Abstract:
The present invention relates to a cathode for use in a field emission device. In a triode-type cathode for use in an electron emission device being a core component constituting a field emission device, the present invention includes forming a catalytic layer at the sidewall of a gate hole and then growing an emitter in the catalytic layer, thus uniformly distributing an electric field generated by a voltage applied to a gate electrode over the emitter. Therefore, the present invention can improve the brightness contrast at a low anode voltage and also can control electrons emitted from the emitter only with the gate voltage.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to a cathode for a field emission device, and more particularly to, a cathode for a field emission device capable of controlling the amount of electrons emitted from an emitter using a gate voltage with no regard to an anode voltage.  
           [0003]    2. Description of the Prior Art  
           [0004]    The field emission device is a core device constituting a cathode in a field emission display. The emission efficiency of the field emission device largely depends on the device structure, the emitter material and the shape of the emitter. Currently, the field emission device can be mainly classified into a diode type having a cathode electrode and an anode electrode, and a triode type having a cathode electrode, a gate electrode and an anode electrode depending on its structure. Materials forming the emitter may include metal, silicon, diamond, diamond-like carbon, carbon nanotube, and the like. Also, materials for forming the diode cathode consist of film or particles (or powder) and may include a diamond or carbon nanotube having a good electron emission characteristic in a low electric field. The diode cathode is disadvantageous in controllability of electron emission and low-voltage driving but is advantageous in the manufacturing process and reliability of electron emission compared to the triode type.  
           [0005]    [0005]FIG. 1 is a cross-sectional view of a device for explaining a field emission device using a conventional cathode.  
           [0006]    Referring now to FIG. 1, a cathode  100  includes a dielectric layer  140  and a gate electrode  150  sequentially formed on a lower substrate  110 . A gate hole  170  is formed in a given region of the dielectric layer  140  and the gate electrode  150 . Also, a catalytic layer  130  is formed on the lower substrate  110 , exposed through the gate hole  170  and the emitter  180  is also formed on the catalytic layer  130 .  
           [0007]    Meanwhile, an anode plate  195  is located at a position facing the cathode  100  by a given distance. The anode plate  195  has an upper substrate  196  in which an anode electrode  197  and a fluorescent material  198  are stacked.  
           [0008]    In the above, the cathode electrode is included in the lower substrate  110 . Materials of the lower substrate  110  may include a glass substrate, a silicon wafer, a dielectric substance on which a conductive material is coated, etc. The dielectric layer  140  may be formed by electron beam evaporator or plasma enhanced chemical vapor deposition (PECVD) method. The gate electrode  150  is made of a metal film and may be formed by sputtering or electron beam deposition method. The gate hole  170  may be formed by photolithography process and reactive ion etching (RIE) process. The catalytic layer  130  is formed of a transition metal series. For example, the catalytic layer  130  may be formed of Ni, Fe or Co. The catalytic layer  130  may be formed by sputtering or electron beam deposition method as like in the method of forming the gate electrode  150 . The emitter  180  is made of any one of carbon nanotube, carbon nanoparticles and carbon fiber and may be formed by plasma chemical deposition method or thermal chemical vapor deposition method.  
           [0009]    An operation of the cathode  100  formed by the above method will be described as follows.  
           [0010]    If a voltage (Va) applied to the anode electrode  197  is consecutively increased, electrons are emitted from the emitter  180  even though a voltage (Vg) is not applied to the gate electrode  150 . The emitted electrons cause a fluorescent phenomenon while colliding with the fluorescent material  198 .  
           [0011]    Meanwhile, if the voltage (Vg) is applied to the gate electrode  150 , the fluorescent phenomenon can be controlled by a small amount of the voltage (Vg) as the distance between the emitter  180  and the gate electrode  150  is smaller than that between the emitter  180  and the anode electrode  197 .  
           [0012]    The cathode  100  has a triode cathode structure. Therefore, there is an advantage that the cathode  100  can be controlled by a very small operating voltage compared to the diode cathode. However, in order to obtain a screen having a high brightness, it is required that the gate voltage (Vg) and the anode voltage (Va) be increased simultaneously. Further, in order to obtain a further higher brightness, it is required that the anode voltage (Va) be further increased. In this case, electrons, which are emitted from an edge of the emitter  180  near the gate electrode  150 , are controlled by the gate voltage (Vg). However, electrons, which are emitted from a central portion of the emitter  180  relatively far spaced from the gate electrode  150 , cannot be controlled by the gate voltage (Vg). Therefore, electrons are only emitted by the anode voltage (Va).  
