Patent Publication Number: US-7714495-B2

Title: Electron emission display having an optically transmissive anode electrode

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0103525, filed on Oct. 31, 2005, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an electron emission display, and more particularly, to an electron emission display having an anode electrode which is coupled to a phosphor layer to receive a high voltage required for accelerating electron beams. 
   2. Description of Related Art 
   Generally, electron emission elements can be classified into those using hot cathodes as an electron emission source, and those using cold cathodes as the electron emission source. 
   There are several types of cold cathode electron emission elements, including Field Emitter Array (FEA) elements, Surface Conduction Emitter (SCE) elements, Metal-Insulator-Metal (MIM) elements, and Metal-Insulator-Semiconductor (MIS) elements. 
   The electron emission elements are arrayed on a first substrate to form an electron emission device. A light emission unit having phosphor layers and an anode electrode is formed on a second substrate. The electron emission device, the second substrate, and the light emission unit establish an electron emission display. 
   In the electron emission display, there is provided an anode electrode for directing the electrons emitted from the first substrate. The anode electrode receives a high voltage required to accelerate the electron beams, thereby reducing the extent to which the surface of the phosphor layer is charged by the electrons. 
   The anode electrode is formed of a transparent conductive material such as indium tin oxide (ITO) or a metallic material such as aluminum. The anode electrode is coupled to the phosphor layers facing the first substrate. The anode electrode functions to heighten the screen luminance by receiving a high voltage required to accelerate the electron beams and by reflecting the visible rays radiated from the phosphor layers to the first substrate back toward the second substrate. 
   The anode electrode is formed by (1) forming an interlayer formed of a polymer material that will be vaporized during a firing process; (2) depositing a conductive material, for example, aluminum, on the interlayer; and (3) removing the interlayer by vaporizing the interlayer material through fine pores of the conductive material. 
   The yield and performance of the anode electrode are greatly affected by a deposition thickness of the conductive material, a distance between the anode electrode and the phosphor layer, a distribution of fine pores in the conductive material, and other similar factors. For example, if the anode electrode lacks a proper distribution of fine pores (e.g., has a relatively low density of the fine pores), it may be easily damaged during the firing process for removing the interlayer, and the light reflective efficiency may be reduced. 
   That is, if the anode electrode is too densely deposited to have the proper distribution of fine pores, the interlayer material cannot be completely vaporized through the fine pores during the firing process, thereby causing the anode electrode to swell. 
   As a result, a portion of the anode electrode peels off. The damaged portion of the anode electrode cannot properly accelerate the electron beam from the first substrate, and thus the light emission efficiency of the phosphor layer corresponding to the damaged portion of the anode electrode is reduced. 
   By contrast, when the density of the fine pores is too high, the light reflective efficiency of the anode electrode is lowered such that the luminance of the image deteriorates. 
   SUMMARY OF THE INVENTION 
   An aspect of the present invention provides an electron emission display that can improve the luminance of an image by reducing the damage to an anode electrode during a firing process for vaporizing an interlayer, and by enhancing a light reflective efficiency of the anode electrode. 
   According to an exemplary embodiment of the present invention, there is provided an electron emission display including: a first substrate, a second substrate facing the first substrate; a plurality of electron emission regions provided on the first substrate; a plurality of phosphor layers formed on a first surface of the second substrate; a black layer formed on the first surface of the second substrate between at least two of the phosphor layers; and an anode electrode coupled to the phosphor and black layers, wherein the anode electrode has a light transmissivity ranging from about 3% to about 15%. 
   The anode electrode may contact the black layer and may be spaced apart from the phosphor layers by a distance (which may be predetermined) therebetween. 
   The distance may be within a range from about 3 μm to about 6 μm. 
   The electron emission display may further include a plurality of cathode electrodes formed on the first substrate; an insulation layer formed on the first substrate and covering the cathode electrodes; and a plurality of gate electrodes formed on the insulation layer, wherein the electron emission regions are electrically connected to the cathode electrodes. 
   The electron emission display may further include a focusing electrode disposed above and insulated from the cathode and gate electrodes. 
   The electron emission display may further include: a first electrode formed on the first substrate, a second electrode formed on the first substrate and spaced apart from the first electrode; a first conductive layer formed on the first substrate and partly covering surfaces of the first electrode, and a second conductive layer formed on the first substrate and partly covering surfaces of the second electrode, wherein at least one of the electron emission regions is formed between the first and second conductive layers. 
