Abstract:
An electron emission device includes components for inhibiting the diffusion of electron beams, decreasing the light emission of incorrect colors, and preventing the diode type electron emission due to the anode electric field. In particular, the electron emission device includes a substrate with grooves, and electron emission regions filling the grooves. Cathode electrodes are provided at the substrate such that the cathode electrodes are electrically connected to the electron emission regions. Gate electrodes are formed over the cathode electrodes while interposing an insulating layer.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to and the benefit of Korean Patent Application No. 10-2004-0012628 filed on Feb. 25, 2004 in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an electron emission device, and in particular, to an electron emission device which has electron emission regions (or sources) formed with a material for emitting electrons when applied with an electric field under a vacuum atmosphere, and a method of fabricating the same.  
         [0004]     2. Description of Related Art  
         [0005]     Generally, the electron emission devices can be classified into two types. A first type uses a hot (or thermoionic) cathode as an electron emission source, and a second type uses a cold cathode as an electron emission source.  
         [0006]     Also, in the second type of electron emission devices, there are a field emitter array (FEA) type, a surface conduction emitter (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.  
         [0007]     The FEA type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as the electron emission source, electrons are easily emitted from the material in a vacuum atmosphere due to an electric field. A sharp-pointed tip structure based on molybdenum (Mo) or silicon (Si), or a carbonaceous material, such as carbon nanotube, graphite and/or diamond-like carbon, has been developed to be used as the electron emission source.  
         [0008]     In an exemplary FEA type electron emission device, cathode electrodes and an insulating layer are formed on a substrate, and gate electrodes are formed on the insulating layer while crossing the cathode electrodes. Opening portions are formed at the gate electrodes and the insulating layer per the crossed regions thereof to partially expose the surface of the cathode electrodes, and electron emission regions are formed on the cathode electrodes within the opening portions.  
         [0009]     The insulating layer can be formed through paste printing such that it has a thickness of 5 μm or more. A mask layer can be formed on the gate electrodes, and the gate electrodes and the insulating layer can then be wet-etched to form opening portions thereat.  
         [0010]     However, when the wet etching is used to form opening portions at the insulating layer, the so-called under-cut phenomenon is generated at the portion of the insulating layer opposite to the etching initiation point thereof due to the etching isotropy, in which the opening width is narrowed as compared to that at the etching initiation point. For this reason, the bottom-sided etching width is smaller than the top-sided etching width with the openings of the insulating layer, and hence, the exposure area of the cathode electrodes to be formed with electron emission regions is reduced.  
         [0011]     Accordingly, with the above-structured electron emission device, it is difficult to form micro pixels and fabricate a high resolution display device, and as the amount of the electron emission material to be given on the cathode electrodes is relatively small, it is also difficult to obtain a high luminance display screen.  
         [0012]     In order to solve the above problem, an insulating layer can be formed with SiO 2  through chemical vapor deposition (CVD) such that it has a thickness of 1-3 μm. However, in this case, as the electron emission regions are formed with a thickness of 2-5 μm due to the characteristic of the thick film processing, such as screen printing, the electron emission regions may be placed higher than the gate electrodes. Consequently, the electrons emitted from the electron emission regions are not focused and/or influenced by the gate electrodes and thereby cause a considerable diffusion of electron beams and/or a diode type electron emission where electrons are mistakenly emitted from the electron emission regions at the pixels to be off-stated due to the influence of the anode electric field.  
       SUMMARY OF THE INVENTION  
       [0013]     In an aspect of the present invention, an electron emission device inhibits the diffusion of electron beams to prevent the incorrect colors from being light-emitted, and minimizes the diode type emission of electrons.  
         [0014]     In an exemplary embodiment of the present invention, the electron emission device includes a substrate having grooves, and electron emission regions formed into the grooves. Cathode electrodes are formed on the substrate such that they are electrically connected to the electron emission regions. Gate electrodes are formed over the cathode electrodes and an insulation layer is located between the cathode electrodes and the gate electrodes.  
         [0015]     The cathode electrodes may be formed with a metallic material selected from chromium (Cr), aluminum (Al), and/or molybdenum (Mo) materials. The cathode electrodes may be placed over the grooves with opening portions corresponding thereto. The height difference between the top surface of the electron emission region and the surface of the cathode electrode may be 1 μm or less.  
         [0016]     The cathode electrodes may be formed on a top surface of the substrate and an inner wall of the grooves and/or with a transparent conductive material. A resistance layer or a nontransparent metallic layer may be formed on a top surface of the cathode electrodes that is not located in an inner surface of the grooves.  
         [0017]     The grooves may have a depth of about 2-3 μm, and the electron emission regions are formed with a material selected from carbon nanotube, graphite, graphite nanofiber, diamond, diamond-like carbon, C 60 , and/or silicon nanowire materials.  
