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High throughput printing processes have been developed for the fabrication of organic flexible sheet devices. However, printing processes inevitably use toxic solvents to prepare inks of organic semiconductors. Here we propose a novel and complementary method for the preparation of flexible sheet electronics. A thermal pressing method has several advantages, such as (i) being solvent-free, (ii) resulting in flexible device with structural durability against bending, (iii) making simultaneous sealing available to prevent physical or atmospheric damage, and (iv) providing seamless application to roll-to-roll processes by combination with toner technology. We have demonstrated that the characteristics of a flexible organic field-effect transistor (OFET) fabricated by the thermal press process were not degraded during or after the bending test until a bending radius of 2 mm was achieved, which is sufficient for the concept of a rolled-up type flexible sheet display.

The usual silicon-based display back planes require fairly high process temperature and thus the development of a low temperature process is needed on flexible plastic substrates. A new type of flexible organic light emitting transistor (OLET) had been proposed and investigated in the previous work. By using ultraviolet/ozone (UV/O3) assisted thermal treatments on wet processed zinc oxide field effect transistor (ZnO-FET), through low-process temperature, ZnO-FETs were fabricated which succeeded to achieve target drain current value and mobility. In this study, physical property evaluation of ZnO was conducted in term of their crystallinity, the increase composition of ZnO formed inside the thin film and the decrease of the carbon impurities originated from aqueous solution of the ZnO itself. The X-ray diffraction (XRD) evaluation showed UV/O3 assisted thermal treatment has no obvious effect towards crystallinity of ZnO in the range of low process temperature. Moreover, through X-ray photoelectron spectroscopy (XPS) evaluation and Fourier transform infrared (FT-IR) spectroscopy evaluation, more carbon impurities disappeared from the ZnO thin film and the increase of composition amount of ZnO, when the thin film was subjected to UV/O3 assisted thermal treatment. Therefore, UV/O3 assisted thermal treatment contributed in carbon impurities elimination and accelerate ZnO formation in ZnO thin film, which led to the improvement in the electrical property of ZnO-FET in the low-process temperature.

The effect of an applied gate electric field on the charge-order phase in β-(BEDT-TTF)2PF6 single-crystal field-effect transistor structure was observed at around room temperature by technical improvement with respect to sample preparation and electrical measurements. A relatively slight but systematic increase of the electrical conductance induced by the applied gate electric field and its temperature dependence was observed at around the metal-insulator transition temperature (TMI). The temperature dependence of the modulated electrical conductance demonstrated that TMI was shifted toward the lower side by application of a gate electric field, which corresponds to partial dissolution of the charge-order phase. The thickness of the partially dissolved charge order region was estimated to be several score times larger than the charge accumulation region.

A gate-induced thermally stimulated current (TSC) on β′-(BEDT-TTF)(TCNQ) crystalline FET were conducted to elucidate the previously observed ferroelectric-like behaviors. TSC which is symmetric for the polarization of an applied VPG and has a peak at around 285 K was assigned as a pyroelectric current. By integrating the pyroelectric current, temperature dependence of the remnant polarization charge was obtained and the existence of the ferroelectric phase transition at 285 K was clearly demonstrated. We have tentatively concluded that the phase transition between dimer Mott insulator and charge ordered phase occurred at around the interface of organic crystal and substrate.

Vertical type field effect transistors (FETs) are expected to be used for various organic devices because of their low-voltage, high-current and high-speed operation. We have fabricated lateral and vertical type FETs using copper-phthalocyanine evaporated films and measured the basic static and dynamic characteristics of these FETs. Although both transistors show field effect characteristics, the vertical type FET showed high-frequency and high-current characteristics under relatively low-voltage conditions as compared with those of lateral type FETs. These results demonstrate that the vertical FET operates as a static induction transistor and the short length between the source, drain and gate electrodes in the device structure improves the device characteristics.

Highly oriented TTF-TCNQ grains were prepared by applying an electric field during the evaporation. We were able to clarify the orientation process of TTF-TCNQ grains and the electrical property corresponding to the long axis of the crystal grain.

Organic static induction transistors (SITs) for display devices are proposed and the basic electrical characteristics of the SITs are investigated. The organic SITs, using a copper phthalocyanine (CuPc) evaporated film as an active layer, have a layered structure of Au (drain)/CuPc/Al (gate)/CuPc/Au (source)/glass. The electrical characteristics show that the current flow from the source to drain electrodes is controlled by relatively low gate voltages. Furthermore, excellent characteristics such as a high current density of approximately 4 mA/cm2 and high-speed operation of less than 0.25 ms are realized by applying a buried Al grid electrode as the Schottky gate.