           [0013]    If the anode voltage (Va) is increased in the conventional triode cathode, a high brightness can be obtained but a dark state of the screen could not be implemented, as described above. Therefore, the contrast characteristic of the screen is degraded.  
           [0014]    The conventional triode cathode is complicated in structure compared to the diode cathode, but could have a decreased operating voltage. However, if the anode voltage (Va) is increased even when the gate voltage (Vg) is not applied, there is a problem that the amount of the electrons emitted from the emitter  180  could not be controlled by the gate voltage (Vg) since electrons are emitted from the emitter  180 .  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention is contrived to solve the above problems and an object of the present invention is to provide a cathode for a field emission device capable of improving the contrast characteristic even at a lower anode voltage and easily controlling electrons emitted from an emitter by a gate voltage, by forming a catalytic layer at the side of a gate hole and growing the emitter in the catalytic layer to distribute a electric field generated by a voltage applied to a gate electrode over all the portions of the emitter.  
           [0016]    In order to accomplish the above object, a cathode for use in a field emission device comprising a catalytic layer and a gate electrode formed in a stack structure along with a dielectric layer on a substrate, an emitter, a gate hole exposing the substrate according to the present invention, is characterized in that the emitter is located at the sidewall of the catalytic layer exposed through the gate hole.  
           [0017]    In the above, the gate electrode and the catalytic layer are located at opposing sides centering around the gate hole and are located at different heights. The gate electrode located to the substrate nearer than the emitter.  
           [0018]    A cathode for use in a field emission device according to the present invention, is characterized in that it a dielectric layer and a catalytic layer stacked on a substrate; a gate hole exposing the substrate; a gate electrode formed at a given region of the exposed substrate; and an emitter formed at the sidewall of the catalytic layer exposed through the gate hole.  
           [0019]    The emitter is made of any one of carbon nanotube, carbon nano particles and diamond having defects using carbon as a major component. The catalytic layer is made of one of transition metals such as Fe, Co and Ni or an alloy or a compound of the transition metals. The catalytic layer is used as a cathode electrode. A cathode electrode is further formed between the catalytic layer and the dielectric layer. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The aforementioned aspects and other features of the present invention will be explained in the following description, taken in conjunction with the accompanying drawings, wherein:  
         [0021]    [0021]FIG. 1 is a cross-sectional view of a device for explaining a field emission device using a conventional cathode;  
         [0022]    [0022]FIG. 2 is a cross-sectional view of a device for explaining a cathode for a field emission device according to a first embodiment of the present invention;  
         [0023]    [0023]FIG. 3( a )˜FIG. 3( d ) are cross-sectional views of devices for explaining a method of manufacturing a cathode for a field emission device according to a first embodiment of the present invention; and  
         [0024]    [0024]FIG. 4˜FIG. 8 are cross-sectional views of devices for explaining a cathode for a field emission device according to another embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]    The present invention will be described in detail by way of a preferred embodiment with reference to accompanying drawings, in which like reference numerals are used to identify the same or similar parts.  
         [0026]    The present invention relates to a triode-type cold cathode device used in a field emission display in a cathode for a field emission device.  
         [0027]    The significant difference between the present invention and a prior art is that an emitter is grown at the side of a gate hole. Further, the present invention uses a catalytic layer to grow an emitter. At this time, the catalytic layer means a metal or a mixed metal layer where a material for forming the emitter is suitably grown. In the cathode for a field emission device, the emitter must be located only at a desired position. Therefore, the emitter is grown at the lower surface of the gate hole in the conventional triode-type cathode but the emitter is grown at the side of the gate hole in the present invention.  
         [0028]    [0028]FIG. 2 is a cross-sectional view of a device for explaining a cathode for a field emission device according to a first embodiment of the present invention.  
