Abstract:
An electron emission device includes a substrate; first electrodes on the substrate and spaced apart from each other in a first direction; a second electrode electrically insulated from the first electrodes and extending in a second direction crossing the first direction; and electron emitters located on sides of each of the first electrodes.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2008-0071208, filed on Jul. 22, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an electron emission device and a light emission device including the same. 
         [0004]    2. Description of the Related Art 
         [0005]    A light emission device can be defined as any device that externally emits recognizable light. A conventional light emission device includes a top substrate including anode electrodes and a fluorescent layer and a bottom substrate including electron emission parts and driving electrodes. Edges of the top and bottom substrates are integrally coupled to each other by a sealing member, and vacuum is generated in the inner space, and thus, the top and bottom substrates and the sealing member constitute a vacuum container. 
         [0006]    In some conventional light emission devices, a driving electrode includes a cathode electrode and a gate electrode parallel to the cathode electrode, and an electron emission device can be on a side surface of the cathode electrode facing the gate electrode. The driving electrode and the electron emission part constitute an electron emission unit. 
         [0007]    The anode electrode is disposed on a surface of the fluorescent layer facing the bottom substrate, thereby constituting a light emission unit, together with the fluorescent layer. 
         [0008]    The conventional light emission device is driven by applying a predetermined driving voltage to the cathode electrode and the gate electrode and a positive direct current voltage of thousands of volts, that is, an anode voltage, to the anode electrode. An electric field is thereby formed around the electron emission part due to a difference between a voltage of the cathode and a voltage of the gate electrode, and electrons are thereby emitted. The emitted electrons are attracted due to the anode voltage and collide with a corresponding portion of the fluorescent layer to thereby emit light. 
         [0009]    When light emission devices are driven by applying a predetermined voltage to the cathode electrode and the gate electrode, electron emission devices disposed in a row concurrently emit electrons for light emission. In addition, the cathode electrode and the gate electrode are disposed on the same layer. Due to these reasons, for light emission devices, screen-division driving, or in other words, local dimming, is difficult to accomplish. 
       SUMMARY OF THE INVENTION 
       [0010]    Exemplary embodiments of the present invention provide an electron emission device in which local dimming is made possible by utilizing a separate electrode insulated from a cathode electrode, and a light emission device including the electron emission device. 
         [0011]    According to an aspect of an exemplary embodiment of the present invention, there is provided an electron emission device including: a substrate; first electrodes on the substrate and spaced apart from each other in a first direction; a second electrode electrically insulated from the first electrodes and extending in a second direction crossing the first direction; and electron emitters located on sides of each of the first electrodes. 
         [0012]    In the electron emission device, a gap may be between adjacent ones of the electron emitters. 
         [0013]    In the electron emission device, the electron emitters may be thinner than the first electrodes. 
         [0014]    In the electron emission device, the electron emitters may include carbide-derived carbon. 
         [0015]    According to another aspect of an exemplary embodiment of the present invention, there is provided a light emission device including: a first substrate and a second substrate facing the first substrate; an electron emission unit including a plurality of electron emission devices on a surface of the second substrate; and a light emission unit including a third electrode on the first substrate and a fluorescent layer on a side of the third electrode facing the second substrate, wherein each of the electron emission devices includes: first electrodes spaced apart from each other in a first direction; a second electrode electrically insulated from the first electrodes and extending in a second direction crossing the first direction; and electron emitters located on sides of each of the first electrodes. 
         [0016]    In the light emission device, a portion of the fluorescent layer corresponding to one of the electron emission devices may be configured to emit light when the electron emitters emit electrons in accordance with voltages applied to the first electrodes and the second electrode. 
         [0017]    The light emission device may further include interconnection lines for supplying an electric current to the first electrodes, wherein the interconnection lines are substantially perpendicular to the second electrode. 
         [0018]    In the light emission device, a gap may be between adjacent ones of the electron emitters. 
         [0019]    In the light emission device, the electron emitters may be thinner than the first electrodes. 
         [0020]    In the light emission device, the electron emitters may include carbide-derived carbon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other features and aspects of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
           [0022]      FIG. 1  is a partial cross-sectional view of a light emission device including an electron emission device, according to an embodiment of the present invention; 
           [0023]      FIG. 2  is a perspective view of the electron emission device of  FIG. 1 ; 
           [0024]      FIG. 3  is a plan view of an electron emission unit including a plurality of electron emission devices such as the one illustrated in  FIG. 2 ; and 
           [0025]      FIG. 4  is a partial cross-sectional view of a light emission device according to an embodiment of the present invention to explain how the light emission device is driven. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Exemplary embodiments of the present invention will now be described more fully with reference to the accompanying drawings, so that the present invention may be more readily understood by one of ordinary skill in the art. The present invention may be embodied in various forms and is not limited to those embodiments that are described hereinafter. 
