Patent Publication Number: US-2007114931-A1

Title: Flat panel display device

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
      This application claims the benefit of Korean Patent Application No. 10-2005-0111985, filed on Nov. 22, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present embodiments relate to a flat panel display device, and more particularly, to a flat panel display device which has low manufacturing costs, can be produced in large sizes, and includes an electron accelerating layer formed using an electron accelerating layer forming paste composition.  
      2. Description of the Related Art  
      Plasma display panels (PDPs) are a type of flat display device, and form an image using electrical discharge. PDPs have become popular due to their excellent display properties such as high brightness and wide viewing angle. PDPs emit visible light from a phosphor material which is excited by ultraviolet (UV) light generated from a gas discharge between electrodes, when DC and AC voltages are applied to the electrodes.  
      PDPs can be either facing discharge PDPs or surface discharge PDPs, according to the location of their electrodes. In the facing discharge structure, a pair of sustain electrodes are respectively located on a front substrate and a rear substrate, and a discharge is generated perpendicular to the substrates. In the surface discharge structure, a pair of sustain electrodes are located on the same substrate, and generate discharge parallel to the substrate.  
       FIG. 1  is an exploded perspective view of a conventional alternate current (AC) type surface discharge PDP.  FIGS. 2A and 2B  are cross-sectional views along horizontal and vertical lines of  FIG. 1 .  
      Referring to  FIGS. 1, 2A , and  2 B, a rear substrate  10  and a front substrate  20  faces each other and are separated by a predetermined distance such that a discharge space in which plasma discharge takes place, is formed therebetween. A plurality of address electrodes  111  are formed on the rear substrate  10  and are covered by a first dielectric layer  12 . A plurality of barrier ribs  13 , which divide the discharge space to define a plurality of discharge cells  14  and prevent electrical and optical cross-talk between the discharge cells  14 , are formed on the upper surface of the first dielectric layer  12 . Red, green, and blue phosphor layers  15  are coated on the inner walls of the discharge cells  14 . The discharge cells  14  are filled with a conventional discharge gas containing Xe.  
      The front substrate  20  is transparent and is coupled to the rear substrate  10  on which the barrier ribs  13  are formed. In each of the discharge cells  14 , a pair of sustain electrodes  21   a  and  21   b  are formed perpendicular to the address electrodes  11  on the lower surface of the front substrate  20 . The sustain electrodes  21   a  and  21   b  are formed of a conductive material which can transmit visible light, such as indium tin oxide (ITO). To reduce the resistance of the sustain electrodes  21   a  and  21   b , bus electrodes  22   a  and  22   b  narrower than the sustain electrodes  21   a  and  21   b  are formed of a metal on the lower surfaces of the sustain electrodes  21   a  and  21   b . The sustain electrodes  21   a  and  21   b  and the bus electrodes  22   a  and  22   b  are covered by a transparent second dielectric layer  23 . A protection layer  24  is formed of MgO on the lower surface of the second dielectric layer  23 . The protection layer  24  prevents damage to the second dielectric layer  23  due to sputtering of plasma particles, and emits secondary electrons to reduce the discharge voltage.  
      The operation of the PDP having the above structure includes an operation for generating an address discharge and an operation for generating a sustain discharge. The address discharge occurs between the address electrode  11  and one of the pair of sustain electrodes  21   a  and  21   b , and at this time, wall charges are formed. The sustain discharge is caused by a potential difference between the pair of sustain electrodes  21   a  and  21   b , and generates discharge in the discharge gas, which generates UV light to excite a phosphor layer  15 , thereby generating visible light. The visible light passes through the front substrate to form an image.  
      When a plasma discharge takes place in a conventional PDP, the discharged gas is ionized, and the excited Xe* generates UV light while stabilizing. Therefore the conventional PDP requires a high energy, sufficient to ionize the discharge gas. As a result, the conventional PDP requires a high driving voltage and exhibits low luminous  
      Korean Patent Application No. 2004-108412 discloses a flat panel display device which includes an electron accelerating layer, which generates an electron beam by accelerating electrons, and a grid electrode formed on the electron accelerating layer.  
