Yoshinori Horii

Simple push coating of polymer thin-film transistors

Organic semiconductors may be processed in solution under ambient conditions; however, liquid manipulation on hydrophobic surfaces is difficult, which may hinder development of devices. Here, a push-coating technique is used to produce large-area semiconducting polymer films over hydrophobic surfaces.

High-Performance Solution-Processed n-Channel Organic Thin-Film Transistors Based on a Long Chain Alkyl-Substituted C60 Derivative

We report on high-performance solution-processed n-channel organic thin-film transistors based on a long-chain alkyl-substituted fullerene derivative, C60-fused N-methylpyrrolidine-meta-dodecyl phenyl (C60MC12), by surface modification of an insulator. C60MC12 films were fabricated on self-assembled monolayer (SAM)-treated gate insulators by spin-coating, which was facilitated by hydrophilic patterning of the edge of the substrate. X-ray diffraction revealed that the crystallinity of C60MC12 films was improved by SAM treatment. The octadecyltrichlorosilane-treated device demonstrated a high mobility of 0.4–0.5 cm2 V-1 s-1, which is comparable with those of amorphous silicon thin-film transistors. An improvement in bias stress stability by the SAM treatment was also observed.

Dependence of electroluminescent properties on cathode metalsin PVCz double-layered organic EL devices

Abstract We have investigated cathode metal dependence of electroluminescence (EL) characteristics of PVCz based EL devices by using Sr, Mg and Ag. The following has been clarified. First, we have obtained luminance as high as 1000 cd/m2 for Poly(Nvinylcarbazole) (PVCz) EL devices without electron transport molecules but only emissive dye by using Mg and Sr metals cathode; while the device with Ag cathode showed a brightness about half as high. Secondly, threshold voltage for electroluminescence and barrier height for charge carrier injection both showed clear dependence on metal work function. Thirdly, chemical shift of core electron binding energy by X-ray photoelectron spectroscopy showed oxidation of Sr metal electrode near PVCz surface even if deposited under background pressure of 10−10 Torr, while that of Mg showed negligible shift.

Soluble Fullerene-Based n-Channel Organic Thin-Film Transistors Printed by Using a Polydimethylsiloxane Stamp

A polydimethylsiloxane stamp was applied for the first time to the fabrication of n-channel thin-film transistors based on soluble small molecule organic semiconducting materials. The stamping method was found to facilitate film transfer onto a gate insulator surface irrespective of its surface free energy. We used [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) and C(60)-fused N-methylpyrrolidine-meta-dodecyl phenyl (C60MC12) as n-channel materials. The stamped thin-film transistors of C60MC12 achieved a high electron mobility of 0.39 cm(2)/(V s) and a current on-off ratio of 1 × 10(7). The mobility of the stamped C60MC12 thin-film transistors did not depend much on the surface free energy of the SiO(2) gate insulator with and without surface treatment using a silane-coupling reagent. In particular, the stamped C60MC12 thin-film transistor exhibited a relatively high mobility of 0.1 cm(2)/(V s) on a high energy surface of untreated SiO(2). In addition, a complementary inverter composed of an n-channel and a p-channel stamped thin-film transistor was demonstrated for the first time, which exhibits a maximum gain of 63 at a supply voltage of 50 V.

Electroluminescence properties of PVCz electroluminescent devices doped with nano-crystalline particles

Abstract We have investigated PVCz multi-layered electroluminescent (EL) devices doped with ZnS based nano-crystalline particles. The particle size of prepared nano-crystal (NC) is varied from 2 to 5 nm. We have observed electroluminescent emission from the nano-crystalline particle doped PVCz polymer EL devices for both ZnS:Mn and Zn x Mg 1− x S:Mn NCs. We have described and discussed current–voltage and luminance–voltage characteristics together with EL spectra for PVCz EL devices doped with nano-crystalline particles. Preparation and characterization of nano-particles are also described and discussed.

Fabrication of a Textile-Based Wearable Blood Leakage Sensor Using Screen-Offset Printing

We fabricate a wearable blood leakage sensor on a cotton textile by combining two newly developed techniques. First, we employ a screen-offset printing technique that avoids blurring, short circuiting between adjacent conductive patterns, and electrode fracturing to form an interdigitated electrode structure for the sensor on a textile. Furthermore, we develop a scheme to distinguish blood from other substances by utilizing the specific dielectric dispersion of blood observed in the sub-megahertz frequency range. The sensor can detect blood volumes as low as 15 μL, which is significantly lower than those of commercially available products (which can detect approximately 1 mL of blood) and comparable to a recently reported value of approximately 10 μL. In this study, we merge two technologies to develop a more practical skin-friendly sensor that can be applied for safe, stress-free blood leakage monitoring during hemodialysis.

Developments of high precision printing processes for fabricating the flexible electronics

For the fabrication of an organic thin film transistor (OTFT) array on a plastic film using printing techniques, fine patterns with widths less than 10 μm were required. We have already succeeded to fabricate the OTFT arrays on a film substrate using microcontact printing and reverse-offset printing of silver nanoparticle ink; a width of the source and drain electrodes of the OTFT fabricated reached 5 μm, and its channel distance was also 5 μm. In this report, we introduce and explain our newly developed printing techniques based on microcontact printing, to obtain fine, high precision, and thick patterns for the manufacturing of the practical printed and flexible electronic devices.