         [0027]      FIG. 1  is a partial cross-sectional view of a light emission device  1  including an electron emission device  22 , according to an embodiment of the present invention,  FIG. 2  is a perspective view of the electron emission device  22  of  FIG. 1 , and  FIG. 3  is a plan view of an electron emission unit  20  including a plurality of electron emission devices  22 , similar to the one illustrated in  FIG. 2 . 
         [0028]    Referring to  FIGS. 1 through 3 , the light emission device  1  according to the current embodiment includes a first substrate  12  and a second substrate  24  positioned parallel to and spaced apart a distance from the first substrate  12 . A sealing member (not shown) may be disposed on edges of the first substrate  12  and second substrate  24 , so that the first and second substrates  12  and  24  are coupled to each other, and vacuum is generated in an inner space to a vacuum degree of about 10 −6  torr. As a result, the first substrate  12 , the second substrate  24 , and the sealing member constitute a vacuum container. 
         [0029]    In the first substrate  12  and the second substrate  24 , a region surrounded by the sealing member may be divided into an effective region corresponding to areas utilized for emission of visible light, and a non-effective region surrounding the effective region. An electron emission unit  20  (see  FIG. 3 ) for emitting electrons is disposed in the effective region of the second substrate  24 , and a light emission unit  10  for emitting visible light is disposed in an effective region of the first substrate  12 . 
         [0030]    The electron emission unit  20  includes the electron emission devices  22 , wherein emission currents of the electron emission devices  22  are individually controlled. The light emission unit  10  is disposed on the first substrate  12  and, when the light emission device  1  operates, receives electrons from the electron emission devices  22  on the second substrate  24  and emits visible light. 
         [0031]    In the described embodiment, each of the electron emission devices  22  includes: a plurality of first electrodes  32  aligned in a direction coplanar with the second substrate  24 , for example, an x-axis direction, and spaced apart a distance from each other and parallel to one another; and electron emission parts  36  respectively positioned on opposite side surfaces of each of the first electrodes  32 . The electron emission parts  36  may be thinner than the electron emission devices  22 . 
         [0032]    Gaps may be formed between adjacent electron emission parts  36  disposed respectively on side surfaces of adjacent first electrodes  32  to prevent the electron emission devices  36  from short-circuiting. Due to the gaps, the electron emission parts  36  are spaced a distance (e.g., a predetermined distance) apart from each other. 
         [0033]    The electron emission parts  36  may each be formed in a line pattern along the lengthwise direction of first electrodes  32 , as illustrated in  FIG. 2 . In other embodiments, although not illustrated in  FIG. 2 , the electron emission parts  36  may alternatively be formed in other patterns, for example, discontinuously spaced apart from each other along the lengthwise direction of the first electrodes  32 . 
         [0034]    Referring to  FIG. 2 , a connecting electrode  321  is commonly connected to end portions of the first electrodes  32  and constitutes an electrode set  322  with the connected first electrodes  32 . 
         [0035]    The first electrodes  32  are disposed on the second substrate  24  and may be thicker than the electron emission parts  36 . To accomplish this, the first electrodes  32  may be formed using a thin film forming process, such as a sputtering process or a vacuum deposition process, or a thick film forming process, such as a screen printing process or a laminating process. In addition, the first electrodes  32  may also be formed using other methods. 
         [0036]    The electron emission parts  36  may include a material that emits electrons when an electric field is applied to the electron emission parts  36  in a vacuum condition. Such a material may be a carbonaceous material and/or a nanometer-sized material. For example, the electron emission parts  36  may include a material selected from the group consisting of carbon nanotubes, graphite, graphite nanofiber, diamond, diamond-like carbon, fullerene C 60 , silicon nanowire, and combinations thereof. 
         [0037]    In addition, the electron emission parts  36  may include carbide-derived carbon that can be manufactured by thermo-chemically reacting a carbide compound with a halogen atom-containing gas so that the carbide compound contains only carbon. 
         [0038]    The carbide compound may include at least one carbide compound selected from the group consisting of SiC 4 , B 4 C, TiC, ZrC x , Al 4 C 3 , CaC 2 , Ti x Ta y C, Mo x W y C, TiN x C y , ZrN x C y , and combinations thereof. The halogen atom-containing gas may be Cl 2  gas, TiCl 4  gas, or F 2  gas. The electron emission parts  36  including the carbide-derived carbon may have excellent uniformity and a long lifetime. 
         [0039]    In the present embodiment, the electron emission parts  36  may be formed using, for example, the screen printing process; however, the present invention is not limited thereto, and thus, the electron emission parts  36  may be formed using other methods. 
