Atsuo Senda

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.

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.

Ceramic composites of lead germanate glass and PZT ceramics

Ceramic composites consisting of two kinds of ferroelectric phases were prepared by adding small amounts (1~5 wt%) of lead germanate (PGO) glass powder to PZT ceramic powders. The composite modified with the PGO glass had relatively large electromechanical coupling factor in comparison with the composite modified with Pb–B–Si glass. High piezoelectricity of the ceramic composite with PGO was due to ferroelectric phase changed from the paraelectric glass phase by crystallization. From a theoretical calculation of relative dielectric constant of the composite, PGO phase segregated locally between PZT grains at high firing temperature. In contrast, at low firing temperature the phase began to cover the PZT phase. As a result, this ceramic composite had large anisotropy between counter extensional mode and thickness longitudinal mode. Furthermore, low temperature sintering of the PZT ceramic composite was achieved by addition of small amounts of PGO glass powder, the melting point of which is comparatively low.

Fluctuations of Tc in YBCO thin films

Abstract Fluctuations of Tc in YBCO films were investigated using improved rf magnetron sputtering equipment. In fabricating high Tc films, the most important factor was precise control of the substrate temperature. Use of a new designed substrate holder led to films which had superior superconducting characteristics over a wide substrate area.