Abstract:
A Field Emission Device (FED) and its method of manufacture includes: forming a substrate; forming a cathode having a cathode aperture on an upper surface of the substrate; forming a material layer having a first through hole with a smaller diameter than that of the cathode aperture on an upper surface of the cathode; forming a first insulator having a first cavity on an upper surface of the material layer; forming a gate electrode having a second through hole on an upper surface of the first insulator; and forming an emitter in a central portion of the cathode aperture.

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 DEVICE AND METHOD OF MANUFACTURING THE SAME earlier filed in the Korean Intellectual Property Office on 14 Sep. 2004 and there duly assigned Serial No. 10-2004-0073365. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a Field Emission Device (FED) and its method of manufacture, and more particularly, to an FED having a good ability to focus electron beams, thereby attaining a high brightness, and its method of manufacture. 
   2. Description of the Related Art 
   Display devices for conventional information communication media include monitors for Personal Computers (PCs), TV receivers, and the like. These display devices are divided into Cathode Ray Tubes (CRTs) and flat panel displays. The CRTs use high-speed thermal electron emission. Improvements in flat panel displays have recently been occurring at a high rate. The flat panel displays include Liquid Crystal Displays (LCDs), Plasma Display Panels (PDPs), Field Emission Devices (FEDs), and the like. 
   FEDs operate using the following method. First, a strong electric field is formed between a gate electrode and emitters, which are disposed at predetermined intervals on a cathode. As a result, electrons are emitted from the emitters. The electrons collide with a fluorescent layer formed on an anode, thus emitting light. An FED has a thickness of a few centimeters. In addition, FEDs have many advantages, including wide viewing angles, low power consumption, low manufacturing costs, and the like. Therefore, FEDs have drawn much attention as a next-generation display, along with LCDs and PDPs. 
   An FED includes a cathode, a first insulator, and a gate electrode sequentially deposited on a substrate. An emitter aperture is formed in the first insulator to expose an upper surface of the cathode. An emitter is placed inside the emitter aperture. A second insulator is formed on the gate electrode, and a focus electrode is formed on an upper surface of the second insulator to focus electron beams emitted from the emitter. 
   However, when a high voltage is supplied to an anode of this FED to obtain a high brightness, electron beams disperse, thus reducing color purity. 
   SUMMARY OF THE INVENTION 
   The present invention provides a Field Emission Device (FED) having a good ability to focus electron beams, thereby attaining a high brightness, and its method of manufacture. 
   According to one aspect of the present invention, a Field Emission Device (FED) is provided comprising: a substrate; a cathode having a cathode aperture and arranged on an upper surface of the substrate; a material layer having a first through hole of a smaller diameter than that of the cathode aperture and arranged on an upper surface of the cathode, the first through hole being arranged above a central portion of the cathode aperture; a first insulator having a first cavity connected to the first through hole and arranged on an upper surface of the material layer; a gate electrode having a second through hole connected to the first cavity and arranged on an upper surface of the first insulator; and an emitter arranged in the central portion of the cathode aperture. 
   A height of the emitter is preferably equal to or less than a height of the cathode aperture. 
   The emitter preferably comprises carbon nano-tubes (CNTs), graphite nano-particles, or nano-diamonds. 
   The height of the cathode aperture is preferably less than 5 μm. The cathode preferably comprises a first electrode arranged on the upper surface of the substrate, and a second electrode having the cathode aperture arranged on the first electrode. 
   A thickness of the first electrode is preferably less than 0.1 μm. 
   The first electrode preferably comprises Indium Tin Oxide (ITO). 
   A thickness of the second electrode is preferably less than 5 μM. The second electrode preferably comprises at least one material selected from the group consisting of Cr, Ag, Al, and Au. 
   The material layer preferably comprises amorphous silicon (a-Si). 
   The FED preferably further comprises a second insulator having a second cavity connected to the second through hole and arranged on an upper surface of the gate electrode. 
   The FED preferably further comprises a focus electrode having a third through hole connected to the second cavity and arranged on an upper surface of the second insulator. 
   According to another aspect of the present invention, a method of manufacturing a Field Emission Device (FED) is provided, the method comprising: forming a cathode on an upper surface of a substrate; forming a predetermined material layer on an upper surface of the cathode and patterning the predetermined material layer to form a first through hole; etching a portion of the cathode exposed by the first through hole to form a cathode aperture, wherein the cathode aperture has a larger diameter than that of the first through hole; forming a first insulator on an upper surface of the material layer; forming a gate electrode on an upper surface of the first insulator and then patterning the gate electrode to form a second through hole; forming a second insulator on an upper surface of the gate electrode; forming a focus electrode on an upper surface of the second insulator and patterning the focus electrode to form a third through hole; etching the second insulator exposed by the third through hole to form a second cavity; etching the first insulator exposed by the second through hole to form a first cavity; and forming an emitter in a central portion of the cathode aperture. 
   Forming the cathode preferably further comprises forming a first electrode on the upper surface of the substrate, and preferably forming a second electrode on an upper surface of the first electrode. 
