Molecular-Wetting Control by Ultrasmooth Pentacene Buffer for High-crystallinity Organic Field-Effect Transistors
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0965-S05-05
Molecular-Wetting Control by Ultrasmooth Pentacene Buffer for High-Crystallinity Organic Field-Effect Transistors Kenji Itaka1,2, Mitsugu Yamashiro3, Jun Yamaguchi1, Masamitsu Haemori1, Seiichiro Yaginuma1, Yuji Matsumoto2,3, and Hideomi Koinuma1,2 1 Graduate school of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8568, Japan 2 CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan 3 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama, 226-8503, Japan
ABSTRACT Organic thin film devices are of interest for a variety of forthcoming ubiquitous electronics applications. In order to build ubiquitous high-performance devices, it is necessary to fabricate crystalline thin films of various organic materials onto ``ubiquitous substrates'' that are dictated by applications. However, many organic thin films crystallize only on a limited selection of substrates. Unfortunately, promising organic molecules, which have a large overlap of pi-orbitals between molecules, cannot migrate freely on a substrate because of stronger cohesion between molecules than interaction between the molecule and the substrate. Therefore, enhancement of the molecule-substrate interaction, i.e. 'molecular wettability' should promote crystallization. We found that an ultrasmooth monolayer of pentacene (C22H14), which can be grown on many general dielectric substrates, changes the molecular wettability of a substrate for other poorly wettable organic materials. We also demonstrate that a field effect transistor (FET) using a crystalline C60 thin film on a pentacene-buffered substrate can have a mobility of 4.9 cm2/Vs, which is 5-fold higher than that of C60 FETs without the buffer. Molecular wetting-controlled substrates can thus offer a general solution to the fabrication of high-performance crystalline plastic and molecular electronics. INTRODUCTION Organic thin film devices are of interest for a variety of electrical applications such as displays1, complementary integrated circuits of field effect transistors (FETs)2 and photovoltaic cells3, and are promising for forthcoming ubiquitous society4. The realization of ubiquitous devices with high performance is necessary to fabricate crystalline thin films of various demanded organic materials onto a “ubiquitous substrate”. However, a lot of organic thin films are crystallized only on the limited substrates, for example, metal and alkali-halide. Although fullerene C60 is promising materials for electric devices because of many interesting functionality, for example, superconductivity5 and n-type FETs6-8,the performance of their FETs was degraded due to poor orientation of C60 thin films on typical dielectric layers like SiO2 and Al2O3. In case of typical bottom-gate FET, organic activation layers must be grown on popular dielectric compounds, such as SiO2, Al2O3.
In order to fabricate intriguing complex devices such as switching devices of thin film FETs, organic thin films
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