Publications (7)6.19 Total impact
Article: Ultrathin polymer gate buffer layer for air‐stable, low‐voltage, n‐channel organic thin‐film transistors[show abstract] [hide abstract]
ABSTRACT: An ultrathin poly(methyl methacrylate) (PMMA) buffer layer was developed to improve the performance of n-channel organic thin-film transistors (OTFTs). The 8 nm-thick PMMA film, prepared by spin-coating, provided a very smooth surface and a uniform coverage on SiO2 surface reproducibly, which was confirmed by X-ray reflectivity (XR) measurement. Then, we fabricated N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) thin-film transistors with and without this 8 nm-thick PMMA insulating layer on SiO2 gate insulators and achieved one-order increase of field-effect mobility (up to 0.11 cm2/(Vs) in a vacuum), one-half decrease of threshold voltage, and reduction of current hysteresis with the PMMA layer. Only TFTs with the PMMA layer displayed n-channel operation in air and showed field-effect mobility of 0.10 cm2/(Vs). We consider that electrical characteristics of n-channel OTFTs were considerably improved because the ultrathin PMMA film could effectively passivate the SiO2 insulator surface and decrease interfacial electron traps. This result suggests the importance of the ultrathin PMMA layer for controlling the interfacial state at the semiconductor/insulator interface and the device characteristics of OTFTs. Copyright © 2009 John Wiley & Sons, Ltd.Polymers for Advanced Technologies 06/2009; 21(7):528 - 532. · 2.01 Impact Factor
Article: Alkyl and alkoxyl monolayers directly attached to silicon: chemical durability in aqueous solutions.[show abstract] [hide abstract]
ABSTRACT: For practical application of self-assembled monolayers (SAMs), knowledge of their chemical durability in acidic or basic solutions is important. In the present work, a series of SAMs directly immobilized on a silicon (111) surface through Si-C or Si-O-C covalent bonds without a native oxide layer were prepared by thermally activated chemical reactions of a hydrogen-terminated Si(111) substrate with linear molecules, i.e., 1-hexadecene, 1-hexadecanol, 1-dodecanol, and n-dodecanal, to investigate the durability of the SAMs to HF and Na2CO3 solutions. While grazing incidence X-ray reflectivity measurements showed that all the as-prepared SAMs had almost the same film density and molecular coverage, keeping the original step and terrace structure of Si(111) as is observed by atomic force microscopy, they gave different degradation behaviors, i.e., pitting and concomitant surface roughening in both solutions. 1-hexadecene SAM was stable against immersion in both solutions, while the other SAMs were damaged within 60 min, most likely due to the difference in chemical bonding modes at the SAM/Si interface, i.e., Si-C and Si-O-C.Langmuir 04/2009; 25(10):5516-25. · 4.19 Impact Factor
Article: N-channel operation of pentacene thin-film transistors with ultrathin polymer gate buffer layer[show abstract] [hide abstract]
ABSTRACT: N-channel operation of pentacene thin-film transistors with ultrathin poly(methyl methacrylate) (PMMA) gate buffer layer and gold source–drain electrode was observed. We prepared pentacene thin-film transistors with an 8-nm thick PMMA buffer layer on SiO2 gate insulators and obtained electron and hole field-effect mobilities of 5.3 × 10−2 cm2/(V s) and 0.21 cm2/(V s), respectively, in a vacuum of 0.1 Pa. In spite of using gold electrodes with a high work function, the electron mobility was considerably improved in comparison with previous studies, because the ultrathin PMMA film could decrease electron traps on SiO2 surfaces, and enhance the electron accumulation by applied gate voltages.
Article: N-channel thin-film transistors based on 1,4,5,8-naphthalene tetracarboxylic dianhydride with ultrathin polymer gate buffer layer
Article: Alternate stacking of transition metal ions and terephthalic acid molecules for the fabrication of self-assembled multilayers[show abstract] [hide abstract]
ABSTRACT: Self-assembled multilayers consisting of transition metal ions and biscarboxyl acid molecules have been fabricated by a layer-by-layer chemisorption technique. As transition metal ion, zirconium (Zr(IV)) or titanium (Ti(IV)) was employed, while terephthalic acid (TPA) was used as biscarboxyl molecule. In the multilayers, two TPA monolayers were bridged by one monolayer of Zr(IV) or Ti(IV) most likely through coordination bonds between the metal ions and the carboxyl groups in the TPA molecules. Although the both transition metal ions were successfully applied to construct multilayers, the multilayer structure of the Ti–TPA system was more disordered than that of the Zr–TPA system as revealed by grazing incidence X-ray reflectivity.
Article: Investigation of electron trapping behavior in n-channel organic thin-film transistors with ultrathin polymer passivation on SiO2 gate insulator[show abstract] [hide abstract]
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 0.8 nm, and that the thickness of the gate passivation layer should be at least 1 nm 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.
Article: Organosilane self-assembled multilayer formation based on activation of methyl-terminated surface with reactive oxygen species generated by vacuum ultra-violet excitation of atmospheric oxygen molecules[show abstract] [hide abstract]
ABSTRACT: A xenon excimer lamp which irradiates vacuum ultra-violet (VUV) light at 172 nm in wavelength was applied to the photochemical surface conversion of n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) in the presence of atmospheric oxygen and subsequent multilayer fabrication. The terminal functional groups of ODS-SAM, –CH3 groups, were converted into polar functional groups, like –COOH, by the reaction with atomic oxygen species generated photochemically through VUV excitation of atmospheric oxygen molecules. The structure of the resulting organosilane multilayer with different numbers of superimposed monolayers (from 1 to 11), prepared on a smooth and hydrophilic silicon substrate by the layer-by-layer (LbL) approach, was examined in terms of molecular organization as well as the intra- or interlayer binding modes in such novel films. Ellipsometry and grazing angle X-ray reflectivity measurements revealed that multilayer films of up to 11 discrete monolayers were successfully obtained, indicating that the self-assembly is a viable technique for the construction of relatively thick (16 nm and above) multilayer films.