Patent Publication Number: US-8531097-B2

Title: Field emitter

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority from Korean Patent Application No. 10-2011-0051938, filed on May 31, 2011, with the Korean Intellectual Property Office, the present disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a field emitter, and more particularly, to a triode type field emitter using a tip type cathode electrode which can significantly reduce leakage current of a gate electrode. 
     BACKGROUND 
     In field emitters using nano materials, carbon nanotubes or carbon nanowires are in the spotlight as electron emitting materials. A carbon nanotube is a structure where a one-dimensional honeycombed plate is wound in a shape of a tube, and shows excellent electrical, mechanical, chemical, and thermal characteristics in applications of various fields. A carbon nanotube having a high aspect ratio can easily emit electrons even in an electric field having a low potential due to its excellent geometric characteristics. 
     Thus, in recent years, electric field displays and lamps using carbon nanotubes are being widely studied in Korea, and studies on emission of electrons in an infinitesimal area such as a tip of X-ray source devices, atomic force microscopes (AFMs), and scanning electron microscopes (SEMS) are also being activly conducted. A structure where an emitter is formed on a tip type cathode electrode is advantageous in producing carbon natotube (CNT) electron beams having high efficiency and high density such as subminiature devices or micro focusing devices. The emitter on the tip type cathode electrode emits electrons in an infinitesimal area and electric fields are concentrated due to its geometric structure. 
       FIG. 1  is a view illustrating a field emitter according to the related art. 
     Referring to  FIG. 1 , the field emitter according to the related art has a triode structure where an emitter  120  is formed on a tip type cathode electrode  110  and a gate electrode  130  for drawing electrons from the emitter  120  is disposed above the emitter  120 . 
     As illustrated in  FIG. 1A , in the triode type field emitter, the gate electrode  130  has a mesh in a form of a net, or as illustrated in  FIG. 1B , has a single hole  132  through which electron beams emitted from the emitter  120  can pass. 
     However, the gate electrode  130  having a mesh can be variously selected according to a thickness of a mesh wire or an opening ratio of the mesh, but cannot prevent leakage of current occurring when electrons emitted from the emitter  120  escape along the mesh. Then, if the leakage current of the gate electrode  130  is high, heat is generated and a possibility of generating an arc between the cathode electrode  110  and the gate electrode  130  increases, reducing stability during electric field emission. 
     The gate electrode  130  having the hole  132  can reduce leakage currents as a size of the hole  132  increases, but a voltage applied to the gate electrode  130  increases as the size of the hole  132  increases. 
     SUMMARY 
     The present disclosure has been made in an effort to provide a field emitter which can drastically lower a leakage current generated when a triode type field emitter using a cathode electrode in a shape of a tip is driven. 
     An exemplary embodiment of the present disclosure provides a field emitter, including: a cathode electrode in a shape of a tip; an emitter having a diameter smaller than a diameter of the cathode electrode and formed on the cathode electrode; and a gate electrode having a single hole and located above the emitter while maintaining a predetermined distance from the emitter. 
     As described above, the present disclosure provides a field emitter where an emitter is formed in a region on a cathode electrode to drastically reduce a leakage current generated in a gate electrode and lower a voltage of the gate electrode. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a configuration of a field emitter according to the related art. 
         FIG. 2  is a view for explaining a cause of leakage of current to a gate electrode in the field emitter according to the related art. 
         FIG. 3  illustrates views of simulations of loci of electrons emitted from emitters in the field emitter according to the related art. 
         FIG. 4  is a view illustrating a configuration of a field emitter according to an exemplary embodiment of the present disclosure. 
         FIG. 5  illustrates a plan view of the field emitter according to the related art and a graph representing an experimental result of electric field emissions. 
         FIG. 6  illustrates a plan view of the field emitter according to the present disclosure and a graph representing an experimental result of electric field emissions. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawing, which form a part hereof. The illustrative embodiments described in the detailed description, drawing, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the present disclosure, a detailed description of known configurations and functions may be omitted to avoid obscure understanding of the present disclosure. 
       FIG. 2  is a view for explaining a cause of leakage of current to a gate electrode in a field emitter according to the related art. 
     Referring to  FIG. 2 , the triode type field emitter according to the related art includes a gate electrode  230  having a single hole  232 , and electrons  250  and  260  emitted from an emitter  220  on a cathode electrode  210  in a shape of a tip are leaked to the gate electrode  230  due to equipotential lines curved according to a geometric shape of the tip type cathode electrode  210 . 