         [0029]    Referring now to FIG. 2, a cathode for a field emission device includes a cathode electrode  220  made of a metal, which is formed in a stripe shape on a lower substrate  210 ; a catalytic layer  230 , a dielectric layer  240  and a gate electrode  250  sequentially stacked on the cathode electrode  220 ; a gate hole  270  formed in the gate electrode  250 , the dielectric layer  240  and the catalytic layer  230 , through which the cathode electrode  220  is exposed; and an emitter  280  formed at the side wall of the catalytic layer  230  exposed through the gate hole  270 .  
         [0030]    In the above, the lower substrate  210  is mainly formed of a glass substrate being an electrically non-conductive material. The cathode electrode  220  is made of a material having a good electrical conductivity and is formed by physical vapor deposition or chemical vapor deposition method. Materials having a good electrical conductivity may include common metal materials.  
         [0031]    The catalytic layer  230  may be formed of any one of transition metals such as Fe, Co and Ni, or an alloy or a compound of the transition metals.  
         [0032]    The gate hole  270  of a desired size is formed at a given region of the gate electrode  250 , the dielectric layer  240  and the catalytic layer  230  by means of photolithography process and dry etching process which are used in the process of manufacturing semiconductor devices. At this time, it is preferred that the dry etching process is a reactive ion etching process.  
         [0033]    The emitter  280  may have a tube type, a fiber type, a particle type or a thin film type and is formed at the sidewall of the catalytic layer  230  by means of growth process. In other words, the emitter  280  is formed by depositing any one of carbon nanotube, carbon nanoparticle and diamond having defects containing carbon as a main component, which have a good electrical emission characteristic at a low electrical field by means of plasma chemical vapor deposition or thermal chemical vapor deposition method. Also, the emitter  280  may be formed using ceramic particles, for example, oxide particles, nitride particles, carbide and semiconductor materials.  
         [0034]    A method of manufacturing the cathode for the field emission device constructed above according to a first embodiment of the present invention will be below described.  
         [0035]    [0035]FIG. 3( a )˜FIG. 3( d ) are cross-sectional views of devices for explaining a method of manufacturing a cathode for a field emission device according to a first embodiment of the present invention.  
         [0036]    Referring now to FIG. 3( a ), the cathode electrode  220 , the catalytic layer  230 , the dielectric layer  240  and the gate electrode  250  are sequentially formed on the lower substrate  210 . Then, the photoresist film  260  is formed on the gate electrode  250 .  
         [0037]    In the above, the lower substrate  210  is formed of a glass substrate being a flat dielectric. The cathode electrode  220  and the gate electrode  250  are made of any one of Mo, Ti, W, Ni, Cr and Pt or an alloy or a compound of them. The cathode electrode  220  and the gate electrode  250  are formed by sputtering or electron beam vapor deposition method. The catalytic layer  230  is made of any one of the transition metals such as Fe, Co and Ni or an alloy or a compound of them. The dielectric layer  240  is made of either silicon oxide (SiO 2 ) or nitride (SiN x ) and is formed by plasma vapor deposition or electron beam vapor deposition method. The emitter  280  grown from the sidewall of the catalytic layer  230  is formed by growing any one of carbon nanotube, carbon nanoparticle and diamond having defects, which contain carbon as a main component by means of plasma chemical vapor deposition or thermal chemical vapor deposition method.  
         [0038]    Referring now to FIG. 3( b ), a given region of the photoresist film  260  is removed by lithography process and etching process to expose a portion of the gate electrode  250  where the gate hole will be formed.  
         [0039]    By reference to FIG. 3( c ), the gate electrode  250 , the dielectric layer  240  and the catalytic layer  230  at a region from which the photoresist film  260  is removed are removed by etching process, thus forming the gate hole  270 . Thereby, the cathode electrode  220  is exposed through the gate hole  270 .  
         [0040]    Referring now to FIG. 3 d , the emitter  280  is formed at the sidewall of the catalytic layer  230  exposed through the gate hole  270 . At this time, the emitter  280  is characterized in that it is grown from the sidewall of the catalytic layer  230  and is protruded from the gate hole  270 , thus completing the cathode  200  having a triode-type structure.  
         [0041]    Thereafter, an anode plate (not shown) is positioned while facing the cathode  200  by a given distance, thus completing a triode-type field emission device.  
