Patent Publication Number: US-8531096-B2

Title: Field emission device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application priority to Korean Patent Application No. 10-2008-0134971, filed on Dec. 26, 2008, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which in its entirety are herein incorporated by reference. 
     BACKGROUND 
     1. Field 
     One or more exemplary embodiments relate to a field emission device and a method of manufacturing the same. 
     2. Description of the Related Art 
     Field emission devices emit electrons from emitters formed on cathodes by forming a strong electric field around the emitters. Such field emission devices may be representatively applied to field emission displays (“FEDs”), which display images by the collision of electrons emitted from a field emission device with a phosphor layer formed on anodes, backlight units (“BLUs”) of liquid crystal displays (“LCDs”), and the like. 
     LCDs display images on a front surface thereof by passing light, generated from a light source installed on a rear surface, through a liquid crystal layer which controls light transmittance therethrough. Examples of the light source installed on the rear surface of the LCD may include a cold cathode fluorescence lamp (“CCFL”) BLU, a white light emitting diode (“WLED”) BLU, a field emission BLU, and various other similar devices. The CCFL BLU provides color reproducibility and is manufactured at low costs. However, since the CCFL BLU uses the element mercury (Hg), the CCFL BLU may pollute the environment and may not increase brightness and contrast. The WLED BLU is dynamically controlled, however it incurs high manufacturing costs and has a complicated structure. The field emission BLU is locally dimmed and impulse/scan-driven to thereby maximize brightness, contrast, and the quality of motion pictures. Thus, the field emission BLU is expected to become widely used as a next-generation BLU. The field emission devices may also be applied to other various systems using electron emission, such as, X-ray tubes, microwave amplifiers, flat lamps, and other similar devices. 
     Micro tips formed of metal such as molybdenum (Mo) have been used as emitters which emit electrons in a field emission device. However, in recent years, carbon nanotubes (“CNTs”) that provide good electron emission characteristics are becoming more widely used as emitters of a field emission device. Field emission devices using CNT emitters are driven with a low voltage, and have good chemical and mechanical stabilities. 
     Since such field emission devices are currently manufactured by performing photo patterning and firing several times, the manufacturing thereof is complicated and incurs heavy expenses. More specifically, metal electrodes such as cathodes may be roughly formed in two ways. In the first way, chromium (Cr), molybdenum (Mo), or the like is deposited by vacuum deposition and then patterned by photolithography. In the second way, silver (Ag), or other similar elements, is stencil-printed and then fired. However, the first method requires vacuum deposition equipment and is complicated, and in the second method, an expensive material is used, and thus, field emission devices are manufactured at high costs. 
     SUMMARY 
     One or more exemplary embodiments include a field emission device and a method of manufacturing the same. 
     Additional aspects, advantages and features will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented exemplary embodiments. 
     One exemplary embodiment of a field emission device includes; a substrate including at least one groove, at least one metal electrode respectively disposed on a bottom surface of the at least one groove, and carbon nanotube (“CNT”) emitters respectively disposed on the at least one metal electrode and including a composite of Sn and CNTs. 
     In one exemplary embodiment, the CNT emitters may further include intermetallic compound layers respectively disposed on the at least one metal electrode. 
     In one exemplary embodiment, each of the intermetallic compound layers may include Sn and a material which is used to form the at least one metal electrode. In one exemplary embodiment, the intermetallic compound layers may further include Cu. 
     In one exemplary embodiment, the at least one metal electrode may include at least one material selected from the group consisting of Ni, Co, Cu, Au, Ag, and any mixture thereof. 
     In one exemplary embodiment, a field emission device includes; a substrate, an insulation layer disposed on the substrate and including at least one groove, wherein the at least one groove exposes a surface of the substrate, at least one metal electrode disposed on the surface of the substrate which is exposed via the at least one groove, and CNT emitters respectively disposed on the at least one metal electrode and including a composite of Sn and CNTs. 
     In one exemplary embodiment a method of manufacturing a field emission device includes; forming at least one groove in a substrate, disposed at least one metal electrode respectively on a bottom surface of the at least one groove, and disposing a composite of Sn and CNTs on the at least one metal electrode. 
