Abstract:
Provided are a method of growing carbon nanotubes and a carbon nanotube device. The method includes: depositing an aluminum layer on a substrate; forming an insulating layer over the substrate to cover the aluminum layer; patterning the insulating layer and the aluminum layer on the substrate to expose a side of the aluminum layer; forming a plurality of holes in the exposed side of the aluminum layer to a predetermined depth; depositing a catalyst metal layer on the bottoms of the holes; and growing the carbon nanotubes from the catalyst metal layer.

Description:
BACKGROUND OF THE INVENTION 
     Priority is claimed to Korean Patent Application No. 2004-12537, filed on Feb. 25, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     1. Field of the Invention 
     The present invention relates to a method of horizontally growing carbon nanotubes (CNTs) and a device having the same, and more particularly, to a method of horizontally growing CNTs of uniform diameter from holes in an alumina template and a device having the same. 
     2. Description of the Related Art 
     The electric and mechanical properties of CNTs have been intensively studied to apply to various devices and applications. CNTs can be formed by vertically and horizontally growing methods. CNTs formed using the vertically growing method are used as an electron emission source in a field emission display (FED). Also, such CNTs may be used as a field emission source in a backlight device for a liquid crystal display (LCD), for example. 
     Horizontally grown CNTs may be applied to inter-connectors, Micro Electro Mechanical System (MEMS) sensors, horizontal field emitter tips, and the like. 
     In the prior art, an electric field is applied between two electrodes between which a patterned catalyst is interposed so as to horizontally grow CNTs. In such a horizontally growing method, it is not easy to accurately control the magnitude of a catalyst. Thus, it is difficult to uniformly control the diameter of CNTs. Also, yield of the CNTs is low and an electric field must be applied. 
     U.S. Pat. No. 6,515,339 discloses a method of horizontally growing CNTs from catalysts which are formed in a shape of nanodots, nanowires, or stripes, between which a predetermined space is formed, and on which a vertical growing preventing layer is disposed. However, in this method, it is difficult to uniformly control the diameter of the CNTs. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method of horizontally growing CNTs of a predetermined diameter using holes formed in an alumina nano-template. 
     The present invention provides a CNT device including CNTs which are horizontally grown from holes formed in an alumina nano-template. 
     According to an aspect of the present invention, there is provided a method of horizontally growing carbon nanotubes, including: depositing an aluminum layer on a substrate; forming an insulating layer over the substrate to cover the aluminum layer; patterning the insulating layer and the aluminum layer on the substrate so as to expose a side of the aluminum layer; forming a plurality of holes in the exposed side of the aluminum layer to a predetermined depth; depositing a catalyst metal layer on the bottoms of the holes; and horizontally growing the carbon nanotubes from the catalyst metal layer. 
     The aluminum layer is deposited using sputtering or e-beam evaporation. 
     It is preferable that forming of the plurality of the holes includes dipping the resultant structure of the patterning of the insulating layer and the aluminum layer into a catalyst so as to be anodically oxidized. 
     It is preferable that depositing of the catalyst metal layer on the bottoms of the holes includes: applying a voltage to a solution selected from the group consisting of a metal sulfate solution, metal chloride solution, and a metal nitrate solution to form the catalyst metal layer. 
     It is preferable that the catalyst metal layer is formed of a metal selected from the group consisting of Ni, Fe, and Co. 
     It is preferable that the carbon nanotubes be grown from the catalyst metal layer using a gas containing carbon by a thermal chemical vapor deposition or a plasma enhanced chemical vapor deposition. 
     According to another aspect of the present invention, there is provided a carbon nanotube device including: a substrate; an aluminum layer which is formed on the substrate and at least one side of which is spaced apart from an edge of the substrate; an insulating layer which covers an upper surface of the aluminum layer; a plurality of holes which are horizontally formed to a predetermined depth from a side of the aluminum layer that is exposed by the insulating layer on the substrate; a catalyst metal layer which is formed on the bottoms of the holes; and carbon nanotubes which are horizontally grown from the catalyst metal layer so as to protrude from the side of the aluminum layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic perspective view for explaining a CNT device which is manufactured using a method of horizontally growing CNTs according to an embodiment of the present invention; 
         FIGS. 2A through 2D  are cross-sectional views for explaining a method of horizontally growing CNTs, according to an embodiment of the present invention; 
         FIG. 3  is a photo observed by a scanning electron microscope (SEM) to show CNTs grown from an aluminum layer between a substrate and an insulating layer; and 
         FIG. 4  is an enlarged view of a portion of the photo of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a method of horizontally growing CNTs, according to a preferred embodiment of the present invention, will be described in detail with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
       FIG. 1  is a schematic perspective view for explaining a CNT device which is manufactured using a method of horizontally growing CNTs according to an embodiment of the present invention. Referring to  FIG. 1 , an aluminum layer  102   a  having a patterned side and an insulating layer  104   a  are sequentially stacked on a substrate  100 . A plurality of holes  103  are arranged in the patterned side of the aluminum layer  102   a , and CNTs  108  protrude through the holes  103 . A catalyst metal layer  106  is formed at the bottoms of the holes  103  so as to grow the CNTs  108 . 
