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Crystals 2019, 9(2), 85; https://doi.org/10.3390/cryst9020085

Critical Evaluation of Organic Thin-Film Transistor Models

1
Institute of Solid State Physics, NAWI Graz, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
2
Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany
3
Joanneum Research Materials, Institute for Surface Technologies and Photonics, Franz-Pichler-Straße 30, 8160 Weiz, Austria
*
Author to whom correspondence should be addressed.
Received: 20 December 2018 / Revised: 23 January 2019 / Accepted: 2 February 2019 / Published: 6 February 2019
(This article belongs to the Special Issue Thin Film Transistor)
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Abstract

The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel.
Keywords: organic thin-film transistor; transistor model evaluation; channel-length dependence; contact resistances; modeling contact effects; equivalent circuit; charge-carrier-mobility extraction organic thin-film transistor; transistor model evaluation; channel-length dependence; contact resistances; modeling contact effects; equivalent circuit; charge-carrier-mobility extraction
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Krammer, M.; Borchert, J.W.; Petritz, A.; Karner-Petritz, E.; Schider, G.; Stadlober, B.; Klauk, H.; Zojer, K. Critical Evaluation of Organic Thin-Film Transistor Models. Crystals 2019, 9, 85.

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