1. Field of the Invention
The present invention relates to a method of growing carbon nanotubes and a method of manufacturing a field emission device using the same, and more particularly, to an inexpensive method of growing carbon nanotubes, where the carbon nanotubes can be grown at a low temperature with a suitable density for an emitter of a field emission device, and an inexpensive method of manufacturing a field emission device using the same, in which the field emission device can be constructed to have superior electron emission characteristics, and damage to a thin film can be reduced during a thermal process.
2. Description of the Related Art
Carbon nanotubes have drawn attention as an electron emission source, that is, an emitter of a field emission device. Methods of forming carbon nanotubes include thermal chemical vapor deposition (CVD), arc discharge, laser ablation, plasma enhanced chemical vapor deposition (PECVD), etc.
In the thermal CVD method, a catalyst metal layer is first formed on an electrode that is formed on a substrate, and then carbon nanotubes are grown on a surface of the catalyst metal layer by injecting a carbon containing gas such as methane (CH4), acetylene(C2H2), ethylene(C2H4), ethane (C2H6), carbon monoxide (CO), or carbon dioxide (CO2) together with hydrogen (H2) gas, nitrogen (N2) gas, or argon (Ar) gas into a reactor, which is maintained at a temperature of 500° C. to 900° C.
Recently, as the size of a field emission device increases, the size of a substrate also becomes larger. A glass substrate may be used as the substrate, because a glass substrate of a large size can be easily made or obtained. Typical glass such as sodalime glass, however, softens at temperature of approximately 480° C. Therefore, it is difficult to use the glass substrate in an in situ process which requires temperature greater than 500° C. for growing the carbon nanotubes. Accordingly, when glass is used as the substrate, either an expensive high temperature glass should be used, or the carbon nanotubes should be moved one by one to desired locations on the glass substrate after the carbon nanotubes are grown in a separate process.
Even though a high temperature glass is used as a substrate material, thin films formed on the substrate such as a gate electrode insulating layer can be peeled off or damaged due to thermal stresses generated between thin films or between a thin film and the substrate, because temperature greater than 500° C. is applied to the glass substrate to grow carbon nanotubes by an in situ process. Therefore, it is difficult to manufacture a commercial large size field emission device using the thermal CVD method due to above mentioned or other reasons. In PECVD method, carbon nanotubes are grown in the similar processes described above, and a catalyst metal is used to grow carbon nanotubes.
Generally, when carbon nanotubes are used to form an emitter of a field emission device, the field enhancement decreases as the gap between the carbon nanotubes decreases, and thus the current density is rapidly reduced. Accordingly, field emission characteristics of the field emission device can be improved by reducing the density of the carbon nanotubes to an appropriate level in growing of carbon nanotubes for an electron emission source of a field emission device.