Organic transistors manufactured using inkjet technology with subfemtoliter accuracy
- *Quantum-Phase Electronics Center, School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan; and
- †Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
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Edited by Zhenan Bao, Stanford University, Stanford, CA, and accepted by the Editorial Board February 7, 2008 (received for review September 5, 2007)
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Fig. 1.Printed Ag nanoparticles using subfemtoliter inkjet. (a and b) Optical microscope image (a) and atomic force microscope (AFM) image (b) of fine dots of Ag nanoparticles deposited by subfemtoliter inkjet printing on the surface of a thin pentacene film after calcination at 130°C. The diameter of the dots is ≈2 μm, and the thickness is 30 nm. The dots were formed with a single printing pass. (c) Optical microscope image of inkjet-printed Ag lines after a single printing pass before calcination. Linewidths between 1 μm and 5 μm were obtained in a controlled manner by adjusting the electric field inside the inkjet nozzle. (d) Optical microscope image of inkjet-printed Ag lines after a single printing pass and after calcination at 130°C. Lines with a linewidth down to 2 μm are uniform and continuous over large areas. (e) Optical microscope image showing the effect of multiple-pass printing on the evolution of the morphology of an inkjet-printed Ag line after calcination. The effective thickness of the line increases from 30 nm after a single pass to 600 nm after 20 passes. (f) Evolution of the electrical resistivity of inkjet-printed Ag lines with the number of passes after calcination at 130°C for 1 h in nitrogen.
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Fig. 2.Structure, micrograph, and AFM image of organic transistors. (a) Schematic cross-section of the organic thin-film transistors with patterned Al gates, ultrathin gate dielectric, vacuum-deposited organic semiconductor, and subfemtoliter inkjet-printed Ag nanoparticle source/drain contacts. (b) Optical microscope images of pentacene TFTs with channel length of 1 μm, 2 μm, and 5 μm after calcination (the linewidth of the inkjet-printed contact lines is 5 μm). (c) AFM image of a pentacene TFT with a channel length of 5 μm and a contact linewidth of 2 μm.
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Fig. 3.Transistor characteristics of p-type pentacene TFTs. (a and b) Output (a) and transfer (b) characteristics of a p-channel pentacene TFT with a channel length of 1 μm and a channel width of 300 μm. The measurements were carried out in air. (c) Transfer characteristics of pentacene TFTs with channel length of 1 μm, 6 μm, 10 μm, and 100 μm, showing the scaling of the maximum drain current with channel length (channel width is 300 μm for all devices). The measurements were taken on TFTs prepared without substrate heating during the pentacene deposition. (d) The resistance of pentacene TFTs in the saturation regime scales linearly with channel length, as predicted by field-effect transistor theory. By extrapolating the linear fit to a channel length of zero, a contact resistance of 5 kΩ·cm is extracted.
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Fig. 4.Electrical characteristics of n-type F16CuPc TFTs and organic CMOS inverter. (a and b) Output (a) and transfer (b) characteristics of an n-channel F16CuPc TFT with a channel length of 10 μm and a channel width of 60 μm. The measurements were carried out in air. (c and d) Optical microscope image (c) and transfer characteristics (d) of an organic complementary inverter. The pentacene TFT has a channel length of 50 μm, the F16CuPc TFT has a channel length of 5 μm, and both TFTs have a channel width of 60 μm. The inverter operates with supply voltages between 1.5 V and 3 V and with a small-signal gain >10.
Footnotes
- ‡To whom correspondence should be addressed. E-mail: someya{at}ap.t.u-tokyo.ac.jp
- © 2008 by The National Academy of Sciences of the USA
