Low-voltage organic transistor with subfemtoliter inkjet source-drain contacts
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Low-voltage organic transistor with subfemtoliter inkjet source–drain contacts Tomoyuki Yokota, Tsuyoshi Sekitani, Yu Kato, and Kazunori Kuribara, Department of Electrical Engineering and Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan Ute Zschieschang and Hagen Klauk, Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany Tatsuya Yamamoto and Kazuo Takimiya, Department of Applied Chemistry, Graduate School of Engineering, Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8527, Japan Hirokazu Kuwabara and Masaaki Ikeda, Nippon Kayaku Co., Ltd., Kita-ku, Tokyo 123-0865, Japan Takao Someya, Department of Electrical Engineering and Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan; Institute for Nano Quantum Information Electronics (INQIE), The University of Tokyo, Meguro-ku, Tokyo 153-8505, Japan Address all correspondence to Takao Someya at [email protected] (Received 6 May 2011; accepted 2 June 2011)
Abstract We have successfully achieved a transconductance of 0.76 S/m for organic thin-film transistors with 4 V operation, which is the largest value reported for organic transistors fabricated using printing methods. Using a subfemtoliter inkjet, silver electrodes with a line width of 1 µm and a channel length of 1 µm were printed directly onto an air-stable, high-mobility organic semiconductor that was deposited on a singlemolecule self-assembled monolayer-based gate dielectric. On reducing the droplet volume (0.5 fl) ejected from the inkjet nozzle, which reduces sintering temperatures down to 90 °C, the inkjet printing of silver electrodes was accomplished without damage to the organic semiconductor.
Printing processes such as inkjet have attracted significant attention for the fabrication of thin-film transistors (TFTs)[1–4] and other active devices, potentially offering less material consumption and lower cost compared with more traditional device manufacturing methods.[5–8] Employing the combination of inkjet and surface modification[9] or electrohydrodynamic jet printing,[10] the spatial resolution of printing has been recently reduced down to 1 µm or less, and applied to the fabrication of organic TFTs.[9–11] The main motivations to miniaturize dimensions of organic TFTs are reduction in power dissipation and increase in operation speed. The cutoff frequency, fT, is formulated by fT = gm/(2πCG), where gm and CG represent transconductance and gate capacitance, respectively; thereby, it is important to increase gm. For organic TFTs with a channel length of 90 nm, which were fabricated by electron beam lithography, gm as high as 0.4 S/m,[12] was reported. Furthermore, D. Frisbie reported on ion-gel gated organic transistors with a large transconductance (0.5 S/m).[13] In order to improve gm in printed organic TFTs, it is important to simultaneously realize an increase in mobility and a decrease in device dimensions. In addition to improving gm, the parasit
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