     In one exemplary embodiment, the method may further include forming intermetallic compound layers respectively on the at least one metal electrode by firing the composite, after the operation of forming the composite of Sn and CNTs. In one exemplary embodiment, the composite may be fired in the range of about 250° C. to about 600° C. 
     In one exemplary embodiment, the at least one metal electrode may be disposed on the bottom surface of the at least one groove by electroless plating. In one exemplary embodiment, the metal electrodes may include at least one material selected from the group consisting of Ni, Co, Cu, Au, Ag, and any mixture thereof. 
     In one exemplary embodiment, the method may further include respectively forming seed layers on the bottom surface of the at least one groove to facilitate the electroless plating. 
     In one exemplary embodiment, the disposing of the composite on the at least one metal electrode may include plating an upper surface of the at least one metal electrode with the composite of Sn and CNTs using an Sn plating solution in which the CNTs are distributed. 
     In one exemplary embodiment, the disposing of the composite on the at least one metal electrode may include plating an upper surface of the at least one metal electrode respectively with Cu layers; and disposing the composite of Sn and CNTs on the at least one metal electrode while the Cu layers are displacement-plated with Sn. 
     In one exemplary embodiment a method of manufacturing a field emission device includes; disposing a metal layer on a substrate, forming at least one metal electrode by patterning the metal layer, disposing an insulation layer on the substrate to cover the at least one metal electrode, patterning the insulation layer to form at least one groove which exposes the at least one metal electrode, and disposing a composite of Sn and CNTs on the at least one metal electrode which is exposed via the at least one groove. 
     In one exemplary embodiment, the method may further forming at least one intermetallic compound layer on the at least one metal electrode by firing the composite. 
     According to the one or more of the above exemplary embodiments, metal electrodes are formed on a substrate by electroless plating, and thus, vacuum deposition and exposure do not need to be performed. Consequently, the costs for manufacturing the field emission devices of the one or more of the above embodiments are reduced. In addition, since CNTs are easily exposed to the outside due to a firing process, a special CNT activation process is not needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects, advantages and features will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a cross-sectional view of an exemplary embodiment of a field emission device; 
         FIG. 2  is a cross-sectional view of another exemplary embodiment of a field emission device; 
         FIG. 3  is a cross-sectional view of another exemplary embodiment of a field emission device; 
         FIG. 4  is a cross-sectional view of another exemplary embodiment of a field emission device; 
         FIGS. 5 through 10  are cross-sectional views illustrating an exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device; 
         FIGS. 11 through 15  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device; 
         FIGS. 16 through 21  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device; and 
         FIGS. 22 through 25  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device. 
     
    
    
     DETAILED DESCRIPTION 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout. 
     It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element&#39;s relationship to another elements as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower”, can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Exemplary embodiments of the present invention are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments of the present invention. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the present invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present invention. 
     All methods described herein can be performed in a suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”), is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as used herein. 
     Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a cross-sectional view of an exemplary embodiment of a field emission device. Referring to  FIG. 1 , the current exemplary embodiment of a field emission device includes a substrate  200  in which at least one groove  205  is formed, and metal electrodes  210  and carbon nanotube (“CNT”) emitters  230 ′ which are respectively formed in the grooves  205 . 
     Exemplary embodiments of the substrate  200  include a glass substrate, although alternative exemplary embodiments include a plastic substrate or other similar materials. The grooves  205  are formed in the substrate  200  to have a predetermined depth. The grooves  205  may be formed substantially parallel to one another, for example, as strips, in the substrate  200 . 
     The metal electrodes  210  are formed on bottom surfaces of the grooves  205 . The metal electrodes  210  correspond to cathodes. The metal electrodes  210  may be formed of a material selected from the group consisting of nickel (Ni), cobalt (Co), copper (Cu), gold (Au), silver (Ag), other materials with similar characteristics and any mixture thereof. In one exemplary embodiment, the metal electrodes  210  may be formed by electroless plating, as described later. Although not shown in  FIG. 1 , seed layers (see seed layers  203  of  FIG. 7 ) may be further formed between the bottom surfaces of the grooves  205  and the metal electrodes  210 . The seed layers facilitate the electroless plating for the metal electrodes  210 , and may include a material selected from the group consisting of palladium (Pd), tin (Sn), a Pd—Sn alloy, dimethylamine borane (“DMAB”), other materials with similar characteristics and any mixture thereof. 
