Toshiharu Minamikawa

Preparation of Pb(Zn0.52Ti0.48)O3 Films by Laser Ablation

Pb(Zr0.52Ti0.48)O3 films were prepared on an r-plane sapphire substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Pb(Zr0.52Ti0.48)O3 films by laser ablation. The composition of the deposited films was found to be fairly close to the composition of the target material for a wide range of the substrate temperature, 400–750°C. The substrate temperature greatly influences the crystal structure; a low substrate temperature produces a pyrochlore phase and a high substrate temperature (750°C) a perovskite phase.

Thermal Analysis of Target Surface in the Ba-Y-Cu-O Film Preparation by Laser Ablation Method

For clarifying the mechanism of material removal from the surface of Ba-Y-Cu-O by a high-intensity pulsed laser beam, a transient temperature distribution was calculated, and the obtained results were compared with the experimental ones. The calculated values well explain the experimental results such as a threshold of the Ba-Y-Cu-O evaporation. It was found that the subsurface temperature exceeds the front surface temperature. Under such conditions, an explosive removal of material can occur resulting in very rapid material removal with no compositional deviation between the target and the deposited film.

Annealing Temperature Dependence of MgO Substrates on the Quality of YBa2Cu3Ox Films Prepared by Pulsed Laser Ablation

The effect of annealing on a MgO substrate was systematically investigated, varying the annealing temperature, for preparation of high-quality YBa2Cu3Ox (YBCO) films by pulsed laser ablation. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) were carried out for characterization of the MgO substrate, and X-ray diffraction (XRD) measurement, including θ-2θ scan, ω-scan (rocking curve) and -scan, and electrical measurement were carried out for characterization of YBCO films. Thermal annealing of MgO above 1000° C in oxygen ambient was found to give rise to a great improvement of the crystallinity and the reproducibility of crystal orientation of YBCO films, while it was also found to induce Ca segregation on the surface of MgO and reduce the oxygen content of YBCO films. Annealing below 1000° C causes no outstanding improvement in the crystal structure of YBCO. On the MgO substrate annealed at 1200° C c-axis-oriented YBCO film was found to reproducibly show a full width at half-maximum (FWHM) of the rocking curve of 0.3°, an FWHM of (005) diffraction of 0.1°, an epitaxial relation without in-plane misorientation, a critical zero temperature of 89 K, and a critical current density of 106 A/cm2 at 77.4 K and zero field.

DC reactive magnetron sputtered ZnO films

Abstract This paper is concerned with a new reactive magnetron sputtering technique using a zinc target and 100% oxygen gas. A solenoid coil around a bell jar was used to cause an increase in the parallel component of the leakage magnetic lines to the target surface. Highly oriented ZnO films ( c -axis orientation) were fabricated on glass substrates at very high deposition rates (10 μm/h). The quality of the ZnO film was determined by X-ray diffraction, reflection electron diffraction, and scanning electron microscopy (SEM). Well-oriented ZnO films were obtained at relatively high oxygen pressures from 0.2 to 0.4 Torr. This sputtering system is more convenient than other existing sputtering systems.

High Rate Deposition of ZnO Film Using Improved DC Reactive Magnetron Sputtering Technique

This paper concerns with a new reactive magnetron sputtering technique using a zinc target and pure oxygen gas. A solenoid coil around a bell jar was used to improve an increase in the parallel component of the leakage magnetic lines to the target surface. Highly oriented ZnO films (c-axis orientation) were fabricated on glass and on (111) gold substrates. Deposition rate reached 10 µm/h at 500 mA. The quality of the ZnO film was determined by X-ray diffraction, reflection electron diffraction (RED), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Deviation σ on the glass substrate is 1.67°. Excellent ZnO films were obtained at relatively high oxygen gas pressures, 0.25 Torr on glass and 0.55 Torr on (111) gold substrate. Low temperature sputtering is possible for small discharge current.