Static induction transistors (SITs) using copper phthalocyanine films and Al Schottky gate electrode are fabricated and the basic electrical characteristics are investigated. The electrical characteristics show that the current flows from the source to drain electrodes is controlled by the Al gate voltage and a typical SIT operation with non-saturating properties is examined. Furthermore, a high power and high frequency operation as organic transistors is obtained.

We have investigated the effect of bias voltage applied to an electrically conductive substrate on the formation of adsorption Langmuir–Blodgett (LB) films. In fabricating the adsorption LB films, we used tetracyanoquinodimethane (TCNQ) with a long alkyl chain as a molecule for spreading monolayers on the subphase and tetramethyl- p -phenylenediamine (TMPD) as a material for adsorbing from the subphase to the monolayers. It is well known that TCNQ and TMPD are acceptor-like and donor-like molecules, respectively. In the visible absorption spectra and Fourier transform infrared reflection–absorption spectra of the adsorption LB films fabricated under several bias conditions, the peaks assigned to TCNQ show a clear dependence on the bias voltage. The electrical conductivity corresponding to the quantity of charge-transfer complex was also obtained. These results demonstrate that the bias-voltage LB technique enables us to control the formation of the charge-transfer complex.

Negative photoelectrical properties are observed in adsorption Langmuir–Blodgett films consisting of merocyanine dye and brilliant green under illumination using two lights. These peculiar properties are strongly dependent on the polarized direction of the two lights and their wavelengths corresponding to the absorption peaks of the two dyes. We have analyzed the photoelectric process between the two dyes, comparing the experimental results and the simulation using the model for photogenerated carriers via trap levels formed between the two dyes.

We have investigated the effect of an electric field on the molecular orientation of tetrathiafulvalene–tetracyanoquinodimethane (TTF–TCNQ) co-evaporated films, using an optical microscope, a scanning tunnelling microscope and X-ray diffraction. It is found that with an electric field applied TTF–TCNQ grows with the b-axis parallel to the electric field.

We have fabricated photoelectric cells using multi-layered organic dyes and evaluated their photoelectric properties. These cells have both functions of color filtering and bias voltage dependence of the dissociation of photoexcited excitons. The photocurrent spectral sensitivity of the multi-layered cells can be controlled by the bias voltage.

Thin film transistors using several p, n-type organic semiconductors were fabricated and their electrical properties of conduction-type, carrier mobility, electrical conductivity, and carrier concentration were evaluated by in-situ field effect measurements.

Photoconductivity (PC) measurements were employed to investigate the photoelectric properties of InAs/GaAs strained-layer structure grown on GaAs (100), (311)A and (111)A substrates. PC results of the sample grown on GaAs (311)A and (111)A substrates showed specific PC signals at lower energy region (around 1.2 eV) from GaAs band-edge. From transient PC measurement varying the sample temperature, activation energies of around 0.19 eV were obtained for the sample grown on (311)A substrate with 1 monolayer of InAs. These activation energies suggest the existence of relatively thick InAs region that are locally formed and/or specific defects formed in thesamples grown on highly oriented substrates.

Langmuir-Blodgett (LB) films containing functional dyes were deposited directly onto optical fibers by the adsorption LB method. A merocyanine derivative having a long alkyl chain and rhodamine B were used as spreading and adsorbing molecules from the aqueous subphase, respectively. During the LB film deposition, absorption spectra from the optical interaction with the LB films at the core portion of the fiber were monitored using a multi-channel photo-detector system. Furthermore, the influence of the excitation light, which was guided into the fiber during the deposition, on the film deposition was investigated. The experimental results indicated that the in-situ optical measurement using optical fibers has high sensitivity and this is one of the promising methods to investigate the molecular interactions and the effect of the incident light on the LB film deposition.

Absorption spectra of adsorption Langmuir-Blodgett (LB) films were measured during and after the deposition of malachite green adsorbed merocyanine LB films on an optical fiber. The experimental results show that the in-situ optical monitoring using optical fibers is one of the powerful method to investigate the optical properties and the molecular interactions in the adsorption LB films.

Field effect and capacitance-voltage characteristics of vacuum evaporated C60 films are studied using metal-oxide-semiconductor structures such as metal / C60 / SiO2 / n+-Si or C60 / source-drain electrodes / SiO2 / n+-Si. The electrical conductivity, carrier type, carrier concentration, and carrier mobility are estimated from these measurements. In particular, electrical characteristics during the deposition in vacuum and the influence of oxygen and nitrogen gases are investigated by the in-situ field effect measurement.

