Patent Publication Number: US-8110975-B2

Title: Field emission display device

Description:
BACKGROUND 
     1. Technical Field 
     The invention relates to a display device and, particularly, to a field emission display device. 
     2. Description of Related Art 
     Currently, because field emission display (FED) devices provide advantages such as low power consumption, fast response speed and high resolution, they are being actively developed. 
     Referring to  FIG. 6 , a conventional FED device  100  according to the prior art includes an insulating substrate  102 , a plurality of electrode down-leads  104  arranged in rows, a plurality of electrode down-leads  106  arranged in columns intersecting the rows to form a matrix, and a plurality of electron emitting units  108 . The lines  104  are parallel and spaced from each other on the insulating substrate  102 . The lines  106  are also parallel and spaced from each other on the insulating substrate  102 . The matrix includes a plurality of grids  118  where the electron emitting units  108  are located. A dielectric insulator  105  is disposed at each column and row intersection. Thus, the dielectric insulator  105  is configured to provide electric insulation between the lines  106  and the lines  104 . 
     Each of the electron emitting units  108  includes an electrode  110  extending from a row of the electrode down-lead  104 , and an electrode  112  extending from a column of the electrode down-lead  106 , and an electron emitter  114 . Each electron emitter  114  has an electron emitter region  116  with one or multiple slit(s) provided for emission of electrons. If moderate voltage is applied to the electron emitter  108 , electrons will emit from one end of the slit and across to the opposite end of the slit based on the electron tunneling process. 
     Generally, the electron emitter  114  is a conduction film including a metal compound, e.g. palladium oxide (PdO). However, when such conductive film is applied to a large area FED, current through the electron emitter  114  will be high when the FED operates. Thus, power consumption is high. Furthermore, the activation for each electron emitter  114  is a process with high energy and long time consumption. At the same time, because the slit of the electron emitter region  116  are formed by splitting the conduction film into two parts, it is difficult to precisely form the electron emitter region  116  of the electron emitter  114  based on the present fabricating technology, e.g. shape and location of the electron emitter region are not easy to control. Therefore, every electron emitter  114  will have different electron emission characteristics preventing uniform electron emission. 
     What is needed, therefore, is an FED device providing low power consumption and improved uniformity of electron emission. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present field emission display device can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present field emission display device. 
         FIG. 1  is a plan view of a field emission display device, in accordance with an illustrated embodiment; 
         FIG. 2  is a cross sectional view along a broken line II-II of the field emission display device of  FIG. 1 ; 
         FIG. 3  is a microscope image of an electron emitting unit of the field emission display device of  FIG. 1 ; 
         FIG. 4  is a current-voltage (I-V) curve of electrical characteristics of field emission display device of  FIG. 1 ; 
         FIG. 5  is Fowler-Nordheim (F-N) curve of electrical characteristics of field emission display device of  FIG. 1 ; and 
         FIG. 6  is a plan view of a conventional field emission display device according to the prior art. 
     
    
    
     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 display device, in one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made to the drawings to describe embodiments of the present field emission display (FED) device, in detail. 
     Referring to  FIG. 1  and  FIG. 2 , an FED device  200 , according to an exemplary embodiment, is shown. The FED device  200  includes an insulating substrate  202  and one or more grids  204  located thereon. 
     In the exemplary embodiment, material of the insulating substrate  202  is, for example, ceramics, glass, resins or quartz. In addition, a size and a thickness of the insulating substrate  202  can be chosen according to need. In this embodiment, the insulating substrate  202  is a glass substrate with a thickness of more than 1 mm (millimeter) and an edge length of more than 1 cm (centimeter). 