     The CNT emitters  230 ′ are respectively formed on the metal electrodes  210  and are used for electron emission. In the present exemplary embodiment, each of the CNT emitters  230 ′ includes a composite of Sn  232  and CNTs  235 . The content of the CNTs  235  in the composite may be between about 20 volume % and about 90 volume %. The CNTs  235  may be formed so as to be exposed to the outside of the composite, e.g., they may be formed on top of a layer of Sn as shown in  FIG. 1 . The composite may further include a metal selected from the group consisting of Ag, Cu, tungsten (W), molybdenum (Mo), Co, titanium (Ti), zirconium (Zr), zinc (Zn), vanadium (V), chromium (Cr), iron (Fe), niobium (Nb), rhenium (Re), manganese (Mn), other materials with similar characteristics and any mixture thereof. In the present exemplary embodiment, the content of the metal further included in the composite may be less than or equal to about 5 wt %. The CNT emitters  230 ′ may be formed by plating upper surfaces of the metal electrodes  210  with the composite of the Sn  232  and the CNTs  235  using an Sn plating solution in which the CNTs  235  are distributed. 
       FIG. 2  is a cross-sectional view of another exemplary embodiment of a field emission device. The exemplary embodiment of a field emission device of  FIG. 2  will now be described in terms of its difference with the previous exemplary embodiment of a field emission device shown in  FIG. 1 . 
     Referring to  FIG. 2 , the current exemplary embodiment of a field emission device includes the substrate  200  in which the at least one groove  205  is formed, and the metal electrodes  210  and CNT emitters  230  which are respectively formed in the grooves  205 . The metal electrodes  210  correspond to cathodes. The metal electrodes  210  may be formed of a material selected from the group consisting of Ni, Co, Cu, Au, Ag, other materials with similar characteristics and any mixture thereof. Seed layers (not shown) may be further formed between the bottom surfaces of the grooves  205  and the metal electrodes  210  in order to facilitate electroless plating performed to form the metal electrodes  210 . 
     The CNT emitters  230  are respectively formed on the metal electrodes  210  and are used for electron emission. Differing from the previous exemplary embodiment, in the present exemplary embodiment, each of the CNT emitters  230  includes an intermetallic compound layer  231  formed on the metal electrode  210 , and the CNT emitters  230  are formed on the intermetallic compound layer  231 . Exemplary embodiments of the intermetallic compound layer  231  may be formed of an intermetallic compound that includes Sn and a material used to form the metal electrodes  210 . In one exemplary embodiment, the intermetallic compound layer  231  may be formed of a ternary intermetallic compound obtained by adding Cu to the intermetallic compound. 
     In one exemplary embodiment, the intermetallic compound layer  231  may be formed by firing the composite of the Sn  232  and the CNTs  235  illustrated in  FIG. 1  at a predetermined temperature. Due to the firing process, the CNTs  235  may be more exposed to the outside than the CNTs  235  of  FIG. 1 , which are not formed by firing, as will be described later in greater detail. When the intermetallic compound layer  231  is formed of a part of the Sn  232  of  FIG. 1 , which melts, an Sn layer  232 ′ may be formed on the intermetallic compound layer  231 . Although not shown in  FIGS. 1 and 2 , a gate electrode (not shown) for electron extraction may be further formed on portions of the upper surface of the substrate  200 , which are in between the grooves  205 . 
       FIG. 3  is a cross-sectional view of another exemplary embodiment of a field emission device. The exemplary embodiment of a field emission device of  FIG. 3  will now be described in terms of its differences with the previous exemplary embodiments of field emission devices of  FIGS. 1 and 2 . 
