Abstract:
The field emission cathode device includes an insulating substrate with a number of cathodes mounted thereon. A number of field emission units are mounted on the cathodes. A dielectric layer is disposed on the insulating substrate and defines a number of voids corresponding to the field emission units. The dielectric layer has an upper and lower section and disposed on the insulating substrate. The dielectric layer defining a plurality of voids corresponding to the field emission units. A number of grids disposed between the upper and lower sections, and wherein each grid are secured by the upper and lower sections of the dielectric layer.

Description:
BACKGROUND 
     1. Technical Field 
     The disclosure relates to field emission displays and, specifically, to a field emission cathode device and display using the device. 
     2. Discussion of Related Art 
     Field emission displays (FEDs) are a new, rapidly developing flat panel display technology. Compared to conventional technologies, such as cathode-ray tube (CRT) and liquid crystal display (LCD) technologies, FEDs are superior in providing a wider viewing angle, lower energy consumption, smaller size, and higher quality. In particular, carbon nanotube-based FEDs (CNTFEDs) have attracted much attention in recent years. 
     Generally, FEDs can be roughly classified into diode and triode structures. Diode structures have only one cathode electrode and only one anode electrode, and are only suitable for displaying characters, not for applications requiring high resolution. The diode structures require high voltage, produce relatively non-uniform electron emissions, and require relatively costly driving circuits. Triode structures were developed from diode structures by adding a gate electrode for controlling electron emission. Triode structures can emit electrons at relatively lower voltages. 
     Referring to  FIGS. 4 and 5 , a triode field emission cathode device  100 , according to the prior art, is disclosed. The field emission cathode device  100  includes an insulating substrate  102 , a number of longitudinal cathodes  104  attached on the substrate  102 , a number of field emission units  110  distributed on the cathodes  104 , a dielectric layer  106 , and a number of gate electrodes  108  directly mounted on the top of the dielectric layer  106 . The cathodes  104  are spaced and parallel. The field emission units  110  are arranged in series on the cathodes  104 . The field emission units  110  are electrically connected to the cathodes  104  and have a number of field emitters mounted thereon. The dielectric layer  106  includes a number of through holes  116  exposing the cathodes  104  and the field emission units  110 . An axis of the gate electrode  108  is perpendicular to that of the cathodes  104 . Due to detachability between the gate electrodes  108  and the dielectric layer  106 , the gate electrodes  108  are prone to sliding and deformation relative to the dielectric layer  106  during packaging of the field emission cathode device  100 . In addition, during operation of the field emission cathode device  100 , the gate electrodes  108  are easily distorted by the electric field, which results in a short circuit between the cathodes  104  and the gate electrodes  108 . Therefore, the distance between the cathodes  104  and the gate electrodes  108  cannot be too short, and preferably exceed 20 microns (μm). However, as the distance between the cathodes  104  and the gate electrodes  108  increases, working voltage of the gate electrodes  108  must increase accordingly. The high working voltage affects the field emission performance of the field emission cathode device  100 . 
     What is needed, therefore, is a field emission cathode device and a field emission display with lower working voltage and a higher field emission performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present field emission cathode device and field emission display can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present field emission cathode device and a field emission displays. 
         FIG. 1  is a schematic view of a field emission cathode device in accordance with the present embodiment. 
         FIG. 2  is a plan view of the field emission cathode device of  FIG. 1 . 
         FIG. 3  is a schematic view of a field emission display in accordance with the present embodiment. 
         FIG. 4  is a plan view of a field emission cathode device according to the prior art. 
         FIG. 5  is a cross-section of the field emission cathode device of  FIG. 4  taken along a line V-V thereof. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present field emission cathode device and field emission display using the same, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Reference will now be made to the drawings to describe one embodiment of the present field emission cathode device and a field emission display using the same, in detail. 
     Referring to  FIG. 1  and  FIG. 2 , a field emission cathode device  10  includes an insulating substrate  12 , a number of parallel longitudinal cathodes  14 , spaced and mounted on the insulating substrate  12 , a number of field emission units  32  electrically mounted on the cathodes  14 , a bottom dielectric layer portion  26  attached on the insulating substrate  12 , a number of strip shaped grids  22  perpendicular to the cathodes  14  in a different plane and distributed on the bottom dielectric layer portion  26 , and an upper dielectric layer portion  28  mounted on the grids. 
     In the present embodiment, the insulating substrate  12  is glass. However other insulating materials, such as silicon dioxide or ceramic, can be used. 
     The cathodes  14  can be copper, aluminum, gold, silver, indium tin oxide (ITO), or a combination thereof. In the present embodiment, the cathodes  14  are silver. 
