Hisao Suzuki

Strain-driven control of piezoelectricity in (Na,Bi)TiO3-BaTiO3 epitaxial thin films

Thermal strain effect on the piezoelectricity was investigated for (Na,Bi)TiO3−BaTiO3 (NBT−BT) thin films on various substrates with (100) and (110) orientations. The compressive-thermal strain caused an increase in the remnant polarization unaccompanied by a decrease in dielectric permittivity, which resulted in enhancement of the piezoelectric coefficient, e*31. For films on (110) substrates, the crystal lattices were distorted to orthorhombic symmetry under both the tensile- and compressive-strains and the in-plane anisotropy of piezoelectricity emerged with e*31 as large as −19 to −20.6u2009C/m2. We conclude that the large piezoelectricity in NBT−BT films on (110) substrates is related to the appearance of orthorhombic phase.

Strain-Induced Electrical Properties of Lead Zirconate Titanate Thin Films on a Si wafer with Controlled Oxide Electrode Structure

This paper shows the electrical properties of ferroelectric thin films with large compressive residual stress. In this study, the large compressive strain was applied to lead zirconate titanate (PZT) thin films by designing the bottom electrode structure on a Si wafer. The materials selected for the bottom electrode were lanthanum nickel oxide (LNO) and lanthanum strontium cobalt oxide [LSCO; (La0.5Sr0.5)CoO3] from the viewpoint of thermal expansion coefficients. As a result, the PZT thin films with morphotropic phase boundary (MPB) composition received compressive residual stress up to approximately 0.8 GPa from the bottom electrode even on a Si wafer. The compressive residual stress concomitantly increased with increasing LSCO layer thickness. In addition, the remanent polarization of the PZT thin films increased with increasing compressive residual stress.

Fabrication of two-dimensional close-packed shell structure in ceramic thin films

Abstract TiO2 thin films with a periodical two-dimensional close-packed hemispherical structure were prepared on Si substrates using pulsed laser deposition and close-packed monolayer polystyrene colloidal crystals as a template. Compared with conventional methods, which use a top-down approach, this route supports low-cost production of a periodic structure. Additionally, it is applicable to various ceramics for use in applications related to photonic crystals, surface self-cleaning materials, data storage media, bioassays, and so on.

TEM MICROSTRUCTURE ANALYSIS FOR COMPRESSIVELY STRESSED Pb(Zr,Ti)O3 THIN FILMS BY CSD-DERIVED LaNiO3 BOTTOM ELECTRODES

Pb(Zr,Ti)O3 (PZT) possesses superior ferroelectric and piezoelectric properties arisen near a morphotropic phase boundary (MPB) composition, PbZr0.53Ti0.47O3. We have prepared a PZT (MPB composition) thin film and perovskite-type LaNiO3 (LNO) electrodes on Si substrate by chemical solution deposition (CSD) method. The CSD-derived LNO bottom electrode applied compressive stress to the PZT film and enhanced the ferroelectric properties of the PZT film. TEM and SAED revealed that stress distribution and microstructures of the PZT/LNO/Si films effectively influenced the ferroelectric properties.

Effects of Oxide Seeding Layers on Electrical Properties of Chemical Solution Deposition-Derived Pb(Mg1/3Nb2/3)O3–PbTiO3 Relaxor Thin Films

Relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) have attracted considerable attention because of their excellent electrical properties, such as high dielectricity and piezoelectricity, for application to super capacitors, piezoelectric actuators, and so on. It is well known that the electrical properties of ferroelectric thin films depend on several parameters, such as crystal orientation, composition, and residual stress. In this study, the effects of the lead titanate and lanthanum nickel oxide seeding layers on the film orientation, electrical properties, and low-temperature crystallization behavior were investigated for Chemical Solution Deposition (CSD)-derived PMN–PT thin films. As a result, PMN–PT thin films with (001)C- and (111)C-preferred orientations were successfully obtained by designing the seeding layers. Both thin films exhibited very good ferroelectricity because of their good crystallinity and preferred orientation.