     Referring to  FIG. 3 , the current exemplary embodiment of a field emission device includes a substrate  400 , an insulation layer  450  in which at least one groove  455  is formed, and metal electrodes  410  and CNT emitters  430 ′ which are respectively formed in the grooves  455 . 
     The insulation layer  450  is formed on the substrate  400  to have a predetermined thickness, and includes the grooves  455  which expose portions of the top surface of the substrate  400 , e.g., in one exemplary embodiment the grooves  455  correspond to areas where the insulation layer  450  has been entirely removed. The metal electrodes  410  are formed on the exposed portions of the surface of the substrate  400 . As described above, the metal electrodes  410  may be formed of one material selected from the group consisting of Ni, Co, Cu, Au, Ag, materials with similar characteristics and any mixture thereof. Although not shown in  FIG. 3 , seed layers may be further formed between the exposed portions of the top surface of the substrate  400  and the metal electrodes  410 . 
     The CNT emitters  430 ′ are respectively formed on the metal electrodes  410  and are used for electron emission. Each of the CNT emitters  430 ′ includes a composite of Sn  432  and CNTs  435 . The content of the CNTs  435  in the composite may be between about 20 volume % and about 90 volume %. The CNTs  435  may be formed so as to be exposed to the outside of the composite. As described above, the CNT emitters  430 ′ may be formed by plating upper surfaces of the metal electrodes  410  with the composite of the Sn  432  and the CNTs  435  using an Sn plating solution in which the CNTs  435  are distributed. 
       FIG. 4  is a cross-sectional view of another exemplary embodiment of a field emission device. The exemplary embodiment of a field emission device of  FIG. 4  will now be described in terms of its differences with the previous exemplary embodiments of field emission devices of  FIGS. 1 to 3 . 
     Referring to  FIG. 4 , the current exemplary embodiment of a field emission device includes the substrate  400 , the insulation layer  450  in which the at least one groove  455  is formed, and the metal electrodes  410  and the CNT emitters  430 ′ which are respectively formed in the grooves  455 . The insulation layer  450  is formed on the substrate  400  to have a predetermined thickness, and includes the grooves  455  which expose portions of the top surface of the substrate  400 . The metal electrodes  410  are respectively formed on the exposed portions of the top surface of the substrate  400 . 
     The CNT emitters  430  are respectively formed on the metal electrodes  410  and are used for electron emission. Each of the CNT emitters  430  includes an intermetallic compound layer  431  formed on the metal electrode  410 , and the CNTs  435  formed on the intermetallic compound layer  431 . The intermetallic compound layer  431  may be formed of an intermetallic compound that includes Sn and a material used to form the metal electrodes  410 . The intermetallic compound layer  431  may be formed of a ternary intermetallic compound obtained by adding Cu to the intermetallic compound. The intermetallic compound layer  431  may be formed by firing the composite of the Sn  432  and the CNTs  435 , which is illustrated in  FIG. 3 , at a predetermined temperature. Due to the firing process, the CNTs  435  may be more exposed to the outside than the CNTs  435  of  FIG. 3 , which are not formed in a firing process, as will be described later in greater detail. When the intermetallic compound layer  431  is formed of a partially melted portion of the Sn  432  of  FIG. 3 , an Sn layer  432 ′ may remain on the intermetallic compound layer  431 . Although not shown in  FIGS. 3 and 4 , a gate electrode (not shown) for electron extraction may be further formed on portions of the upper surface of the substrate  400 , which are in between the grooves  455 . 
     Exemplary embodiments of methods of manufacturing the aforementioned exemplary embodiments of field emission devices will now be described.  FIGS. 5 through 10  are cross-sectional views illustrating an exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device. 
     Referring to  FIG. 5 , first, a substrate  200  is prepared. Exemplary embodiments of the substrate  200  may include one of glass, plastic, other materials having similar characteristics, or a combination thereof. Then, an etch mask  202  having a predetermined pattern is formed on the substrate  200 . The etch mask  202  may be formed by forming a material layer on the upper surface of the substrate  200  and patterning the material layer. 