     That is, since the electrons  250  and  260  are moved by force of electric fields and the electric fields are perpendicular to the equipotential line  240 , the electrons  250  and  260  are moved by force in a direction perpendicular to the equipotential line  240 . 
     As illustrated in  FIG. 2 , the equipotential line  240  around the cathode electrode  210  is curved due to a sharp shape of the tip type cathode electrode  210 , such that the electron  260  emitted from the emitter  220  located at a periphery of the cathode electrode  210  fails to directly proceed toward the hole  232  of the gate electrode  230  due to the influence of the curved equipotential line  240 , causing the electrons to be deflected outward, resulting in leakage of currents. 
       FIG. 3  illustrates views of simulations of loci of electrons emitted from emitters in the field emitter according to the related art. 
     Referring to  FIG. 3A , it can be seen that unlike an emitter  322  formed on a planar cathode electrode  321  of  FIG. 3B , when it comes to an emitter  312  formed on a tip type cathode electrode  311 , electron beams  314  generated at peripheries of the emitter  312  fail to be drawn toward a hole  313   a  of the gate electrode  313  but are deflected to the outside of the hole  313   a.    
     That is, as illustrated in  FIG. 3A , it can be seen that loci of electron beams  314  generated at opposite peripheries of the emitter  312  are severely distorted, but electron beams emitted from a central portion of the emitter  312  pass the hole  313   a  relatively smoothly. 
     Thus, in the exemplary embodiment of the present disclosure, an emitter on a tip type cathode electrode is formed only in a region where electron beams are not deflected so that leakage of current can be reduced while achieving an advantage of the emitter formed on the tip type cathode electrode. 
       FIG. 4  is a view illustrating a configuration of a field emitter according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 4 , the field emitter according to the present disclosure includes a tip type cathode electrode  410 , an emitter  420  formed in a region on the cathode electrode  410 , and a gate electrode  430  having a single hole  432  and located above the emitter  420  while maintaining a predetermined distance B from the emitter  420 . 
     The emitter  420  has a diameter d smaller than a diameter D of the cathode electrode  410  and maintains a predetermined distance e between a periphery of the cathode electrode  410  and an end of the emitter  420 , restraining the current from being leaked to the gate electrode  430 . Then, the diameter d of the emitter  420  may be varied according to the diameter D of the cathode electrode  410 , a diameter A of the hole  432  of the gate electrode  430 , and a distance B between the cathode electrode  410  and the gate electrode  430 . 
     The diameter d of the emitter  420  is smaller than the diameter D of the cathode electrode  410 , and a minimum diameter of the emitter  420  may be determined according to an area for withdrawing desired currents. 
     The diameter A of the hole  432  of the gate electrode  430  may be larger than the diameter d of the emitter  420  and smaller than  10  times of the diameter D of the cathode electrode  410 . 
     The distance B between the cathode electrode  410  and the gate electrode  430  may be larger than 0 and smaller than 10 times of the diameter D of the cathode electrode  410 . 
       FIG. 5  illustrates a plan view of the field emitter according to the related art and a graph representing an experimental result of electric field emissions. 
     Referring to  FIG. 5A , in the field emitter used in the experiment, an emitter  510  is formed on a cathode electrode having a diameter of 500 μm, and a gate electrode  520  having a hole of 2 mm and an anode electrode (not shown) are spaced apart from each other by a distance of 5 mm. 
     Referring to  FIG. 5B , an anode current is approximately 200 μA at an anode voltage of 3 kV and a gate voltage of 2 kV, that is, a leakage current of the gate electrode  520  is approximately 100 μV. Thus, a leakage current of the gate electrode with respect to an anode current is approximately 50%. 
       FIG. 6  illustrates a plan view of the field emitter according to the present disclosure and a graph representing an experimental result of electric field emissions. 
     Referring to  FIG. 6A , in the field emitter used in the experiment to which a size of the field emitter is applied according to the present disclosure, a diameter of a tip type cathode electrode  610  is approximately 2 mm, a diameter of an emitter  620  formed on the cathode electrode  610  is 650 μm, and a diameter of a hole  630  of a gate electrode  632  is 1 mm. 
     Referring to  FIG. 6B , it can be seen that when an anode current of approximately 200 μA is emitted at an anode voltage of 3 kV and a gate voltage of 1.4 kV, a leakage current of the gate electrode is rarely generated. 
     Thus, when compared with the experimental result of  FIG. 5 , it can be seen that the field emitter according to the present disclosure can phenomenally reduce leakage current and lower a gate voltage. 
     From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.