We have developed a new type electrical probing system based on an atomic force microscope. This method enables us to measure simultaneously the surface topography and surface potential of thin films containing the crystal grains. The obtained local potential changes give an insight into conduction through the grains and their boundaries.

The doping effect of acceptor molecule tetracyanoquinodimethane (TCNQ) and donor molecule tetramethyltetraselenafulvalene (TMTSF) in an organic semiconductor was investigated by field effect measurements in merocyanine (MC) films. The electrical conductivity and carrier concentration of TCNQ-doped MC films were increased compared with those of undoped MC film. An efficient doping effect was observed at the doping concentration of approximately 9%. The electrical conductivity, on the other hand, was decreased by doping of the donor molecule TMTSF in MC film. However, no inversion of the conduction type was obtained. Furthermore, the transport mechanism of TCNQ-doped MC film and undoped film was elucidated from the temperature dependence of electrical parameters. These results demonstrate that TCNQ and TMTSF molecules act as acceptor and donor impurities in MC film, respectively, and the doping of these molecules is effective to control the electrical properties of organic semiconductors.

We have demonstrated the inverter operation of stacked-structure CMOS devices using pentacene and ZnO as active layers. The fabrication process of the device is as follows: A top-gate-type ZnO thin-film transistor (TFT), working as an n-channel transistor, was formed on a glass substrate. Then, a bottom-gate-type pentacene TFT, as a p-channel transistor, was fabricated on top of the ZnO TFT while sharing a common gate electrode. For both TFTs, solution-processed silicone-resin layers were used as gate dielectrics. The stacked-structure CMOS has several advantages, for example, easy patterning of active material, compact device area per stage and short interconnection length, as compared with the planar configuration in a conventional CMOS circuit.

We have fabricated printed active antenna for flexible information tag which have a loop antenna combined with step-edge vertical channel organic field-effect transistor (SVC-OFET). Fabrication using printing process, characterization of SVC-OFETs, and performances of active antenna elements are discussed in detail.

STM/STS measurements have been carried out for TTF-TCNQ complex films evaporated on hydrogen-terminated silicon substrates, and the variation of tunneling spectra has been investigated on morphologically different crystal grains. Very thin semiconductive adsorbed layers were found to cover the as-deposited film surfaces. By removing the adsorbed layers, the intrinsic electronic structures of two different phases were revealed. A 'needle phase' which appears at the early stage of film growth has a semiconductive character and a 'granular phase' which grows later has a metallic character similar to bulk crystals. The electronic structure of the needle phase is considered to be affected by the substrate although the crystallographic structure is similar to the bulk crystal of TTF-TCNQ.

We investigated the electrical properties of hole transport materials such as TPD, α-NPD and m-MTDATA using in-situ field effect measurement. TPD, α-NPD and m-MTDATA films showed p-type semiconducting properties, and their electrical parameters such as conductivity, carrier mobility and carrier concentration were obtained. We also examined the effect of the substrate temperature during vacuum deposition and the thermal treatment after deposition, on the electrical parameters of the films. Experimental results showed that conductivity and carrier mobility decreased as the substrate temperature increased over the glass transition temperature. These decreases in conductivity and carrier mobility as a result of thermal treatment appear to be strongly related to the degradation mechanism of organic electroluminescent devices.

We have fabricated a static induction transistor structure by using copper phthalocyanine (CuPc) films. Its layer-structure is Au(drain)/CuPc/Al(gate)/CuPc/Au(source)/glass. The source-drain current is controlled by the Al gate bias-voltage when the drain voltage is positive but is almost independent of it when the drain voltage is negative. The current-voltage characteristics are governed by the space-charge-limited conduction which depends on shallow traps.

Organic static induction transistor (OSIT) is a promising driving device for the displays, since it shows high-speed, high-power and low-voltage operation. In this study, the OSIT with fine gate electrode patterned by electron beam exposure were fabricated. We investigated the basic electrical characteristics of copper phthalocyanine OSIT and compared with the calculation results obtained by two-dimensional (2D) device simulator. The experimental results show that the gate modulation improved by reducing the electrode gap and on/off current ratio depends on the gate gap.

The control of the organic field-effect transistor characteristics is necessary to produce the integrated circuits using organic semiconductors. Variations in the poly (3-hexylthiophene) field-effect transistor characteristics upon post-treatment such as thermal treatment and voltage treatment in N2 atmosphere have been investigated. The controllability and reproducibility of the threshold voltage and mobility were achieved as a result of the post-treatments.

Organic field-effect transistors (FETs) which employ (BEDT-TTF)(TCNQ) films for active layer have been fabricated and characterized. Their FET characteristics exhibited both p-channel and n-channel operation by changing the gate and drain voltages. For a particular bias condition, the I-V curves revealed behavior where both electrons and holes simultaneously are injected from source and drain electrodes. These bipolar type characteristics are strongly related to the structure of donor and acceptor molecular layers. The degree of charge transfer of approximately 0.2 was estimated by Raman spectroscopy.