Patent Publication Number: US-2009225516-A1

Title: Flat panel display apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0020570, filed on Mar. 5, 2008, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a flat panel display apparatus, and more particularly, to a flat panel display apparatus having a heat dissipation mechanism. 
     2. Description of the Related Art 
     Recently, flat panel display apparatuses have been intensively developed. Examples of flat panel display apparatuses include a liquid crystal display (LCD), a plasma display apparatus, a field emission display device, and a vacuum fluorescent display device. 
     An electron emission element included in such flat panel display apparatuses may have a hot cathode or a cold cathode as an electron emission source. Examples of electron emission elements using a cold cathode include a field emission device (FED) type electron emission element, a surface conduction emitter (SCE) type electron emission element, a metal insulator metal (MIM) type electron emission element, and a ballistic electron surface emitting (BSE) type electron emission element. 
     In the FED type electron emission element, electrons are easily emitted due to an electric field difference in a vacuum state when a material having a small work function or a large beta function is used to form an electron emission source. A device in which a tip structure having a sharp top end formed of molybdenum (Mo), silicon (Si), etc., or a carbon-based material such as graphite, diamond like carbon (DLC), etc., or a nano material such as nano tube or nano wire is used to form an electron emission source has been developed. 
     The FED type electron emission element may be of a top gate type and an under gate type according to the arrangement of a cathode and a gate electrode, or may be a diode, a triode, a tetrode, etc., according to the number of electrodes. In a conventional electron emission element, electrons are emitted from an electron emission source by an electric field formed between a cathode and a gate electrode. Electrons are emitted from an electron emission source disposed around an electrode that acts as a negative electrode between the cathode and the gate electrode. The emitted electrons proceed toward an electrode that acts as a positive electrode at an initial stage, are led by a strong electric field of an anode, and are accelerated toward a phosphor layer. 
     Due to a large amount of current, much heat is generated by the anode of the conventional FED type electron emission element. As such, the temperature of the entire panel increases and thus, several problems may occur. For example, since the heat generated by the anode has a high temperature of 100° C. or greater, a glass substrate may be destroyed by thermal expansion. In addition, other elements that have low heat resistance are affected so that the defective rate of a product increases. In particular, since light is emitted from the anode and a front substrate on which the anode is installed, a heat-dissipating plate may not be directly installed on a flat panel display apparatus and, therefore, the flat panel display apparatus may not be able to be effectively cooled. 
     In order to solve these problems, in the prior art, the generated heat is cooled by an external cooling fan. However, an external fan does not always provide effective cooling and causes the manufacturing costs of a flat panel display apparatus to be relatively high. 
     SUMMARY OF THE INVENTION 
     Aspects of the present invention provide a flat panel display apparatus in which heat generated by an anode and a front substrate on which the anode is installed can be effectively cooled. 
     A flat panel display apparatus includes a display unit for displaying images, a first semiconductor and a second semiconductor electrically connected to the display unit, and a heat sink electrically connected to the first semiconductor and to the second semiconductor. 
     The heat sink may be opposite to the display unit and may dissipate heat generated by the display unit away from the display unit. Light generated by the display unit may be emitted in a direction away from the heat sink. 
     The first semiconductor may be a P-type semiconductor and the second semiconductor may be an N-type semiconductor. Further, the display unit and the heat sink may comprise different conductive materials and the display unit may be connected to the first semiconductor and to the second semiconductor via a metal conducting wire. The metal conducting wire may be connected to a non-effective region of the display unit that does not display images. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a partial perspective view showing a schematic configuration of an electron emission type backlight unit having an electron emission source according to an embodiment of the present invention. 
         FIG. 2  is a cross-sectional view taken along line II-II of  FIG. 1 . 
         FIG. 3  is a plan view showing a schematic configuration of a flat panel display apparatus according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     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 partial perspective view showing the schematic configuration of an electron emission type backlight unit having an electron emission source according to an embodiment of the present invention, and  FIG. 2  is a cross-sectional view taken along line II-II of  FIG. 1 . 
     As illustrated in  FIGS. 1 and 2 , an electron emission type backlight unit  100  comprises electron emission elements  101  disposed in parallel and forming an emission space  103  in a vacuum state, a front panel  102 , and a spacer  60  that maintains a distance between the electron emission element  101  and the front panel  102 . 
