Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

After twenty years of partly quiet and ten years of partly enthusiastic research into lead-free piezoceramics there are now clear prospects for transfer into applications in some areas. This mimics prior research into eliminating lead from other technologies that resulted in restricted lead use in batteries and dwindling use in other applications. A figure of merit analysis for key devices is presented and used to contrast lead-containing and lead-free piezoceramics. A number of existing applications emerge, where the usage of lead-free piezoceramics may be envisaged in the near future. A sufficient transition period to ensure reliability, however, is required. The use of lead-free piezoceramics for demanding applications with high reliability, displacements and frequency as well as a wide temperature range appears to remain in the distant future. New devices are outlined, where the figure of merit suggests skipping lead-containing piezoceramics altogether. Suggestions for the next pertinent research requirements are provided.

Transferring lead-free piezoelectric ceramics into application

Perovskite lead-free dielectrics for energy storage applications

Multilayer ceramic capacitor (MLCC) production and sales figures are the highest among fine-ceramic products developed in the past 30 years. The total worldwide production and sales reached 550 billion pieces and 6 billion dollars, respectively in 2000. In the course of progress, the development of base-metal electrode (BME) technology played an important role in expanding the application area. In this review, the recent progress in MLCCs with BME nickel (Ni) electrodes is reviewed from the viewpoint of nonreducible dielectric materials. Using intermediate-ionic-size rare-earth ion (Dy2O3, Ho2O3, Er2O3, Y2O3) doped BaTiO3 (ABO3)-based dielectrics, highly reliable Ni-MLCCs with a very thin layer below 2 µm in thickness have been developed. The effect of site occupancy of rare-earth ions in BaTiO3 on the electrical properties and microstructure of nonreducible dielectrics is studied systematically. It appears that intermediate-ionic-size rare-earth ions occupy both A- and B-sites in the BaTiO3 lattice and effectively control the donor/acceptor dopant ratio and microstructural evolution. The relationship between the electrical properties and the microstructure of Ni-MLCCs is also presented.

https://iopscience.iop.org/article/10.1143/JJAP.42.1/pdf

Base-Metal Electrode-Multilayer Ceramic Capacitors: Past, Present and Future Perspectives

The effect of rare-earth elements, La, Sm, Dy, Ho and Er, on the microstructure in BaTiO3(BT)–MgO–rare-earth oxide based system was studied. Larger amount of MgO was required to suppress the grain growth for the larger ionic radius rare-earth ion (La, Sm)-doped samples than for the smaller ion (Dy, Ho, Er)-doped samples. Also, substitution modes of rare-earth elements and Mg in BT lattice were investigated. The solubility of rare-earth ions in BT lattice and the substitution ratio of rare-earth ions into Ba-site decreased as ionic radius decreases. This suggests that the formation of core-shell structures in BT–MgO–rare-earth oxide based system is dependent on the substitution ratio of rare-earth ions into Ba-site.

The effect of rare-earth (La, Sm, Dy, Ho and Er) and Mg on the microstructure in BaTiO3

The impedance of a BaTiO3 (BT)-based multilayer ceramic capacitor with a nickel internal electrode (Ni-MLCC) was investigated by measuring the frequency domain at various temperatures. All the obtained impedance data could be successfully fitted to a 4-RC section electrical equivalent network. The 4-RC section electrical equivalent network was successfully correlated to the microstructure: the core, the shell, the grain boundary, and the ceramic/internal electrode interface regions. Based on this electrical equivalent network, the electrical properties including the Curie-Weiss law, the current-voltage characteristics, and dc electrical degradation, were well explained. A model for the degradation behavior for BT-based Ni-MLCC with thin active layer thickness was proposed.

https://iopscience.iop.org/article/10.1143/JJAP.40.5624/pdf

dc-Electrical Degradation of the BT-Based Material for Multilayer Ceramic Capacitor with Ni internal Electrode: Impedance Analysis and Microstructure

Electrical properties and microstructures of a holmium-doped (Ba1.01Mg0.01)O1.02(Ti0.98Zr0.02)O2 system were studied. Additions of Ho2O3 had little effect in preventing the dielectrics from reducing at high temperature, but the resistivity at low temperature increased with increasing amount of Ho2O3 when treated in oxidizing atmosphere at the cooling stage. From transmission electron micrograph (TEM) observation, it was noted that the microstructure exhibited a grain core-grain shell structure. Newly developed X7R multilayer ceramic capacitors with Ni electrodes revealed highly reliable electrical properties.

https://iopscience.iop.org/article/10.1143/JJAP.30.2307/pdf

X7R Multilayer Ceramic Capacitors with Nickel Electrodes

The sintering characteristics and the reaction of additives with BaTiO3 (BT) were examined for two materials having Nb-rich composition (Comp.N) and Co-rich composition (Comp.C) to elucidate the relation between the stability of the core–shell microstructure and the Nb/Co ratio in the BT–Nb2O5–Co3O4 system. TEM observation revealed that the concentration gradient of Nb and Co existed in the shell region although Nb and Co macroscopically distributed homogeneously. X-ray diffraction analysis showed that the shell formation preceded the densification and completed at about 1280°C for both Comp.N and Comp.C as determined from differential scanning calorimetry. A diffusion couple experiment disclosed that Co had a larger diffusivity than Nb and that the diffusion of Co was suppressed when the sample was codoped with a sufficient amount of Nb. On the basis of these experimental results, new mechanisms of the formation and collapse of core–shell structure in the BT–Nb2O5–Co3O4 system were proposed.

Hiroshi Kishi

Papers

Base-Metal Electrode-Multilayer Ceramic Capacitors: Past, Present and Future Perspectives

The effect of rare-earth (La, Sm, Dy, Ho and Er) and Mg on the microstructure in BaTiO3

dc-Electrical Degradation of the BT-Based Material for Multilayer Ceramic Capacitor with Ni internal Electrode: Impedance Analysis and Microstructure

X7R Multilayer Ceramic Capacitors with Nickel Electrodes

Sintering Characteristics in the BaTiO3–Nb2O5–Co3O4 Ternary System: II, Stability of So-called “Core–Shell” Structure