Abstract
In this work, self-assembled carbon nanotubes field effect transistors (CNT-FET) with semiconducting single-walled carbon nanotubes (SWNTs) as the channel were synthesized using Ni-Cr alloy as the catalysts. The Ti、Cr、Ni、Ti were deposited sequentially without breaking the vacuum to form Ti/Ni/Cr/Ti multi-layer stack on heavily doped n+ silicon wafer with 100 nm SiO2 layer on top by an E-gun system. After the deposition, thin films were patterned using lithography process and wet chemical etching. While the patterned multi-layer films were heated to the process temperature, of 900℃, Ni diffused into Cr and formed Ni-Cr alloy from Ti/Ni/Cr/Ti film at high temperature. Therefore Ni nano-particles were precipitated from Cr matrix. Single-walled carbon nanotubes were synthesized between two pre-defined Ti/Ni/Cr/Ti metal lines by means of thermal chemical vapor deposition (CVD) at 900℃ for 10 min. The C2H2 was used as reactant gas and the mixture of Ar and H2 was used as a carrier gas. The SWNTs were synthesized between two pre-defined Ti/Ni/Cr/Ti metal lines, which were used as source and drain in CNT-FET and the heavily doped n+ silicon wafer was used as a back-gate electrode. The spacing between two metal lines in the CNT-FETs was 2-10 μm. The SWNTs synthesized between two Ti/Ni/Cr/Ti metal lines were verified by Raman spectrum and AFM height images. The distribution of CNT diameters was in a range from 1.1 to 1.9 nm, with an average of 1.4 nm. The SWNTs grown using Ni-Cr alloy catalysts exhibit more homogeneous CNTs than those synthesized using Ni catalysts. The semiconducting characteristics of the CNTs using the Ni-Cr alloy catalysts were demonstrated by the transistor characteristics of the CNT-FETs fabricated.