. In addition, since the exhaust pipe is attached to protrude from a rear surface of the cathode substrate, the presence of the exhaust pipe restricts the amenability to reduce the thickness of the display device and to thereby manufacturing a thin type display device; moreover, the rear space of the display device occupied by the exhaust pipe is not suitable for use for another purpose, thus concomitantly decreasing space utilization. 
   Meanwhile, a portion adjacent to the edge of the cathode substrate is a region provided to perforate the exhaust hole, and thus cannot be used as an effective display region where a visual video image is displayed. Therefore, according to the related art, an ineffective region is necessarily generated due to the necessity for a perforation of the exhaust hole. 
   An impure gas generally remains in the panel space after the vacuum exhaust process. Therefore, a getter material that reacts well with an impure gas is injected into the panel, and is activated. The activated getter adsorbs the impure gas in the panel, and induces an internal space to a high vacuous state. According to the related art, the getter is dispersedly disposed in the exhaust pipe or an empty space in the panel except for a display region where electrodes are arranged. At this point, since the getter is exposed to an emission space of electron beams, a portion of electrons emitted from an emitter may be distorted in an unexpected path by interacting with the getter material. Also, since the getter after absorbing the impure gas becomes useless but still remains in the panel, a blank space for carrying the getter is separately required, and a separate supporting structure for fixedly supporting the getter is required. Consequently, according to the related art, the panel structure is complicated, and the degree of freedom of the design is restricted in the intensively designed panel structure. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide an improved field emission display device and an improved field emission type backlight device. 
   It is another object to provide a field emission display device and a field emission type backlight device that can reduce the number of processes by providing a single structure for both exhaust and sealing functions. 
   It is yet another object to provide a field emission display device and a field emission type backlight device that increases the space utilization of the rear of a panel and is advantageous for the manufacture of a compact, slim and lightweight structure. 
   It is still another object to provide a field emission display device and a field emission type backlight device suitable for a large screen display by eliminating an ineffective region for exhaust of impure gases. 
   It is a further object to provide a field emission display device and a field emission type backlight device having a simplified internal panel structure by eliminating a separate supporting structure for mounting a getter. 
   According to an aspect of the present invention, a field emission display device is provided with a cathode substrate and an anode substrate disposed to face each other and a vacuum-exhausted panel space is interposed between the cathode substrate and the anode substrate to generate a variable, visual, video images. The field emission display device is constructed with a sealing member disposed along the edges of the cathode substrate and the anode substrate to seal the panel space. The sealing member is constructed with at least one inlet exposed to the panel space and an exhaust passage through which the inlet communicates with an outside of the field emission display device. 
   According to another aspect of the present invention, a field emission type backlight device is provided with a cathode substrate and an anode substrate disposed to face each other and a vacuum-exhausted panel space is interposed between the cathode substrate and the anode substrate to provide uniform light to a video image forming panel. The field emission type backlight device is constructed with a sealing member disposed along the edges of the cathode substrate and the anode substrate to seal the panel space. The sealing member is constructed with at least one inlet exposed to the panel space and an exhaust passage through which the inlet communicates with an outside of the backlight device. 
   The sealing member may have a rectangular frame shape, and may include a pair of frit bars constituting the longer sides of the sealing member and a pair of exhaust tubes in which the exhaust passage is formed constituting the shorter sides of the sealing member. 
   The inlet may include a plurality of holes formed at intervals in a length direction taken along the exhaust tubes or one hole may be formed in an elongated shape in a length direction taken along the exhaust tubes. 
   Each of the exhaust tubes may be made from a hollow member having a square cross section and having a first surface facing the anode substrate and a second surface facing the cathode substrate, or each of the exhaust tubes may be made from a cylindrical hollow member. Each of the frit bars may be made from a solid member having a square cross section. Also, the flit bars and the exhaust tubes are made from a glass material. 
   The frit bars and the exhaust tubes may be attached to each other through heat fusion of a frit paste interposed therebetween. 
   A frit paste to attach the substrates through a heat fusion may be formed in upper and lower surfaces of the sealing member respectively facing the cathode substrate and the anode substrate. 