     Each of the electron emission elements  101  comprises a first substrate  110 , first electrodes  120 , an insulator layer  130 , second electrodes  140 , and an electron emission source  150  ( FIG. 2 ). 
     The first electrodes  120  and the second electrodes  140  are disposed on the first substrate  110  to cross one another, and the insulator layer  130  is disposed between the second electrodes  140  and the first electrodes  120  to electrically insulates the second electrodes  140  and the first electrodes  120 . Electron emission source holes  131  are formed in regions in which the second electrodes  140  from the first electrodes  120  cross one another, and an electron emission source  150  is disposed in the electron emission source holes  131  ( FIG. 2 ). 
     The first substrate  110  may be a plate-shaped member having a thickness. Quartz glass, glass containing an impurity such as a small amount of Na, plate glass, a SiO 2 -coated glass substrate, an aluminum oxide or a ceramic substrate may be used as the first substrate  110 . In addition, a flexible material may be used to form a flexible display apparatus. 
     The first electrodes  120  and the second electrodes  140  may be generally formed of an electrically conductive material, for example, Al, Ti, Cr, Ni, Au, Ag, Mo, W, Pt, Cu, Pd, etc., or an alloy thereof, a printed conductor comprised of glass and metal, such as Pd, Ag, RuO   2    or Pd—Ag, or a metal oxide, a transparent conductor, such as In 2 O 3  or SnO 2 , or a semiconductor material such as polysilicon, etc. 
     The insulator layer  130  insulates the first substrate  110  from the second electrodes  140 . The insulator layer  130  may be generally formed of an insulating material. For example, the insulating material may be a silicon oxide, a silicon nitride, a frit, among others. The frit may be a PbO—SiO 2 -based frit, a PbO—B 2 O 3 —SiO 2 -based frit, a ZnO—SiO 2 -based frit, a ZnO—B 2 O 3 —SiO 2 -based frit, a Bi 2 O 3 —SiO 2 -based frit, or a Bi 2 O 3 —B 2 O 3 —SiO 2 -based frit. However, the present invention is not limited to these materials. 
     The electron emission source  150  includes an electron emission material. Carbon nano tubes (CNTs) having a small work function and a large beta function may be used as the electron emission material. In particular, CNTs have an excellent electron emission characteristic and are easily driven by a low voltage, and thus are often used to form large-scale devices. However, the present invention is not limited to CNTs, and a carbon-based material such as graphite, diamond, diamond-like carbon (DLC), etc., or a nano material such as nano tube, nano wire, or nano rod, etc., may also be used as the electron emission material. Alternatively, the electron emission material may include carbide-driven carbon. 
     The front panel  102  comprises a second substrate  90  that transmits visible rays, a phosphor layer  70  ( FIG. 2 ) disposed on the second substrate  90  and excited by electrons emitted from the electron emission elements  101  to generate visible rays, and third electrodes  80  that accelerate the electrons emitted from the electron emission elements  101  toward the phosphor layer. 
     The second substrate  90  may be formed of the same material as the first substrate  110  as described above, and may transmit visible rays. 
     The third electrodes  80  may be formed of the same material as the first electrodes  120  or the second electrodes  140  as described above. 
     The phosphor layer  70  is formed of a cathode luminescence (CL) type phosphor that is excited by accelerated electrons and generates visible rays. Phosphor that can be used to form the phosphor layer  70  may be phosphor for red light including SrTiO 3 :Pr, Y 2 O 3 :Eu or Y 2 O 3 S:Eu, phosphor for green light including Zn(Ga, Al) 2 O 4 :Mn, Y 3 (Al, Ga) 5 O 12 :Tb, Y 2 SiO 5 :Tb, ZnS:Cu, Al, etc., or phosphor for blue light including Y 2 SiO 5 :Ce, ZnGa 2 O 4 , ZnS:Ag, Al, etc. However, the present invention is not limited to the above-mentioned phosphors. 
     In order to operate the electron emission type backlight unit  110  according to an embodiment of the present invention, a space between the phosphor layer  70  and the electron emission elements  101  is maintained in a vacuum state. Accordingly, a glass frit that seals a vacuum space with the spacer  60  that maintains a distance between the phosphor layer  70  and the electron emission elements  201  may be further used. The glass frit is disposed around the vacuum space to seal it. 
