Berlin 2005 – scientific programme

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HL: Halbleiterphysik

HL 61: Organische Halbleiter

HL 61.6: Talk

Wednesday, March 9, 2005, 12:00–12:15, TU P270

Optimisation of contacts for downscaling of organic thin-film transistors — •M. Leufgen¹, U. Bass¹, M. Michelfeit¹, T. Borzenko¹, G. Schmidt¹, J. Geurts¹, L. W. Molenkamp¹, and P. Mackie² — ¹Universität Würzburg, Physikalisches Institut (EPIII), Am Hubland, D-97074 Würzburg, Germany — ²Avecia Ltd., PO Box 42, Hexagon House, Blackley, Manchester M9 8ZS, UK

When downscaling the channel length of organic thin-film transistors (OTFTs), the conductance is increasingly governed by the electrical contact resistance. We verified this behaviour for DH4T-based bottom-contact OTFTs with different contact metals (Au/Ti, Pd). The electrical behaviour of the Au contacts was hampered by the Ti adhesion layer, while the Pd contacts, although electrically superior, suffered from insufficient mechanical stability.
We report two alternative strategies to overcome these drawbacks: (i)For Au/Ti, we developed a two-layer resist technique for UV lithography. The resulting undercut guarantees smooth and homogeneous metal contact edges, confirmed by SEM, and an improved Au/DH4T-contact. (ii)Sputtered Pt contacts have the necessary adhesion on SiO₂ and a good contact to the organic layer. In this context we optimised an e-beam lithography process, resulting in an undercut in the resist combined with a sub-100 nm resolution for large area structures (channel width of several 100 µm). Operating devices were fabricated both by vacuum deposition of DH4T and by spin cast deposition of diluted semiconducting polymers.