Tsuyoshi Hioki

Film Thickness Dependence of Dielectric Property and Crystal Structure of PbTiO3 Film Prepared on Pt/SiO2/Si Substrate by Metal Organic Chemical Vapor Deposition

The crystal structure of PbTiO3 film, which was prepared on a Pt/SiO2/Si substrate by metal organic chemical vapor deposition, was investigated along with its dielectric properties. The relative dielectric constant increased with increasing film thickness. Crystal structure difference was observed below 0.3 µm of film thickness, as compared to that above 0.3 µm of thickness; i.e., the lattice constant ratio of the c-axis to a-axis, the intensity ratio of (00l) to (h00) reflections and the average crystallite size decreased, and the nonuniform stress increased with decrease in the film thickness. These crystal imperfections for below 0.3 µm thickness might be related to the existence of a low relative dielectric constant layer near the substrate.

Preparation of Pb(Zr, Ti)O3 Thin Films on Glass Substrates.

Lead-zirconate-titanate (PZT) thin films were prepared on non-alkaline glass substrates widely used in liquid crystal display (LCD) devices, by plasma-assisted magnetron RF sputtering with an immersed coil. After preparation of the PZT thin film, the glass was available for use in LCD device processing. No mutual diffusion of the elements was recognized between the glass substrate and the bottom electrode. The PZT layer had a dense film structure with rectangular and columnar grains, and only its perovskite phase was crystalline. PZT thin films on a glass substrate had leakage current densities of about 10-8 A/cm2, acceptable hysteresis loop shapes with the remanent polarization (Pr) of 45 µC/cm2 and the coercive field (Ec) of 90 kV/cm. Ferroelectric properties on a glass substrate almost conform with those on a Si-based substrate.

Preparation of Pb(Zr, Ti)O3 Thin Films by Plasma-Assisted Sputtering

A novel plasma-assisted RF magnetron sputtering system with an immersed coil antenna between a target and a substrate was applied for preparing Pb(Zr, Ti)O3 (PZT) thin films. The antenna enabled the generation of inductively coupled plasma (ICP) independently of the target RF source. The plasma assisted by the antenna resulted in the changes of ion fluxes and these energy distributions irradiating to the substrate. The crystalline phase of the deposited PZT thin films was occupied by the perovskite phase depending on the antenna power. In addition, a high deposition rate, modified uniformity of film thickness, and a dense film structure with large columnar grains were obtained as a result of effects of the assisted plasma. The application of the plasma-assisted sputtering method may enable the preparation of PZT thin films that have excellent properties.

Modification of semiconductive BaTiO3 film and its electrical properties

Nonlinear V-I characteristics were observed in semiconductive BaTiO3 film heated at 550 °C for 2 h in air. The temperature dependency of the resistivity appeared to be the minimum near 120 °C for this heat treatment. It was estimated from the keeping time dependency of the resistivity that the oxidation in this film occurs first at the grain boundary between columnar grains and then goes to the inner of the grains. The structure made up of both the semiconductive grains and the oxidized interfaces with high resistivity was considered to generate these properties. Nonlinear V-I characteristics also appeared from diffusion of Bi element from the surface of the BaTiO3 film. These results show the possibility of the generation of new properties by the modification of grain boundaries between columnar grains of semiconductive BaTiO3 film, which is comparable to that of the sintered body of semiconductive BaTiO3-based functional ceramic.