Spectroscopic Study on N2O-Plasma Oxidation of Hydrogenated Amorphous Silicon and Behavior of Nitrogen

A novel oxidation process in hydrogenated amorphous silicon (a-Si:H) utilizing nitrous oxide (N2O) plasma was established and studied in detail. The interfacial neutral defect density for the sample prepared in this process at 300°C is greatly reduced compared with that obtained using O2 plasma. The distribution and behavior of N incorporated in this oxide was examined in detail by means of X-ray photoelectron spectroscopy (XPS). As a result, the accumulation of N near the SiO2/a-Si:H interface was confirmed. At low oxidation temperature, the N bonded to O exists near the oxide surface. The reasons for the reduction of the interfacial neutral defect density and for the accumulation of N near the interface are also shown. It is also clarified that this process utilizes the advantages of both the effect of atomic O and the accumulation of N near the interface.

Highly Moisture-Resistive SiNx Films Prepared by Catalytic Chemical Vapor Deposition

Silicon nitride (SiNx) films on Si and poly(ethylene terephthalate) (PET) substrates were prepared at approximately 150°C by catalytic chemical vapor deposition (Cat-CVD), using a SiH4/NH3 gas mixture. A water vapor transmission rate as low as 0.2 g/m2day and an O2 gas transmission rate of 0.6 cm3/m2day were achieved for a stoichiometric Si3N4 film of 77 nm thickness. Although these transmission rates depended on N/Si ratio, no optical absorption was observed under preferable deposition conditions.

Novel oxidation process of hydrogenated amorphous silicon utilizing nitrous oxide plasma

A novel oxidation process in hydrogenated amorphous silicon (a‐Si:H) using nitrous oxide (N2O) plasma was studied in detail for the first time. The N2O‐plasma oxidized a‐Si:H has an excellent interface whose interfacial defect density is largely reduced compared with the O2‐plasma oxidized a‐Si:H. It was elucidated that this oxide layer has almost stoichiometric composition and contains a small amount of N piling up at the interface between the oxide layer and a‐Si:H layer. It also turned out that this process has less ion damage than the O2‐plasma oxidation process. The reason for the reduction of the interfacial defect density is attributed to the presence of N at the interface and/or less ion damage in this process.

Influence of Laser Irradiation and Ambient Gas in Preparation of PZT Films by Laser Ablation

Pb(Zr 0.52 Ti 0. 48 )O 3 (PZT) films were prepared on r-plane sapphire substrates by the laser ablation method utilizing ArF excimer laser in O 2 or N 2 O environment. The composition of the films deposited in O 2 environment was found to be fairly close to the composition of the target material for a wide range of substrate temperatures, 400 – 750 °c. Increasing the laser fluence (the laser power density) for the ablation enhances the formation of the perovskite structure rather than the pyrochlore one. Use of N 2 O ambient gas instead of O 2 gas enhances the formation of the perovskite structure of PZT films. Furthermore, it was found that a laser irradiation on the growing film surface during deposition enhances the formation of the perovskite structure.

Preparation of Low-Stress SiNx Films by Catalytic Chemical Vapor Deposition at Low Temperatures

Silicon nitride (SiNx) films were prepared by catalytic chemical vapor deposition (Cat-CVD) at low substrate temperatures below 130°C. The stress in the films was low, typically lower than 100 MPa, and could be varied from compressive to tensile by changing the deposition conditions used. The cause of the changes in stress was investigated from the relationship between film properties and deposition conditions. Stress was more compressive when the SiH4 flow rate was high, while it was more tensile when the substrate temperature and gas pressure were high. This is attributed to the shrinkage of the film accompanied by gas desorption from the growing surface. The gas desorption is enhanced by the elevation of substrate temperature and the attack of atomic hydrogen. The gas desorption also leads to low hydride densities and high mass densities. The SiNx films prepared by Cat-CVD can be used for passivating organic materials.