Quality metrology of carbon nanotube thin films and its application for carbon nanotube-based electronics

Large area, highly uniform, and density controllable carbon nanotube (CNT) films, either well-aligned or random network, are required for practical application of CNT-based electronics. Mass production methods for such CNT films and corresponding quality metrology, which are critical for pushing the CNT-based transistor technology to manufacturing, should be developed in advance. Much progress has been made on fabrication of CNT films; however, there still lacks a metrology for thoroughly quantifying their quality until now. In this paper, through comparing study of CNT films fabricated by dip-coating (DC) and direct deposition (DD) methods, local anisotropy in the film is revealed to impact the performance uniformity of devices so fabricated in a spatial scale dependent manner. The anisotropy effect should be taken into account for the quality characterization of CNT films, which was not noticed in previous studies. Based on these findings, we propose a four-parameter metrology to quantify the overall quality of the CNT films, which includes the local tube density (D_L), global density uniformity (C_v), local degree of order (O_L), and the relative tube proportion in a certain orientation (P_θ) at a location. The four-parameter characterization and corresponding device performance confirm DC films are superior to DD films for practical application. The four-parameter metrology is not only powerful for overall quality evaluation of CNT films, but also able to predict the fluctuation of devices’ performance. Therefore, this material metrology is important for devices and circuits design and valuable for pushing the CNT-based transistor technology forward.