Hiroshi Koezuka

Macromolecular electronic device: Field‐effect transistor with a polythiophene thin film

The first solid‐state field‐effect transistor has been fabricated utilizing a film of an organic macromolecule, polythiophene, as a semiconductor. The device characteristics have been optimized by controlling the doping levels of the polymer. The device is a normally off type and the source (drain) current can be modulated by a factor of 102–103 by varying the gate voltage. The carrier mobility and the transconductance have also been determined to be ∼10−5 cm2/V s and 3 nS, respectively, by means of electrical measurements.

Field-effect transistor with polythiophene thin film

Abstract The first actual field-effect transistor (FET) has been fabricated utilizing polythiophene as an active semiconducting material. The device is normally-off type and the source-drain current can be largely increased by a factor of 10 2 –10 3 by applied gate voltages. Other device parameters have been also determined by electric measurements. The stability of the device is quite excellent and it works well even after the heat-treatment in air.

Polythienylenevinylene thin‐film transistor with high carrier mobility

A thin‐film transistor (TFT) with high carrier mobility has been fabricated using precursor‐route poly(2,5‐thienylenevinylene) (PTV) as semiconductor. The carrier mobility has been determined to be 0.22 cm2/V s, which is in the same level of that of amorphous silicon TFT. It has also been made clear that the carrier mobility is linearly proportional to the conversion ratio from the insulated precursor polymer to π‐conjugated PTV. The π‐conjugation length is crucial to obtain high carrier mobility in π‐conjugated polymer TFT.

Polythiophene field-effect transistor: Its characteristics and operation mechanism

Abstract A novel field-effect transistor (FET) with an electrochemically-polymerized polythiophene thin film as an active p-type semiconductor has been fabricated for the first time. The FET is a normally-off type and the source current ( I s ) has been enhanced by a factor of more than 10 3 under applied negative gate biases. The conduction channel has been shown to be due to the accumulation of majority positive carriers. It has also been made clear that the electrical conductivity and the thickness of the polythiophene film have a crucial effect on the FET characteristics. The operation mechanism for the FET has been discussed in detail.

Polythiophene field‐effect transistor with polypyrrole worked as source and drain electrodes

The field‐effect transistor has been fabricated, where polythiophene works as a semiconductor and a couple of polypyrrole layers act as a source and/or a drain electrode. The modulation ratio of the channel current with gate voltages has reached ca. 105, which is the largest one among organic FETs. This large modulation has been attributed to the depression of the channel current at no gate bias. It has been elucidated that the depression is caused by the barrier against hole transport formed inside the polythiophene layer and near the interface with polypyrrole.

Field-effect transistor utilizing conducting polymers

Abstract The field-effect transistor (FET) device utilizing two kinds of conducting polymer, polypyrrole and polythiophene, has been fabricated. Polypyrrole acts as source and/or drain and polythiophene works as a semiconductor in that device. The source-drain current can be largely modulated by a factor of ca. 105 by applied gate biases. The stability of the device is excellent even after heating it in air. It has been also demonstrated that the conducting polymer FET can be driven by practically small voltages.

Field-effect transistor with a conducting polymer film

Abstract Spin-coated conducting polymer films of poly(3-hexylthiophene) (PHT) and poly(2,5-thienylene vinylene) (PTV) have been demonstrated to be useful in a field-effect transistor (FET) as a semiconducting layer. The device with a doped PHT film shows enhance-type FET characteristics although they are unstable. On the other hand, the one with a non-doped PTV film shows very stable and excellent FET characteristics with large source current.

Macromolecular Electronic Device

Abstract A thin-film transistor (TFT) with high carrier mobility has been fabricated using poly(2,5-thienylenevinylene)(PTV) as semiconductor. The carrier mobility has been obtained to be 0.22cm2/Vsec, which is in the same level as that of amorphous silicon TFT. It has been indicated that the enlargement of the π-conjugation length is crucial for the improvement of the carrier mobility. It has been also demonstrated that the molecular orientation is another important factor in terms of the device characteristics.

Organic Molecular Beam Deposition of α-Sexithienyl

We fabricated the molecular-oriented thin films of α-sexithienyl (6T) by an organic molecular beam deposition (OMBD) technique. The molecular orientations were evaluated from electronic spectra. The 6T molecules were aligned almost exactly parallel to the surface normal in the film deposited at a low deposition rate under 10-9 Torr. Furthermore, the 6T molecules in the film fabricated under 10-9 Torr have been found to form uniform aggregates. The aggregation has been analyzed by a molecular exciton model to give the molecular tilt angle of 85.7°.

NEXAFS spectroscopic studies of molecular orientation in α-sexithienyl evaporated thin films on metal films

Abstract The molecular orientation of evaporated α-sexithienyl (6T) films on gold (Au), silver (Ag) and copper (Cu) films at room temperature were studied by polarized near edge X-ray absorption fine structure (NEXAFS) spectroscopy and infrared reflection absorption spectroscopy (IR-RAS). The polarized NEXAFS spectra of 6T on Ag and Cu films exhibit a strong angular dependence of C1s → π∗ resonance intensity. Combining the results with theoretical simulations and auxiliary information from IR-RAS, it was found that 6T molecules in the film on Ag and Cu films are highly oriented with their molecular axes inclining by about 70° to the substrate surface. On the other hand, NEXAFS of 6T on Au film showed only a little dependence, indicating that 6T molecules are in nearly random orientation.