         [0018]     In an exemplary embodiment of the present invention, a method of fabricating the electron emission device is provided. The method includes cathode electrodes that are formed on the substrate such that they have first opening portions. Portions of the substrate exposed through the first opening portions are etched to form grooves. An insulating layer and gate electrodes are formed on the cathode electrodes such that they have respective second and third opening portions corresponding to the grooves. Electron emission regions are formed within the grooves and the first opening portions of the cathode electrodes by filling them with an electron emission material.  
         [0019]     In an exemplary embodiment of the present invention, a method of fabricating an electron emission device is provided. The method includes a substrate that is partially etched to form grooves. A transparent electrode material is coated onto a surface of the substrate including an inner wall of the grooves to form cathode electrodes. An insulating layer and gate electrodes are formed on the cathode electrodes such that they have respective first and second opening portions corresponding to the grooves. Electron emission regions are formed over the cathode electrodes within the inner wall of the grooves with an electron emission material. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     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.  
         [0021]      FIG. 1  is a partial exploded perspective view of an electron emission device according to a first embodiment of the present invention.  
         [0022]      FIG. 2  is a partial sectional view of the electron emission device according to the first embodiment of the present invention.  
         [0023]      FIGS. 3A, 3B ,  3 C,  3 D, and  3 E schematically illustrate the steps of fabricating the electron emission device according to the first embodiment of the present invention.  
         [0024]      FIG. 4  is a partial sectional view of an electron emission device according to a second embodiment of the present invention.  
         [0025]      FIGS. 5A, 5B ,  5 C,  5 D, and  5 E schematically illustrate the steps of fabricating the electron emission device according to the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0026]     As shown in  FIGS. 1 and 2 , the electron emission device of the first embodiment includes first and second substrates  2  and  4  facing each other with an inner space. An electron emission structure is provided at the first substrate  2  to emit electrons, and a light emission or display structure is provided at the second substrate  4  to emit visible rays due to the electrons.  
         [0027]     Specifically, cathode electrodes  6  are stripe-patterned on the first substrate  2  in a first direction (e.g., in a y-axis direction of  FIG. 1 ). An insulating layer  8  is formed on the entire surface of the first substrate  2  by depositing SiO 2  onto the first substrate  2  through CVD such that the insulating layer  8  covers the cathode electrodes  6 . The insulating layer  8  has a thickness of about 1-3 μm. Gate electrodes  10  are stripe-patterned on the insulating layer  8  in a second direction crossing the cathode electrodes  6  (e.g., in an x-axis direction of  FIG. 1 ).  
         [0028]     In the present invention, the technique of forming the insulating layer  8  and the thickness of the insulating layer  8  are provided for exemplary purposes and the present invention is not limited to the above described technique and/or thickness.  
         [0029]     When the crossed regions of the cathode and the gate electrodes  6  and  10  are defined as the pixel regions, at least one opening portion  8   a  is formed at the insulating layer  8  and at least one opening portion  10   a  is formed at the gate electrode  10  for the respective pixel regions. Electron emission regions  12  are formed within the opening portions  8   a  and  10   a  while being electrically connected to the cathode electrodes  6 .  
         [0030]     In the first embodiment, to solve the problem of having the insulating layer  8  being a thin thickness of about 3 μm, the portions of the first substrate  2  to be formed with electron emission regions  12  are each etched with a depth of about 2-3 μm to thereby form grooves  14 , and portions of the electron emission regions  12  are formed within the grooves  14 .  
         [0031]     Opening portions  6 a (as shown in  FIG. 2 ) are formed at the cathode electrodes  6  corresponding to the grooves  14 , and the electron emission regions  12  simultaneously fill the grooves  14  of the first substrate  2  and the opening portions  6 a of the cathode electrodes  6  such that they contact the lateral sides of the cathode electrodes  6 .  
         [0032]     The electron emission regions  12  are formed with a material for emitting electrons under the application of an electric field, such as a carbonaceous material and/or a nanometer-sized material. In one embodiment, the electron emission regions  12  are formed using carbon nanotube, graphite, graphite nanofiber, diamond, diamond-like carbon, C 60 , and/or silicon nanowire materials.  
         [0033]     Phosphor layers  16  and black layers  18  are formed on the surface of the second substrate  4  facing the first substrate  2 . An anode electrode  20  is formed on the phosphor layers  16  and the black layers  18  with a metallic material, such as aluminum. The anode electrode  20  receives a high voltage required for accelerating the electron beams toward the phosphor layers  16 . In addition, the anode electrode  20  reflects the visible rays radiated toward the first substrate  2  to the second substrate  4  to thereby further heighten the screen luminance.  