     The field emission device  200  of the exemplary embodiment has a plurality of grids  204  arranged in an array. Each grid  204  includes a first electrode down-lead  211 , a second electrode down-lead  212 , a third electrode down-lead  213 , a fourth electrode down-lead  214  and an electrode emitting unit  215 . The first, second, third and fourth electrode down-leads  211 ,  212 ,  213 ,  214  are located on the periphery of the grid  204 . The first and the second electrode down-leads  211 ,  212  are parallel to each other. The third and the fourth electrode down-leads  213 ,  214  are parallel to each other. The first electrode down-lead  211  and the second electrode down-lead  212  cross the third electrode down-lead  213  and the fourth electrode down-lead  214 . A suitable orientation of the first, second, third and fourth electrode down-leads  211 ,  212 ,  213 ,  214  is that they be set at an angle with respect to each other. The angle approximately ranges from 10 degrees to 90 degrees. In the present embodiment, the angle is 90 degrees. In addition, a distance between the first electrode down-lead  211  and the second electrode down-lead  212  is in an approximate range from 50 μm to 2 cm. A distance between the third electrode down-lead  213  and the fourth electrode down-lead  214  is in an approximate range from 50 μm to 2 cm. 
     In the present embodiment, the electrode down-leads  211 ,  212 ,  213 ,  214  are made of conductive material, for example, metal. In practice, the electrode down-leads  211 ,  212 ,  213 ,  214  are formed by applying conductive slurry on the insulating substrate  202  using printing process, e.g. silk screen printing process. The conductive slurry composed of metal powder, glass powder, and binder. For example, the metal powder can be silver powder and the binder can be terpineol or ethyl cellulose (EC). Particularly, the conductive slurry includes 50% to 90% (by weight) of the metal powder, 2% to 10% (by weight) of the glass powder, and 10% to 40% (by weight) of the binder. In the present embodiment, each of the electrode down-leads  211 ,  212 ,  213 ,  214  is formed with a width ranging from 30 μm to 100 μm and with a thickness ranging from 10 μm to 50 μm. However, it is noted that dimensions of each electrode down-lead  211 ,  212 ,  213 ,  214  can vary corresponding to dimension of each grid  204 . 
     Furthermore, the field emission device  200  of the exemplary embodiment can further include a plurality of insulators  205  sandwiched between the first or second electrode down-leads  211 ,  212  and the third or fourth electrode down-leads  213 ,  214  to avoid short-circuiting. That is, the insulators  205  are disposed at every intersection of any two electrode down-leads  211 ,  212 ,  213 ,  214  for providing electrical insulation between the electrode down-leads  211 ,  212  and the electrode down-leads  213 ,  214 . In the present embodiment, the insulator  205  can be a dielectric insulator. 
     One electrode emitting unit  215  is located in each grid  204 . Each electrode emitting unit  215  includes a first electrode  216 , a second electrode  217  and at least one electron emitter  218 . The first electrode  216  is disposed corresponding to the second electrode  217 . In addition, the first electrode  216  spaces apart from the second electrode  217 . The electron emitter  218  is disposed between the first electrode  216  and the second electrode  217 . In the exemplary embodiment, each electrode emitting unit  215  includes a plurality of electron emitters  218 . Moreover, the electron emitters  218  are located over the insulating substrate  202 . That is, there is a space between the electron emitters  218  and the insulating substrate  202 . The space is provide to enhance the field emission abilities of the electron emitters  218 . 
     The first electrode  216  is connected to the first electrode down-lead  211 . The second electrode  217  is connected to the third electrode down-lead  213 . The electron emitters  218  are electrically connected to the second electrode  217 . That is, referring to  FIG. 1 , one end of each electron emitter  218  is connected to the second electrode  217 . An opposite end of each electron emitter  218  serving as an electron emitting tip  218   a  faces but is spaced from the first electrode  216  by a predetermined distance ranging from 1 μm to 1000 μm. 
     The first electrodes  216  of the electron emitting units  215  arranged in a row of the grids  204  are electrically connected to the first electrode down-lead  211 . In addition, the second electrodes  217  of the electron emitting units  215  arranged in a column of the grids  204  are electrically connected to the third electrode down-lead  213 . In the present embodiment, the first electrode  216  serves as a anode and the second electrode  217  serves as an cathode. 
