Mikiko Yoshida

Surface Potential Control of an Insulator Layer for the High Performance Organic FET

It has been indicated that the pentacene crystal growth near the channel region is the most essential factor for determining pentacene FET properties and strongly depends on the surface energy of the substrate. In this study, surface modification effect of the SiO 2 /Si substrate by several kinds of polymers was investigated for the purpose of controlling surface potential and improve the FET properties. Matching the surface energy between the insulator and semiconductor layers using a polymer surface modifier gave improvement of the pentacene crystal growth and its FET properties. It was revealed that the molecular diffusion on a solid substrate and crystal growth mechanism were essential to give the effects.

Compression test system for a single submicrometer particle

A compression test system was developed for measuring the strength of a single particle with a cross-sectional dimension of less than 1μm. The test system used a small diamond plate that has a flat platen to compress the particle on a diamond substrate. To avoid compressing multiple particles and to avoid direct contact between the platen and the substrate, the flat area was comparable in size to the tested particle. Mechanical processes such as polishing, however, have difficulty in fabricating such a small area. Here, fabrication of a micrometer-sized flat area was achieved by using focused ion beam technology. The resulting compression test system successfully measured the strength of a single submicrometer particle. Results showed that the mean strength of alumina particle with nominal mean diameter of 0.7μm was 2.9GPa.

High Performance Organic FET with Double-Semiconductor Layers

The over-coating effect of a second semiconductor layer on a pentacene field-effect transistor (FET) was investigated. Me-PTC (n-type) coating gave improvements of the field-effect mobility and I DS for pentacene (p-type) FET. Such remarkable improvements were not observed in the TiOPC (p-type) coated pentacene (p-type) FET. These phenomena indicate that n-type semiconductor coating on a p-type semiconductor layer reduce the effect of trapped electrons at the crystal grain boundary. Besides, the over-coated layer also prevents the effect of water molecules adsorbed on pentacene crystals. Consequently, it was revealed that the p/n type hetero double-layered structure is effective to improve FET properties.

Memory effects of pentacene MFS-FET

The metal-ferroelectrics-semiconductor field effect transistor (MFS-FET) was fabricated on Si substrate by using semiconductive pentacene thin film and ferroelectrics lead titanate zirconate Pb(Zr,Ti)O 3 (PZT) thin film prepared by the sol-gel technique. The memory effects were estimated by the cyclic I d -V g characteristic measurements. MFS-FET with an intermediate insulator layer between the gate electrode and the PZT layer gave the clear square hysteresis loop. The shape of the hysteresis loop was much dependent on the preparation condition of the PZT thin film. The surface morphology of the PZT layer contributes to the difference of the shape of the hysteresis loop.

Highly Sensitive Organic Photo-FET Using Photosensitive Polymer Insulator

We fabricated a photo field effect transistor (photo FET) having a poly (N-vinyl carbazole) (PVK) insulator layer. PVK was employed as a photosensitive insulator material for the Photo FET. In this photo FET, illumination of a blue light to the PVK insulator drastically improved the field effect mobility and the gate-switching ratio. This result would be due to that the photo-generated carriers in the PVK layer were effectively accumulated in the gate capacitor of the photo FET.

Evaluation of Dielectric Properties of Ferroelectric Fine Particles Fabricated by Focused Ion Beam Technique

In this study, we propose a method for evaluating the dielectric property of a single fine particle using the focused ion beam technieque. Lead zirconate titanate (PZT) particles (Sakai Chemical Industry LQ) were sintered at 1473 K for 2 h to fabricate bulk PZT. The bulk PZT was milled to fabricate sample particles. The particles were dispersed on a Au surface substrate, and were shaped into a parallel-plate capacitor using the focused ion beam (FIB) technique. The FIB technique was used to deposite tungsten, W, with a square shape on top of the particle sample as an upper electrode, and the particles were shaved into a rectangular shape; the area of the electrode was 2×10-12 m2 and the thickness of the PZT segment was 2×10-6 m. The capacitance of the fabricated PZT particle sample was successfully measured by compensating the parasitic capacitance of the experimental setup. Consequently, the relative permittivity of the PZT particle sample was 1250 at 105 Hz. This value was comparably close to the 1750 of the bulk PZT. The issue of electric contact between the particles and the substrate should be overcome in order to discuss permittivity quantitatively.

Optimization of p/n multilayer structure for organic photoreceptor device

Organic photoreceptor devices fabricated with titanyl phthalocyanine as a p-type semiconductor and perylene dye as a n-type semiconductor were fabricated with various p/n multilayer structures. Fabrication of the device including p/n junction gave one-order increase in on/off ratio as compared with that without the junction. When the device has multiple p/n junctions, the decrease of driving voltage was also observed. The multilayer p/n structure shows the improvement of the device performance.

Preparation and properties of thin films of polysilane copolymers, poly(dimethylsilylene-co-methyl-n-propylsilylene)s

Abstract Oriented thin films and unoriented thin films of polysilane copolymers, poly(dimethylsilylene-co-methyl-n-propylsilylene)s, were prepared by friction transfer and solution cast method, and their properties were compared with each other. There were two solid states in the polysilane copolymers at room temperature. One is the stable phase, which absorbs the light around 300nm and emits the light at 360nm. Another is the metastable phase, which has the absorption band around 340nm and the fluorescence at 355nm.

Dynamic mechanical properties of extruded rods of poly(dimethylsilylene-co-methyl-n-propylsilylene)

Tractable polysilanes were prepared by the copolymerization of a methyl-n-propylsilylene (MP) unit into poly(dimethylsilylene), which neither dissolves in common solvents nor melts before decomposition. Although poly(dimethylsilylene-co-methyl-n-propylsilylene) has poor solubility in the composition range of the dimethylsilylene (DM) unit to the MP unit (DM/MP = 7/3 ∼ 9/1), the copolymers form the columnar mesophase at elevated temperatures. Highly oriented rods were prepared via the extrusion of the copolymers with a circular tube die in a temperature range in which the transition to the columnar mesophase began to occur (70°C when DM/MP = 7/3 and 8/2 and 120°C when DM/MP = 9/1). The extruded rods were characterized in detail by dynamic viscoelasticity and wide-angle X-ray diffraction (WAXD) to clarify the structure–mechanical-property relationship. The orientation functions of the extruded rods were determined by the azimuthal intensity distribution of the WAXD reflection. The orientation function and dynamic storage modulus increased with an increasing extrusion ratio. The dynamic storage modulus at −150°C was 8 ∼ 10 GPa at the highest extrusion ratio and correlated well with the crystal orientation function. The dynamic storage modulus at room temperature was lowered by the structural relaxations at −100 ∼ +30°C, which corresponded to the molecular motion of the rigid molecular chains of the copolymer and the local molecular motion of the MP unit.

Polysilane Photoluminescence Specific to Oriented Thin Films

Abstract Highly oriented ultrathin films of poly (dimethylsilylene) and poly (diethylsilylene) were prepared by friction-transfer technique. Photoluminescence spectra of the films were different from those of powder sample. The luminescence peak of thin film was observed at 10nm shorter wavelength than that of powder. The difference remained from −200° C to 250° C.