Abstract:
A field emission flat light source and a manufacturing method thereof are provided. The field emission flat light source includes an anode ( 110 ), a cathode ( 120 ), a light guide plate ( 130 ) and a separation body ( 140 ). The anode ( 110 ) and the light guide plate ( 130 ) are separated by the separation body ( 140 ). The cathode ( 120 ) is provided in the contained space ( 150 ) formed by the anode ( 110 ), the light guide plate ( 130 ) and the separation body ( 140 ). The anode ( 110 ) includes an anode substrate ( 112 ), a metal reflective layer ( 114 ) provided on the anode substrate ( 112 ) and a light emitting layer ( 116 ) provided on the metal reflective layer ( 114 ). The cathode ( 120 ) includes a cathode substrate ( 122 ) and an electron emitter ( 124 ) provided on the surface of the cathode substrate ( 122 ). The thermal conductivity of the field emission flat light source is improved. The field emission flat light source is applied to the field of the liquid crystal display or the illumination light.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to light sources, and more particularly relates to a reflective field emitting flat light source and a method for making the same. 
       BACKGROUND OF THE INVENTION 
       [0002]    The field emission flat light source can be widely used in various illumination fields, owing to the advantages of the former, such as energy-saving, environmental protection, and being able to work in harsh environments (such as high and low temperature environment), the thin, etc.. Comparing with the conventional back light module, the field emission flat light source has not only a simple structure, but also a power saving feature, a small size, easy to be large-area flatted, high brightness, thus satisfying the requirements for the future development needs of the flat light source. While the field emission flat light source has irreplaceable advantages in the future of competition in the market, however, there are still some problems to be solved in the practical application. 
         [0003]    When the conventional field emission flat light source is applied to the back light module for a liquid crystal display, the anode emitting layer of the field emission light source is close to the liquid crystal panel and is sandwiched between the cathode and the liquid crystal panel. After a long term of bombardment of the anode from the electron emitted from the cathode, the temperature will raise. If the heat is difficult to be dissipated by radiation, the serving life of the liquid crystal panel will be affected, and it may also cause the thermal deformation, even rupture of the anode. In addition, the heat dissipation problem still needs to be solved even not applied to the back light module, because the glass substrate, which is often used as anode, has a relatively poor heat dissipation characteristic. Furthermore, since the anode serves as the light incidence surface, it is difficult to assemble metal heat sink device on the surface of the anode. 
       SUMMARY OF THE INVENTION 
       [0004]    In one aspect of the present disclosure, it is necessary to provide a field emission flat light source having a better heat dissipation performance and a method for making the same. 
         [0005]    A field emission flat light source includes: an anode, a cathode, a light-transmittable panel, and a isolater, the anode and the light-transmittable panel are in a flat plate shape, the anode is parallel to the cathode; wherein the anode and the light-transmittable panel is separated by the isolater; the anode, the light-transmittable panel, and the isolater cooperatively forms a vacuum confined space, the cathode is suspended in the vacuum confined space; the anode comprises an anode substrate, a metal reflective layer positioned on the anode substrate, and an emitting layer positioned on the metal reflective layer; the cathode comprises a plurality of cathode substrates which are separately disposed and electron emitter formed on surfaces thereof. 
         [0006]    Preferably, the cathode substrates are parallel metal wires or the cathode substrates form a network composed of metal wires. 
         [0007]    Preferably, the electron emitter has a structure type of film, quasi-one-dimensional, and cone, or a composition structure composed of type of film, quasi-one-dimensional, and cone; the electron emitter is selected from the group consisting of diamond film, carbon nanotubes, carbon nanotube walls, copper oxide nanowires, zinc oxide nanowires, zinc oxide nanorods, four-angle-shaped nano zinc oxide, and iron oxide nanowires. 
         [0008]    Preferably, the anode substrate is glass or ceramic; the emitting layer is phosphor, light-emitting film or luminescent glass. 
         [0009]    Preferably, the anode further comprises an opaque anode electrode sandwiched between the anode substrate and the metal reflective layer. 
         [0010]    Preferably, the opaque anode electrode is Cr, Mo or Al electrode. 
         [0011]    Preferably, the anode further comprises a transparent anode electrode sandwiched between the anode substrate and the metal reflective layer or between the metal reflective layer and the emitting layer. 
         [0012]    Preferably, the transparent anode electrode is ITO transparent electrode. 
         [0013]    A method for making the field emission flat light source includes the following steps: 
         [0014]    making an anode: depositing a metal reflective layer on a anode substrate using vapor plating, electroplating or sputtering method, then preparing an emitting layer on the metal reflective layer using coating or magnetron sputtering method; making a cathode: preparing electron emitter on a cathode substrate using spraying or direct growth method; and 
         [0015]    assembling the field emission flat light source: firstly, placing the obtained anode on a horizontal operation table, securing a isolater on peripheral of the anode, securing the cathode on the isolater, leading out the electrode and ensuring that the cathode and anode are in parallel; then pressing the light-transmittable panel to the isolater, securing and sealing; finally sealing and vacuum pumping the assembled the field emission flat light source through an exhaust pipe. 
