Yukio Hamaji

Effects of Rare-Earth Oxides on the Reliability of X7R Dielectrics

The effects of rare-earth oxides, e.g., La, Nd, Sm, Dy and Yb, on the reliability of multilayer capacitors (MLCs) with X7R dielectrics and Ni electrodes were investigated. Microstructures of the dielectrics were analyzed by transmission electron microscopy (TEM) and electron probe microanalysis (EPMA) in order to characterize the rare-earth ions. Incorporation of rare-earth ions to BaTiO3 ceramics depended on their ionic radius, resulting in different microstructures and electric performances of dielectrics. Dy ions provided BaTiO3 ceramics with ideal X7R characteristics and high reliability. The mechanism governing leakage current was discussed in terms of the voltage dependence of leakage current. Electric properties and related reliability of the capacitors were attributed to solubility, distribution of rare-earth oxides and their occupation site in BaTiO3.

Synthesis and Characterization of Bi4Ti3O12 Thin Films by Sol-Gel Processing

Stoichiometric Bi4Ti3O12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, and characterization of the resulting Bi4Ti3O12 thin films. The formation of metallic alkoxide and acetate alkoxide are indispensable, soluble precursors for these multicomponent systems. The double alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. The development of the polymerizable solution system containing Bi and Ti required choosing appropriate solvents and metallo-organic sources for the two components. Bismuth acetate, titanium methoxyethoxide and the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi4Ti3O12 were obtained onto platinized Si substrates by spin casting, followed by heat-treated at 700°C. These films were later characterized by X-ray diffraction and SEM. The measured dielectric and ferroelectric properties of Bi4Ti3O12 were as follows: dielectric constant 120, dielectric loss 0.5%, remanent polarization Pr=4 µC/cm2, coercive field Ec=1.8 kV/cm.

GROWTH OF (BA,SR)TIO3 THIN FILMS BY THE HYDROTHERMAL-ELECTROCHEMICAL METHOD AND EFFECT OF OXYGEN EVOLUTION ON THEIR MICROSTRUCTURE

Thin films in the system BaTiO 3 –SrTiO 3 have been grown on Ti electrodes with control of the Ba/Sr composition in aqueous solutions of (Ba, Sr) (OH) 2 by the hydrothermal-electrochemical method. Barium contents of the solid-solution films were always lower than those of the synthesis solutions used. The BaTiO 3 and the (Ba, Sr)TiO 3 solid-solution films included “crater-shape” defects that resulted from the breakaway of the growing film, whereas no such defects were observed in the SrTiO 3 film. This dependence of the defect generation on the film composition was interpreted to be caused by differences of anodically evolved oxygen gas pressure in “short-circuiting paths” that exists characteristically in the films grown by this method.

Study of the Valence State of the Manganese Ions in PbTiO3 Ceramics by Means of ESR

ESR measurements have been carried out on Mn ions in PbTiO3 ceramics. Mn ions in the PbTiO3 ceramics are incorporated at Ti4+ sites with mixed valence states of Mn2+ and Mn4+. The proportion of Mn2+ ions is the highest for the calcined powder and changes during the firing process. After the firing it decreases with increasing the firing temperature in the range from 800°C and 1100°C, and increases at temperatures above 1150°C. Additionally, the proportion changes with the amount of Mn ions. The proportion of Mn2+ decreases with increasing Mn dopants up to 0.20 wt%. In the range from 0.20 wt% and 0.25 wt% of MnO2 it increases steeply, and the Mn2+ and Mn4+ ratio is not varied when more than 0.25 wt% MnO2 is doped. Piezoelectric properties of Mn doped PbTiO3 can be explained by the changes of the valence states of Mn ions.

CONTRIBUTION OF ELECTROLYSIS CURRENT TO GROWTH OF SRTIO3 THIN FILM BY THE HYDROTHERMAL-ELECTROCHEMICAL METHOD

The electrolysis treatment of the hydrothermal-electrochemical method has been modified so that it permits SrTiO 3 thin films to be grown on Ti electrodes being oxidized anodically in Sr(OH) 2 solutions far beyond a thickness limit of several tens of nanometers hitherto attained. The relation between the total current passed through the Ti anode and the amount of the resulting SrTiO 3 film was analyzed on the basis of a reaction model that interprets the anodic current to be compensated with electrons generated partly by oxidation of Ti and partly by decomposition of H 2 O. Current efficiency for the film growth was estimated to be in the range from 0.8 to 3% depending on the Ti electrode potential.

