In this research, the effect of Ar/N2-plasma sputtering gas pressure on the LaBxNy tunnel and block layer was investigated for pentacene-based floating-gate memory with an amorphous rubrene (α-rubrene) passivation layer. The influence of α-rubrene passivation layer for memory characteristic was examined. The pentacene-based metal/insulator/metal/insulator/semiconductor (MIMIS) diode and organic field-effect transistor (OFET) were fabricated utilizing N-doped LaB6 metal layer and LaBxNy insulator with α-rubrene passivation layer at annealing temperature of 200°C. In the case of MIMIS diode, the leakage current density and the equivalent oxide thickness (EOT) were decreased from 1.2×10-2 A/cm2 to 1.1×10-7 A/cm2 and 3.5 nm to 3.1 nm, respectively, by decreasing the sputtering gas pressure from 0.47 Pa to 0.19 Pa. In the case of floating-gate type OFET with α-rubrene passivation layer, the larger memory window of 0.68 V was obtained with saturation mobility of 2.2×10-2 cm2/(V·s) and subthreshold swing of 199 mV/dec compared to the device without α-rubrene passivation layer.

We examined single crystal growth of benzothienobenzothiophene-based organic semiconductors by solution coating method using liquid crystal and investigated its electrical characteristics. As the results, we revealed that the averaged mobility in the saturation region reached 2.08 cm2/Vs along crystalline b-axis, and 1.08 cm2/Vs along crystalline a-axis.

We investigated a control of the crystalline orientation of soluble organic semiconductor single crystals using liquid crystal solvents aligned by the electric field to improve the performance of organic thin-film transistors. We clarified that the semiconductor single crystal grows to the direction parallel to the liquid crystal alignment oriented by the lateral electric field.

We deposited thin films of thiophene/phenylene co-oligomers (TPCOs) onto poly(tetrafluoroethylene) (PTFE) layers that were friction-transferred on substrates. These films were composed of aligned molecules in such a way that their polarizations of emissions and absorbances were larger along the drawing direction than those perpendicular to that direction. Organic field-effect transistors (OFETs) fabricated with these films indicated large mobilities, when the drawing direction of PTFE was parallel to the channel length direction. The friction-transfer technique forms the TPCO films that indicate the anisotropic optical and electronic properties.

The novel ladder-shaped polydiacetylene with a terephthalamide linker in the molecular center, namely poly(TPh-bisDA) was synthesized by photo-polymerization. The characteristics of thin films of polymer were dependent upon a casting solvent, but no significant change of backbone conformation of the PDA was observed. Obtained film is expected to be applied to the semi-conducting materials for organic field effect transistors (OFET).

We fabricated solution-processed organic complementary inverters based on α,ω-bis(2-hexyldecyl)sexithiophene (BHD6T) for p-channel and C60-fused N-methylpyrrolidine-meta-dodecyl phenyl (C60MC12) for n-channel. The BHD6T and C60MC12 thin-film transistors showed high field-effect mobilities of 0.035 and 0.057 cm2/Vs, respectively. The complementary inverter with a supply voltage of 50 V exhibited inverting voltages of 26.8 V for forward and 27.0 V for backward sweeps and a high gain of 76.

We have succeeded in developing high-performance p-type of organic semiconductors with phenylethynyl groups, which have high filed-effect mobilities (>3 cm2V-1s-1) by improving molecular planarity. A single crystal of the organic semiconductors has a herringbone structure. It plays an important role for carrier transport. In addition, we found that they had lower contact resistances to Au electrodes as well. Then, we used the materials for the carrier injection layer deposited onto another organic semiconductor we developed recently, which achieved a high field-effect mobility, and a low threshold voltage (Vth).

Control of electronic states of dye molecules (organic semiconductors) by introducing appropriate substituent groups has been examined. NH2 (electron-releasing group) and NO2 (electron-withdrawing group) were introduced in thiacarbocyanine dye to modify the electronic states of the dyes. The effect of modification was examined based on the properties of photoelectric cells made by the dye derivatives. Clear increase in photocurrent, more than ten times, was observed when modified dyes were used instead of the original dye. The result shows that the introduction of substituent groups for organic semiconductors is quite effective to control the electronic states, and the introduction can be regarded as doping in molecular level.