Fabrication of Thin-Film Transistors Using PECVD-Grown Carbon Nanotubes and Their Application to Integrated Circuits
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Fabrication of Thin-Film Transistors Using PECVD-Grown Carbon Nanotubes and Their Application to Integrated Circuits Takashi Mizutani1 and Shigeru Kishimoto1,2 1
Quantum Engineering, Nagoya University, Nagoya 464-8603, Japan.
2
Venture Business Laboratory, Nagoya University, Nagoya 464-8603, Japan.
ABSTRACT Medium scale integrated circuits with 108 CNT-TFTs have been fabricated using CNTs grown by plasma enhanced chemical vapor deposition (PECVD) which has the advantage of preferential growth of CNTs with semiconducting behavior in the FET current–voltage characteristics. High-speed operation with a switching time of 0.51 Ps/gate, which is highest in the CNT-TFT integrated circuits to our knowledge, was demonstrated by a 53-stage ring oscillator. Characterization of CNT-TFTs using scanning probe microscopy has also been performed. The island-like structure in the electrical properties of the CNT network was observed even in a high-density CNT network in the subthreshold regime. This was explained by the decrease of the effective number of CNTs which contribute the electrical conduction. INTRODUCTION Nanoscale electronics made from carbon nanotubes (CNTs) such as transistors [1,2] and biosensors [3,4] are more versatile than those that rely on conventional microelectronics. However, their development for practical application has been hindered by the difficulty in integrating many CNT transistors that have a small off current with high uniformity and high reproducibility because of the possibility of metallic CNT incorporation. Thin-film transistors (TFTs) with a CNT network as a channel are expected to be suitable for circuit applications that overcome such barriers because it should be possible to suppress the off current by choosing a moderate CNT density that is less than the percolation threshold of metallic CNTs (m-CNTs). It might also be possible to improve the uniformity of the device taking the advantage of averaging effect of the CNT random network. Even though there are many reports which studied the fabrication of CNT-TFTs [510], there are few which studied the integration of the CNT-TFTs [11-13]. In addition, the integration scale and operation speed are not sufficient. In this study, we report the fabrication of CNT-FETs/TFTs using CNTs grown by plasma enhanced chemical vapor deposition (PECVD) which has the advantage of preferential growth of CNTs with semiconducting behavior in the FET current–voltage (I-V) characteristics [14,15]. The fabrication technology has been applied to implement medium scale integrated circuits with 108 CNT-TFTs [16]. Characterization of CNT-TFTs using scanning probe microscopy has also been performed to get a better understanding of the CNT-TFT operation [17].
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EXPERIMENTAL RESULTS Fabrication of thin-film transistors CNTs used for the FET/TFT channel were grown by grid-inserted microwave PECVD on a SiO 2 /p+-Si substrate [18]. Backgate electrode configuration was employed. Typical I D -V GS characteristics of the fabricated CNT-FETs measured at room temperature ar
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