Masaaki Iizuka

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.

Organic static induction transistor for display devices

Abstract 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.

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.

Fabrication and device characterization of organic light emitting transistors

We have fabricated organic light emitting transistors (OLET) combining static induction transistor with organic light emitting diode and investigated static and dynamic characteristics. The luminance of OLET is controlled by gate voltages as low as 1 V and excellent dynamic operation is obtained at 60 Hz. The results obtained here show that the OLET is a suitable element for flexible sheet displays.

High-Speed Operation of Vertical Type Organic Transistors Utilizing Step-Edge Structures

An organic transistor having a novel structure, step-edge vertical-channel organic field-effect transistor (SVC-OFET), with a short channel length has been fabricated by a low-cost self-alignment process. The short channel is formed in the vertical direction along the side wall of a step-edge structure. The SVC-OFET structure also has an advantage in reducing the parasitic capacitance between the gate and drain electrodes. A short channel and reduced capacitance are important properties for a high-speed operation. The cutoff frequency achieved was approximately 900 kHz, which is a very high value for organic transistors.

Organic static induction transistor for color sensors

Abstract Copper phthalocyanine (CuPc) and merocyanine (MC) dyes show p-type semiconducting properties and have different absorption peaks in the visible spectral range. We fabricated new organic color sensors with the static induction transistor (SIT) structure using these dyes and investigated their photoelectric properties. The photocurrent from the source to the drain electrodes is controlled by the gate voltage and the pinch-off gate voltage is changed drastically by illumination. These phenomena can be explained in terms of the field-dependent and wavelength-dependent quantum efficiency in an organic SIT.

Fabrication and characterization of field effect transistors using donor and acceptor stacked layers

We fabricated field-effect transistors (FETs) using donor (TMTSF) and acceptor (TCNQ) stacked layers, and we investigated the change of conductivity in the charge transfer (CT) complex layer by applying gate voltages. Two types of FETs having TMTSF/TCNQ and TCNQ/TMTSF structures are examined. The stacked-layer FET shows a large transconductance compared with a single-layer FET. The experimental results demonstrate that the CT complex layer formed between donor and acceptor films mainly works as a conduction channel. Furthermore, the change in the degree of charge transfer (corresponding to conductivity change) is confirmed by infrared absorption spectra.

Self-organized growth of tetrathiafulvalene-tetracyanoquinodimethane molecular wires using the coevaporation method under a static electric field

Wire-like crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF–TCNQ) charge-transfer complexes were grown under a static electric field by employing electric-field assisted evaporation. TTF–TCNQ molecular wires grew from the edges of two gold electrodes opposite to each other along the electric lines of force, and finally make a connection at their front end to form a single wire. Self-organization of the wire bridge is derived from a higher local electric field between the tips of the opposing molecular wires. Oriented molecular wires, which have diffuse branches, exhibit the effects of a local electric field. Preferential growth of TCNQ at the tip of the molecular wire during coevaporation of TTF and TCNQ is clearly revealed by microscopic Raman spectroscopy. Asymmetrical growth of coevaporated TTF–TCNQ wire under a static electric field is dominated by the drift motion of TCNQ−.

Fabrication and Electrical Characterization of Tetrathiafulvalene-tetracyanoquinodimethane Molecular Wires

We have fabricated tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) molecular wires between a parallel cathode and anode (100 µm electrode gap) using the co-evaporation technique with an applied electric field. Wire-shaped microcrystals of TTF-TCNQ grew along the electric field. We have succeeded in fabricating connected wires with an optimum applied voltage. A narrow-gap (20 µm) electrode was used to grow wires with a low applied voltage, which make it possible to fabricate the connected wires easily. The measured I-V curve indicated Ohmic contact between the gold electrode and TTF-TCNQ. Semiconductor-like conduction of the fabricated TTF-TCNQ sample was shown by the temperature dependence of conductivity. Some of the co-evaporated TTF-TCNQ wires may tend to be semiconducting due to nonstoichiometry of TTF1-δ-TCNQ1.