Takeshi Okamura

Preparation of n-ZnO/p-Si Heterojunction by Sol-Gel Process

N-type ZnO thin films with a crack and columnar-free structure were successfully prepared on p-type Si substrates by the sol-gel process. The current-voltage (I-V) characteristics of the heterojunction of n-ZnO/p-Si show a rectification with strong electrical breakdown strength of higher than 107 V/cm. The capacitance-voltage (C-V) characteristics show an approximate linear C-2-V relationship in the reverse bias condition. These results indicate that the ZnO films prepared by the sol-gel process are good enough to be used as a semiconducting material in electrical devices.

Epitaxial growth and electrical properties of ferroelectric Pb(Zr0.9Ti0.1)O3 films by reactive sputtering

Ferroelectric Pb(Zr0.9Ti0.1)O3 thin films have been successfully obtained on the pt/(0001)sapphire substrates and the Pt/SiO2/(100)Si substrates by reactive sputtering of the multimetal target. The films with perovskite structure have been grown at substrate temperatures of 600-620°C. The epitaxial films have been obtained on the Pt/(0001) sapphire substrates and the oriented. films have been obtained on the Pt/SiO2/(100)Si substrates. The crystallinity of the Pb(Zr0.9Ti0.1)O3 film depended on the substrate temperature and the crystallinity of the platinum film used as the bottom electrode. The films showed ferroelectricity, and the switching speed was measured as 50 ns at 8 V for the 0.60 µm film on the Pt/SiO2/(100)Si substrate.

DIELECTRIC PROPERTIES OF RARE-EARTH-ADDED CORDIERITE AT MICROWAVE AND MILLIMETER WAVE FREQUENCIES

Dense cordierite ceramics were obtained by adding rare-earth oxides at sintering temperatures between of 1355–1420°C. The room-temperature dielectric constants of the cordierite at microwave and millimeter-wave frequencies were evaluated by using the dielectric resonator method. The dielectric permittivity (er) and dissipation factor (tan δ) were determined to be 4.9 and 1.6×10-4 at 18 GHz, 4.9 and 2.6×10-4 at 59 GHz, respectively. An 80-mm-long waveguide fabricated with cordierite thus obtained, showed a low transmission loss (<1 dB) at frequency range of 55 to 65 GHz.

Junction Properties and Gap States of ZnO Thin Film Prepared by Sol-Gel Process

N-type ZnO thin films with a crack- and columnar-free structure were successfully prepared on p-type Si substrates by the sol-gel process. The current-voltage (I-V) characteristics of the heterojunction of n-ZnO/p-Si show a rectification, and the capacitance-voltage (C-V) characteristics show an approximately linear C-2-V relationship in the reverse bias condition. In the ZnO thin film, two gap states located at 0.054 eV and 0.12 eV below the conduction band were measured by isothermal capacitance transient spectroscopy (ICTS).

Junction Properties and Gap States in Nb-Doped TiO2 Thin Films

Nb-doped TiO2 thin films were successfully prepared on p-type crystalline Si substrates using the sol-gel process. The current-voltage (I-V) characteristics of the heterojunctions between TiO2 and Si show a rectification and the capacitance-voltage (C-V) characteristics an approximate linear C-2-V relationship in the reverse-bias condition. By application of an isothermal capacitance transient spectroscopy (ICTS) method on these junction diodes, it is found that two gap states are located at 0.027 eV and 0.22 eV below the conduction band edge (Ec).

Preparation of Ferroelectric PbTiO3 Thin Film by Reactive Sputtering

Ferroelectric PbTiO3 thin films have been successfully obtained. The films were fabricated by reactive sputtering using a simple metal composite as a target. Without postannealing, the films with perovskite structure have been obtained at substrate temperatures of 600-620°C. The spontaneous polarization (Ps) and the coercive field (Ec) of a 0.70 µm-thick film were measured as 37 µC/cm2 and 86 kV/cm, respectively.

Preparation of TiO2-SnO2 Solid Solution Film by Ion Beam Sputtering

Thin film of rutile-type TiO2-SnO2 solid solution was successfully prepared by reactive ion beam sputtering without postannealing. The crystallinity of the film was highly dependent on the temperature of the substrate. The (101)-oriented film with rutile structure was obtained at substrate temperatures higher than 300°C.

Epitaxial Growth of TiO2-SnO2 Solid Solution Film by Reactive Ion Beam Sputtering

Epitaxial thin film of rutile-type TiO2-SnO2 solid solution has been successfully prepared. The film was fabricated on a sapphire (012) substrate by the reactive ion beam sputtering method using a TiO2-SnO2 ceramic target. The crystallinity of the film was dependent on the substrate temperature. The (101)-oriented film was grown at temperatures higher than 300°C. An epitaxial film was obtained by heat-treatment at temperatures higher than the miscibility gap.

Epitaxial growth of ferroelectric Pb(Zr/sub 0.9/Ti/sub 0.1/)O/sub 3/ films by reactive sputtering of multi metal target

Ferroelectric epitaxial Pb(Zr/sub 0.9/Ti/sub 0.1/)O/sub 3/ thin films have been successfully obtained on platinum-coated sapphire substrates by reactive sputtering of the multimetal target. The films with a perovskite structure have been epitaxially grown at substrate temperatures of 600-620 degrees C. The crystallinity of the Pb(Zr/sub 0.9/Ti/sub 0.1/)O/sub 3/ film depended on the substrate temperature and the crystallinity of the platinum film used as a bottom electrode. The remanent polarization and the coercive field of a 0.75- mu m-thick film were measured as 13.9 mu C/cm/sup 2/ and 60.0 kV/cm, respectively.<<ETX>>