         [0034]     Alternatively, the anode electrode may be formed with a transparent conductive material, such as indium tin oxide (ITO). In this case, the anode electrode (not shown) is formed on the surface of the phosphor and the black layers facing the second substrate. The anode electrode may be formed on the entire surface of the second substrate, or partitioned into a plurality of portions with a predetermined pattern.  
         [0035]     Referring still to  FIGS. 1 and 2 , spacers  22  are arranged between the first and the second substrates  2  and  4 , and the first and the second substrates  2  and  4  are attached to each other at their peripheries using a glass or seal frit with a low melting point. The inner space between the first and the second substrates  2  and  4  is exhausted to be in a vacuum state to thereby construct an electron emission device. The spacers  22  are arranged in correspondence with the non-luminescence regions where the black layers  18  are placed. In addition, a mesh-type grid electrode (not shown) may be disposed between the first and the second substrates  2  and  4  to focus the electron beams.  
         [0036]     The above-structured electron emission device is driven by applying predetermined voltages to the cathode electrodes  6 , the gate electrodes  10 , and the anode electrode  20 . For instance, driving voltages with a voltage difference of several to several tens of volts are applied to the cathode and the gate electrodes  6  and  10 , and a direct current voltage of several hundreds to several thousands of volts is applied to the anode electrode  20 .  
         [0037]     Accordingly, electric fields are formed around the electron emission regions  12  at the pixels where the voltage difference between the cathode and the gate electrodes  6  and  10  exceeds the threshold voltage, and electrons are emitted from these electron emission regions  12 . The emitted electrons are attracted by the high voltage applied to the anode electrode  20 , are directed toward the second substrate  4  and are collided against the corresponding phosphor layers  16  to thereby emit light.  
         [0038]     In the electron emission device according to the first embodiment, since the electron emission regions  12  are placed within the grooves  14  provided at the first substrate  2 , the electron emission regions  12  are standing at a plane lower than a plane of the gate electrodes  10 . Accordingly, the electrons emitted from the electron emission regions  12  are focused while passing the gate electrodes  10  to thereby minimize the diffusion of the electron beams. Furthermore, the gate electrodes  10  weaken the influence of the anode electric field to the electron emission regions  12 , and effectively inhibit the diode type electron emission where electrons are mistakenly emitted from the electron emission regions at the pixels to be off-stated due to the influence of the anode electric field.  
         [0039]     Consequently, the screen color purity and the color representation are enhanced, and higher voltage can be applied to the anode electrode  20  to thereby heighten the screen luminance.  
         [0040]     A method of fabricating the electron emission device according to the first embodiment of the present invention will be now explained with reference to  FIGS. 3A  to  3 E.  
         [0041]     First, as shown in  FIG. 3A , a metallic layer  24  to be used as cathode electrodes is formed on the first substrate  2  (e.g., a transparent substrate). The metallic layer  24  is made with a metallic material, such as a chromium (Cr) material, an aluminum (Al) material and/or a molybdenum (Mo) material. The metallic layer  24  is patterned using a mask pattern (not shown), thereby making opening portions  24 a to be formed with the grooves  14  of  FIG. 3B .  
         [0042]     Thereafter, as shown in  FIG. 3B , the first substrate  2  is etched using the metallic layer  24  as a mask to thereby form the grooves  14  with a predetermined depth. The etching of the first substrate  2  is made by dipping it in an etching solution containing about  14 . 3 % of fluoric acid for about five minutes such that the resulting grooves  14  have a depth of about 2-3 μm.  
         [0043]     Considering that the thickness of the insulating layer and the electron emission region is in the range of about 1-3 μm and about 2-5 μm, respectively, the depth of the groove  14  is established to be about 2-3 μm such that the height difference between the top surface of the electron emission region  12  and the surface of the cathode electrode  6  should be kept to be about 1 μm or less. In one embodiment, the depth of the groove  14  is controlled depending upon the thickness of the insulating layer and/or the electron emission regions  12 .  
         [0044]     For explanatory convenience, it is illustrated in  FIGS. 1 and 2  that the top surface of the electron emission region  12  and the surface of the cathode electrode  6  are placed at the same plane; however, as indicated above, the first embodiment of the present invention is not thereby limited.  
         [0045]     As shown in  FIG. 3C , the metallic layer  24  is stripe-patterned to thereby form cathode electrodes  6 . SiO 2  is deposited onto the entire surface of the first substrate  2  over the cathode electrodes  6  to thereby form an insulating layer  8  with a thickness of about 1-3 μm. Opening portions  8   a  are formed at the insulating layer  8  to thereby expose the grooves  14 .  
         [0046]     Thereafter, as shown in  FIG. 3D , a metallic layer to be used as gate electrodes  10  is deposited onto the insulating layer  8 , and patterned to thereby form stripe-patterned gate electrodes  10  proceeding in a direction perpendicular to the cathode electrodes  6  (or perpendicular to an x-axis direction of  FIG. 3D ). Opening portions  10   a  are also formed at the gate electrodes  10  to thereby expose the grooves  14 .  
