Growth Of Low-Dimensional Carbon Materials And Study Of Carbon Nanotube Field Effect Transistors

The system of carbon allotropes spans an astounding range of extremes. As the fourth allotrope of condensed carbon, the one-dimensional carbon nanotubes (CNTs) have attracted considerable interest since their discovery. A major breakthrough occurred in recent years when two-dimensional graphene was successfully prepared. It has opened up new research space for low-dimensional carbon materials, which is explored to fields of physics, chemistry, electronics and biology because of their unique physical structure and electrical characteristics. The main purpose of this thesis is to obtain CNT-field effect transistors (FETs) with high performance especially with high switching ratio. In addition, the preparation of the material was also studied.The main content of the thesis is divided into the following four parts:1. Preparation and characterization of low-dimensional carbon materials:High density long straight CNT arrays and large graphene were prepared by improved chemical vapor deposition on silicon wafer. Then scanning electron microscopy, atomic force microscopy and Raman spectroscopy were used to characterize them. For CNT powder, we compared it in the dispersion of ethanol and dimethyl formamide, and made collection of CNTs from Langmuir film by lifting the substrate off DI-water while rotating. CNTs are well dispersed and with certain orientations.2. Improve the current on/off ratio (ION/IOFF) of CNT-FETs:Metal electrodes of devices were fabricated using photolithography techniques. Current-voltage curves were characterised via testing equipment for semiconductor transistors. By etching the device, remove the part of the oxide insulating layer, and then apply electrical cutting, the ION/IOFF increased 10-105 times.3. The influence of channel length alteration on the performances of CNT-FETs: Buffered oxide etching was used to remove approximately a 60 nm layer from the original 100 nm silicon dioxide layer, to thin the dielectric layer of the back gate. Channel length of the CNT-FETs was changed along with the etching process. The dependence of drain-source current on gate voltage was measured to analyze the performance of the device, including the transconductance, carrier mobility,ION/IOFF, etc. The results indicate that the devices still keep good quality.4. The influence of gate voltage scanning for the device performance:Continuous multiple gate voltage scannings were applied, and as obtained IDS-VGS curves were studied. The transfer characteristic curves showed that the CNT-FET performance was impacted for the current gradually decreases. Ultimately, devices were with a small IOFF (<2 nA) and larger ION/IOFF.