TTF–TCNQ co-evaporated films were fabricated on variously surface–modified substrates and the structural investigation was carried out by scanning electron microscope and X-ray diffraction measurements. It was, indicated that the molecular orientation was controllable on a properly modified substrate by chosing an evaporation condition. Furthermore, the selective growth of the TTF–TCNQ film was achieved on the surface-modified substrate using a standard photolithographic technique.

Optical and electrical changes in several kinds of organic films after ion implantation were investigated. Vacuum evaporated organic films were irradiated by 30-100 keV N + ion beam. The ion dose was varied from 10 14 to 10 16 ions/cm 2 . The surface resistivity varies 9 orders of magnitude from the order of 10 17 ohm/ □ to 10 8 ohm/ □. Furthermore, the film color changes to dark brown with increasing dose, and main optical absorption peaks of the organic molecule itself decreased. The electrical and optical changes by ion implantation seem to reflect chemical elements and physical properties of these films originated from the molecular structure. Furthermore, the large increase in conductivity by ion beam irradiation is due to the formation of carbon clusters in the organic films. These experimental results suggest that the modification of optoelectric properties and three dimensional wiring in organic films by ion implantation are promising techniques for molecular electronic devices.

The orientations of TTF-TCNQ films co-evaporated onto several kinds of organic buffer layers were investigated. The c*-axis of TTF-TCNQ was normal to the substrates. However, the direction of the b-axis was random on CaF2 and cadmium-stearate LB film deposited CaF2 substrates. The b-axis of TTF-TCNQ evaporated on polytetra- fluoroethylene (PTFE) rubbing layer arranged across the rubbing direction, but the film contained many grooves due to PTFE rubbing. TTT-TCNQ films on calcium-stearate/PTFE buffer layer had flat surface, even though the degree of the b-axis orientation was not high.

We have investigated thermal oxidation of silicon, and dry and wet etching characteristics of the oxide layer after N+ (Ar−) ion implantation and subsequent annealing. An oxidation resistance is observed in the N+ implanted silicon with doses more than 1 × 1015 N+ /cm2. The etch rate of the oxide layer in a diluted HF solution is enhanced with a dose of 1 × 1015 N+ / cm2, whereas an etching resistance is observed for the samples with doses more than 2 × 1015 N+ /cm2. However, only the etching resistance appears in the dry etching. These resistances are also observed by argon implantation and easily removed by subsequent annealing. These results indicate that the oxidation and etching resistances are related to a thin oxynitride formation and the surface modification by ion implantation.

The formation of carbon clusters in ion implanted organic films was examined by electrical conductivity and optical absorption measurements. The surface resistivity of the films decreased by seven orders of magnitude after the ion implantation. The main optical absorption peaks of the film decreased gradually with increasing ion dose, and the absorption profile of the film was changed into a broad and monotonical one. Ion implanted polyethylene films had strong peaks at shorter wavelengths in the absorption spectrum. These results demonstrate that carbon clusters containing fullerenes (C60, C70) were created in organic films by ion implantation.

IR and inelastic electron tunneling spectroscopy (IETS) techniques are employed to investigate adsorption Langmuir-Blodgett monolayers deposited on silicon substrate with a thin SiO2 film. Merocyanine dye (MC) and crystal violet (CV) are used as a spreading material and an adsorption dye from an aqueous subphase, respectively. IR and IETS data show that the carboxyl group in the MC molecule and the substituent group in the CV molecule are concerned with the adsorption mechanism.

The effects of organic buffer layers consisting of Langmuir-Blodgett (LB) monolayers on the film growth of organic materials were investigated. Tetracyanoquinodimethane (TCNQ) was vacuum-evaporated onto the LB monolayers formed on silicon and glass substrates. The crystallinity and molecular orientation in the evaporated films were analyzed by using X-ray diffraction measurement. These results revealed that the organic buffer layer using LB films strongly affects the orientation of the TCNQ molecules, and the LB films are suitable materials to use for investigating the growth mechanism in relation to the interaction between evaporated molecules and the organic buffer layer.

Microstructures formed in InAs/GaAs multiple quantum well structures grown on variously oriented GaAs substrates have been investigated. Details of structure and the optical properties of the microstructures are evaluated by X-ray diffraction and low temperature photoluminescence measurements. Results show the formation of the microstructure depending on the substrate orientation and growth conditions.