         [0016]    Preferably, the method further includes: depositing a transparent or opaque anode electrode on the anode substrate using magnetron sputtering or vapor plating method, or depositing a transparent anode electrode on the metal reflective layer. 
         [0017]    Since the metal reflective layer is introduced and the cathode is arranged between the anode and the light-transmittable panel, the emitting layer is kept a distance away from the light-transmittable panel, therefore when the described field emission flat light source is applied to the back light module, it can avoid the issues such as the service life of the liquid crystal panel caused by emitting layer being too close to the liquid crystal panel of the display. In addition, the metal reflective layer  114  is made of metal having good heat dissipation ability, thus increasing the stability and the service life of the field emission flat light source. 
         [0018]    The cathode substrates are parallel metal wires or the cathode substrates form a network composed of metal wires, and electron emitters are coated on the cathode substrates, such arrangement is in favor of the distribution between the electron emitters, increasing the distance between the tips of the electron emitters, thus increasing the number of the electron emitters which can effectively release the electrons, and a light source with high emission efficiency and stability is obtained. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is a front, cross-section view of a field emission flat light source according to an embodiment of the present disclosure; 
           [0020]      FIG. 2  is a side, cross-section view of the field emission flat light source of  FIG. 1 ; 
           [0021]      FIG. 3  is a front, cross-section view of a field emission flat light source according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         [0023]    Referring to  FIG. 1  and  FIG. 2 , an embodiment of a field emission flat light source, which is substantially rectangular, includes an anode  110 , a cathode  120 , a light-transmittable panel  130 , and a plurality of isolaters  140 . 
         [0024]    The anode  110  includes an anode substrate  112  having a flat plate shape, a metal reflective layer  114  positioned on the anode substrate  112 , and an emitting layer  116  positioned on the metal reflective layer  114 . The anode  110  is parallel to the cathode  120 . The light-transmittable panel  130  is shaped as a flat plate and positioned oppose to the anode  110 . The plurality of isolaters  140  are positioned between the anode  110  and the light-transmittable panel  130 . The anode  110 , the light-transmittable panel  130 , and the plurality of isolaters  140  cooperatively forms a vacuum confined space  150 . The cathode  120  is positioned and suspended in the vacuum confined space  150 . The cathode  120  includes a plurality of cathode substrates  122 , which are separately disposed. Each cathode substrate  122  has two ends secured on the opposite isolaters  140 , respectively. The surface of the cathode substrate  122  is coated with electron emitter  124 . 
         [0025]    The anode  110  and the cathode  120  are connected to a power source (not shown) via wires. When the power is turned on, the electron emitter  124  on the surface of the cathode substrate  122  releases electrons due to the applied electric field, and the emitting layer  116 , which is subjected to the accelerated electrons released from the cathode, starts to illuminate. The fluorescence emitted by the emitting layer  116  goes through the gap between the plurality of the cathode substrates  122  and emits through the light-transmittable panel  130 . Due to the metal reflective layer  114  formed on the anode substrate  112 , part of the fluorescence emitted by the emitting layer  116  will be reflected upwardly by the metal reflective layer  114 , thus largely enhancing the luminous intensity and luminous efficiency of the field emission flat light source. 
         [0026]    Since the metal reflective layer  114  is introduced and the cathode  120  is arranged between the anode  110  and the light-transmittable panel  130 , the emitting layer  116  is kept a distance away from the light-transmittable panel  130 , therefore when the described field emission flat light source is applied to the back light module, it can avoid the issues such as the short service life of the liquid crystal panel caused by emitting layer  116  being too close to the liquid crystal panel of the display. In addition, the metal reflective layer  114  is made of metal having good heat dissipation ability, thus increasing the stability and the service life of the field emission flat light source. 
         [0027]    In the illustrate embodiment, the cathode substrates  122  are composed of parallel metal wires suspended in the vacuum confined space  150 , and a plane defined by the cathode substrates  122  is parallel to the plane where the anode substrate  112  located. The surface of the cathode substrates  122  is disposed of the electron emitter  124  made of diamond film. 
         [0028]    In the illustrate embodiment, the cathode substrates  122  is made of glass. The metal reflective layer  114  is made of aluminum, which has a high reflection rate. The emitting layer  116  is made of luminescent glass having a substantially flat plate shape. 
         [0029]    Referring to  FIG. 3 , in an alternative embodiment, the anode  110  of the field emission flat light source further includes an anode electrode  118 . The anode electrode  118  is made of opaque metal and is sandwiched between the metal reflective layer  114  and the anode substrate  112 . 
         [0030]    In addition, the anode electrode  118  may also be transparent, as long as it is sandwiched between the metal reflective layer  114  and the emitting layer  116 , or between the metal reflective layer  114  and the anode substrate  112 , as shown in  FIG. 3 . 