     Referring to  FIG. 6 , portions of the upper surface of the substrate  200 , which are exposed via the etch mask  202 , are subject to, for example, etching or sand blasting, thereby forming the grooves  205  having a predetermined depth. Alternative exemplary embodiments include alternative methods of groove formation. Next, referring to  FIG. 7 , seed layers  203  may be respectively formed on the bottom surfaces of the grooves  205  to facilitate electroless plating that is later performed to form metal electrodes  210 . The seed layers  203  may include one material selected from the group consisting of Pd, Sn, a Pd—Sn alloy, DMAB, other materials having similar characteristics and any mixture thereof. The seed layers  203  may be formed by coating a solution including a material selected from the group consisting of Pd, Sn, a Pd—Sn alloy, DMAB, other materials having similar characteristics and any mixture thereof over the structure of  FIG. 6  and then removing the etch mask  202 . Exemplary embodiments of the formation of the coating may include dipping, stencil printing, inkjet printing or other similar methods. 
     Referring to  FIG. 8 , the metal electrodes  210  are respectively formed on the seed layers  203 . In one exemplary embodiment, the metal electrodes  210  may be formed by electroless plating. For the sake of convenience, the seed layers  203  are not shown in  FIG. 8 , and likewise in the following figures. The metal electrodes  210  may be formed of a material selected from the group consisting of Ni, Co, Cu, Au, Ag, other materials having similar characteristics and any mixture thereof. For example, in one exemplary embodiment wherein the metal electrodes  210  are formed of Ni, phosphorus (P) or boron (B) may be added to the Ni. For example, in one exemplary embodiment wherein the metal electrodes  210  are formed of Co, P may be added to the Co. 
     Referring to  FIG. 9 , a composite of Sn  232  and CNTs  235  is formed on the metal electrodes  210 . The content of the CNTs  235  in the composite may be between about 20 volume % and about 90 volume %. The Sn  232  has a melting point of about 232° C. The composite may further include, in addition to the Sn  232 , a metal material selected from the group consisting of Ag, Cu, W, Mo, Co, Ti, Zr, Zn, V, Cr, Fe, Nb, Re, Mn, other materials having similar characteristics and any mixture thereof. In such an exemplary embodiment, the content of the metal material further included in the composite may be equal to or less than about 5 weight %. In one exemplary embodiment, the composite of the Sn  232  and the CNTs  235  may be formed by electroless plating using a Sn plating solution in which the CNTs  235  are distributed. Alternative exemplary embodiments include configurations wherein the CNTs  235  may be formed by electroplating or other similar methods. When the composite of the Sn  232  and the CNTs  235  is formed as described above, if the CNTs  235  are properly exposed to the outside of the composite, the composite itself may serve as the CNT emitters  230 ′ of  FIG. 1 , without undergoing a firing process which is described later. However, if the CNTs  235  are not exposed to the outside of the composite, the firing process is performed. 
     Referring to  FIG. 10 , the composite of the Sn  232  and the CNTs  235  formed on the metal electrodes  210  is fired at a predetermined temperature, thereby forming CNT emitters  230 . The composite may be fired in the range of about 250° C. to about 600° C. When the composite is fired as described, the Sn  232  of the composite reacts with the material used to form the metal electrodes  210 , thereby forming intermetallic compound layers  231  respectively on the metal electrodes  210 . The exposed CNTs  235  are formed on the intermetallic compound layers  231 . More specifically, when the composite is fired at a predetermined temperature, the Sn  232  included in the composite melts and moves downward. The melted Sn  232  reacts with the material used to form the metal electrodes  210 , thereby forming the intermetallic compound layers  231 . For example, in one exemplary embodiment wherein the metal electrodes  210  are formed of electroless-plated Ni, the intermetallic compound layers  231  may be formed of an intermetallic compound including Sn and Ni, for example, Ni 3 Sn 4 . As described above, the Sn  232  included in the composite is melted and moved downward by the firing process, and thus the CNTs  235  included in the composite are naturally exposed to the outside of the composite due to the downward flow of the Sn from the upper portion of the composite. If a part of the Sn  232  included in the composite melts and forms the intermetallic compound layers  231 , Sn layers  232 ′ may be respectively formed on the intermetallic compound layers  231 . 