   A getter may be injected into the sealing member to adsorb an impure gas and disposed on the exhaust passage of the impure gas. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a plan view of a field emission display device constructed as an embodiment of the principles of the present invention; 
       FIG. 2  is an exploded oblique view of a display region of the field emission display device of  FIG. 1 , constructed as an embodiment of the principles of the present invention; 
       FIG. 3  is a cross-sectional view of the field emission display device of  FIG. 1  taken along line III-III, constructed as an embodiment of the principles of the present invention; 
       FIG. 4  is an oblique view of a sealing member shown in  FIG. 3 , constructed as an embodiment of the principles of the present invention; 
       FIG. 5  is an oblique view of an exhaust tube included in the sealing member shown in  FIG. 4 , constructed as an embodiment of the principles of the present invention; 
       FIG. 6  is a vertical sectional view of a field emission display device constructed as another embodiment of the principles of the present invention; 
       FIG. 7  is an oblique view of an exhaust tube included in the field emission display device of  FIG. 6 , constructed as another embodiment of the principles of the present invention; 
       FIG. 8  is a vertical cross-sectional view of a field emission display device constructed as still another embodiment of the principles of the present invention; 
       FIG. 9  is an oblique view of an exhaust tube included in the field emission display device of  FIG. 8 , constructed as an embodiment of the principles of the present invention; 
       FIG. 10  is an oblique view of an exhaust tube included in the field emission display device of  FIG. 8 , constructed as another embodiment of the principles of the present invention; and 
       FIG. 11  is a vertical cross-sectional view of a field emission display constructed as a further embodiment of the principles of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.  FIG. 1  is a plan view of a field emission display device according to an embodiment of the present invention. Referring to  FIG. 1 , field emission display device  100  is constructed with an anode substrate  120  and a cathode substrate  110  overlapping each other. Anode substrate  120  and cathode substrate  110  are attached to each other by a sealing member  150  formed along the entirety of the peripheral edges of anode substrate  120  and cathode substrate  110  to effectively form a closed rectangular shape. Sealing member  150  forms a roughly rectangular frame. An inner region surrounded by sealing member  150  serves as a display region P emitting light to display an visual image. Sealing member  150  may be constructed with a pair of diagonally opposite exhaust tubes  151  and a pair of frit bars  152  formed parallel to each other in the right and left and the upper and lower sides, respectively, of display region P. Exhaust tubes  151  and frit bars  152  may be attached to each other by a heat fusion of a frit paste  161  interposed therebetween. 
   A plurality of cathode electrodes  111  and gate electrodes  115  are disposed in display region P to be supplied with controlled signals from external circuit substrates, to extend to an outside of display region P. A terminal region (not shown) is formed outside display region P to electrically connect end portions of cathode electrodes  111  and gate electrodes  115  to the external circuit substrates. 
     FIG. 2  is an exploded oblique view of display region P of field emission display device  100  of  FIG. 1 , constructed as an embodiment of the principles of the present invention.  FIG. 3  is a cross-sectional view of field emission display device  100  of  FIG. 1  taken along line III-III, as an embodiment of the principles of the present invention. Referring to  FIG. 2 , cathode electrodes  111  are formed in a stripe pattern at regular intervals in the y direction and a dielectric layer  113  covering cathode electrodes  111  is formed on cathode substrate  110 . Gate electrodes  115  are formed in a stripe pattern in the x direction crossing cathode electrodes  111  on dielectric layer  113 . A plurality of emitters  112  protruding from cathode electrodes  111  are formed in a crossing region where cathode electrodes  111  and gate electrodes  115  cross each other, and are connected to cathode electrodes  111  to be provided with an electrical current. A plurality of emitter holes  116  are formed in gate electrodes  115  to expose the sharp, conical tips of emitters  112 . Gate electrodes  115  and the tips of emitter  112  are spaced from each other by distances on a submicron scale, and a number of electrons are emitted from emitters  112  by a high electric field formed between gate electrodes  115  and emitters  112 . An anode electrode  121  is disposed on anode substrate  120 , and a bias voltage is applied to anode electrode  121  to accelerate the electrons emitted from emitters  112 . Anode electrode  121  is a common electrode forming the same voltage for an entire display region, and may be made from a plane electrode, as illustrated in  FIG. 2 . Anode electrode  121  may be made from an optically transparent electrode material, for example, indium-tin-oxide (ITO), etc., considering an optical extraction efficiency. Anode electrode  121  is covered with a phosphor layer  125 , and phosphor layer  125  may include a red phosphor layer  125 R, a green phosphor layer  125 G, and a blue phosphor layer  125 B. Phosphor layer  125  is transited to an excited state by a collision with an electron beam B, and then emits a display light having inherent wavelengths depending on types of the phosphor while falling to a ground state. Phosphor layer  125  having different emitting colors is divided by a black matrix  123  having a pattern. Black matrix  123  has a dark color and a high light absorbing efficiency to maintain a high contrast ratio by absorbing an external light. Black matrix  123  also prevents color mixing due to the optical interference between neighboring emitting colors. Referring to  FIG. 3 , a panel space G maintaining a high vacuum of, for example, more than 10 −6  Torr, is formed between anode substrate  120  and cathode substrate  110 . Panel space G is maintained at a set height by a plurality of spacers  170  disposed therein. 