      However, the flat panel display device disclosed in the above application cannot be produced in a large size, and has high manufacturing costs.  
     SUMMARY OF THE INVENTION  
      The present embodiments provide a flat panel display device, a plasma display panel, having high luminous efficiency and a low operating voltage and being produced in large sizes, and an electron accelerating layer forming paste composition which is used to produce the devices.  
      According to an aspect of the present embodiments, there is provided a flat panel display device including: a first substrate and a second substrate which face each other and are separated from each other by a predetermined distance; a plurality of barrier ribs which define a space between the first and second substrates to form a plurality of cells and are located between the first and second substrates; a discharge gas filling the cells; a phosphor layer formed on the inner walls of the cells; a plurality of first electrodes formed on the inner surface of the first substrate; a plurality of second electrodes on the inner surface of the second substrate located in a direction crossing the first electrodes; a plurality of third electrodes formed on the first electrodes; and an electron accelerating layer which emits a first electron beam into the cells to excite the discharge gas when a voltage is applied to the first and third electrodes, and which is interposed between the first and third electrodes, wherein the electron accelerating layer is formed by printing an electron accelerating layer forming paste composition, drying the printed composition, and then baking the dried composition, and contains at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, and an insulating material.  
      According to an aspect of the present embodiments, there is provided a plasma display device including: a first substrate that is transparent; a second substrate parallel to the first substrate; emission cells defined by barrier ribs between the first substrate and the second substrate; address electrodes extending in a direction in which the emission cells extend; a rear dielectric layer covering the address electrodes; a phosphor layer located in the emission cells; pairs of sustain electrodes extending in a direction crossing the address electrodes; a front dielectric layer covering the sustain electrodes; an electron accelerating layer located on a surface of the front dielectric layer; and a discharge gas in the emission cells, wherein the electron accelerating layer is formed by printing an electron accelerating layer forming paste composition, drying the printed composition, and baking the dried composition, and contains at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, and an insulating material.  
      According to an aspect of the present embodiments, there is provided an electron accelerating layer forming paste composition used to produce a flat panel display device and including: at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, an insulating material, a binder, and a solvent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present embodiments will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIG. 1  is an exploded perspective view of a conventional plasma display panel (PDP);  
       FIGS. 2A and 2B  are sectional views, respectively along horizontal and vertical lines of the conventional PDP shown in  FIG. 1 ;  
       FIGS. 3A and 3B  are images of nanoparticles covered with an oxide film according to an embodiment;  
       FIG. 4  is a view of an electron emission source of an electron accelerating layer according to an embodiment;  
       FIG. 5  illustrates an electron emission mechanism of an electron accelerating layer according to an embodiment;  
       FIG. 6  is a sectional view of a flat panel display device according to an embodiment;  
       FIG. 7  is a graph of Xe energy levels;  
       FIG. 8  is sectional view of a flat panel display device according to another embodiment; and  
       FIG. 9  is an exploded perspective view of a PDP according to an embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present embodiments will now be described in detail with reference to the attached drawings.  
      The present embodiments provide a flat panel display device and a plasma display panel, each utilizing an accelerating electron source that can be processed in a paste state and is capable of multiple tunneling.  
      According to an embodiment, a paste composition can be formed into an electron accelerating layer through printing, drying, and baking processes. The paste composition includes: at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, which emits electrons; an insulating material; a binder; and a solvent. The nanoparticle has a diameter of from about 5 to about 200 nm.  
      The nanoparticle is formed when an oxide film is formed, and reacts with a C 6 -C 10  alcohol to form the oxide film. Since the amount of C 6 -C 10  alcohol which reacts with the nanoparticle can be controlled, the size of the nanoparticle can be controlled.  
      The C 6 -C 10  alcohol may be for example, hexyl alcohol, heptyl alcohol, octyl alcohol, capryl alcohol, nonyl alcohol, decyl alcohol or mixtures thereof.  