The new integrated circuit concept that forms electronic equipment by the textile structure using the flexible fiber that has equipped the field effect transistor, the light emitting diode, the wiring pattern, etc. was proposed [1,2]. In this report, the structure of the filamentous body as a basic structure of the kumihimo with various electronic functions was examined. There are many kinds of one in the kumihimo by the number and how to unite the plaited thread used. Although such a highly efficient kumihimo-structure electronic integrated circuit can be realized using kumihimo with much thread, it becomes that much complicated. In order to simplify an argument here, square-type kumihimo that uses eight plaited threads is employed, and a basic logical circuit composition and the element arrangement on plaited thread are examined. Eight plaited-threads are divided into two groups that have four threads respectively, and they exist in the plane that intersected perpendicularly mutually. However, kumihimo is a 1-dimensional system fundamentally, it can be extended in the length direction if necessary, and it is considered that a quite complicated function is also realizable for a circuit with few input and output. Here, plaited thread that belongs to one group for convenience will be called warp and the other group will be called woof. The circuit composition and a concrete structure of threads for kumihimo are discussed.

The new integrated circuit concept that forms electronic equipment by the textile structure using the flexible fiber that has equipped the field effect transistor, the light emitting diode, the wiring pattern, etc. is proposed [1]. In this report, the structure of the filamentous body as a basic structure of the cloth with various electronic functions was examined. In order to simplify circuit composition, an active element such as field effect transistors, the electrode pattern for wiring, and the pads for connection are formed on the warp, and the electrode pattern for wiring and the pad for connection are formed on the woof. The circuit composition and a concrete structure of the warp and the woof are discussed.

The authors have investigated organic thin films fabricated by a bias-voltage applied Langmuir-Blodgett (LB) technique, which is based on the adsorption LB method. The bias voltage is applied between a conductive indium-tin-oxide coated glass substrate and a subphase through a platinum black counter electrode. Malachite green and 2-dodecyl-7,7,8,8-tetracyanoquinodimethane (C12TCNQ) are used as an adsorbing and a spreading molecule from the aqueous subphase, respectively. Ultraviolet-visible absorption spectra of the LB films demonstrate that the quantity of adsorbing and spreading molecules can be controlled by applying the bias voltage.

We have demonstrated NAND and NOR logic circuit operations of stacked-structure complementary thin-film transistors (TFTs) using 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) and soluble ZnO as active layers. Bottom-gate-type TIPS-pentacene TFTs, as p-channel transistors, were formed on n-channel ZnO TFTs with common gate electrodes. Solution-processed silicone-resin layers were used as gate dielectric and electrical interconnection layers between lower and upper TFTs. The stacked-structure integrated circuits have several advantages such as ease of active layer formation, compact device area per stage, and the short length of the interconnection compared with the planar configuration in a conventional logic circuit.

Wet processed ZnO films for semiconductor layers bring positive impact on fabrication of field-effect transistors (FETs) in terms of their low process temperature and manufacturing cost reduction. In our work, with the aim of fabricating organic light-emitting transistors (OLETs) using transparent ZnO FETs as the driver transistors, we have fabricated a wet processed ZnO film as a semiconductor layer, and investigated the effects of ultraviolet/ozone (UV/O3)-assisted thermal treatments on ZnO FET characteristics. The results on the carrier mobility and thermal treatment temperature of ZnO films showed that the carrier mobility is almost proportional to treatment temperature, and the UV/O3-assisted thermal treatment lowers the thermal treatment temperature. Moreover, devices subjected to UV/O3-assisted thermal treatments showed excellent electrical characteristics compare with devices without the treatments. These results show that the UV/O3-assisted thermal treatment is expected to facilitate OLET fabrication on flexible plastic films.

Step-edge vertical-channel organic field-effect transistors (SVC-OFETs) with a very short channel have been fabricated by a novel electrospray deposition (ESD) method. ESD is the direct patterning process in which a solution is sprayed by using an electric field between the nozzle and electrodes formed on samples. The electrosprayed solution accumulates on the electrode pattern, and SVC-FETs based on 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) and a ZnO layer formed by ESD showed typical p- and n-channel FET characteristics, respectively. The results demonstrate that this ESD direct wet patterning is a useful method for complementary inverters and integrated circuit applications.

In-situ observations of vapor-phase growth of tetrathiafulvalene (TTF)-tetracyanoquinodimethane (TCNQ) crystals under an electric field were conducted without influencing the actual crystal growth process. The shortest incubation time of TTF-TCNQ nuclei and the highest initial growth rate of the crystals are obtained on the anode side and in high electric field regions. It is demonstrated that the distribution of molecules thermally diffusing on the substrate surface is controlled by an external electric field. These results indicate the potential for selective growth of highly conductive organic wires for micro- and nanoscale wiring in organic nanodevices.