Tohru Kasanami

Controlling the Crystal Orientations of Lead Titanate Thin Films

Various substrates were investigated for use in crystal-oriented PbTiO3 thin films deposited by rf magnetron sputtering. In fabricating ferroelectric thin films with controlled crystal orientations, a close relationship was found between the thermal expansion coefficients of the films and substrates. Where the thermal expansion coefficient of the substrate was larger than that of the film, as in the case of a single-crystal MgO substrate, horizontal compressive mechanical stress along the plane of the film led to a c-axis-oriented film. Conversely, where the thermal expansion coefficient of the substrate was smaller than that of the film, as in the case of a quartz glass substrate, tensile stress in the film gave rise to an a-axis-oriented film. The Curie point of the film material determined the amount of mechanical stress present during cooling. Based on the above, new substrates of glass ceramics for use in c-axis-oriented films were developed.

The Polishing Effect of ZnO Thin Films on SAW Filters

SAW filters in a structure of ZnO/IDT/glass, have periodic convex and concave roughness on the surface of ZnO thin films which is caused by IDT electrodes. This investigation reports that the convex and concave roughness affects the SAW velocity, and mechanical polishing of the ZnO thin films has great effect on SAW filter frequency characteristics.

Preparation of Ferroelectric Thin Films by RF Magnetron Sputtering

PbTiO3 films were prepared by rf magnetron sputtering at various sputtering conditions. It was found that the composition of deposited films is strongly dependent on the sputtering gas pressure and the gas ratio of Ar/O2, and that the crystal orientation of the film is decided by the substrate, the substrate temperature and the target composition. A-axis oriented PbTiO3 film was fabricated on the substrate of the quartz glass where tensile stress occurred against the film. During the sputtering, plasma spectra of PbTiO3 were measured by optical emission spectroscopy. Pb vaporization from the substrate could be observed by this method, and consequently the formation mechanism of PbTiO3 film was investigated.