       FIGS. 11 through 15  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device. 
     Referring to  FIG. 11 , at least one groove  305  is formed on a substrate  300  to have a predetermined depth. More specifically, in one exemplary embodiment, an etch mask (not shown) is disposed on the upper surface of the substrate  300 , and then portions of the upper surface of the substrate  300 , which are exposed via the etch mask, are subject to, for example, etching or sand blasting, thereby forming the grooves  305  having a predetermined depth. Alternative exemplary embodiments include alternative methods of groove  305  formation. Next, seed layers  303  may be respectively formed on the bottom surfaces of the grooves  305 . As described above, the seed layers  303  may include a material selected from the group consisting of Pd, Sn, a Pd—Sn alloy, DMAB, other materials having similar characteristics and any mixture thereof. 
     Referring to  FIG. 12 , metal electrodes  310  are respectively formed on the seed layers  303 . In one exemplary embodiment, the metal electrodes  310  may be formed by electroless plating. The metal electrodes  310  may be formed of a material selected from the group consisting of Ni, Co, Cu, Au, Ag, other materials having similar characteristics and any mixture thereof. Referring to  FIG. 13 , Cu layers  315  are respectively formed on the metal electrodes  310 . Exemplary embodiments include configurations wherein the Cu layers  315  may be formed by electroless plating or by electroplating. 
     Referring to  FIG. 14 , in the present exemplary embodiment upper surfaces of the metal electrodes  310  are plated with a composite of Sn  332  and CNTs  335  by displacement plating. More specifically, the composite of the Sn  332  and the CNTs  335  may be formed on the metal electrodes  310  by displacement-plating the Cu layers  315  with Sn using a Sn plating solution in which the CNTs  335  are distributed. The content of the CNTs  335  in the composite may be between about 20 volume % and about 90 volume %. The composite may further include, in addition to the Sn  332 , a metal material selected from the group consisting of Ag, Cu, W, Mo, Co, Ti, Zr, Zn, V, Cr, Fe, Nb, Re, Mn, other materials having similar characteristics and any mixture thereof. In such an exemplary embodiment, the content of the metal material further included in the composite may be equal to or less than about 5 weight %. When the composite of the Sn  332  and the CNTs  335  is formed as described above, if the CNTs  335  are properly exposed to the outside of the composite, the composite itself may serve as the CNT emitters  130 ′ of  FIG. 1 , without undergoing a firing process which is described later. However, if the CNTs  335  are not exposed to the outside of the composite, the firing process is performed. 
     Referring to  FIG. 15 , the composite of the Sn  332  and the CNTs  335  formed on the metal electrodes  310  is fired at a predetermined temperature, thereby forming CNT emitters  330 . The composite may be fired in the range of about 250° C. to about 600° C. When the composite is fired as described, the Sn  332  of the composite reacts with the material used to form the metal electrodes  310 , thereby respectively forming intermetallic compound layers  331  on the metal electrodes  310 . The exposed CNTs  335  are respectively formed on the intermetallic compound layers  331 . More specifically, when the composite is fired at a predetermined temperature, the Sn  332  included in the composite melts and moves downward. The melted Sn  332  reacts with the material used to form the metal electrodes  310 , thereby forming the intermetallic compound layers  331 . For example, in the exemplary embodiment wherein the metal electrodes  310  are formed of electroless-plated Ni, the intermetallic compound layers  331  may be formed of an intermetallic compound including Sn and Ni, for example, Ni 3 Sn 4 . If Cu remains within the composite after the displacement plating is performed, the intermetallic compound layers  331  formed after the firing process may further include Cu, and thus, the intermetallic compound layers  331  may be formed of a ternary intermetallic compound. As described above, the Sn  332  included in the composite is melted and moved downward by the firing process, and thus, the CNTs  335  included in the composite are naturally exposed to the outside of the composite. If a part of the Sn  332  included in the composite melts and forms the intermetallic compound layers  331 , Sn layers  332 ′ may be respectively formed on the intermetallic compound layers  331 . 
