Yoshirou Kuromitsu

Effect of glass composition on the densification and dielectric properties of BaTiO3 ceramics

An ongoing research goal of thick film capacitors and multilayer capacitors is to lower the firing temperature of the dielectrics. This paper presents the results of using three simple glass systems including PbO–B2O3, PbO–SiO2, and Bi2O3–B2O3 as sintering aids for hydrothermal synthesized BaTiO3. Glasses with different ratios of the modifier/glass former were employed. Effects of adding these glass systems on the BaTiO3 ceramics sintered at 850°C were investigated through measuring and analyzing the density, grain size and dielectric property. It was found that BaTiO3 sintered with glasses composed of 90 mol% PbO–10 mol% SiO2 or 90 mol% PbO–10 mol% B2O3 to 60 mol% PbO–40% B2O3 are helpful to reduce the firing temperature for typical thick film and MLCC applications. They possess high dielectric constant (≈1650) due to their high densification characteristics with the grain size of ≈0.7 μm. In addition, glasses composed of 90 mol% Bi2O3–10 mol% B2O3 to 40 mol% Bi2O3–60 mol% B2O3 are beneficial for thin dielectric layer applications, on account of the high sintering density and a small grain size of ≈0.1 μm with an acceptable K value.

Development of a surface-treatment method for AIN substrates to improve adhesion with thick-film conductors

A surface-treatment method for AIN substrates to improve adhesion with thick-film conductors has been developed based on the interfacial reaction mechanism between 96% alumina and glasses. The surface-treated AIN substrates were prepared through a combination of oxidation and sol-gel processes. An oxidation atmosphere with high PO2 and low PH2O, which produced the densest Al2O3 layer on AlN, was selected as the oxidation conditions for the surface treatment. A SiO2 layer was deposited on the Al2O3 layer, using the dipping technique with a sol-gel solution. The surface-treated AlN substrates with adequate thicknesses of Al2O3 and SiO2 as the surface-treatment layers showed a good adhesion strength with conventional thick-film conductors. This is the same result as with the 96% alumina substrates, although the adhesion strength of the conductors with bare AlN substrates was poor. These results suggest that glasses in the thick-film conductors react with the surface-treated AlN substrates in the same way as ...

Atomic structures of a liquid-phase bonded metal/nitride heterointerface

Liquid-phase bonding is a technologically important method to fabricate high-performance metal/ceramic heterostructures used for power electronic devices. However, the atomic-scale mechanisms of how these two dissimilar crystals specifically bond at the interfaces are still not well understood. Here we analyse the atomically-resolved structure of a liquid-phase bonded heterointerface between Al alloy and AlN single crystal using aberration corrected scanning transmission electron microscopy (STEM). In addition, energy-dispersive X-ray microanalysis, using dual silicon drift X-ray detectors in STEM, was performed to analyze the local chemistry of the interface. We find that a monolayer of MgO is spontaneously formed on the AlN substrate surface and that a polarity-inverted monolayer of AlN is grown on top of it. Thus, the Al alloy is bonded with the polarity-inverted AlN monolayer, creating a complex atomic-scale layered structure, facilitating the bonding between the two dissimilar crystals during liquid-phase bonding processes. Density-functional-theory calculations confirm that the bonding stability is strongly dependent on the polarity and stacking of AlN and MgO monolayers. Understanding the spontaneous formation of layered transition structures at the heterointerface will be key in fabricating very stable Al alloy/AlN heterointerface required for high reliability power electronic devices.

New Process of Barrier‐Rib Formation for AC PDPs

A new barrier-rib formation process called the blade-deforming process (BD process) has been developed for AC plasma display panels (PDPs) to reduce the manufacturing cost. It is a very simple and inexpensive method consisting of printing, blade-deforming, and firing. This process can make desired barrier-rib shapes with a high aspect ratio.

Fracture Process of Aluminum/Aluminum Nitride Interfaces during Thermal Cycling

Al circuit substrates, which are composed of a sintered AlN plate and pure Al plate joined to both sides of the AlN plate, are used for semiconductor power devices. It is important to prevent fracture of the Al/AlN interface to ensure normal and stable device operation. In this study, the fracture process of Al/AlN interface during thermal cycling was investigated using advanced scanning electron microscopy (SEM). Al circuits joined to an AlN plate were plastically deformed with thermal cycling. Al grains were divided with the formation of sub-boundaries due to the plastic deformation. After 2000 thermal cycles, a crack was generated at edges of the Al/AlN interface and propagated gradually to the center of the substrate. Cross-sectional observation, using an angle selective backscattered electron detector (AsB), revealed that the Al grain size near the Al/AlN interface decreased to 3 m or less, and the crack proceeded along the Al grain boundaries. To clarify the temperature dependence of the fracture process, a repeated bending test was performed at various temperatures. Shear strains were induced at the Al/AlN interface by the repeated bending. The rate of crack propagation tends to be higher at higher temperatures for bending test. In substrates bent at 373 K or higher, the crack proceeded after the Al grains had been refined. These results indicate that fine-grained Al resulting from thermal cycling is formed by creep deformation and recrystallization at higher temperatures. Thus, improving the creep strength of the Al plate is thought to be effective for prevent cracking during thermal cycling. The effect of additive elements in the Al plate was also discussed in this study.

23.3: Surface Fluorination of MgO Protective Film to Reduce Chemical Reactivity with H2O and CO2

Just after fabrication of a MgO protective film by EB deposition, a surface modification of the film with a fluorinating gas was performed. This technique achieved a remarkable reduction in the amount of outgassing from the film, and therefore it can be expected to shorten the duration of the gas-evacuation process in PDP manufacturing.

Interactions Between AL2O3 Substrate and Glass Melts

The quality of bonding between a glass and a ceramic is a factor determining the properties and lifetimes of electronic components such as hybrid ICs, HID lamps, and TV tubes. The bonding is characterized by interfacial reaction and thermal expansion coefficient.

Structural and electrical characterization of electro spray deposited PZT sol-PZT nanopowder composite thick films

In piezoelectric market, infrared detectors, pyroelectric and piezoelectric sensors, microwave devices, actuators, transducers, non-volatile random access memories, and micro electromechanical systems are fabricated using lead zirconate titanate (PZT) based films. These films are deposited by chemical vapor deposition, physical vapor deposition spin coating, screen printing and electrospray deposition (ESD) technique. Among them, ESD is the most preferred method because of its high material efficiency, simplicity of experimental set up, wide choice of precursor and low cost. Therefore, the purpose of this study is to fabricate and characterize the ESD deposited PZT films. In our study, Pb(Zr0.52 Ti0.48)O3(PZT) nano powders (Nanotech Corp. Turkey) and MMC PZT sol (Mitsubishi Corp. Japan) combinations were mixed in various concentrations. Prepared composite PZT slurries were coated with ESD technique. Fabricated PZT thick films were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction method (XRD) to evaluate surface and crystal structure of the films. The results show that, MMC sol and PZT nanopowder combinations provide smooth and homogeneous film surface, dense and non-cracked film microstructure was observed using excess PbO during sintering.