Flexible and transparent all-carbon thin-film transistors and integrated circuits
Carbon nanotube (CNT) thin films are expected to enable the fabrication of high-performance, flexible, and transparent electronic devices with a relatively simple technique [1, 2]. In this work, we report all-carbon thin film transistors (TFTs) and integrated circuits (ICs), in which all materials are organics or carbon nanotube. The active channels and passive elements (electrodes, interconnections) have been formed by CNT thin film.
We fabricated top-gate-type TFTs and ICs on a polyethylene naphthalate (PEN) film substrate. The channel was formed by a single-walled CNT thin film with a linear density of about 0.5 tubes/μm. The electrodes and interconnections also consist of thicker single-walled CNT films (transparency: 85 % at 550 nm, sheet resistance: 150 Ω/sq). A polymethylmethacrylate (PMMA) layer with a thickness of 660 nm was used as the gate insulator. The CNT thin films were grown by floating-catalyst chemical vapor deposition technique , collected by a membrane filter, and then transferred on the PEN substrate. The PMMA layer was spin-coated on the substrate. The patterning of CNT films and PMMA layer were carried out by conventional photolithography and plasma etching processes.
The fabricated devices have the transparency of 80% in average. The all-carbon TFT show on/off ratio of 1.5x105. and mobility of 1,027 cm2/Vs evaluated by the rigorous model  (321 cm2/Vs by parallel plate model). An various kinds of functional integrated circuits are demonstrated at an relatively low operation voltage of 5 V. A bending test verified the good flexibility of the all-carbon devices.
Acknowledgments: This work was partially supported by '08 NEDO Grant, R&D promotion scheme funding international joint research promoted by NICT, ALCA-JST, Grant-in-Aid of MEXT, the Aalto University MIDE program via the CNB-E project, and the Academy of Finland (Pr. No. 128445). Canatu Oy provided transparent CNT thin films for electrodes.
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