Sei Uemura

Influence of moisture on device characteristics of polythiophene-based field-effect transistors

We investigated a field-effect transistor (FET) based on a poly(3-n-hexylthiophene) (P3HT) to determine the influence of moisture on device characteristics and thus gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind. The fundamental output characteristics, which include effective field-effect modulation and saturation behavior in the output current, remained almost the same for every current–voltage profile in a vacuum, N2 and O2. By contrast, operation in N2 humidified with water resulted in enlarged off-state conduction and deterioration in the saturation behavior, in the same manner as that experienced with exposure to room air. We concluded that atmospheric water had a greater effect on the susceptibility of the device operation to air than O2, whose p-type doping activity as regards P3HT caused only a small increase in the conductivity of the active layer and a slight decrease in the field-effect mobility with exposure at ambient pres...

Surface Potential Control of an Insulator Layer for the High Performance Organic FET

It has been indicated that the pentacene crystal growth near the channel region is the most essential factor for determining pentacene FET properties and strongly depends on the surface energy of the substrate. In this study, surface modification effect of the SiO 2 /Si substrate by several kinds of polymers was investigated for the purpose of controlling surface potential and improve the FET properties. Matching the surface energy between the insulator and semiconductor layers using a polymer surface modifier gave improvement of the pentacene crystal growth and its FET properties. It was revealed that the molecular diffusion on a solid substrate and crystal growth mechanism were essential to give the effects.

Threshold voltage stability of organic field-effect transistors for various chemical species in the insulator surface

The relationship between the threshold voltage (Vt) stability and the chemical species of the insulator surface was investigated by using organic field-effect transistors with different types of self-assembled monolayers on a SiO2 insulator. The Vt shift induced by gate bias stressing was considerably increased by the introduction of long-chain chemical species to the SiO2 surface. In order to obtain high-performance and high-stability organic transistors, insulator surfaces with short-chain chemical species that can improve transistor performance without degrading stability are required.

Investigation for surface modification of polymer as an insulator layer of organic FET

We have investigated a double layer structured polymer gate dielectric for the organic field-effect transistor (FET) with the purpose of improving the performance of the polymer gate insulator. A polymer gate dielectric often causes a large hysteresis in the transfer characteristics of the organic FET. In this study, a water-soluble clay mineral layer was inserted between the PMMA and pentacene layer. It brought about improvement of the drain current and disappearance of the hysteresis.

Influence of fine roughness of insulator surface on threshold voltage stability of organic field-effect transistors

We have investigated the influence of the surface roughness of an insulator on the threshold voltage shift caused by gate bias stressing in organic field-effect transistors (OFETs). Our investigation was conducted for OFETs with SiO2 insulators. We observed that the threshold voltage shift is extremely sensitive to changes in the fine roughness of the SiO2 surface; the shift increased with the roughness. The large shift in OFETs with rough SiO2 insulators can be attributed to lattice distortion in pentacene layers deposited on rough SiO2 surfaces.

High-resolution full-color LCD driven by OTFTs using novel passivation film

A full-color twisted-nematic type liquid crystal display (TN-LCD) of 1.4-in diagonal size driven by organic thin-film transistors (TFTs) has been fabricated. This TN-LCD has 80/spl times/80/spl times/3 (RGB) pixel arrays addressed by pentacene TFTs with a channel width of 50 /spl mu/m. The contact resistance between the pentacene film and the source/drain electrodes has been reduced by selecting the exposure condition of the photoresist in patterning the electrodes. In addition, a solution-processed passivation film with a novel structure, consisting of photosensitive polyvinylalcohol and organosiloxane glass resin, has been developed to protect the TFTs against degradation induced by integration with TN-LCD devices. Consequently, it has been confirmed that the organic-TFT-driven TN-LCD fabricated in this paper is capable of displaying full-color moving images at a resolution of 80 pixels per inch.

An organic red-emitting diode with a water-soluble DNA–polyaniline complex containing Ru(bpy)32+

A Ru(bpy)32+-based red-emitting diode with a fast turn-on response was fabricated by employing a novel, processable and water-soluble DNA–photopolymerized PAn complex containing Ru(bpy)32+.

Photopolymerized Conducting Potyaniline Micropattern and Its Application

Abstract Photopolymerization of aniline derivatives was revealed to be induced by photoinduced electron transfer (PIET) between tris(2,2′-bipyridyl)ruthenium complex (Ru(bpy) 3 2+) and electroactive molecule. Characterization of the polyaniline prepared should be necessary to compare its potential with chemically or electrochemically polymerized polyaniline. From the results of cyclic voltammetry (CV), ER and 1 H-NMR analysis, the polymer was identified as polyaniline. GPC analysis of photopolymerized polyaniline indicated that the polyaniline has molar mass of about several thousands. Further, an application of the present photopolymerized polyaniline system was also proposed.

High-mobility solution-processed organic thin-film transistor array for active-matrix color liquid-crystal displays

Abstract— A solution-processed organic thin-film-transistor array to drive a 5-in.-diagonal liquid-crystal display has been fabricated, where semiconductor films, a gate dielectric film, and passivation films have all been formed using solution processes. A field-effect mobility of 1.6 cm2/V-sec, which is among the highest for solution-processed organic thin-film transistors ever reported, was obtained. This result is due to semiconductor material with large-grain-sized pentacene crystals formed from a solution and adoption of three-layered passivation films that minimize the performance degradation of organic thin-film transistors.

High Performance Organic FET with Double-Semiconductor Layers

The over-coating effect of a second semiconductor layer on a pentacene field-effect transistor (FET) was investigated. Me-PTC (n-type) coating gave improvements of the field-effect mobility and I DS for pentacene (p-type) FET. Such remarkable improvements were not observed in the TiOPC (p-type) coated pentacene (p-type) FET. These phenomena indicate that n-type semiconductor coating on a p-type semiconductor layer reduce the effect of trapped electrons at the crystal grain boundary. Besides, the over-coated layer also prevents the effect of water molecules adsorbed on pentacene crystals. Consequently, it was revealed that the p/n type hetero double-layered structure is effective to improve FET properties.