   The electron emission regions may be formed of a material selected from the group consisting of carbon nanotubes, graphite, graphite nanofibers, diamonds, diamond like carbon, C 60 , silicon nanowires, and combinations thereof. 
   According to another exemplary embodiment of the present invention, there is provided a method of manufacturing an electron emission display, including: forming phosphor and black layers on a substrate; forming an interlayer on the phosphor and black layers; removing a portion of the interlayer that corresponds to the black layers; depositing a conductive material for an anode electrode on the substrate; and removing the interlayer through a firing process. 
   A light transmissivity of the anode electrode may be adjusted varying a thickness and/or a roughness of the interlayer. 
   The light transmissivity of the anode electrode may be within a range from about 3% to about 15%. 
   The interlayer may be formed to have a thickness within a range from about 3 μm to about 6 μm such that, when the interlayer is removed through the firing process, a distance between the anode electrode and the phosphor layers is within the range from about 3 μm to about 6 μm. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention. 
       FIG. 1  is a partial exploded perspective view of an electron emission display according an embodiment of the present invention; 
       FIG. 2  is a partial sectional view of the electron emission display of  FIG. 1 ; and 
       FIG. 3  is a partial sectional view of an electron emission display according to another embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following detailed description, only certain exemplary embodiments of the present invention are shown and described, by way of illustration. As those skilled in the art would recognize, the described exemplary embodiments may be modified in various ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive. 
     FIGS. 1 through 3  show an electron emission display  1  according to an embodiment of the present invention. In this exemplary embodiment, the electron emission display  1  having an array of FEA elements is illustrated. 
   Referring to  FIGS. 1 and 2 , the electron emission display  1  includes first and second substrates  10  and  12  facing each other with a distance (which may be predetermined) therebetween. A sealing member (not shown) is provided at the peripheries of the first and second substrates  10  and  12  to seal them together. The space defined by the first and second substrates and the sealing member is exhausted to form a vacuum envelope (or vacuum chamber) kept to a degree of vacuum of about 10 −6  Torr. 
   A plurality of electron emission elements are arrayed on the first substrate  10  to form an electron emission device  100 . The electron emission device  100  is combined with a light emission unit  110  provided on the second substrate  12  to form the electron emission display  1 . 
   A plurality of cathode electrodes (first driving electrodes)  14  are arranged on the first substrate  10  in a stripe pattern extending along a first direction, and a first insulation layer  16  is formed on the first substrate  10  to cover the cathode electrodes  14 . A plurality of gate electrodes (second driving electrodes)  18  are formed on the first insulation layer  16  in a stripe pattern extending along a second direction crossing the first direction at a right angle. 
   Each crossed area of the cathode and gate electrodes  14  and  18  defines a unit pixel (or pixel unit). One or more electron emission regions  20  are formed on the cathode electrode  14  at each unit pixel. Openings  161  and  181  corresponding to the electron emission regions  20  are formed on the first insulation layer  16  and the gate electrodes  18  to expose the electron emission regions  20 . 
   The electron emission regions  20  may be formed of a material which emits electrons when an electric field is applied thereto under a vacuum atmosphere, such as a carbonaceous material and/or a nanometer-sized material. For example, the electron emission regions  20  may be formed of carbon nanotubes, graphite, graphite nanofibers, diamonds, diamond-like carbon, C 60 , silicon nanowires, or combinations thereof. Alternatively, the electron emission regions  20  may be formed as a molybdenum-based or silicon-based pointed-tip structure. 
   In the foregoing description, the gate electrodes  18  are arranged above the cathode electrodes  14  with the first insulation layer  16  interposed therebetween, but the invention is not limited to this case. That is, the gate electrodes may be disposed under the cathode electrodes with the first insulation layer interposed therebetween. In this case, the electron emission regions may be formed on sidewalls of the cathode electrodes on the first insulation layer. 