       FIGS. 3A and 3B  are images of nanoparticles covered with the oxide film. In  FIG. 3A , the nanoparticles have an average diameter of about 200 nm. In  FIG. 3B , the nanoparticles have an average diameter of about 5 nm. The nanoparticles are chemically synthesized, and the thickness of the oxide film covering the nanoparticles can be controlled by controlling the amount of reacting alcohol as described above. As a result, the size of the particles can be controlled.  
      According to an embodiment, an electron accelerating layer forming paste composition is used to produce a flat panel display device. The electron accelerating layer forming paste composition includes at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, as well as an insulating material, a binder, and a solvent.  
      The binder may be an acrylate based polymer or a cellulose based polymer.  
      The organic solvent may include at least one material selected from the group consisting of terpinol, butyl carbitol acetate, toluene, butyl cellosolve, and texanol.  
       FIG. 4  is a view of an electron emission source formed of silicon nanocrystallites according to an embodiment.  FIG. 5  illustrates an electron emission mechanism of an electron accelerating layer according to an embodiment. Referring to  FIG. 5 , electrons are excited by a lower electrode. The excited electrons are injected from the lower electrode to an electron accelerating layer. In the electron accelerating layer, the diameter of the silicon nanoparticles is sufficiently smaller than the average free path of electrons in the nanocrystallite. Therefore, relatively few electrons injected into the silicon nanoparticle collide with the silicon nanoparticle. That is, electrons arrive at an intersurface while passing the nanoparticles.  
      The silicon nanoparticles or conductive nanoparticles are covered with an oxide film, for example, an organic oxide layer. Therefore, the oxide film between the nanocrystallites catches the voltage applied, forming a strong field intensity region. Since the oxide layer is very thin, electrons easily pass through the oxide film by tunneling. Whenever electrons pass through strong field intensity regions, electrons are accelerated while moving toward a surface electrode. When electrons arrive in the vicinity of the surface electrode, the energy of the electrons may be almost equivalent to the applied voltage, which is much higher than a thermal equilibrium state. As a result, the electrons having high energy can pass through the surface electrode by tunneling toward the discharge gas.  
      According to an embodiment, an electron emission source having such a multiple tunneling effect is prepared through screen printing, which is suitable for a large-sized display having low manufacturing costs.  
      According to an embodiment, the silicon nanoparticle or the conductive nanoparticle is prepared using a physical method or a chemical method.  
      In the physical method, bulk silicon or conductive particles are pulverized by mechanical milling, and then the pulverized particles are physically blended. The diameter of the particles can be controlled by high temperature heat treatment. In this case, when the silicon nanoparticles are exposed to air, an oxide film is grown to a few nanometers. The covered silicon nanoparticles are dispersed with an insulating material, a binder, and a solvent to prepare a paste composition. However, in this physical method, it is difficult to obtain a uniform particle size and to reduce the particle size to less than a few nanometers.  
      In the chemical method, particle sizes can be controlled by chemical synthesis. As compared to the physical method, the chemical method is advantageous in that uniform particle sizes can be obtained and particle sizes can be reduced to less than a few nanometers. In addition, when silicon nanoparticles or conductive nanoparticles are synthesized, an organic material can be capped on the particles.  
      The electron accelerating layer forming paste composition according to an embodiment is screen printed, dried, and baked, thereby forming silicon nanoparticles or conductive nanoparticles covered with the insulating material on a substrate. The insulating material may be, for example, Al 2 O 3 , SiO 2 , PbO, or glass frit.  
       FIG. 6  is a sectional view of a flat panel display device having a direct current facing discharge structure according to an embodiment. Referring to  FIG. 6 , a first substrate  110 , which is a rear substrate, and a second substrate  120 , which is a front substrate, are arranged to face each other with a constant distance therebetween. The first substrate  110  and the second substrate  120  can be formed, for example, of transparent glass. A plurality of barrier ribs  113 , which divide a space between the first and second substrates  110  and  120  into a plurality of cells  114  and prevent electrical and optical cross-talk between the cells  114 , are formed between the first and second substrates  110  and  120 . Red (R), green (G), and blue (B) phosphor layers  115  are coated on the inner walls of the cells  114 . The cells  114  are filled with a discharge gas containing, for example, Xe, N 2 , D 2 , H 2 , CO 2 , Kr or a mixture thereof. The discharge gas can generate ultraviolet (UV) light when excited by external energy such as an electron beam. The discharge gas used in the present embodiments can function as a discharge gas.  
