Shigekazu Kuniyoshi

Schottky gate static induction transistor using copper phthalocyanine films

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.

Device characteristics of lateral and vertical type organic field effect transistors

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.

Device Characteristics of Organic Static Induction Transistor Using Copper Phthalocyanine Films and Al Gate Electrode

We have fabricated organic static induction transistors (SITs) using copper phthalocyanine (CuPc) films. The organic SITs have a layered structure of Au (drain)/CuPc/Al (gate)/CuPc/Au (source)/glass. The electrical characteristics of SITs show that the source-drain current is controlled by the bias voltage applied to the Al gate electrode and a typical SIT operation with unsaturated current characteristics is examined. Furthermore, excellent characteristics such as low voltage and high speed operation as organic transistors are obtained by choosing an appropriate thickness for each layer.

Evaluation of Electrical Properties of Evaporated Thin Films of Metal-Free, Copper and Lead Phthalocyanines by In-Situ Field Effect Measurements.

We have fabricated thin-film transistors consisting of evaporated thin films of metal-free, copper and lead phthalocyanines, and estimated the electrical parameters of carrier mobility, carrier concentration and electrical conductivity by in-situ field effect measurements. We have also investigated the effect of introducing of oxygen gas into the vacuum chamber and of thermal annealing on the electrical parameters of the films. We found that the carrier concentration and carrier mobility are strongly influenced by the metals in the phthalocyanine molecules and by oxygen gas exposure.

Control of molecular orientation in TTF–TCNQ co-evaporated films by applying an electric field

Abstract 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.

Optical and electrical properties of selectively adsorbed Langmuir-Blodgett films

Abstract Malachite-green (MG) dye which does not contain a long alkyl chain can be adsorbed from aqueous solution onto Langmuir-Blodgett films consisting of arachidic acid (AR) only or a mixture of the acid and merocyanine (MC) dye. A special interaction exists between MC and MG molecules; MG molecules are more selectively adsorbed to MC molecules than to AR molecules. The adsorption Langmuir-Blodgett films show negative photoelectrical properties which are strongly related to the interaction between the two functional dyes.

Electrical and optical investigations of carbon clusters formed in organic films by ion implantation

Abstract 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.

Inelastic Electron Tunneling Spectroscopy of Langmuir-Blodgett Monolayers on Silicon Substrate

An inelastic electron tunneling spectroscopy (IETS) technique is employed to investigate Langmuir-Blodgett monolayers deposited on silicon substrates. Thermally formed SiO2 layers are used as a tunneling barrier to obtain reliable and sensitive signals. IETS data, which are compared to IR and Raman data, show the stability and chemical reactions of organic monolayers at the metal or SiO2 interface.

Fabrication of n- and p-channel step-edge vertical-channel transistors by electrospray deposition

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.

Control of molecular adsorption by a bias-voltage applied Langmuir-Blodgett technique☆

Abstract 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.