         [0042]    The cathode for the field emission device according to the present invention is not limited to the above description but may be formed in several similar structures.  
         [0043]    Next, a cathode for a field emission device according to another embodiment of the present invention will be now described.  
         [0044]    [0044]FIG. 4˜FIG. 8 are cross-sectional views of devices for explaining a cathode for a field emission device according to another embodiments of the present invention.  
         [0045]    A cathode for a field emission device according to a second embodiment of the present invention will be below described by reference to FIG. 4.  
         [0046]    Referring now to FIG. 4, a catalytic layer  430 , a cathode electrode  420 , a dielectric layer  440  and a gate electrode  450  are sequentially stacked on a lower substrate  410 . A buffer layer  490  is coated on the gate electrode  450 . Upon etching process of forming a gate hole  470 , the cathode electrode  420  and the catalytic layer  430  as well as the buffer layer  490  and the dielectric layer  440  are etched to expose the surface of the lower substrate  410  at the lower side of the gate hole  470 . An emitter  480  is formed at the sidewall of the catalytic layer  430  exposed through the gate hole  470 , thus completing the cathode  400  for a field emission device according to a second embodiment of the present invention.  
         [0047]    In the above, the reason why the buffer layer  490  is coated on the gate electrode  450  is that the emitter  480  grown from the catalytic layer  430  prevents shorting with the gate electrode  450 . At this time, the buffer layer  490  formed on the gate electrode  450  is formed of silicon oxide (SiO 2 ) or nitride (SiN x ) such as the dielectric layer  440 .  
         [0048]    As shown in FIG. 4, the cathode  400  for the field emission device according to another embodiments of the present invention has the catalytic layer  430  formed on the lower substrate  410  and the cathode electrode  420  formed thereon. In other words, unlike the cathode shown in FIG. 2, the cathode electrode  420  is located on the catalytic layer  430  because the catalytic layer  430  is deposited before the cathode electrode  420 . The cathode electrode  420  serves as a conductive material for supplying a voltage applied from an external power supply (not shown) to the emitter  480 .  
         [0049]    A cathode for a field emission device according to a third embodiment of the present invention will be below described by reference to FIG. 5.  
         [0050]    A cathode  500  shown in FIG. 5 employs the catalytic layer  530  as the cathode electrode.  
         [0051]    Referring now to FIG. 5, a catalytic layer  530 , a dielectric film  540  and a gate electrode  550  are sequentially stacked on the lower substrate  510 . Upon etching process of forming a gate hole  570 , the gate electrode  550 , the dielectric layer  540  and the catalytic layer  530  are etched to expose the lower substrate  510  at a lower side of the gate hole  570 . An emitter  580  is formed at the sidewall of the catalytic layer  530  exposed through the gate hole  570 , thus completing the cathode  500  for a field emission device according to a third embodiment of the present invention.  
         [0052]    In the above, the catalytic layer  530  is formed of a material having an electrical conductivity so that the catalytic layer  530  serves as a cathode electrode. Therefore, in the cathode  500  for the field emission device according to a third embodiment of the present invention, additional cathode electrode is not formed.  
         [0053]    At this time, the catalytic layer  530  is formed of any one of the transition metals such as Fe, Co and Ni or an alloy or a compound of them and is formed in thickness of 20 nanometer (nm)˜5 micron.  
         [0054]    A cathode for a field emission device according to a fourth embodiment of the present invention will be below described by reference to FIG. 6.  
         [0055]    Referring now to FIG. 6, the cathode has a catalytic layer  630  and a dielectric layer  640  sequentially stacked on one side of a lower substrate  610  and a dielectric layer  640  and a gate electrode  650  sequentially stacked on the other side of the lower substrate  610 , centering around the gate hole  670 . Also, an emitter  680  is formed at the sidewall of the catalytic layer  630 , thus completing the cathode  600  for the field emission device according to a fourth embodiment of the present invention.  
         [0056]    In other words, the catalytic layer  630  is formed at one side of the lower substrate  610  centering around the gate hole  670  and the gate electrode  650  is formed at the other side of the catalytic layer  630  centering around the gate hole  670 . The catalytic layer  630  is formed of any one of the transition metals such as Fe, Co and Ni or an alloy or a compound of them and is used as the cathode electrode, as shown in FIG. 5. Meanwhile, the gate hole  670  may have a given shape, preferably cylindrical or rectangular.  
