S. Kuniyoshi

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.

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.

Fabrication and characterization of field effect transistors of layered structure consisting of TMTSF and TCNQ

Abstract We have fabricated new-type field effect transistors (FETs) of layered structure consisting of TMTSF (donor molecule) layer and TCNQ (acceptor molecule) layer and tried to control the electric conductivity of charge transfer complex layer formed at the interface by applying electric field through the gate electrode. The source-drain current of the TMTSF/TCNQ/SiO2 FET varies corresponding to the gate voltages and the transconductance is larger than that of the TCNQ single-layer FET. Moreover, the dependence of the source-drain current on the gate voltage is reversed by changing the depositing order of donor and acceptor molecules.

Formation of TTF-TCNQ charge-transfer complex in co-evaporated films

Abstract We have investigated the formation process of charge-transfer (CT) complex and the electric conductivity of TTF-TCNQ co-evaporated films by varying the growth temperature (Tg). The molar ratio of TTF to TCNQ in the co-evaporated film is constant at a value of 1.0 in the Tg range between 31°C and 42°C. The formation of the single crystal of the CT complex is enhanced and the electric conductivity increases with Tg. The temperature dependence of the surface conductivity is explained by the combination of the single-crystalline conduction of the grains and the activation-type conduction of the amorphous phase between the grains.

Thermally stimulated current of pentacene Schottky diode

Thermally stimulated current (TSC) and current-voltage measurements were carried out for Schottky diodes using pentacene thin films in order to investigate the relation between carrier traps and electrical conduction. Two type of TSC peaks originated from the traps at the metal-pentacene interface and in the depletion layer were observed. The current-voltage characteristics of the diodes were governed by the space charge limited conduction depending on these traps.

Determination of effects of purity and atmospheric gases on electrical properties of perylene thin films by field effect measurement

We have fabricated thin-film field effect transistors (TFTs) using perylene derivatives (PTCDI, BPPC) and estimated electrical parameters such as carrier mobility, carrier concentration and electrical conductivity by in-situ field effect measurements. It is found that the evaporated perylene thin films show n-type semiconducting properties, and FET characteristics are strongly dependent on the purity of the starting materials, the amount of exposure to oxygen gas, and the thermal annealing.

Optical and electrical evaluation of adsorption Langmuir-Blodgett films of C/sub 18/TCNQ/TMPD and C/sub 18/TCNQ/PPD

Abstract We have studied optical and electrical properties in donor molecule adsorbed TCNQ Langmuir-Blodgett (LB) films. In fabricating the adsorption LB films, C 18 TCNQ was used as a spreading material for LB films and TMPD or PPD was used as an adsorbate. The results show that the concentration of donor molecule in aqueous subphase affects the quantity of charge-transfer (CT) complex of the adsorption LB films and the electric conductivity strongly depends on the degree of CT complex formation in the adsorption LB films.

Evanescent wave optical fiber sensor using adsorption LB films

Abstract An optical fiber sensor for albumin detection has been fabricated and tested. The adsorption Langmuir–Blodgett (LB) method was employed to form organic thin films on the optical fiber. The spectral change can be monitored by the interaction between the evanescent light from the fiber core and the adsorption LB films. A relatively high sensitivity and linear relationship between the spectral change and the albumin concentration were obtained.

Photoelectric Effect in Single and Double Layers of Metal-Free and Lead Phthalocyanines Evapolated films

Abstract Photoelectric properties of evapolated metal-free phthalocyanine (H2Pc) and lead phthalocyanine (PbPc) films were investigated in the sandwich type cells using three kinds of metal electrodes (Au, Al, Pb). Current-voltage (I-V) characteristics and short circuit photo current (Isc) spectra strongly depended on metal electrodes. It is indicated that a charge separation of photo generated carriers occurred at the interface between H2Pc and PbPc from Isc spectra of double layered (H2Pc/PbPc and PbPc/H2Pc) cells.