Masayuki Fujimoto

Analysis of misfit relaxation in heteroepitaxial BaTiO3 thin films

Abstract The misfit relaxation mechanism of BaTiO3 thin films of different thicknesses grown two-dimensionally on SrTiO3(100) substrates by pulsed laser deposition was analysed using X-ray diffraction and transmission electron microscopy. Major defects in partially relaxed films are misfit dislocations with Burgers vectors of type a(100), threading dislocations connected to those dislocations, and inclined threading dislocations with Burgers vectors of type a(110). Misfit and threading dislocations with equivalent Burgers vectors of type a(100) constitute half-loops. a(110) threading dislocations are formed by the kinetic reaction between these half-loops. In addition, two types of dislocation dissociation in a(100) misfit dislocations and a(110) threading dislocations are found by high-resolution observation. The dissociation of this misfit dislocation takes place with increasing film thickness and generates stacking faults with displacement vectors of type 1/2a(101). Misfit relaxation depends on the hal...

Preparation and characterization of a- and b-axis-oriented epitaxially grown Bi4Ti3O12-based thin films with long-range lattice matching

a- and b-axis-oriented epitaxial Bi4Ti3O12 films were prepared on (101)TiO2 (rutile) substrates at 630 °C by metalorganic chemical vapor deposition and their perfect epitaxial growths were confirmed by several x-ray diffraction measurements. As the bottom electrode, (101)-oriented conductive materials with the same rutile-type structure as the TiO2, RuO2, and IrO2, were epitaxially grown on (101)TiO2, (012)Al2O3, and (110)Al2O3 substrates. Finally, a- and b-axis-oriented Bi4Ti3O12-based materials, (Bi4−xNdx)(Ti3−yVy)O12, were epitaxially grown on these conductive substrates with high reproducibility and a well-saturated P–E hysteresis loop with a remanent polarization above 20 μC/cm2 was observed. These results open the long-range lattice matching growth (the c-axis lattice parameter is about 3.3 nm) of a- and b-axis-oriented bismuth layer-structured ferroelectrics on conductive electrodes.

Defect structure in homoepitaxial non-stoichiometric strontium titanate thin films

Abstract The defect structure of non-stoichiometric strontium titanate thin films epitaxially grown on SrTiO3(100) substrates by pulsed-laser deposition was studied using transmission electron microscopy and X-ray diffraction. The A-site-excess SrTiO3 thin film adopted a completely unrelaxed pseudomorphic perovskite structure with an enlarged lattice parameter normal to the surface. Excess SrO was accommodated as Ruddlesden-Popper planar faults showing a peculiar three-dimensional mosaic structure, without forming secondary phases or dislocations due to non-stoichiometry. Biaxial compressive stress induced by lattice mismatch between the film and substrate was estimated at 9,7 GPa. Such a highly strained film is attributable to planar fault formation, which increases the cell volume and suppresses misfit dislocations. The B-site-excess SrTiO3 thin-film microstructure consisted of crystalline SrTiO3 and amorphous TiO2-rich phases. The slight increase in the lattice parameter normal to the surface and crystallographic shear structure with a TiO2 double layer suggest the low solubility of excess TiO2.

Thin-film inductor for gigahertz band with CoFeSiO-SiO/sub 2/ multilayer granular films and its application for power amplifier module

In this article, we report that multilayer nanogranular thin film and its application for power amplifier (PA) module.

BaTiO3 thin films grown on SrTiO3 substrates by a molecular-beam-epitaxy method using oxygen radicals

BaTiO3 (BT) thin films were grown by a molecular-beam-epitaxy method using an oxygen radical source. BaO and TiO2 layers were alternately deposited on SrTiO3 (001) (ST) substrates, and the structure of the thin films obtained was evaluated by x-ray diffraction, reflection high-energy electron diffraction, transmission electron microscopy, atomic force microscopy, and x-ray photoelectron spectroscopy. The BT thin films were oriented in the [001] direction and epitaxially grown without misfit dislocations. The lattice constants of the thin films varied with distance from the interface of BT and ST. Near the interface the a value was shorter than that for bulk BT while the c value was longer than that for bulk BT. The surface analysis indicated that adsorbed oxygen was enriched on the BaO-terminated surface in comparison with the TiO2-terminated surface.