     The electron emission type backlight unit  100  having the above structure operates in the following manner. A negative (−) voltage is applied to the first electrodes  120  disposed in the electron emission elements  101  and a positive (+) voltage is applied to the second electrodes  140  so that electrons are emitted from the electron emission source  150  toward the second electrodes  140  due to an electric field formed between the first electrodes  120  and the second electrodes  140 . In this case, when a larger positive voltage is applied to the third electrodes  80  than to the second electrodes  140 , the electrons emitted from the electron emission source  150  are accelerated toward the third electrodes  80 . The electrons excite the phosphor layer  70  adjacent to the third electrodes  80  so that visible rays are generated therefrom. The emission of electrons may be controlled by a voltage applied to the second electrodes  140 . 
     The negative voltage is applied to the first electrodes  120  to create a proper potential difference required for electron emission between the first electrodes  120  and the second electrodes  140 . 
     The electron emission type backlight unit  100  illustrated in  FIGS. 1 and 2  may be a backlight unit for a non-emissive display device such as a thin film transistor-liquid crystal display (TFT-LCD) used as a surface light source. In addition, in order to generate visible rays from a surface light source and to create images, or in order to constitute a backlight unit having a dimming function, the first electrodes  120  and the second electrodes  140  of the electron emission elements  101  may be disposed to cross one another. Accordingly, one of the first electrodes  120  and the second electrodes  140  are formed to have a main electrode portion and a branch electrode portion. The main electrode portion crosses other electrodes, and the branch electrode portion protrudes from the main electrode portion and is disposed to oppose other electrodes. An electron emission layer may be formed in the branch electrode portion or a portion of the main electrode portion that faces the branch electrode portion. 
       FIG. 3  is a plan view showing the schematic configuration of a flat panel display apparatus according to an embodiment of the present invention. Referring to  FIG. 3 , a flat panel display apparatus  1  according to the present embodiment comprises an electron emission type backlight unit  100 , a first semiconductor  10 , a second semiconductor  20 , a heat sink  30 , and a metal conducting wire  40 . 
     High temperatures are generated by third electrodes (anodes) of a conventional FED type electron emission element due to a large amount of current and several problems occur as described previously. Due to a large amount of current, much heat is generated by the anode of a conventional FED type electron emission element, thereby causing the temperature of the entire panel to increase and leading to several problems, as described above. 
     In embodiments of the present invention, however, heat generated in a front side of the flat panel display apparatus can be effectively dissipated toward a rear side of the flat panel display apparatus by using a thermoelectric device. 
     Specifically, a thermoelectric module electrically connects n-type or p-type thermoelectric semiconductors in series and thermally connects them in parallel. In one embodiment, the thermoelectric module may have an upside down “└” shape (a ┌-shape) to serially circuit bond a p-type element and an n-type element to metal electrodes. When a current flows through from the n-type element to the p-type element so that electrodes at two branching end parts of the p-n couple are negative and positive electrodes, respectively, holes in the p-type element move toward a negative electrode and electrons in the n-type element move toward a positive electrode. As such, since the holes and the electrons are heated from p-n junction electrodes and are moved to the other branching end electrode, an upper junction is cooled and absorbs heat from the periphery and a lower branching end dissipates heat. Such a phenomenon is referred to as the Peltier effect, and is used as a heat pipe for cooling. 
     That is, the Peltier effect occurs when a direct current flows through a circuit formed of two different metals having the same shape, and heat is absorbed at one junction and heat is dissipated at other junction. When the direction of the current is reversed, heat absorption and heat dissipation are reversed as well. Thus, when an electrical load is applied to two different metals having connected cross-sections, heat dissipation and cooling occur simultaneously at each cross-section of the metals and can be expressed by the following equation: 
       | Qp|=αab*T   j   *I=π*I    
     where |Qp| is an absolute value of heat generated per unit time, αab is a relative thermal conducting capability of two metals a and b according to the ambient temperature, π=αab*T j  is a Peltier coefficient, and I is a current. 