         [0040]    In the electron emission unit  20  used in exemplary embodiments, screen division driving, that is, local dimming, may be more readily performed. To accomplish this, the electron emission device  22  further includes a second electrode  26 . Specifically, the second electrode  26  is disposed on the second substrate  24  and extends in the x-axis direction. A dielectric layer  28  is disposed on the second electrode  26  and electrically insulates the second electrode  26  from the first electrodes  32 . The first electrodes  32  are disposed on the dielectric layer  28 . The local dimming performed by the second electrode  26  will be described below. 
         [0041]    Referring to  FIGS. 2 and 3 , the electron emission devices  22  are consecutively aligned in the effective region of the second substrate  24 . Interconnection lines  42  for applying a driving voltage to the first electrodes  32  of the electron emission devices  22  are disposed between the electron emission devices  22 . 
         [0042]    Here, the interconnection lines  42  are aligned in a direction coplanar with the second substrate  24 , for example, a y-axis direction of  FIG. 3 , and are electrically connected to electrode sets  322  of electron emission devices  22  aligned in the same direction. 
         [0043]    Although in  FIG. 3  interconnection lines  42  electrically connected to the electron emission devices  22  are formed separately for neighboring electron emission devices  22  in the x direction in  FIG. 3 , the present inventive concept is not limited thereto. That is, first electrodes of an electron emission device and first electrodes of a neighboring electron emission device in the x direction may share one connecting electrode. In other words, the first electrodes of an electron emission device may be disposed on the left side of a connecting electrode and the first electrodes of a neighboring electron emission device may be disposed on the right side of the connecting electrode, for example, symmetrically along the connecting electrode. Accordingly, interconnection lines connected to the first electrodes of the neighboring electron emission devices need not be separately formed, and one interconnection line may be utilized for the first electrodes of neighboring electron emission devices. 
         [0044]    Referring to  FIG. 1 , the light emission unit  10  includes a third electrode  14  on an inner surface of the first substrate  12  and a fluorescent layer  16  on a surface of the third electrode  14  facing the second substrate  24 . 
         [0045]    The fluorescent layer  16  may include mixed phosphors, including a red phosphor, a green phosphor, and a blue phosphor, to emit white light. The fluorescent layer  16  may be disposed in the entire effective region of the first substrate  12 . The third electrode  14  may be applied with an anode voltage by a power source unit disposed outside the vacuum container and may function as an anode. 
         [0046]    The third electrode  14  may be formed of a transparent conductive material, such as indium tin oxide (ITO), such that visible light emitted from the fluorescent layer  16  can pass therethrough. 
         [0047]    The third electrode  14  may also be formed of aluminum. In this case, the third electrode  14  may be formed to have a very small thickness, for example, thousands of Å, and have micro holes through which electron beams pass. 
         [0048]    Spacers (not shown) are disposed between the first substrate  12  and the second substrate  24  to resist pressure applied to the vacuum container and to maintain a substantially constant distance between the first substrate  12  and the second substrate  24 . 
         [0049]    In the light emission device  1 , each of the electron emission devices  22  and a corresponding portion of the fluorescent layer  16  constitute one pixel. The light emission device  1  is driven by applying a driving voltage to the interconnection line  42  (see  FIG. 3 ), an address voltage to the second electrode  26 , and a positive direct current voltage of 10 kV or more, that is, an anode voltage, to the third electrode  14 . 
         [0050]    Therefore, some pixels, in which a difference between a voltage of the first electrodes  32  and a voltage of the second electrodes  26  is equal to or greater than a threshold value, are selected, an electric field is formed on the dielectric layer  28  between the first electrodes  32  and the second electrodes  26  of the selected pixels, and electrons (illustrated as e −  in  FIG. 4 ) are emitted from the electron emission parts  36  of the selected pixels. The electrons emitted from the electron emission parts  36  due to the electric field formed between the first electrodes  32  and the second electrodes  26  are attracted due to the anode voltage and thus, collide with a corresponding portion of the fluorescent layer  16  to thereby emit light. 
         [0051]    However, for regions where the address voltage is not applied or in which the difference between the voltage of the first electrodes  32  and the voltage of the second electrodes  26  is smaller than the threshold value, an electric field is not formed between the first electrodes  32  and the second electrodes  26  and thus electrons are not emitted from these electron emission devices  22 . Accordingly, pixels corresponding to these electron emission devices  22  do not emit light. 
         [0052]      FIG. 4  is a partial cross-sectional view of a light emission device  22  according to an embodiment of the present invention to explain how the light emission device  22  is driven. 
         [0053]    Referring to  FIG. 4 , the light emission device  1  according to the current embodiment may be driven by applying a driving voltage to the first electrodes  32  and an address voltage to the second electrode  26 . An electrode applied with a lower voltage among the driving voltage and the address voltage functions as a cathode electrode and an electrode applied with a higher voltage functions as a scan electrode. In one exemplary embodiment, the first electrodes  32  by which the electron emission parts  36  are formed function as the cathode electrodes and the second electrodes  26  functions as the scan electrodes. 
