Michael K. Cinibulk
Development of Oxide Fiber Coatings for Oxide and Non-Oxide Composites

Abstract
The lack of oxide analogues to carbon and boron nitride fiber coatings to provide crack deflection at the fiber-matrix interface has been a major impediment to the development of dense oxide fiber-reinforced ceramic-matrix composites. For this reason, currently available oxide CMCs do not contain fiber coatings, but rely on the inherent weakness of a porous matrix to prevent stress concentrations on the fiber. The most pervasive lifetime and temperature limitations for ceramic composites are related to sintering of the matrix in porous oxides and oxidative degradation at the fiber-matrix interface in non-oxides. Where dense oxide matrices are desired a fiber coating becomes a necessity. While several oxide coating concepts have been explored over the past 15 years it has been only relatively recently that effective oxide coatings have been developed and demonstrated to enable crack deflection in tow-based fiber-reinforced composites to at least 1200°C. Significant gains in lifetime at high temperatures of alumina-based composites with monazite (LaPO₄) fiber coatings have been demonstrated, and even greater benefits are expected by transitioning this technology to more refractory oxide and non-oxide composites. A brief review of the development of this technology for both oxide and non-oxide composites will be presented.

Yoshihiko Imanaka
Embedded Ceramic Passive Technology for RF-Module Substrates

Abstract
Embedding various passive elements, such as capacitors, filters, and inductors, in one system module is an effective way to achieve miniaturization, cost reduction, and higher performance in RF communications products. Much R&D regarding embedded capacitors has been conducted using different circuit board technologies. Low-Temperature Cofired Ceramics (LTCC) appears to be a promising technology for obtaining embedded modules. However, one drawback is its relatively high cost.

For the next generation of low-cost RF modules, we propose a resin circuit board embedding a ceramic passive film using unique aerosol deposition (AD). This circuit board makes it possible to meet all the required demands simultaneously. AD making use of solidification through bombardment of nano-size ceramic particles that form a ceramic-film below the endurance temperature of the resin. Therefore, this deposition is the key method for our proposed printed wiring board (PWB) embedding ceramic passive elements.

The microstructure and dielectric properties of BaTiO₃ AD film for a decoupling capacitor on a PWB, and the electrical characteristics and reliability of the prototype of the embedded passive components are introduced in this presentation. Also, prospective concepts for future RF-modules and the expectation of electric ceramics for RF-application will also be discussed.

Abstract
Novel nanoparticle-dispersed amorphous silica (Si-O) membranes have been designed and synthesized by the liquid precursor method. Some metals expected to have high-temperature hydrogen affinity have been selected for the nanoparticles. This is expected to be essential to enhance the high-temperature hydrogen permselectivity of the amorphous Si-O membranes. As our initial study, Ni-nanoparticle dispersed amorphous Si-O membranes have been successfully synthesized by an in-situ compositing method: (1) Preparation of a homogeneous solution precursor for the Si-Ni-O system, (2) Dip-coating of the solution precursor on a mesoporous anodic alumina support, and (3) Heat treatment at 873 K in air, subsequently, at 773 K under a hydrogen flow. TEM observation revealed that Ni-nanoparticle-dispersed amorphous Si-O layer with a thickness of about 400 nm was deposited on the mesoporous support. The nanocomposite membrane exhibited H₂ permeance of 1.4x10^-7 mol/m²sPa at 773 K, and the permeability ratios of H₂/N₂ and H₂/He were measured to be 84 and 5, respectively. To study the mechanism of the unique H2 permselectivity, hydrogen chemisorption isotherm analysis at 773 K was performed on the powered samples of the nanocomposite membrane materials, Ni prepared from NiNO₃•6H₂O, and Ni-free amorphous Si-O. As a result, an apparent reversible hydrogen adsorption was detected for the nanocomposite powders. On the contrary, the Ni power exhibited only irreversible strong hydrogen adsorption, while Ni-free amorphous Si-O showed no interaction with hydrogen. Based on the results, the reversible hydrogen adsorption is an important property for the selective enhancement in the H₂ permeance at 773 K of the nanocomposite membranes. At the presentation, the effect of the nanoparticle-dispersion on the hydrogen permselectivity will be discussed from a view point of a novel nanostructure design concept for the development of hydrogen permselective ceramic membranes at high-temperatures.

This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) as a part of the R&D Project on “Highly Efficient Ceramic Membranes for High-Temperature Separation of Hydrogen” promoted by the Ministry of Economy, Trade and Industry (METI), Japan.

Susan Trolier-McKinstry
Microcontact printed thin films for capacitors

Abstract
There is an ongoing need to develop new technologies to enable further down-scaling of layer thicknesses in multilayer ceramic devices, particularly in multilayer capacitors (MLC). There are about 10¹² MLC prepared annually. Currently, they are made by tape casting powder slurries, screen-printing, and laminating. In order to prepare a thin film version of such a capacitor, it is essential to demonstrate films with high dielectric constants (>1000) over a wide temperature range, stacking of these films into a multilayer configuration, and an inexpensive means of assembling the films. This paper will demonstrate chemical solution deposited BaTiO3 films on Ni foils with permittivities >1500 down to film thicknesses <150 nm with good temperature stability. Microcontact printing of chemical solutions of both the dielectric and electrode layers was explored as an economical means of preparing patterned thin film-based MLC without requiring photolithography. For this purpose, methanol/acetic acid-based BaTiO₃ solutions were spun onto elastomeric stamps, printed onto substrates, pyrolyzed, and crystallized. Both oxide and normal metal electrodes have also been microcontact printed. The line edge roughness produced this way was on the order of a tenth of a micron, which should enable very small margins. The printed layer thickness was also very uniform. Multilayer stacking was also demonstrated. Consequently, microcontact printing appears to be an interesting alterative means of preparing MLC with layer thicknesses in the range of <0.2 mm.

Abstract
Films of metallic and ceramic materials are the key elements to integrated electronic devices. Films are usually deposited either by screen printing, tape casting or sol-gel technique, and then fired to induce integrity. However, crack formation and propagation during firing are usually encountered due to the occurrence of in-plane stress induced by the restriction of the substrate imposed on the film shrinkage, which is known as constrained sintering. The crack formation mainly takes place in two stages. During the initial stage of firing, the cracks are formed due to the difference between the vapour pressure and capillary pressure of the slurry. In the second stage, mismatch occurs due to the differential shrinkage between the film and substrate, resulting in significant cracks in the film. Therefore, additives giving increased plasticity are added to the slurry, and/or slow heating rates are employed in order to relax the mismatch strain. Another significant problem in constrained sintering is that the sintering temperature of the deposited film tends to increase compared to that of the bulk material, giving thermal damage to the substrate. Due to these drawbacks, centrifugal sintering without any external pressure applying media is suggested as a novel high pressure firing/sintering technique, in which centrifugal force is introduced by the high speed rotation of furnace chamber during the process of sintering.

Centrifugal sintering process has been successfully applied to the firing of BaTiO3 films in which pore volume and amount of cracks were drastically reduced resulting in highly densified films. Furthermore, with this technique grain orientation in bismuth titanate film was achieved. X-ray diffraction analysis confirmed the presence of a very high degree of crystallographic texture with a Lotgering factor as high as f~96%. Microstructural analysis revealed that plate like bismuth titanate grains adopted brick-wall microstructure with their c-axis oriented parallel to the centrifugal force.