   A second insulation layer  24  is formed on the first insulation layer  16  covering the gate electrodes  18 , and a focusing electrode  22  is formed on the second insulation layer  24 . The gate electrodes  18  are insulated from the focusing electrode  22  by the second insulation layer  24 . Openings  221  and  241  through which electron beams pass are formed through the second insulation layer  24  and the focusing electrode  22 . Each one of the openings  221  of the focusing electrode  22  is formed to correspond to one unit pixel to generally focus the electrons emitted from one unit pixel. 
   Phosphor layers  26  such as red, green and blue phosphor layers  26 R,  26 G and  26 B are formed on a surface of the second substrate  12  facing the first substrate  10 , and black layers  28  for enhancing the contrast of the screen are arranged between the phosphor layers  26  (e.g., a black layer  28  is formed between at least two of the phosphor layers  26 ). The phosphor layers  26  may be formed to correspond to the respective unit pixels defined on the first substrate  10 . 
   An anode electrode  30  formed of a conductive material such as aluminum is coupled to the phosphor and black layers  26  and  28 . The anode electrode  30  functions to heighten the screen luminance by receiving a high voltage required to accelerate the electron beams and by reflecting the visible rays radiated from the phosphor layers  26  to the first substrate  10  back toward the second substrate  12 . 
   Alternatively, the anode electrode  30  can be formed of a transparent conductive material, such as Indium Tin Oxide (ITO), instead of the metallic material. In this case, the anode electrode  30  is placed on the second substrate  12 , and the phosphor and black layers  26  and  28  are formed on the anode electrode  30 . Alternatively, the anode electrode  30  may include a transparent conductive layer and a metallic layer. 
   The anode electrode  30  has a light transmissivity within a range (which may be predetermined) defined by the distribution of fine pores dispersed in the anode electrode  30 . When the distribution of the fine pores is represented as the light transmissivity, the anode electrode  30  of this embodiment is designed to have a light transmissivity within a range from about 3% to about 15%. 
   When the transmissivity of the anode electrode  30  is less than 3%, an interlayer material used in a process for forming the anode electrode  30  may not be effectively vaporized. In order to form the anode electrode  30 , an interlayer is formed on the phosphor layers  26 , and the anode electrode  30  is formed by depositing a conductive material, such as aluminum, on the interlayer. Then, a firing process is performed to remove the interlayer by vaporizing the interlayer. At this point, if the transmissivity of the anode electrode  30  is less than 3%, the interlayer layer material is not effectively vaporized. As a result, a portion of the anode electrode  30  may swell out and peel off, and the anode electrode  30  may be damaged. 
   In addition, a medium voltage of about 5 kV is applied to the anode electrode  30 . Therefore, when the light transmissivity of the anode electrode  30  is less than 3%, the damaged portion of the anode electrode  30  cannot properly accelerate the electron beam from the first substrate  10 . Thus, an amount of electrons reaching the phosphor layer  26  is reduced, thereby deteriorating the luminance of the image. On the other hand, when the light transmissivity of the anode electrode  30  is greater than 15%, the light reflective efficiency of the anode electrode  30  is lowered, thereby deteriorating the luminance of the image. 
   Therefore, the distribution of the fine pores in the anode electrode  30  is chosen to provide a range from 3% to 15% light transmissivity to the anode electrode  30 . This distribution of fine pores reduces damage to the anode electrode  30  and allows a sufficient amount of the electrons to reach the phosphor layer  26  while increasing the light reflective efficiency of the anode electrode  30 . Therefore, the luminance of the image can be enhanced. 
   In this embodiment, the anode electrode  30  is arranged such that it contacts the black layer(s)  28  and is spaced apart from the phosphor layers  26  by a distance (which may be predetermined) within a range from about 3 μl to about 6 μm. Therefore, the bonding force of the anode electrode  30  to the second substrate  12  increases by the contact with the black layer(s)  28 . In addition, when the anode electrode  30  is spaced apart from the phosphor layers  26 , it can obtain a sufficient flatness without being affected by a surface roughness of the phosphor layers  26 , thereby maximizing the light reflective efficiency. 
   The above-described anode electrode  30  can be formed by (1) forming an interlayer on the phosphor and black layers  26  and  28 ; (2) removing a portion of the interlayer corresponding to the black layer  28 ; (3) depositing a conductive material, such as aluminum, on the entire surface of the second substrate  12 ; and (4) removing the rest of the interlayer through a firing process. A photoresistant material can be used as the interlayer. The light transmissivity of the anode electrode  30  can be effectively adjusted by varying a thickness and/or a surface roughness of the interlayer. 
