Together with the group of Takao Someya and Tsuyoshi Sekitani at the University of Tokyo we have fabricated organic thin-film transistors (TFTs) in which the source and drain contacts are defined by subfemtoliter-inkjet-printing of silver nanoparticles directly onto the surface of the organic semiconductor.

Unlike regular inkjet printers, which dispense ink droplets with a volume of several picoliters and create dots with a diameter of 30 to 50 microns, the subfemtoliter inkjet system dispenses droplets with a volume of less than 1 femtoliter and a diameter of less than 1 micron.

Due to the small size of the inkjet-printed droplets, the organic solvent evaporates before the droplets reach the semiconductor surface, so that spreading of the material on the surface is efficiently suppressed.

The ink consists of monodispersed silver nanoparticles with a diameter of 2 to 3 nm. Because of the small size of the nanoparticles, a relatively low sintering temperature of about 120 °C is sufficient to remove the dispersing agent and fuse the nanoparticles into homogeneous metallic lines with near-bulk electrical conductivity. At this low sintering temperature the morphology of the organic semiconductors is not disturbed.

This allows organic TFTs with a channel length of 1 micron to be manufactured in a top-contact geometry with a relatively small contact resistance.

Flexible Low-Voltage Organic Transistors with High Thermal Stability at 250 °C
T. Yokota, K. Kuribara, T. Tokuhara, U. Zschieschang, H. Klauk, K. Takimiya, Y. Sadamitsu, M. Hamada, T. Sekitani, T. Someya
Advanced Materials, vol. 25, no. 27, pp. 3639-3644, July 2013

Low-voltage organic transistor with subfemtoliter inkjet source–drain contacts
T. Yokota, T. Sekitani, Y. Kato, K. Kuribara, U. Zschieschang, H. Klauk, T. Yamamoto, K. Takimiya, H. Kuwabara, M. Ikeda, T. Someya
MRS Communications, vol. 1, no. 1, pp. 3-6, November 2011

Organic transistors manufactured using inkjet technology with subfemtoliter accuracy
T. Sekitani, Y. Noguchi, U. Zschieschang, H. Klauk, T. Someya
Proceedings of the National Academy of Sciences of the U.S.A., vol. 105, no. 13, pp. 4976-4980, April 2008

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