       FIGS. 16 through 21  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device. 
     Referring to  FIG. 16 , a substrate  400  is prepared, and then a metal layer  410 ′ is formed on the substrate  400 , in one exemplary embodiment the metal layer  401 ′ may be formed by electroless plating. The metal layer  410 ′ may be formed of a material selected from the group consisting of Ni, Co, Cu, Au, Ag, materials having similar characteristics and any mixture thereof. For example, in the exemplary embodiment wherein the metal layer  410 ′ is formed of Ni, P or B may be added to the Ni. For example, in the exemplary embodiment wherein the metal layer  410  is formed of Co, P may be added to the Co. In one exemplary embodiment, a seed layer (not shown) may be formed on the upper surface of the substrate  400 , before the metal layer  410 ′ is formed, to facilitate electroless plating which is later performed to form the metal layer  410 ′. The seed layer may include a material selected from the group consisting of Pd, Sn, a Pd—Sn alloy, DMAB, other materials having similar characteristics and any mixture thereof. 
     Referring to  FIG. 17 , the metal layer  410 ′ is patterned to form at least one metal electrode  410  on the substrate  400 . Referring to  FIG. 18 , an insulation layer  450  is formed on the substrate  400  to have a predetermined thickness so as to cover the metal electrodes  410 . Next, referring to  FIG. 19 , the insulation layer  450  is patterned to form at least one groove  455  in the insulation layer  450  in order to expose the metal electrodes  410 . 
     Referring to  FIG. 20 , a composite of Sn  432  and CNTs  435  is formed on the metal electrodes  410 . In one exemplary embodiment, the content of the CNTs  435  in the composite may be between about 20 volume % and about 90 volume %. The Sn  232  has a melting point of about 232° C. The composite may further include, in addition to the Sn  432 , a metal material selected from the group consisting of Ag, Cu, W, Mo, Co, Ti, Zr, Zn, V, Cr, Fe, Nb, Re, Mn, other materials having similar characteristics and any mixture thereof. In such an exemplary embodiment, the content of the metal material further included in the composite may be equal to or less than about 5 weight %. In one exemplary embodiment, the composite of the Sn  432  and the CNTs  435  may be formed by electroless plating using a Sn plating solution in which the CNTs  435  are distributed. Alternative exemplary embodiments include configurations wherein the CNTs  435  may be formed by electroplating. When the composite of the Sn  432  and the CNTs  435  is formed as described above, if the CNTs  435  are properly exposed to the outside of the composite, the composite itself may serve as CNT emitters, without undergoing a firing process which is described later. However, if the CNTs  435  are not exposed to the outside of the composite, the firing process is performed. 
     Referring to  FIG. 21 , the composite of the Sn  432  and the CNTs  435  formed on the metal electrodes  410  is fired at a predetermined temperature, thereby forming CNT emitters  430 . The composite may be fired in the range of about 250° C. to about 600° C. When the composite is fired as such, the Sn  432  of the composite reacts with the material used to form the metal electrodes  410 , thereby respectively forming intermetallic compound layers  431  on the metal electrodes  410 . The exposed CNTs  435  are formed on the intermetallic compound layer  410 . More specifically, when the composite is fired at a predetermined temperature, the Sn  432  included in the composite melts and moves downward. The melted Sn  432  reacts with the material used to form the metal electrodes  410 , thereby forming the intermetallic compound layers  431 . In the exemplary embodiment wherein the metal electrodes  410  are formed of electroless-plated Ni, the intermetallic compound layers  431  may be formed of an intermetallic compound including Sn and Ni, for example, Ni 3 Sn 4 . As described above, the Sn  432  included in the composite is melted and moved downward by the firing process, and thus, the CNTs  435  included in the composite are naturally exposed to the outside of the composite. If a part of the Sn  432  included in the composite melts and forms the intermetallic compound layers  431 , Sn layers  432 ′ may be respectively formed on the intermetallic compound layers  431 . 
       FIGS. 22 through 25  are cross-sectional views illustrating another exemplary embodiment of a method of manufacturing an exemplary embodiment of a field emission device. 
