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Abstract: Electron trapping behavior at the interface between N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) film and thermal SiO2 was investigated by utilizing ultrathin poly(methyl methacrylate) (PMMA) gate passivation layers. From the capacitance–voltage analysis for the PTCDI-C13/PMMA/SiO2 interface, it is found that the electron tunneling appeared with PMMA thinner than 0.8nm, and that the thickness of the gate passivation layer should be at least 1nm for preventing injection-type hysteresis in the capacitance–voltage curve. The effective electron mobility of organic thin-film transistors (OTFTs) based on PTCDI-C13 with SiO2 gate insulator was increased by suppressing shallow-level interface traps on SiO2 with the PMMA layer, which can be partially accounted for by the multiple trap and release model. In this work, the thickness and the density of the PMMA layers were precisely controlled with a simple spin-coating process. Even 1.3-nm thick PMMA layer caused the improvements of the electron mobility and the air stability of the n-channel conduction. [Copyright &y& Elsevier]

An ultrathin polymethyl methacrylate PMMA buffer layer was developed to improve the performance of nchannel organic thinfilm transistors OTFTs. The 8 nmthick PMMA film, prepared by spincoating, provided a very smooth surface and a uniform coverage on SiO2surface reproducibly, which was confirmed by Xray reflectivity XR measurement. Then, we fabricated N,N′ditridecyl3,4,9,10perylenetetracarboxylic diimide PTCDIC13 thinfilm transistors with and without this 8 nmthick PMMA insulating layer on SiO2gate insulators and achieved oneorder increase of fieldeffect mobility up to 0.11 cm2Vs in a vacuum, onehalf decrease of threshold voltage, and reduction of current hysteresis with the PMMA layer. Only TFTs with the PMMA layer displayed nchannel operation in air and showed fieldeffect mobility of 0.10 cm2Vs. We consider that electrical characteristics of nchannel OTFTs were considerably improved because the ultrathin PMMA film could effectively passivate the SiO2insulator surface and decrease interfacial electron traps. This result suggests the importance of the ultrathin PMMA layer for controlling the interfacial state at the semiconductorinsulator interface and the device characteristics of OTFTs. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: N-channel operation of thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTCDA) with a 9-nm-thick poly(methyl methacrylate) (PMMA) gate buffer layer was examined. The uniform coverage of the ultrathin PMMA layer on an SiO2 gate insulator, verified by X-ray reflectivity measurement, caused the increase of electron field-effect mobility because of the suppression of electron traps existing on the SiO2 surface. In addition, air stability for n-channel operation of the NTCDA transistor was also improved by the PMMA layer which possibly prevented the adsorption of ambient water molecules onto the SiO2 surface. [Copyright &y& Elsevier]