         [0031]    In alternative embodiment, the cathode substrates  122  form a network composed of metal wires. Preferably, the surface of the metal wire is coated with electron emitter  124 . The electron emitter  124  may have a structure type of film, quasi-one-dimensional, and cone, or a composition structure composed of type of film, quasi-one-dimensional, and cone. Furthermore, the electron emitter  124  may be made of other materials, such as carbon materials, e.g. carbon nanotubes, carbon nanotube walls, or copper oxide nanowires, or oxide materials, e.g. zinc oxide nanowires, zinc oxide nanorods, four-angle-shaped nano zinc oxide, or iron oxide nanowires. 
         [0032]    Moreover, in alternative embodiment, the cathode substrates  122  may be made of glass or ceramic. The emitting layer  116  may be phosphor or a light-emitting film coated on the surface of the metal reflective layer  114 . Besides, the anode electrode  118  may be a metal electrode or non-metallic electrode, such as opaque Cr, Mo or Al electrode, or transparent ITO electrode. 
         [0033]    An embodiment of a method for making the field emission flat light source as shown in  FIG. 3  will be described in greater details. 
         [0034]    Step one, preparing an anode. An anode electrode  118  is deposited on an anode substrate  112  using magnetron sputtering or vapor plating method, a metal reflective layer  114  is then prepared on a surface of the anode electrode  118 . The metal reflective layer  114  may be prepared using vapor plating, electroplating or sputtering method. Then an emitting layer  116 , which may be whiter phosphor or color phosphor, is prepared on the metal reflective layer  114 , such that whiter or color light will be emitted when the electron bombard the phosphor. When the emitting layer  116  is a powder type, it can be prepared by coating; when the emitting layer  116  is a light-emitting film, it can be prepared using magnetron sputtering method. 
         [0035]    Step two, preparing a cathode  120 . The cathode  120  includes cathode substrates  122  and electron emitter  124 . The cathode substrates  122  are parallel metal wires or the cathode substrates  122  form a network composed of metal wires. The electron emitter  124  may be one-dimensional nanomaterial or a film-type material. The electron emitter  124  may be prepared using spraying or direct growth method. For example, a carbon nanotube electron emitter  124  is sprayed on the cathode substrates  122 . 
         [0036]    Step three, assembling the field emission flat light source. Firstly, the obtained anode  110  is placed on a horizontal operation table, isolaters  140  are placed on peripheral of the anode  110 , secured using low glass powder. Then the cathode  120  is secured on the isolaters  140 , out the electrode are led out. The cathode  120  and anode  110  are ensured in parallel. Then the light-transmittable panel  130  is pressed to the isolaters  140 , secured and sealed. Finally, the assembled the field emission flat light source is sealed and vacuum pumped through an exhaust pipe. 
         [0037]    The above the field emission flat light source and the making method will further be described below with reference to specific examples. 
       EXAMPLE  1   
       [0038]    In this example, ITO glass having a thickness of 4 mm was used as an anode substrate. The anode substrate was ultrasonic cleaned successively with acetone, ethanol, deionized water for 15 min, then blow-dried or dried. A reflective aluminum layer having a thickness of about 2 μm was vapor plated on the ITO glass, followed by screen printing a white-light phosphor layer having a thickness of about 35 μm on the surface of the reflective aluminum layer. Nickel wires were used as cathode substrate, and since the nickel wire could serve as the catalyst for directly growing of the carbon nanotubes, the carbon nanotube was used as electron emitter. The nickel wires were placed in a middle portion of a quartz tube, and then the sample was subjected to surface treatment by introducing hydrogen for 1 hour under the protection of argon at a temperature of 650° C. The temperature was raised to the growth temperature and a mixture gas containing acetylene or methane was introduced for 5 to 20 minutes. Finally the sample was cooled to room temperature under the protection of argon and carbon nanotube electron emitter was obtained. After the preparation of the cathode, the device was assembled according to the method described above, and then it was placed on an exhaust platform and the space was vacuum pumped and sealed off until the vacuum is less than 10 −4  Pa. 
       EXAMPLE 2 
       [0039]    In this example, ceramic plate having a thickness of 4 mm was used as an anode substrate. The ceramic plate was ultrasonic cleaned successively with acetone, ethanol, deionized water for 15 min, then blow-dried or dried. A chromium electrode having a thickness of about 300 m was deposited on the ceramic plate using magnetron sputtering. A reflective aluminum layer having a thickness of about 1 μm was vapor plated on the ceramic substrate with chromium electrode, followed by screen printing a white-light phosphor layer having a thickness of about 35 μm on the surface of the reflective aluminum layer. Copper oxide nanowires were used as cathode substrate. The copper powder slurry was brushed on a surface of the conductive ITO layer, and then sintered at a temperature of 400° C. in air for 3 hours to directly grow the copper oxide nanowires on the surface of the cathode substrate. After the preparation of the cathode, the device was assembled according to the method described above, and then it was placed on an exhaust platform and the space was vacuum pumped and sealed off until the vacuum is less than 10 −4  Pa. 
         [0040]    Field emission light source having the above structure is excellent in heat dissipation, thus it can be widely applied to illumination source or liquid crystal display and other fields. In addition, the described making method is simple and easy for application. 
         [0041]    Although the invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as sample forms of implementing the claimed invention.