   Disposed between the first and second substrates  10  and  12  are spacers  32  for uniformly maintaining a gap between the first and second substrates  10  and  12 . The spacers  32  are arranged corresponding to the black layer(s)  28  so that the spacers  32  do not obstruct the phosphor layers  26 . 
   The above-described electron emission display is driven when a voltage (which may be predetermined) is applied to the cathode, gate, focusing, and anode electrodes  14 ,  18 ,  22 , and  30 . 
   For example, the cathode electrodes  14  may serve as scanning electrodes receiving a scanning drive voltage, and the gate electrodes  18  may function as data electrodes receiving a data drive voltage (or vise versa). The focusing electrode  22  receives a voltage for focusing the electron beams, for example, 0V or a negative direct current voltage ranging from several to several tens of volts. The anode electrode  30  receives a voltage for accelerating the electron beams, for example, a positive direct current voltage ranging from hundreds through thousands of volts. 
   Electric fields are formed around the electron emission regions  20  at unit pixels where a voltage difference between the cathode and gate electrodes  14  and  18  is equal to or higher than a threshold value and thus the electrons are emitted from the electron emission regions  20 . The emitted electrons are attracted to the corresponding phosphor layers  26  by the high voltage applied to the anode electrode  30 , and the electrons strike the phosphor layers  26 , thereby exciting the phosphor layers  26  to emit light. 
   During the above-described driving operation by the anode electrode  30  having the above-described light transmissivity, the light reflective efficiency of the anode electrode  30  increases while a sufficient amount of electrons lands on the phosphor layers  26 , thereby realizing a high luminance image. In addition, the anode electrode  30  is stable against the high voltage. 
     FIG. 3  shows an electron emission display  1 ′ according to another embodiment of the present invention. In this exemplary embodiment, the electron emission display  1 ′ having an array of SCE elements is illustrated. 
   First and second electrodes  36  and  38  are arranged on a first substrate  34  and spaced apart from each other. Electron emission regions  44  are formed between the first and second electrodes  36  and  38 . First and second conductive layers  40  and  42  are formed on the first substrate  34  between the first electrode  36  and the electron emission region  44 , and between the electron emission region  44  and the second electrode  38 , respectively. The first and second conductive layers  40  and  42  partly cover the first and second electrodes  36  and  38 . The first and second electrodes  36  and  38  are electrically connected to the electron emission region  44  by the first and second conductive layers  40  and  42 . 
   In this embodiment, the first and second electrodes  36  and  38  may be formed of a variety of conductive materials. The first and second conductive layers  40  and  42  may be particle-thin film formed of a conductive material such as nickel, gold, platinum, or palladium. 
   The electron emission regions  44  may be formed of graphite carbon and/or carbon compound. For example, the electron emission regions  44  may be formed of a material selected from the group consisting of carbon nanotubes, graphite, graphite nanofibers, diamonds, diamond-like carbon, fullerene (C 60 ), silicon nanowires, and combinations thereof. 
   When voltages are applied to the first and second electrodes  36  and  38 , current flows in a direction parallel with surfaces of the electron emission regions  44  through the first and second conductive layers  40  and  42  to realize the surface conduction electron emission. The emitted electrons are attracted to phosphor layers  26 ′ (with black layers  28 ′ therebetween) by a high voltage applied to an anode electrode  30 ′ at a second substrate  12 ′, and strike and excite the corresponding phosphor layers  26 ′ formed on the second substrate  12 ′. 
   Although the electron emission displays  1  and  1 ′ having FEA elements and SCE elements are described in the above exemplary embodiments, the present invention is not limited to these examples. That is, the present invention may be applied to an electron emission display having other types of electron emission elements, such as MIM elements and MIS elements. 
   According to embodiments of the present invention, by providing the anode electrode with a light transmissivity within the above-described range, the interlayer material can be effectively vaporized during the interlayer firing process. As a result, damage to the anode electrode can be reduced or prevented. Furthermore, the electron beam transmissivity and the light reflective efficiency can be increased. 
   While the invention has been described in connection with certain exemplary embodiments, it is to be understood by those skilled in the art that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications included within the spirit and scope of the appended claims and equivalents thereof.