Ferroelectric properties and fatigue characteristics of Bi4Ti3O12 thin films by sol-gel processing

Stoichiometric Bi4Ti3O12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, ferroelectric properties and fatigue characteristics of the resulting Bi4Ti3O12 thin films. The complex alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. Bismuth acetate and titanium methoxyethoxide, the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi4Ti3O12 were obtained onto platinized Si substrates by spin casting, followed by heat treated at 700° C. The value of the dielectric constant and loss at 400 Hz, 100 mVrms, 25° C of this virgin films were 132 and 0.8%, respectively. This thin films with single phase layerd perovskite-like structure had very good D-E hysteresis characteristics. The remnant polarization, P r, and coercive field, E c, of this virgin films were 5.5 µ C/cm2 and 6.2 kV/cm, respectively. The remnant polarization of this thin films, P r+, P r-, and 2P r, were nearly constant up to 108 cycles. At 4×108 cycles, the decay in remnant polarization, P r+, P r-, and 2P r, was observed to be about 35% of the initial values, respectively. The coercive field was drastically increased after 108 cycles. The D-E hysteresis loop after 108 cycles was not completely saturated. After 108 cycles, leakage current was typically increased. We considered that the fatigue characteristics observed in our study are resulted from increasing of leakage current.

Microstructures and Dielectric Properties of Fine-Grained BaTiO3 Ceramics

BaTiO 3 powders of 0.2 μm and 0.5 μm particle size diameters were prepared by changing the calcination temperature of BaTiO 3 synthesized by a hydrolysis method. Glass frit mainly consisting of SiO 2 was added as a sintering aid. In the case of using 0.2 μm powder, grains grew to 0.5 μm in diameter at sintering. Ceramics exhibited no secondary phase caused by glass frit at the grain boundary and showed a large dielectric constant at the Curie temperature. On the other hand, in the case of using 0.5 μm powder, grain size remained the same as the calcined powder size. Ceramics had a grain boundary layer of 1 nm thickness and showed stable temperature dependence of the dielectric constant. Ununiform lattice distortion, as calculated by the Hall method, was greater in the latter ceramics. It is considered that the ununiform lattice distortion was caused by the stress from the grain boundary layer, resulting in the lowering of the dielectric constant at the Curie temperature and the increase of the dielectric constant in the ferroelectric phase.

DiCI4a: New barium titanate based material for MLCs with Ni electrode

Abstract A new barium titanate based X7R material has been developed for MLCs with Ni electrode. Dielectric properties of the new material are; K =3600, DF =1.6%, insulation resistance =6500ω · μF as RC product, when the dielectric layer thickness is 10μm. Performance on an accelerated life test was much superior to conventional base metal MLCs. This new material contains dysprosium oxide and cobalt oxide as main dopants to barium titanate. The performances presented in the above are attributed to this new formulation.

Fabrication of PbTiO3 Ceramic Fibers by Sol-Gel Processing

The sol-gel processing was applied to the fabrication of PbTiO3 fibers. Pb(CH3COO)2·3H2O and Ti(OC3H7i)4 were refluxed with stirring in 2-methoxyethanol to form Pb-methoxyethoxide and Ti-methoxyethoxide, respectively, followed by mixing with stirring in 2-methoxyethanol to form Pb−Ti double alkoxide. The hydrolysis and polycondensation reaction of this double alkoxide gave polymerized products, and as a result the viscosity of the solution increased, suggesting that linear polymers were produced through the hydrolysis and polycondensation reaction. Homogeneous PbTiO3 gel fibers were drawn from the spinnable viscous solutions, which were wellcrystallized into perovskite type PbTiO3 at 650°C. The heat-treated fibers were a few centimeters long and from 10 to 100 μm in diameter. The fiber was made up of extremely uniform grains. Electron diffraction revealed a preferred growth of (101) planes along the fiber axis, which might be due to the linear molecular characteristics of the alkoxide.