      In each of the cells  114 , a first electrode  131  extending in a direction is formed on the upper surface of the first substrate  110 , and a second electrode  132  extending in a direction crossing the first electrode  131  is formed on the lower surface of the second substrate  120 . Here, the first electrode  131  and the second electrode  132  are respectively a cathode electrode and an anode electrode. The second electrode  132  can be formed of a transparent conductive material, such as ITO, to transmit visible light. A dielectric layer (not shown) can further be formed on the second electrode  132 .  
      An electron accelerating layer  140  is formed on the upper surface of the first electrode  131 , and a third electrode  133 , which is a grid electrode, is formed on the electron accelerating layer  140 . The electron accelerating layer  140  can be formed by printing, drying, and baking the electron accelerating layer forming paste composition containing at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, an insulating material, a binder, and a solvent. For example, the electron accelerating layer  140  may be formed of oxidized porous silicon.  
      The electron accelerating layer  140  emits an E-beam into the cell  114  through the third electrode  133  by accelerating electrons supplied by the first electrode  131  when a voltage is applied to the first electrode  131  and the third electrode  133 . The E-beam emitted into the cell  114  excites the discharge gas, which generates UV light while stabilizing. The UV light excites the phosphor layer  115  to generate visible light, which is emitted toward the second substrate  120 , thereby forming an image.  
      The E-beam preferably has an energy high enough to excite the discharge gas and low enough not to ionize the discharge gas. Therefore, a voltage applied to the first electrode  131  and the third electrode  133  should allow the E-beam to have the optimal electron energy to excite the discharge gas.  
       FIG. 7  is a graph showing energy levels of Xe, which is a UV light source. Referring to  FIG. 7 , about 12.13 eV of energy is required to ionize Xe, and more than about 8.28 eV is required to excite Xe. More specifically, 8.28 eV, 8.45 eV, and 9.57 eV are respectively required to excite Xe to 1S 5 , 1S 4 , and 1S 2  states. The excited Xe* generates UV light of approximately 147 nm while stabilizing. Excimer Xe 2 * is generated by colliding the excited Xe* with Xe in a grounded state, and the Xe 2 * generates UV light of approximately 173 nm while stabilizing.  
      Accordingly, in an embodiment, an E-beam emitted into the cell  114  by the electron accelerating layer  140  can have an energy of from about 8.28 to about 12.13 eV to excite the Xe. In this case, the E-beam may have an energy of from about 8.28 to about 9.57 eV or from about 8.28 to about 8.45 eV. Also, the E-beam may have an energy of from about 8.45 to about 9.57 eV.  
      When V 1 , V 2 , and V 3  represent the voltages applied respectively to the first electrode  131 , the second substrate  120 , and the third electrode  133 , V 1 &lt;V 3 &lt;V 2 . When these voltages are respectively applied to the electrodes, an E-beam is emitted into the cell  114  by the voltages applied to the first electrode  131  and the third electrode  133  through the electron accelerating layer  140 .  
      The discharge gas may be, in addition to Xe, a gas that can generate UV light which has a long enough wavelength to pass through glass, such as N 2 . Since discharge does not take place, a compound gas can be used. In addition, The display device using the electron accelerating layer may be less sensitive to gas contamination than a discharge display. Accordingly, the discharge gas can be, for example, Xe, N 2 , D 2 , H 2 , CO 2 , Kr or mixtures thereof.  
       FIG. 8  is sectional view of a flat panel display device according to another embodiment. The differences from the flat panel display device shown in  FIG. 6  will be described. Referring to  FIG. 8 , a second electrode  132 ′ is formed in a mesh structure so that visible light generated in the cells  114  can be transmitted. The third electrode  133 ′ is formed in a mesh structure so that electrons accelerated by the electron accelerating layer  140  can readily be emitted into the cells  114 .  