         [0047]     It is explained above that the opening portions  8   a  are formed at the insulating layer  8  after the deposition of the insulating layer  8 , and the opening portions  10   a  are formed at the gate electrodes  10  after the formation of the gate electrodes  10 , but the opening portions  8   a  and  10   a  of the insulating layer  8  and the gate electrodes  10  may alternatively be formed through only one etching process after the deposition of the insulating layer  8  and the formation of the gate electrodes  10 .  
         [0048]     Next, the grooves  14  are internally filled with a paste-phased mixture containing an electron emission material and a photosensitive material. The electron emission material can be formed with a carbon nanotube material, a graphite material, a graphite nanofiber material, a diamond material, a diamond-like carbon material, a C 60  material, and/or a silicon nanowire material.  
         [0049]     As shown in  FIG. 3E , ultraviolet rays  30  (indicated by the arrow) illuminated (or are applied to) the paste-phased mixture filled within the grooves  14  through the backside of the first substrate  2  to selectively harden it, and the non-hardened mixture is removed in the development of the electron emission regions  12 , thereby forming the electron emission regions  12  with a thickness of about 2-5 μm.  
         [0050]     Finally, spacers  22  are fixed onto the first substrate  2 , and phosphor and black layers  16  and  18  are formed on the second substrate  4  together with an anode electrode  20 . The first and the second substrates  2  and  4  are attached to each other at their peripheries using a glass frit. The inner space between the first and the second substrates  2  and  4  is exhausted to thereby complete the electron emission device.  
         [0051]     As shown in  FIG. 4 , an electron emission device according to a second embodiment of the present invention is provided. The electron emission device of  FIG. 4  includes cathode electrodes  6 ′ provided at the first substrate  2 . The cathode electrodes  6 ′ of the second embodiment are formed with a transparent conductive material, such as an indium tin oxide (ITO) material, and are also provided on the inner surface of the grooves  14 ′. Furthermore, a resistance layer  26  is formed on the cathode electrodes  6 ′ to enhance the uniformity in electron emission.  
         [0052]     Alternatively, a nontransparent metallic layer may be used instead of the resistance layer  26  to lower the electrical resistance of the cathode electrodes.  
         [0053]     In the above described structure according to the second embodiment, since the electron emission regions  12 ′ contact the cathode electrodes  6 ′ at all the sides thereof except for the top side, the contact area between the electron emission regions  12 ′ and the cathode electrodes  6 ′ is increased. Consequently, the contact resistance between the electron emission regions  12 ′ and the cathode electrodes  6 ′ is lowered, thereby reducing the driving voltage, and enhancing the uniformity in electron emission.  
         [0054]     A method of fabricating the electron emission device according to the second embodiment of the present invention will be now explained with reference to  FIGS. 5A  to  5 E.  
         [0055]     As shown in  FIG. 5A , a mask pattern (not shown) is first used to form grooves  14 ′ at the first substrate  2 . The etching of the first substrate  2  is made using substantially the same method as related to the electron emission device according to the first embodiment.  
         [0056]     After the removal of the mask pattern, as shown in  FIG. 5B , a transparent conductive material, such as ITO, is coated onto the entire top surface of the first substrate  2 , and patterned to thereby form the stripe-shaped cathode electrodes  6 ′. The cathode electrode  6 ′ is also formed on the inner surface of the groove  14 ′.  
         [0057]     A resistance layer  26  or a nontransparent metallic layer (not shown) is formed on the cathode electrodes  6 ′, and patterned to make opening portions  26   a  to be placed with the electron emission regions  12 ′. In one embodiment, the resistance layer  26  or the nontransparent metallic layer is not formed on the part of the cathode electrode  6 ′ within the groove  14 ′ so that the electron emission regions  12 ′ can be formed using a backside exposure technique (e.g., with ultraviolet rays  30 ).  
         [0058]     As shown in  FIG. 5C , SiO 2  is deposited onto the structure of the first substrate  2  to form an insulating layer  8  with a thickness of about 1-3 μm, and the insulating layer  8  is patterned to make opening portions  8   a  thereat. Thereafter, as shown in  FIG. 5D , a metallic layer is deposited onto the insulating layer  8 , and patterned to thereby form stripe-shaped gate electrodes  10  proceeding in a direction perpendicular to the cathode electrodes  6 ′ (or perpendicular to an x-axis direction of  FIG. 5D ). Opening portions  10   a  are also formed at the gate electrodes  10  corresponding to the opening portions  8   a  of the insulating layer  8 .  
         [0059]     As shown in  FIG. 5E , the electron emission regions  12  are then formed using substantially the same method as that related to the first embodiment (e.g., with ultraviolet rays  30 ).  
         [0060]     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.