     Referring to  FIG. 22 , a metal layer (not shown) is formed on a substrate  500  by electroless plating, and then, is patterned so as to form at least one metal electrode  510  on the substrate  500 , similar to the previous exemplary embodiment. Next, an insulation layer  550  is formed on the substrate  500  so as to cover the metal electrodes  510 , and then, is patterned so as to form at least one groove  555  in the insulation layer  550  in order to expose the metal electrodes  510 , similar to the previous exemplary embodiment. 
     Referring to  FIG. 23 , Cu layers  515  are formed respectively on the metal electrodes  510 . Exemplary embodiments include configurations wherein the Cu layers  515  may be formed by electroless plating or by electroplating or other similar methods. Referring to  FIG. 24 , upper surfaces of the metal electrodes  510  are plated with a composite of Sn  532  and CNTs  535  by displacement plating. More specifically, the composite of the Sn  532  and the CNTs  535  may be formed on the metal electrodes  510  by displacement-plating the Cu layers  515  with Sn using a Sn plating solution in which the CNTs  535  are distributed. In one exemplary embodiment, the content of the CNTs  535  in the composite may be between about 20 volume % and about 90 volume %. The composite may further include, in addition to the Sn  532 , a metal material selected from the group consisting of Ag, Cu, W, Mo, Co, Ti, Zr, Zn, V, Cr, Fe, Nb, Re, Mn, other materials having similar characteristics and any mixture thereof. In such an exemplary embodiment, the content of the metal material further included in the composite may be equal to or less than about 5 weight %. When the composite of the Sn  532  and the CNTs  535  is formed as described above, if the CNTs  535  are properly exposed to the outside of the composite, the composite itself may serve as CNT emitters, without undergoing a firing process which is described later. However, if the CNTs  535  are not exposed to the outside of the composite, the firing process is performed. 
     Referring to  FIG. 25 , the composite of the Sn  532  and the CNTs  535  formed on the metal electrodes  510  is fired at a predetermined temperature, thereby forming CNT emitters  530 . The composite may be fired in the range of about 250° C. to about 600° C. When the composite is fired as described, the Sn  532  of the composite reacts with the material used to form the metal electrodes  510 , thereby respectively forming intermetallic compound layers  531  on the metal electrodes  510 . The exposed CNTs  535  are respectively formed on the intermetallic compound layers  531 . More specifically, when the composite is fired at a predetermined temperature, the Sn  532  included in the composite melts and moves downward. The melted Sn  532  reacts with the material used to form the metal electrodes  510 , thereby forming the intermetallic compound layers  531 . In the exemplary embodiment wherein Cu remains in the composite after the displacement plating is performed, the intermetallic compound layers  531  formed after the firing process may further include Cu, and thus, the intermetallic compound layers  531  may be formed of a ternary intermetallic compound. As described above, the Sn  532  included in the composite is melted and moved downward by the firing process, and thus, the CNTs  535  included in the composite are naturally exposed to the outside of the composite. If a part of the Sn  532  included in the composite melts and forms the intermetallic compound layers  531 , Sn layers  532 ′ may be formed on the intermetallic compound layers  531 . 
     As described above, according to the one or more of the above exemplary embodiments, metal electrodes are formed by electroless plating, and thus, vacuum deposition equipment and exposure equipment are not needed. Consequently, the costs for manufacturing the exemplary embodiments of field emission devices are reduced. In addition, upper surfaces of the metal electrodes are electroless-plated with a composite of Sn and CNTs, and thus, the CNTs are exposed to the outside of the composite. Moreover, since Sn has a low melting point and is easily oxidized, if firing is performed at a temperature equal to or greater than the melting point of Sn, the Sn is first oxidized within the composite. Thus, oxidization of the CNTs is prevented as much as possible, and thus, the firing may be performed even under an air atmosphere. Furthermore, while an intermetallic compound is formed by Sn melting and moving downward during the firing process, the CNTs are naturally exposed to the outside of the composite. Therefore, a special CNT activation process is not needed. 
     It should be understood that the exemplary embodiments described therein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments.