We investigated a field-effect transistor (FET) based on a poly(3-n-hexylthiophene) (P3HT) to determine the influence of moisture on device characteristics and thus gain a deep understanding of the mechanism underlying the susceptibility to air of the operation of FETs of this kind. The fundamental output characteristics, which include effective field-effect modulation and saturation behavior in the output current, remained almost the same for every current–voltage profile in a vacuum, N2 and O2. By contrast, operation in N2 humidified with water resulted in enlarged off-state conduction and deterioration in the saturation behavior, in the same manner as that experienced with exposure to room air. We concluded that atmospheric water had a greater effect on the susceptibility of the device operation to air than O2, whose p-type doping activity as regards P3HT caused only a small increase in the conductivity of the active layer and a slight decrease in the field-effect mobility with exposure at ambient pressure. We discuss the mechanism of the significant distortion in the operation induced by moisture in terms of the difference between the influence of water and O2 on the device characteristics.

Influence of fine roughness of insulator surface on threshold voltage stability of organic field-effect transistors Appl. Phys. Lett. 93, 033308 (2008); 10.1063/1.2957987 Effects of the permanent dipoles of self-assembled monolayer-treated insulator surfaces on the field-effect mobility of a pentacene thin-film transistor Appl. Phys. Lett. 90, 132104 (2007); 10.1063/1.2457776 Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator J. Appl. Phys. 96, 6431 (2004); 10.1063/1.1810205High capacitance organic field-effect transistors with modified gate insulator surface

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We developed a novel field-effect transistor (FET) type photorewritable memory using a photochromic interface layer between the active layer and the gate insulator layer. A diarylethene (DAE) derivative was employed as a photochromic material and pentacene was employed as an active layer. DAE has two types of photoisomer, i.e., the closed- and open-ring isomers. In this study, it was clarified that the highest occupied molecular orbital (HOMO) level of the closed-ring DAE worked as an interfacial deep trap level, and that the generation of the interfacial deep trap level by photoisomerization induced the photoswitching and photomemory behaviors of transistor properties.

We have investigated the influence of the surface roughness of an insulator on the threshold voltage shift caused by gate bias stressing in organic field-effect transistors (OFETs). Our investigation was conducted for OFETs with SiO2 insulators. We observed that the threshold voltage shift is extremely sensitive to changes in the fine roughness of the SiO2 surface; the shift increased with the roughness. The large shift in OFETs with rough SiO2 insulators can be attributed to lattice distortion in pentacene layers deposited on rough SiO2 surfaces.