Potential mapping on organic devices: 3D simulations and experiments

D.S.H. Charrier, M. Kemerink, E. Smalbrugge, T. Vries, de, R.A.J. Janssen

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Scanning Kelvin Probe Microscopy and Electric Force Microscopy offer a unique opportunity to measure local (surface) potentials with nanometer resolution on actual devices. Therefore, these techniques are becoming more and more popular for characterizing physical aspects of organic thin film devices [1] like charge transport in polymer transistors [2] and charge generation in organic solar cells [3]. Unfortunately these techniques are extremely sensitive to the entire experimental geometry which severely limits the obtainable resolution. Here we present a numerical model that enables a quantitative description of experimental curves on a number of relevant organic devices. In addition, a strong and unexpected charging of common dielectric materials is found. We have focused our experiments and simulations on a study of the surface potential of samples with a standard organic transistor layout without active layer. A potential difference was applied between two flat electrodes, i.e. source and drain in FET operation, separated by an insulating micron-sized channel. It appeared that the measured potential profile strongly depends on whether the tip is parallel or orthogonal to the channel. Moreover, only a fraction (~0.6-0.9) of the applied voltage was observed in measured voltage traces. In order to understand the electrostatic interaction between the tip and the surface, and to explain these results we simulated the entire system of tip consisting of apex, cone and cantilever and sample in three dimensions using a commercial finite element program. The 3D simulations work for arbitrary potentials and realistic tip and cantilever geometries. It is shown to nicely reproduce the experimental features and yields valuable information on experimentally obtainable resolution versus tip-sample distance and tip-channel orientation. The increasing resolution with decreasing tip-sample distance is found to be due to the relative increase of the contribution of the apex area to the total probe-sample capacitance. The simulations fit the experimental surface potential using reasonable numerical parameters. Using the numerical tool to interpret experimental potential profiles of channels on different substrate materials, we found, to our surprise, that supposedly charge-free, insulating substrates do not at all behave as ideal dielectrics, but show significant charging effects when bias-stressed under ambient conditions.
Originele taal-2Engels
TitelProceedings of the Materials Research Society Symposium: Organic Thin-film Electronics-Materials, Processes, and Applications (MRS Spring Meeting 2007), 9-13 April 2007, San Francisco, California, USA
Plaats van productieSan Francisco, CA, USA
UitgeverijMaterials Research Society
Pagina's1-25
ISBN van geprinte versie978-1-605-60437-4
StatusGepubliceerd - 2007
EvenementOrganic Thin-Film Electronics: Materials, Processes, and Applications, April 9-13, 2007, San Francisco, CA, USA - San Francisco, CA, Verenigde Staten van Amerika
Duur: 9 apr 200713 apr 2007
http://www.mrs.org/s07-program-o/

Publicatie series

NaamMaterials Research Society Symposium Proceedings
Volume1003
ISSN van geprinte versie0272-9172

Congres

CongresOrganic Thin-Film Electronics: Materials, Processes, and Applications, April 9-13, 2007, San Francisco, CA, USA
LandVerenigde Staten van Amerika
StadSan Francisco, CA
Periode9/04/0713/04/07
AnderMaterials Research Society Spring Meeting 2007
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Citeer dit

Charrier, D. S. H., Kemerink, M., Smalbrugge, E., Vries, de, T., & Janssen, R. A. J. (2007). Potential mapping on organic devices: 3D simulations and experiments. In Proceedings of the Materials Research Society Symposium: Organic Thin-film Electronics-Materials, Processes, and Applications (MRS Spring Meeting 2007), 9-13 April 2007, San Francisco, California, USA (blz. 1-25). (Materials Research Society Symposium Proceedings; Vol. 1003). San Francisco, CA, USA: Materials Research Society.