      Hereinbefore, the first substrate  110  has referred to a rear substrate and the second substrate  120  has referred to a front substrate. However, the present embodiment can be applied to the case where the first substrate  110  on which the electron accelerating layer  140  is formed is the front substrate and the second substrate  120  is the rear lower substrate.  
      A plasma display panel according to another embodiment includes: a first substrate that is transparent; a second substrate parallel to the first substrate; emission cells defined by barrier ribs between the first substrate and the second substrate; address electrodes extending in a direction in which the emission cells extend; a rear dielectric layer covering the address electrodes; a phosphor layer located in the emission cells; a plurality of pairs of sustain electrodes extending in a direction crossing the address electrodes; a front dielectric layer covering the sustain electrodes; an electron accelerating layer located on a surface of the front dielectric layer; and a discharge gas in the emission cells, wherein the electron accelerating layer is formed by printing an electron accelerating layer forming paste composition, drying the printed composition, and baking the dried composition, and contains at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, and an insulating material.  
      The electron accelerating layer forming paste composition includes at least one nanoparticle selected from a silicon nanoparticle and a conductive nanoparticle, an insulating material, a binder, and a solvent. The nanoparticle may have a diameter of from about 5 to about 200 nm.  
      The nanoparticle is formed when an oxide film is formed. Herein, the oxide film is formed by reacting the nanoparticle with a C 6 -C 10  alcohol.  
      The C 6 -C 10  alcohol may be for example, hexyl alcohol, heptyl alcohol, octyl alcohol, capryl alcohol, nonyl alcohol, the decyl alcohol or mixtures thereof.  
      The insulating material may be, for example, Al 2 O 3 , SiO 2 , PbO, or glass frit.  
      The electron accelerating layer may be formed for example, of oxidized porous silicon.  
       FIG. 9  is an exploded perspective view of a PDP  200  according to an embodiment.  FIG. 9  shows the structure of a front panel  210  and a rear panel  220  of the PDP  200 . The front panel  210  includes a front substrate  211 , pairs of sustain electrodes  214  including Y electrodes  212  and X electrodes  213  on the rear surface  211   a  of the front substrate  211 , a front dielectric layer  215  covering the pairs of sustain electrodes  214 , and an electron accelerating layer  216  covering the front dielectric layer  215 . The Y electrodes  212  and X electrodes  213  respectively include transparent electrodes  212   b  and  213   b  formed of, for example, ITO, and bus electrodes  212   a  and  213   a  formed of a conductive metal. The bus electrodes  212   a  and  213   a  are connected to connecting cables installed at opposite sides of the PDP  200 .  
      The rear panel  220  includes a rear substrate  221 , address electrodes  222  extending in a direction crossing the direction in which the sustain electrodes  214  extend, on the front surface  221   a  of the rear substrate  221 , a rear dielectric layer  223  covering the address electrodes  222 , barrier ribs  224  defining emission cells  226  on the rear dielectric layer  223 , and a phosphor layer  225  formed on the emission cells  226 . The address electrodes  222  are connected to connecting cables installed at opposite sides of the PDP  200 .  
      As described above, in a flat panel display device and a PDP according to the present embodiments, an electron accelerating layer emits an E-beam that excites a discharge gas. The flat panel display device and PDP require low operating voltages and have high luminous efficiency.  
      As also described above, an acceleration emission source having a multiple tunneling effect can be processed in a paste state, so that a screen printing method can be used. When voltages are applied to both ends of the electron emission source, electrons undergo continuous multiple tunneling in an insulating material covering a conductive particle to be emitted. By using screen printing, a large-sized device can be produced with low manufacturing costs. According to the present embodiments, a large sized PDP having a low operating voltage and a high emission efficiency can be produced with low manufacturing costs.  
      While the present embodiments have 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 detail may be made therein without departing from the spirit and scope of the present embodiments as defined by the following claims.