       FIGS. 2A through 2D  are cross-sectional views for explaining a method of horizontally growing the CNTs  108 , according to an embodiment of the present invention. 
     As shown in  FIG. 2A , an aluminum layer  102  having a predetermined thickness is deposited on a substrate  100 . The substrate  100  may be formed of quartz, glass, silicon wafer, an indium tin oxide (ITO) electrode, or the like. The aluminum layer  102  may be deposited to the thickness of about 1000–10000 Å using sputtering or e-beam evaporation. 
     An insulating layer  104  is deposited on the aluminum layer  102  and serves to prevent holes  103  from being formed in regions except an exposed side of an aluminum layer ( 102   a  in  FIG. 2B ) during an anodic oxidation process that will be described later. The insulating layer  104  may be formed of alumina, silicon oxide, or silicon nitride. 
     As shown in  FIG. 2B , the insulating layer  104  and the aluminum layer  102  are patterned to form the aluminum layer  102   a  and an insulating layer  104   a . The patterning process includes phenomenon and etching that are well known in a semiconductor process and thus will be omitted herein. Here, the side of the aluminum layer  102   a  is exposed. 
     As shown in  FIG. 2C  and  FIG. 1 , a plurality of holes  103  having a predetermined length and a diameter of several tens of nanometers are formed from the exposed side of the aluminum layer  102   a  toward inside thereof. The holes  103  may be formed using an anodic oxidation process that is an electric and chemical etching method. In more detail, the substrate  100  on which the aluminum layer  102   a  has been formed is dipped into an electrolyte, and then a predetermined voltage is applied to the aluminum layer  102   a  and an electrode (not shown). The exposed side of the aluminum layer  102   a  is then anodically oxidized, and thus the holes  103  are horizontally formed from the exposed side of the aluminum layer  102   a . As shown in  FIG. 2C  and  FIG. 1 , a plurality of the holes  103  are arranged in a line. However, when the thickness of the aluminum layer  102   a  increases, the holes  103  may be arranged in a plurality of lines. In other words, since a distance between holes  103  mainly depends on an applied voltage, the number of lines in which the holes  103  are to be arranged may be controlled by controlling the thickness of an aluminum layer  102   a  and an applied voltage. Also, the length of the holes  103  may be controlled by controlling the time of applying the voltage. An oxide aluminum layer (not shown) is formed around the holes  103 . 
     Referring to  FIG. 2C  again, the stack structure in which the holes  103  have been formed is dipped into a sulfate, chloride, or nitrate solution of a transition metal, and then a direct current (DC) voltage, an alternating current (AC) voltage, or a pulse voltage is applied so as to electrically and chemically deposit nanoparticles of the transition metal on the bottoms of the holes  103 . The transition metal may be Fe, Ni, Co, or alloys of Fe, Ni, and Co. The deposited transition metal is a catalyst metal layer  106  for growing the CNTs  108 . The catalyst metal layer  106  may be formed to the thickness of about 0.5–2 nm. 
     As shown in  FIG. 2D , the CNTs  108  are grown from the catalyst metal layer  106  through the holes  103  formed in the side of the aluminum layer  102   a . The CNTs  108  may be grown using thermal chemical vapor deposition (CVD) or plasma enhanced CVD (PECVD). In more detail, the resultant structure is disposed inside a reaction chamber in which the temperature is kept at about 500–900° C., and then a gas containing carbon is injected into the reaction chamber so as to horizontally grow the CNTs  108  from the side of the catalyst metal layer  106  through the holes  103  in the side of the aluminum layer  102   a . The gas containing carbon may be CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 , CO, or the like. The diameter of the CNTs  108  is limited to the diameter of the holes  103 , i.e., about several nanometers to several tens of nanometers 
       FIG. 3  is a photo observed by an SEM to show CNTs grown from an aluminum layer between a substrate and an insulating layer, and  FIG. 4  is an enlarged view of a portion of the photo of  FIG. 3 . Referring to  FIGS. 3 and 4 , CNTs are horizontally grown to have several tens of nanometers. 
     In the above-described embodiment, it has been described that CNTs are horizontally grown from a patterned side of an aluminum layer on a substrate but other embodiments not limited to this can be used. In other words, holes through which the CNTs are grown can be in any direction in which a surface of the aluminum layer is exposed and thus available for patterning. Thus, the CNTs may be horizontally grown from any exposed side portion according to the pattern of the aluminum layer. 
     As described above, in a method of horizontally growing CNTs, according to the present invention, the diameter of holes formed in an alumina template can be controlled according to the conditions of anodic oxidation. A catalyst metal layer formed on the bottoms of the holes depends on the diameter of the holes. Thus, the CNTs can be grown to have the same diameter as the holes. As a result, the diameter of the CNTS can be controlled by controlling the diameter of the holes. Also, since the CNTs are grown along the horizontal direction of the holes, horizontal growing of the CNTs can be controlled according to a process of forming the holes. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.