   The first electrode is preferably formed to a thickness of less than 0.1 μm. The first electrode is preferably formed of Indium Tin Oxide (ITO). 
   The second electrode is preferably formed to a thickness of less than 5 μm. The second electrode is preferably formed of at least one material selected from the group consisting of Cr, Ag, Al, and Au. 
   The material layer is preferably formed of amorphous silicon (a-Si). 
   Forming the cathode hole preferably comprises isotropically etching a portion of the second electrode exposed by the first through hole. 
   The height of the emitter is preferably formed to be equal to or less than the height of the cathode aperture. 
   Forming the emitter preferably comprises filling the cathode aperture with an electron emission material and patterning the filled electron emission material. The electron emission material is preferably formed of carbon nano-tubes (CNTs), graphite nano-particles, or nano-diamonds. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof, will be readily apparent as the present invention 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 sectional view of a Field Emission Device (FED); 
       FIG. 2  is a sectional view of an FED according to an embodiment of the present invention; 
       FIGS. 3A through 3D  are Scanning Electron Microscopy (SEM) images of an FED according to an embodiment of the present invention; 
       FIGS. 4A through 4D  are images formed by an FED according to an embodiment of the present invention when 70V, 80V, 90V, and 100V are respectively supplied to a gate electrode; and 
       FIGS. 5A through 5I  are views of a method of manufacture of an FED according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a sectional view of an FED. Referring to  FIG. 1 , a cathode  12 , a first insulator  14 , and a gate electrode  16  are sequentially deposited on a substrate  10 . An emitter aperture  25  is formed in the first insulator  14  to expose an upper surface of the cathode  12 . An emitter  30  is placed inside the emitter aperture  25 . A second insulator  18  is formed on the gate electrode  16 , and a focus electrode  20  is formed on an upper surface of the second insulator  18  to focus electron beams emitted from the emitter  30 . 
   However, when a high voltage is supplied to an anode (not shown) of such an FED to obtain a high brightness, electron beams disperse, thus reducing color purity. 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the present invention are shown. Like reference numerals in the drawings denote like elements. 
     FIG. 2  is a sectional view of a FED according to an embodiment of the present invention. 
   Referring to  FIG. 2 , the FED includes a substrate  110 , a cathode  112  in which a cathode aperture  212  is formed, a gate electrode  116  formed on the cathode  112 , and an emitter  130  formed in a central portion of the cathode aperture  212 . 
   The substrate  110  can be composed of glass. The cathode electrode  112  includes a first electrode  112   a  formed on an upper surface of the substrate and a second electrode  112   b  formed on an upper surface of the first electrode  112   a . The cathode  112  is much thicker than a cathode of conventional FEDs. The cathode aperture  212  is formed in the second electrode  112   b.    
   The first electrode  112   a  has the thickness of less than about 0.1 μm and is composed of a transparent conducting material such as Indium Tin Oxide (ITO). The upper surface of the first electrode  112   a  forms a bottom surface of the cathode aperture  212 . The second electrode  112   b  is composed of at least one material selected from the group consisting of Cr, Ag, Al, and Au. The second electrode  112   b  has a thickness of less than 5 μm, and preferably, 0.1 to 5 μm. Since the cathode aperture  212  penetrates the second electrode  112   b , the cathode aperture  212  has the same height as the second electrode  112   b.    
   A predetermined material layer  113  is formed on an upper surface of the second electrode  112   b  to cover a portion of an upper surface of the cathode aperture  212 . A first through hole  213  is formed in the material layer  113  above the central portion of the cathode aperture  212 . The first through hole  213  has a smaller diameter than that of the cathode aperture  212 . The material layer  113  is composed of amorphous silicon (a-Si), for example. 
   The emitter  130  is formed in the central portion of the cathode aperture  212 . The emitter  130  has a much smaller diameter than that of the cathode aperture  212 . The height of the emitter  130  is equal to or less than the height of the cathode aperture  212 . Therefore, the electron beam produced by the emitter  130  can be more focused than in conventional FEDs. 
   The emitter  130  is composed of carbon nano-tubes (CNTs), graphite nano-particles, nano-diamonds, or the like. 
   A first insulator  114  is formed to a predetermined thickness on an upper surface of the material layer  113 . A first cavity  214  connected to the first through hole  213  is formed in the first insulator  114 . The first insulator  114  is composed of an insulating material, such as SiO 2 . 
   A gate electrode  116  is formed on an upper surface of the first insulator  114  to extract electrons from the emitter  130 . The gate electrode  116  is disposed perpendicular to the cathode  112 . A second through hole  216  connected to the first cavity  214  is formed in the gate electrode  116 . The gate electrode  116  is composed of a conducting metal or a transparent conducting material, for example. The transparent conducting material can be, for example, ITO. 
   A second insulator  118  is formed to a predetermined thickness on an upper surface of the gate electrode  116 . A second cavity  218  connected to the second through hole  216  is formed in the second insulator  118 . The second insulator  118  is composed of an insulating material, such as SiO 2 . 
   A focus electrode  120  is formed on an upper surface of the second insulator  118 . A third through hole  220  connected to the second cavity  218  is formed in the focus electrode  120 . The focus electrode  120  controls the loci of electron beams emitted from the emitter  130 . The focus electrode  120  is composed of a conducting metal or a transparent conducting material, for example. The transparent conducting material can be, for example, ITO. 
   In the FED according to the present embodiment, the emitter  130  has a much smaller diameter than that of the cathode aperture  212 , and the height of the emitter  130  formed in the central portion of the cathode aperture  212  is equal to or less than the height of the cathode aperture  212 . As a result, the electron beams emitted from the emitter  130  are more focused than in conventional FEDs. 
     FIGS. 3A through 3D  are Scanning Electron Microscopy (SEM) images of an FED according to an embodiment of the present invention. In more detail,  FIGS. 3A and 3B  are SEM images of cross-sections of the FED.  FIG. 3C  is a plan view of the FED, and  FIG. 3D  is a magnified view of the image of  FIG. 3C . Referring to  FIGS. 3A through 3D , a thick cathode electrode having a cathode aperture is formed on a substrate. An emitter is formed in the central portion of the cathode aperture, and has a much smaller diameter than that of the cathode aperture. 
     FIGS. 4A through 4D  are images formed by the FED according to an embodiment of the present invention when 70V, 80V, 90V, and 100V are respectively supplied to a gate electrode. A voltage of 1.5 kV is supplied to an anode, and a voltage of 0V is supplied to a focus electrode. Referring to  FIGS. 4A through 4D , a higher voltage supplied to the gate electrode results in a higher resolution. 
   A method of manufacturing an FED according to an embodiment of the present invention will now be described with reference to  FIGS. 5A through 5I . 
   First, referring to  FIG. 5A , a cathode  112  is formed on a substrate  110 . The cathode  112  is composed of first and second electrodes  112   a  and  112   b . The substrate  110  is composed of glass, for example. The first electrode  112   a  is formed by depositing a transparent conducting material, such as ITO, to the thickness of less than about 0.1 μm on an upper surface of the substrate  110 . The second electrode  112   b  is formed by depositing at least one material selected from the group consisting of Cr, Ag, Al, and Au on an upper surface of a first electrode  112   a . The second electrode  112   b  has a thickness of less than 5 μm, and preferably, 0.1 to 5 μm. 
   Referring to  FIG. 5B , a predetermined material layer  113  is formed on an upper surface of the second electrode  112   b , and patterned to form a first through hole  213 . The material layer  113  is composed of amorphous silicon (a-Si), for example. 
   Referring to  FIG. 5C , a cathode aperture  212  is formed by isotropically etching a portion of the second electrode  112   b  exposed by the first through hole  213 . As a result, the cathode aperture  212  formed in the second electrode  112   b  has a larger diameter than that of the first through hole  213 . 
   Referring to  FIG. 5D , a first insulator  114  is formed on an upper surface of the material layer  113 , and then a gate electrode  116  is formed on the first insulator  114 . The first insulator  114  is formed by depositing an insulating material, such as SiO 2 , to a predetermined thickness on the upper surface of the material layer  113 . The gate electrode  116  is formed by depositing a metal or a transparent conducting material, for example, on an upper surface of the first insulator  114 . The transparent conducting material is, for example, ITO. 
   Referring to  FIG. 5E , the gate electrode  116  is patterned to form a second through hole  216 . 
   Referring to  FIG. 5F , a second insulator  118  is formed on an upper surface of the gate electrode  116 , and then a focus electrode  120  is formed on the second insulator  118 . The second insulator layer  118  is formed by depositing an insulating material, such as SiO 2 , to a predetermined thickness on the upper surface of the gate electrode  116 . The focus electrode  120  is formed by depositing a metal or a transparent conducting material on an upper surface of the second insulator  118 . The transparent conducting material is, for example, ITO. 
   Referring to  FIG. 5G , the focus electrode  120  is patterned to form a third through hole  220 . 
   Referring to  FIG. 5H , a second cavity  218  connected to the third through hole  220  is formed in the second insulator  118 , and a first cavity  214  connected to the second through hole  216  is formed in the first insulator  114 . The second cavity  218  is formed by etching the second insulator  118  exposed by the third through hole  220 . The first cavity  214  is formed by etching a portion of the first insulator  114  exposed by the second through hole  216 . 
   Referring to  FIG. 5I , an emitter is formed in a central portion of the cathode aperture  212 . The height of the emitter  130  is equal to or less than the height of the cathode aperture  212 . The emitter  212  is formed by filling the cathode aperture  212  with a predetermined electron emission material and then patterning the electron emission material. The electron emission material is, for example, CNT, graphite nano-particles, nano-diamonds, or the like. 
   A FED according an embodiment of the present invention includes a cathode having a greater thickness than an electrode of a conventional FED. In addition, the cathode has a cathode aperture having a greater diameter than that of the emitter. As a result, in the FED according to the present invention, electron beams are highly focused to obtain a high brightness, thereby realizing high-resolution images. 
   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 modifications in form and detail can be made therein without departing from the spirit and scope of the present invention as defined by the following claims.