         [0054]    When the driving voltage and the address voltage are applied, electrons (illustrated as e −  in  FIG. 4 ) are emitted from the electron emission parts  36 . 
         [0055]    In the current embodiment, in the electron emission unit  20  (see  FIG. 3 ), the first electrodes  32  corresponding to each interconnection line  42  are arranged perpendicular to the second electrodes  26  to provide local dimming. Specifically, when the driving voltage is applied to the first electrodes  32  and the address voltage is applied to the second electrode  26 , electrons emitted from the electron emission parts  36  by the first electrodes  32  are attracted due to an anode voltage and collide with a corresponding portion of the fluorescent layer  16  to thereby emit light. Accordingly, some pixels corresponding to the selected electron emission devices  22  selectively emit light. 
         [0056]    In other words, when a driving voltage is applied to the first electrodes  32  through the interconnection line  42  (see  FIG. 3 ) of the electron emission unit  20  in a selected column, and an address voltage is applied to the second electrode  26  in a selected row, the first electrodes  32  in the selected column and the second electrode  26  in the selected row are selected. In this case, an electric field is formed in dielectric layer  28  between the first electrodes  32  and the second electrode  26 , and thus, electrons are emitted from the electron emission parts  36  connected to the interconnection line  42 . Meanwhile, for a column to which the address voltage is not applied or in which the difference between the voltage of the first electrodes  32  and the voltage of the second electrode  26  is smaller than a threshold value, an electric field is not formed and the light emission unit  10  does not emit light. 
         [0057]    That is, since a row (in a y-axis direction of  FIG. 3 ) in which a voltage applied to the first electrodes  32  and a column (in an x-axis direction of  FIG. 3 ) in which a voltage applied to the second electrode  26  may be concurrently selected to determine pixels in which electrons are emitted for light emission, an electron emission device in which local dimming is possible and a light emission device including the electron emission device may be realized. 
         [0058]    Meanwhile, the electron emission parts  36  may have smaller thicknesses than the first electrodes  32 . In this case, the difference between a thickness of the first electrodes  32  and a thickness of the electron emission parts  36  may be about 1 μm to 10 μm. If the difference between the thickness of the first electrodes  32  and the thickness of the electron emission parts  36  is less than 1 μm, a shielding effect of an electric field due to the anode voltage is reduced and high voltage stability may be degraded, and thus, high luminosity, high efficiency, and a long lifetime may not be realized. On the other hand, if the difference between the thickness of the first electrodes  32  and the thickness of the electron emission parts  36  is more than 10 mm, the distance between a top surface of the first electrodes  32  and a top surface of the electron emission parts  36  is increased, and thus, the associated driving voltage may be increased. 
         [0059]    In the latter case, on the second substrate  24 , the first electrodes  32  that are thicker than the electron emission parts  36  change the electric field around the electron emission parts  36 , and thus, the electron emission parts  36  are less affected by the electric field due to the anode voltage. By maintaining the thickness difference in the range of 1 μm to 10 μm, even when an anode voltage of 10 kV or more is applied to the third electrode  14  to improve the luminosity of a light emission surface, the first electrodes  32  may weaken the electric field due to the anode voltage and the electron emission parts  36 , and thus, emission caused by the electric field due to the anode voltage may be effectively suppressed or reduced. 
         [0060]    Accordingly, for the light emission device  1  according to exemplary embodiments, an anode voltage may be increased to improve the luminosity of a light emission surface, and emission may be suppressed to accurately control the luminosity of pixels. In addition, the light emission device  1  has high voltage stability, the generation of arcing in a vacuum container may be minimized or reduced, and inner structures may be protected from being damaged by the arcing. 
         [0061]    As described above, an electron emission device in which local dimming is possible and a light emission device including the electron emission device may thus be realized. 
         [0062]    Also, an electron emission device and light emission device according to embodiments of the present invention may be suitable for securing desired resistance. 
         [0063]    Also, an electron emission device and light emission device according to embodiments of the present invention may be manufactured as large structures for use as a display panel. 
         [0064]    Also, an electron emission device and light emission device according to embodiments of the present invention may be applied with a high voltage because the electrodes are thicker than the electron emission parts. 
         [0065]    Also, an electron emission device and light emission device according to embodiments of the present invention may use an electron emission part formed by patterning a carbide-derived carbon, so that non-uniform emission performance is improved and a simpler cold cathode structure may be manufactured. 
         [0066]    While the present invention has been 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 without departing from the spirit and scope of the present invention as defined by the following claims and variations thereof.