         [0057]    As such, the cathode  600  for the field emission device according to a fourth embodiment of the present invention has a structure in which the emitter  680  and the gate electrode  650  are facing each other with the gate hole  670  intervened. Thus, generation of a leakage current between the emitter  680  and the gate electrode  650  can be minimized.  
         [0058]    A cathode for a field emission device according to a fifth embodiment of the present invention will be below described by reference to FIG. 7.  
         [0059]    Referring now to FIG. 7, a dielectric layer  740 , a catalytic layer  730  and a cathode electrode  790  are sequentially stacked on a lower substrate  710 . The cathode electrode  790 , the catalytic layer  730  and the dielectric layer  740  at a given region are etched to form a gate hole  770  through which the lower substrate  710  is exposed. A gate electrode  750  is formed at a given region of the exposed lower substrate  710  and an emitter  780  is also formed at the side wall of the catalytic layer  730  exposed through the gate hole  770 , thus completing the cathode  700  for the field emission device according to a fifth embodiment of the present invention.  
         [0060]    The catalytic layer  730  is formed of any one of the transition metals such as Fe, Co and Ni or an alloy or a compound of them and is formed in thickness of 20 nanometer (nm)˜5 micron. Meanwhile, the gate hole  770  may have a given shape, preferably rectangular.  
         [0061]    A cathode for a field emission device according to a sixth embodiment of the present invention will be below described by reference to FIG. 8.  
         [0062]    Referring now to FIG. 8, a dielectric layer  840 , a catalytic layer  830  and a buffer layer  890  are sequentially stacked at one side of a lower substrate  810  and a gate electrode  850 , the dielectric layer  840  and a buffer layer  890  are sequentially stacked on the other side of the lower substrate  810 , centering around a gate hole  870 . An emitter  880  is formed at the sidewall of the catalytic layer  830  exposed through the gate hole  870 , thus completing the cathode  800  for the field emission device according to a sixth embodiment of the present invention.  
         [0063]    As shown in FIG. 8, the catalytic layer  830  is formed only at a side facing the gate electrode  850  centering around the gate hole  870 . Also, the gate electrode  850  is formed at an opposite side of the anode electrode (not shown) centering around the emitter  880 .  
         [0064]    In the above, the catalytic layer  830  is formed of any one of the transition metals such as Fe, Co and Ni or an alloy or a compound of them. Meanwhile, the gate hole  870  may have a given shape, preferably cylindrical or rectangular.  
         [0065]    As the cathode  800  in FIG. 8 has the emitter  880  and the gate electrode  850  facing each other centering around the gate hole  870 , it provides a triode-type cathode while minimizing a leakage current between the emitter  880  and the gate electrode  850 . The cathode  800  having the structure of FIG. 8 can be manufactured by a similar method to that described in FIG. 2.  
         [0066]    As above, the cathode for the field emission device according to the sixth embodiment of the present invention can minimize a leakage current between the emitter  880  and the gate electrode  850 .  
         [0067]    As mentioned above, the present invention includes forming an emitter at the sidewall of a catalytic layer exposed through a gate hole. Therefore, the present invention has advantages that it can control the shape of the emitter and also can easily control the amount of electrons emitted from the emitter using a voltage applied to a gate electrode with a little less affected by the anode voltage.  
         [0068]    Further, the present invention includes forming the emitter having a good electron emission characteristic at a low electric field. Therefore, the present invention has advantages that it can reduce the size of the gate voltage for controlling the amount of electrons emitted from the emitter. In addition, the present invention can prohibit generation of a leakage current between the emitter and the gate electrode by forming the emitter and the gate electrode at a position facing each other, centering around the gate hole.  
         [0069]    The present invention has been described with reference to a particular embodiment in connection with a particular application. Those having ordinary skill in the art and access to the teachings of the present invention will recognize additional modifications and applications within the scope thereof.  
         [0070]    It is therefore intended by the appended claims to cover any and all such applications, modifications, and embodiments within the scope of the present invention.