     Consequently, in the Peltier effect, heat dissipation and absorption occur when a current flows through a junction between two different materials. If heat is generated when a current flows in one direction, heat is absorbed when the current flows in an opposite direction. Thus, the Peltier effect is reversible. If a current flows through the junction, heat generation or absorption due to the Peltier effect occurs in addition to the Joule heat effect occurring when a current flows through a conductor. 
     Referring back to  FIG. 3 , the third electrodes  80  of the front panel  102  of the electron emission type backlight unit  100  may be generally formed of an electrically conductive material, as described above. Examples of electrically conductive materials include a metal such as Al, Ti, Cr, Ni, Au, Ag, Mo, W, Pt, Cu, or Pd, etc., or an alloy thereof, a printed conductor comprised of glass and a metal, such as Pd, Ag, RuO   2    or Pd—Ag, or a metal oxide, a transparent conductor, such as In 2 O 3  or SnO 2 , or a semiconductor material such as polysilicon, etc. High temperature heat is generated in the third electrodes  80  due to a large amount of current. 
     The heat sink  30  may be formed at a rear side of the flat panel display apparatus  1 . More generally, the heat sink  30  may be formed at a side opposite to the direction in which light is generated (see arrow A of  FIG. 3 ) in the electron emission type backlight unit  100  of the flat panel display apparatus  1 . In other words, in the transmission type flat display panel apparatus  1  in which light generated in the electron emission type backlight unit  100  is emitted through the front panel  102 , an additional heat sink cannot be attached to the third electrodes  80  to dissipate heat generated by the third electrodes  80 . As such, according to an embodiment of the present invention, the heat sink  30  is disposed at the rear side of the flat panel display apparatus  1 . The first semiconductor  10 , the second semiconductor  20 , and the metal conducting wire  40  connecting the first semiconductor  10  and the second semiconductor  20  are provided between the front panel  102  and the heat sink  30 . The heat sink  30  may be formed of a conductive material different from the material of the third electrodes  80  in order to generate the Peltier effect. In one embodiment, the heat sink  30  is a Peltier heat sink. 
     The first semiconductor  10  is formed to be connected to one end of the third electrodes  80  of the front panel  102  and one end of the heat sink  30  via the metal conducting wire  40 . 
     Similarly, the second semiconductor  20  is formed to be connected to another end of the third electrodes  80  of the front panel  102  and another end of the heat sink  30  via the metal conducting wire  40 . 
     The ends of the third electrodes  80  to which the metal conducting wire  40  is connected may be regions that do not transmit light, for example, regions of a black matrix. Due to the above structure, the effect for cooling heat generated in the third electrodes  80  can be achieved without loss of emitted light. 
     As noted above, the first semiconductor  10  may be a P-type semiconductor, and the second semiconductor  20  may be an N-type semiconductor. In this case, when a current is applied to the first semiconductor  10  from the second semiconductor  20 , due to the Peltier effect, the third electrodes  80  act as a cooling unit, and the heat sink  30  acts as a heating unit. Thus, heat generated by the third electrodes  80  is transferred to the heat sink  30  and is dissipated toward the outside of the flat panel display apparatus  1 . 
     The first semiconductor  10  and the second semiconductor  20  may be disposed on both side surfaces of the flat panel display apparatus  1 , as illustrated in  FIG. 3 . 
     Due to the above structure of embodiments of the present invention, heat generated in the third electrodes and in the front substrate in which the third electrodes are installed can be effectively dissipated. Thus, the life span and various characteristics of the flat panel display apparatus  1  can be improved. In addition, since heat is controlled using an electronic device, precise temperature control can be achieved by embodiments of the present invention. In addition, rapid cooling can be performed after power is supplied, and local cooling can also be performed. Furthermore, the flat panel display apparatus according to embodiments of the present invention can be operated in any position or direction regardless of the device&#39;s orientation. Furthermore, the cooling unit can be downsized and lightened, and low noise and low vibration cooling can be implemented. 
     The electron emission type backlight  100  is illustrated as an emission unit in which light is generated, but the present invention is not limited thereto. In other words, the present invention can be applied to any flat panel display apparatus in which heat is generated, such as an LCD or a plasma display apparatus, and in particular, a transmission type flat panel display apparatus. 
     In the flat panel display apparatus according to embodiments of the present invention, heat generated by the anode and the front substrate in which the anode is installed can be effectively dissipated. 
     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.