Local Epitaxial Growth of (103) One-Axis-Oriented SrBi2Ta2O9 Thin Films Prepared at Low Deposition Temperature by Metalorganic Chemical Vapor Deposition and Their Electrical Properties

We compared a directly crystallized SrBi2Ta2O9 (SBT) film with one crystallized by solid-phase reaction from the fluorite phase prepared by metalorganic chemical vapor deposition (MOCVD). The region of the Bi/Ta mole ratio showing large remanent polarization (2Pr) was narrow for the film directly crystallized from the gas phase compared with that crystallized by solid-phase reaction. Moreover, the Bi/Ta mole ratio showing the maximum 2Pr value differed according to the preparation method used. The crystallinity and the orientation of the SBT phase directly crystallized from the gas phase were strongly influenced by those of the substrate; the (103)-oriented SBT grains directly crystallized from the gas phase grew hetero-epitaxially on (111)-oriented Pt grains. As a result, the direct crystallization of the film from the gas phase lowered the crystallization temperature of the SBT phase and resulted in a (103) one-axis-oriented film.

Molecular dynamics calculations about misfit dislocations at the BaTiO3/SrTiO3-interface

Abstract When BaTiO 3 thin films are deposited on SrTiO 3 (001) substrates at low temperatures at approximately 700°C, at first epitaxial growth without defects occurs, but at a critical thickness it changes into pseudomorphic growth by introducing misfit dislocations. Cross-sectional high-resolution transmission-electron microscopy shows that these dislocations lie at the interface and stacking faults on (101) planes are also observed. Molecular dynamics simulations were performed in order to understand the formation of these dislocations. The critical thickness for occurrence of misfit dislocations is found to be approximately four monolayers with a slight increase with temperature. The misfit dislocations dissociate into partial dislocations and migrate to the interface by forming stacking faults on (101) planes.

BaTiO3/SrTiO3 thin films grown by an MBE method using oxygen radicals

Abstract BaTiO 3 (BTO) thin films were grown by an MBE method using an oxygen radical source. BaO and TiO 2 layers were alternately-deposited on a SrTiO 3 (001) substrate (STO), and the structure of the thin film obtained was evaluated by X-ray diffraction, reflection high energy electron diffraction and transmission electron microscopy. The BTO thin films were epitaxially grown and oriented in the (001) direction. The lattice constants of the thin film varied with distance from the interface of BTO and STO. Near the interface, the a -value was shorter than that for bulk BTO while the c -value was longer than that for bulk BTO.

Isothermal capacitance transient spectroscopy of grain-boundary interfacial states in Bi-doped SrTiO3 ceramics

It is shown that an isothermal capacitance transient spectroscopy (ICTS) technique is applicable to evaluate the interfacial state of SrTiO3 ceramics. ICTS signals were observed for Bi‐doped and undoped SrTiO3 ceramics, and ascribed to interfacial states of grain boundaries. The interfacial states were located at Ei=0.7 eV below the conduction band for the Bi‐doped samples and at Ei=0.5 eV for the undoped sample. This result indicates that the dopant bismuth caused deeper interfacial states in energy. The semiquantitative simulation of the ICTS signals suggests that the interfacial density of states of the SrTiO3‐Bi2O3 system is more broad compared with other electronic ceramics such as ZnO‐Bi2O3 and SiC‐BeO systems.

Defect Structure of Nonstoichiometric Perovskite

The Po2 dependance on electrical conductivity and the oxygen diffusion in non-stoichiometric BaTiO3 and (Ba, Ca) TiO3 ceramics were investigated. It is confirmed that the electrical conductivity of A-site-excess specimen at high temperature is decreasing with decrease of oxygen pressure. The mechanism is discussed with the oxygen defect structure, defect structure, barium titanate, calcium doping, Semi-conductor, nonstoichiometry, electrical conductivity, oxygen diffusivity.