     Each emission unit  32  includes a number of field emitters mounted thereon. While the field emitters can be metal or silicon having sharp tips or carbon nanotubes, in the present embodiment, carbon nanotubes are used. The field emission units  32  are located on the cathodes  14 . 
     The dielectric layer  26  is latticed, consisting of a plurality of perpendicularly intersected strips to define a plurality of voids  262  therein. The dielectric layer  26  is deposed on the insulating substrate  12  and extends across a part of the cathodes  14 , such that some parallel strips of the dielectric layer  26  are sandwiched between adjacent cathodes  14  and other strips perpendicular thereto extend across the cathodes  14 . Each void  262  corresponds to one field emission unit  32 . The dielectric layer is insulating material, such as glass, silicon dioxide, or ceramic. The dielectric layer comprises of a bottom dielectric layer portion  26  and an upper dielectric layer portion  28 . The dielectric layer is thicker than 15 μm, in the present embodiment being 20 μm. 
     The grids  22  are parallel and distributed on the bottom dielectric layer portion  26 , separating the bottom dielectric layer portion  26  and upper dielectric layer portion  28  mounted on the grids  22 . The bottom dielectric layer portion  26  mounted below the grids  22 . The grids  22  are perpendicular to the cathodes  14  in a different plane. Each of the grids  22  covers a number of voids  262  of the bottom dielectric layer portion  26 . There can be a plurality of grids  22  that cover corresponding voids  262  of the bottom dielectric layer portion  26 . The bottom dielectric layer portion  26  supports the grids  22 . The upper dielectric layer portion  26  can fix the grids  22 . The grid  22  has a metal mesh with holes structure. The holes have an effective diameter that is equal largest round particle that can pass through. The holes can have an effective diameter that is from 3 μm to 1000 μm with distance between the grids  22  and the cathodes  14  exceeding or equaling 10 μm. In the present embodiment, the grids  22  are stainless steel, with the distance between the grids  22  and the cathodes  14  of about 15 μm. 
     In operation, different voltages are applied to the cathodes  14  and the grids  22 . Generally, the voltage of the cathodes  14  is zero or connected to ground. The voltage of the gate electrodes  22  ranges from ten to several hundred volts (V). The electrons emitted by the field emitter of the field emission units  32  move towards the grids  22  under the influence of the applied electric field induced by the grids  22 , and are then emitted through the holes of the mesh. The cathodes  14  are insulated from each other, as are the grids  22 . Thus, the field emission currents at different field emission units  32  can easily be modulated by selectively changing the voltages of the grids  22  and the cathodes  14 . It is to be understood that the number of cathodes  14  and grids  22  can be set as desired to achieve the proper modulation. 
     In the field emission cathode device  10 , the grids  22  firmly fixed by the dielectric layer portions  26 ,  28  such that risk of distortion of the grids  22  creating an uneven distance between the grids  22  and the cathodes  14  (resulting uneven emission of the electrons) is prevented. Thus, the electron emission current of the field emission cathode device  10  is uniform. Even if the distance between the grids  22  and the cathodes  14  is relatively short, the grids  22  will not touch the cathodes  14 . Therefore, short circuit between the cathodes  14  and the grids  22  is prevented, allowing work voltage of the field emission cathode device  10  to be easily controlled. 
       FIG. 3  shows a field emission display  200  using field emission cathode device  10 . The field emission display  200  includes an anode electrode device  212  facing field emission cathode device  10 . 
     The distance between the grids  22  and the cathodes  14  exceeds or equals 10 μm. 
     The anode electrode device  212  of the present embodiment includes a glass substrate  214 , a transparent anode  216  disposed on the glass substrate  241 , and a phosphor layer  218  spread on the transparent anode  216 . An insulated spacer  220  is disposed between the anode electrode device  212  and the substrate  12  to maintain a vacuum seal. The edges of the grids  22  are fixed to the spacer  220 . The transparent anode  216  can be an indium tin oxide (ITO) thin film. 
     In operation, different voltages are applied to the cathodes  14 , the grids  22  and the anode  216 . Generally, the voltage of the cathodes  14  is zero or connected to ground. The voltage of the gate electrodes  22  is ten to several hundred volts. The electrons emitted by the field emitter of the field emission units  32  move towards the grids  22  under the influence of the applied electric field induced by the grids  22 , and are then emitted through the meshes of the grids  22 . Finally the electrons reach the anode  216  under the electric field induced by the anode  216  and collide with the phosphor layer  218  located on the transparent anode  216 . The phosphor layer  218  then emits visible light to accomplish display function of the field emission display  200 . The cathodes  14  are insulated from each other, as are grids  22 . Thus, field emission currents at different field emission units  32  can be easily modulated by selectively changing the voltages of the grids  22  and the cathodes  14 . 
     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.