Limitations of the tuning of interface dipoles for the reduction of the contact resistance in organic thin-film transistors

James Borchert; Tobias Wollandt; Ute Zschieschang; Florian von Wrochem; Boyu Peng; Paddy K. L. Chan; R. Thomas Weitz; Klaus Kern; Sabine Ludwigs; Hagen Klauk

doi:10.1117/12.2568003

20 August 2020 Limitations of the tuning of interface dipoles for the reduction of the contact resistance in organic thin-film transistors

James Borchert, Tobias Wollandt, Ute Zschieschang, Florian von Wrochem, Boyu Peng, Paddy K. L. Chan, R. Thomas Weitz, Klaus Kern, Sabine Ludwigs, Hagen Klauk

Author Affiliations +

Proceedings Volume 11476, Organic and Hybrid Field-Effect Transistors XIX; 1147616 (2020) https://doi.org/10.1117/12.2568003
Event: SPIE Organic Photonics + Electronics, 2020, Online Only

Conference Poster

Abstract

Achieving gigahertz transit frequencies in low-voltage organic thin-film transistors (TFTs) will require a contact resistance below about 1 Ohm-cm [1,2]. A general approach to reduce the contact resistance in organic devices is to modify the surface of the metal contacts with a chemisorbed interface layer, ostensibly by reducing the nominal injection barrier. Combined with a thin gate dielectric, this approach can enable contact resistances below 30 Ohm-cm and transit frequencies above 10 MHz at low voltages in coplanar organic TFTs [3,4]. However, further reduction of the contact resistance depends strongly on non-idealities of the interface other than the nominal barrier height according to the Schottky-Mott limit. We show a detailed study on the efficacy of interface layers based on various thiols to improve the contact resistance in coplanar dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) TFTs. We compare the contact resistance of multiple sets of TFTs to results from ultraviolet photoelectron spectroscopy measurements and find strong evidence that Fermi-level pinning prevents a significant reduction of the contact resistance below about 100 Ohm-cm in DNTT TFTs. Therefore, we conclude that this approach may not be a generally sufficient method by itself to eliminate the contact resistance in organic TFTs.

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James Borchert, Tobias Wollandt, Ute Zschieschang, Florian von Wrochem, Boyu Peng, Paddy K. L. Chan, R. Thomas Weitz, Klaus Kern, Sabine Ludwigs, and Hagen Klauk "Limitations of the tuning of interface dipoles for the reduction of the contact resistance in organic thin-film transistors", Proc. SPIE 11476, Organic and Hybrid Field-Effect Transistors XIX, 1147616 (20 August 2020); https://doi.org/10.1117/12.2568003

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