   In order to drive field emission display device  100 , a negative (−) voltage is applied to cathode electrodes  111 , and a positive (+) voltage is applied to anode electrodes  121 . At this point, electron beam B is emitted from the tip of emitters  112  by a high electric field formed by gate electrodes  115  and anode electrodes  121 , and the emitted electron beam B collides with the corresponding phosphor layer  125 , and thus light is emitted. 
   Sealing member  150  is disposed between anode substrate  120  and cathode substrate  110  to seal panel space G. Frit paste  162  is formed on the upper and lower surfaces of sealing member  150  to attach anode substrate  120  and cathode substrate  110  to sealing member  150 , and a space between sealing member  150  and cathode substrate  110  and anode substrate  120  is sealed by the heat fusion of flit paste  162 . 
     FIG. 4  is an oblique view of sealing member  150  shown in  FIG. 3  as an embodiment of the principles of the present invention and  FIG. 5  is an oblique view of an exhaust tube  151  included in sealing member  150  as an embodiment of the principles of the present invention. Sealing member  150  forms a roughly rectangular frame, and is constructed with frit bars  155  constituting long sides of sealing member  150  extending in a horizontal direction (the x direction) and exhaust tubes  151  constituting short sides of sealing member  150  extending in a vertical direction (the y direction). Frit bars  155  seal a space between cathode substrate  110  and anode substrate  120  and support cathode substrate  110  and anode substrate  120  to maintain a regular interval between cathode substrate  110  and anode substrate  120 . Frit bars  155  may be made from a solid member having a square cross section, as illustrated in  FIG. 4 . 
   Exhaust tubes  151  serve as exhaust passages for discharging an impure gas in panel space G to the outside during the exhaust process performed in a manufacturing process of the display device. For this purpose, each of exhaust tubes  151  is made from a hollow member forming a flowing passage to guide the impure gas. At least one inlet  152  is formed in a side wall of each of exhaust tubes  151  facing toward panel space G. For example, a plurality of inlets  152  may be formed at intervals in a length direction of exhaust tubes  151  (in the y direction). The impure gas in panel space G is forced to enter exhaust tubes  151  through inlets  152  by a negative pressure formed by a vacuum pump, and is discharged to the outside via exhaust tubes  151 . Exhaust tubes  151  support a space between anode substrate  120  and cathode substrate  110  with frit bars  155 . For example, a supporting strength is required to withstand a pressure applied in a process of pressurizing and attaching cathode substrate  110  and anode substrate  120  to each other or to withstand a pressure difference between the inside of panel space G which is maintained in a vacuum state and the external atmospheric pressure. At this point, since exhaust tubes  151  are supported in the vertical direction (z direction) by sidewalls  153  between inlets  152 , a concrete factor such as a number or a length of inlets  152  may be determined in a range that secures the minimum supporting strength. Also, if inlets  152  are formed in an end portion  151   a  of exhaust tubes  151  extending outside panel space G, the vacuum pressure of the vacuum pump cannot be delivered to panel space G, that is, the pressure is reduced. Therefore, inlets  152  should not be formed in end portions  151   a  of exhaust tubes  151 . Exhaust tubes  151  and frit bars  155  may be made from a glass material. 
     FIG. 6  is a vertical cross-sectional view of a field emission display device  101  constructed as another embodiment of the principles of the present invention, and  FIG. 7  is an oblique view of an exhaust tube  251  included in field emission display  101  device illustrated in  FIG. 6 , according to another embodiment of the principles of the present invention. Referring to  FIG. 7 , an inlet  252  is formed in a side wall of exhaust tube  251  facing toward panel space G and is elongated in a length direction of exhaust tube  251  (y direction). At this point, if inlet  252  is formed in an end portion  251   a  of exhaust tube  251  extending outside a panel space, sucking pressure may be lost, and thus  14  end portion  251   a  of exhaust tube  251  may have a closed cross section. 
     FIG. 8  is a vertical cross-sectional view of a field emission display device  102  constructed as still another embodiment of the principles of the present invention, and  FIG. 9  is a perspective view of an exhaust tube included in field emission display device  102  of  FIG. 8  according to an embodiment of the principles of the present invention. Exhaust tube  351  is made from a cylindrically hollow member. A fitting gasket (not shown) connected to a vacuum pump (not shown) is fitted to an end portion  351   a  of exhaust tube  351  extending outside a panel space G. The fitting gasket generally has a cylindrical shape corresponding to a pipe. Accordingly, exhaust tube  351  may be connected to the vacuum pump through a general fitting gasket having an appropriately sized diameter, and thus the inconvenience of preparing a special type of fitting gasket may be eliminated. A plurality of inlets  352  for an impure gas may be formed in a side wall of exhaust tube  351  facing toward panel space G at set intervals in a length direction of exhaust tube  351  (in the y direction).  FIG. 10  is an oblique view of an exhaust tube included in field emission display device  102  of  FIG. 8  according to another embodiment of the present invention. Referring to  FIG. 10 , exhaust tube  451  has a cylindrical shape and has two inlets  452  elongated in a length direction of the exhaust tube (y direction). At least more than one inlet may be formed in the exhaust tube of the present invention, and the number of inlets is not limited. Also, as long as the exhaust tube includes a flowing passage formed therein to guide the impure gas, its cross section is not limited to the square shape shown in  FIG. 5  or the cylindrical shape shown in  FIGS. 9 and 10 , and may be variously changed. 
