CNT Field Emission Characterization

There are two CNT FED research areas. Because CNT is vertically aligned on the substrate, the first research area directly uses recent silicon tip or metal tip technology of the semiconducting process. ETRI is using this method to get the high quality FED. The second research area is a screen printing method mixing with CNT and conducting polymer. Samsung Advanced Institute of Technology is using this method for the large area FED. This method has good advantage of reducing a FED producing cost. Recently, Samsung Advanced Institute of Technology developed the 15 inch full color FED. In this section, we describe the emission characteristic of the vertically aligned CNT.  Figure 1 shows the FED characterization of the vertically aligned CNT synthesizing by thermal CVD at 950 ℃. After making 300 nm silicon oxidization substrate, Ti film coated on the silicon oxidization substrate to use the cathode, and finally CNT synthesized on the metal catalyst film.
The distance between the anode and cathode is 200 μm. In the figure, Turn on voltage of CNT’s FED is 0.8 V/μm. When the current reaches the maximum voltage (3.7 V/μm) and current (2.9 mA), the FED becomes breakdown. Because the CNT has very high current density at very low voltage comparing with silicon or metal emitter tip, CNT becomes very great candidate of the source of the electron emitter source, and also Fowler-Nordheim graph shows the linear in the graph chart because of tunneling of electron emission.

Figure 2 shows the field emission characteristics of carbon nanotubes that grow  vertically on the silicon substrates using thermal CVD methods at 750 °C. High density silicon substrates are used for the use of cathode electrodes at the bottom of carbon nanotubes and the distances between the tips and the anode are kept with 350 mm. In the figures, the electron emission characteristics of carbon nanotubes show  turn-on at 3.2 v/mm and breakdown at 4.4 mA after increasing slowly to the maximum currents of 4.4 mA.
These electron emission characteristics indicate a little lower current densities than those of the carbon nanotubes grown at 950 °C but these densities indicate much higher than those of the current silicon and metal emitting tips at the low  supplied voltages so that carbon nanotubes can be expected to be in use in numerous fields in the case of carbon nanotube applications for the electron field emission. Futhermore, carbon nanotube’s field emission is due to the electron emission tunneling because Fowler-Nordheim curves show the straight lines.

Figure 3 shows the field emission characteristics of carbon nanotubes that are grown on the soda-lime glass at 550 °C. After the 100 nm deposition of Ti films on the soda-lime glass, carbon nanotubes were grown on the Ni metal films with the reaction of methane gas. The distances between the carbon nanotube tip and the anode are kept with 200 mm.
In the figure, the electron emission characteristics of carbon nanotubes shows turn-on at 3.7 V/mm and breakdown at 4.2 mA, reaching the maximum currents of 4.2 mA. These electron emission characteristics indicate lower current densities than those of carbon nanotubes grown at 950 °C or 750 °C.
It is considered that these differences of the current densities are due to the crystallity and vertical growth properties. However, the field emission characteristics of carbon nanotube grown at 550 °C indicate much higher current densities than those of the current silicon or metal emitter tips so that carbon nanotubes can be applied for the electron field emission sources in the case of various display constructions on the glass substrates.