     In the present embodiment, each of the first electrodes  216  has a length ranging from 20 μm to 1.5 cm, a width ranging from 30 μm to 1 cm and a thickness ranging from 10 μm to 500 μm. Each of the second electrodes  217  has a length ranging from 20 μm to 1.5 cm, a width ranging from 30 μm to 1 cm and a thickness ranging from 10 μm to 500 μm. Usefully, the first electrode  216  has a length ranging from 100 μm to 700 μm, a width ranging from 50 μm to 500 μm and a thickness ranging from 20 μm to 100 μm. The second electrode  217  has a length ranging from 100 μm to 700 μm, a width ranging from 50 μm to 500 μm and a thickness ranging from 20 μm to 100 μm. In addition, the first electrode  216  and the second electrode  217  of the present embodiment are formed by printing the conductive slurry on the insulating substrate  202 . As mentioned above, the conductive slurry forming the first electrode  216  and the second electrode  217  is the same as the electrode down-leads  211 ,  212 ,  213 ,  214 . 
     In the present embodiment, the electron emitters  218  of each electron emitting unit  215  are arranged in an array. Moreover, the electron emitters  218  are evenly spaced from each other by a distance in the range from 1 μm to 1000 μm. The electron emitter  218  of the present embodiment can be selected from a group consisting of silicon wire, carbon nanotubes, carbon fiber and carbon nanotube yarn. For example, a plurality of carbon nanotube yarns arranged in parallel can be chosen to serve as the electron emitters  218  of the electron emitting unit  215 , as shown in  FIG. 3 . In practice, one end of each carbon nanotube yarn is electrically connected to, for example, the second electrode  217  via a conductive gel. Additionally, the carbon nanotube yarns extend toward the first electrode  216 . Thus, an opposite end of each carbon nanotube yarn points toward the first electrode  216  and is spaced from the first electrode  216  by a distance in the range from 1 μm to 1000 μm. The carbon nanotube yarns employed in the present embodiment have lengths ranging from 10 μm to 1 cm. In addition, a distance between adjacent carbon nanotube yarns is in an approximate range from 1 μm to 1000 μm. Each of the carbon nanotube yarns includes a plurality of carbon nanotubes. Specifically, each of the carbon nanotube yarns includes a plurality of carbon nanotube segments, which are joined end to end by van der Waals attractive force. In addition, each of the carbon nanotube segments includes substantially parallel carbon nanotubes. The carbon nanotubes of the present embodiment can be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes. A length of each carbon nanotube is in an approximate range from 10 μm to 100 μm and a diameter of each carbon nanotube is less than 15 nm. 
     Referring to  FIG. 2 , the FED device  200  of the present embodiment further includes a fixed element  219  disposed on the second electrode  217 . The second electrode  217  is configured to fix the electron emitters  218  on the second electrode  217 . 
     Referring to  FIG. 4 , the electrical characteristics of the FED device  200  of the exemplary embodiment is shown. The electrons are emitted from the electron emitters  218  if a voltage of more than 110V is applied to the FED device  200 . A current of about 700 nA is generated if the voltage of about 150V is applied to the FED device  200 . The power consumption of each electron emitting unit  215  is about 105 μV. Referring to  FIG. 5 , it shows that the FED device  200  of the exemplary embodiment is performed to have filed emission property. 
     In conclusion, because a distance exists between the first electrode and the second electrode, no leak current will flow between the two electrodes when the FED device operates. Thus, power consumption of the FED device is reduced. Furthermore, due to even distribution of the electron emitting units, equal distance between each electron emitter and each second electrode, and parallel arrangement of the electron emitters, uniformity of electron emission of the FED device is improved. 
     Finally, it is to be understood that the above-described embodiments are intended to illustrate rather than limit the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.