     FIG. 11  is a vertical cross-sectional view of a field emission display device  103  according to a further embodiment of the present invention. Field emission display device  103  illustrated in  FIG. 11  is constructed an anode substrate  120  and a cathode substrate  110  disposed facing each other, and a sealing member  350  sealing a panel space G between cathode substrate  110  and cathode substrate  120  and maintaining a vacuum state. Sealing member  350  is constructed with an exhaust tube  351  to exhaust an impure gas in panel space G. In particular, in this embodiment, a getter  180  is disposed inside exhaust tube  351 . Getter  180  includes ingredients having an excellent absorption of an impure gas, and may include, for example, more than one kind of metal oxide powder selected from W, Ti, Zr, Al, V, and Fe as a chief ingredient, but is not limited thereto. Getter  180  induces panel space G to a high vacuum state by absorbing and removing the impure gas remaining in panel space G after an exhaust process. In a getter-activation process after the exhaust process, getter  180  may be activated for example, by injecting getter  180  into exhaust tube  351 , and applying a voltage to getter  180  from an external power source or irradiating a laser from an external light source. 
   In the related art, getter  180  is exposed as it is to an emission space of an electron beam B, and a structure for isolating getter  180  from the emission space is not provided. As a result, stability of electron beam B decreased, for example, a flow of electrons inside the emission space was distorted by getter  180 . According to an embodiment of the principles of the present invention, getter  180  injected into exhaust tube  351  is structurally isolated from the emission space of electron beam B, thereby completely preventing an interaction between getter  180  and the emitted electrons, and the distortion of a flow of the electrons, and inducing a stable flow of the electrons. Also, in the related art, a separate supporting structure to fixedly support getter  180  is required, but according to an embodiment of the principles of the present invention, exhaust tube  350  also serves as a supporting structure for getter  180 , and thus a convenient design is obtained. 
   The present invention is described in relation to a field emission display device, but technical features of the present invention are not limited to a display device displaying a visual image, and can be applied to a field emission type backlight device having a substantially similar structure. For example, in a field emission type backlight device of the present invention, a white phosphor layer emitting white light of multiple wavelengths may be included, instead of red, green, and blue phosphor layers emitting different colors arranged in an array shape in the anode substrate. In another field emission type backlight device, phosphors of different emitting colors are arranged in an array shape, and a light diffusion film for mixing multi-color lights of different wavelength ranges may be disposed in the front of the field emission type backlight device. 
   The field emission display device and the field emission type backlight device of the present invention can achieve the following effects. 
   The field emission display device and the field emission type backlight device have increased space utilization for a rear space of the panel and are suitable for a compact, slim and lightweight design. Specifically, since an exhaust pipe protruding from rear surface of the panel as in the related art is not required, the requirement for a rear space is eliminated, thereby providing a compact, slim and lightweight display device. Also, a rear space may be utilized as a mounting space of electrical equipment for improving performance and for increasing the space utilization. 
   Since the processing and the time required for a perforation of the exhaust hole and an attachment of the exhaust pipe are reduced, the manufacturing cost decreases. Also, damages or defects of the panel that can be generated during the perforation of the exhaust hole or the attachment of the exhaust pipe, can be eliminated. 
   Since an invalid region wasted to form the exhaust hole in the related art decreases, a larger valid pixel region is obtained for a panel of the same size. 
   Since the getter material for absorption of the remaining impure gas is provided in the sealing member, the supporting structure separately disposed in the panel to mount the getter material is eliminated, the inner structure of the intensively designed panel is simplified, and the flexibility of the panel design is improved. Also, according to the present invention, since the getter material is disposed in the sealing structure to be isolated from the emission space of the electron beam, the stability of the electron beam is improved. 
   Since the sealing structure for the vacuum exhaust is provided, compared with the related art where the exhaust structure and the sealing structure are separately provided, the number of processes can be largely reduced. 
   In the related art, the size of the exhaust hole is restricted to minimize a wasted pixel region, and thus a time delay is generated in the vacuum exhaust process. However, since the size of the exhaust passage is freely increased in the present invention, the vacuum exhaust is rapidly performed and the manufacturing unit cost is reduced. 
   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 may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.