Key Engineering Materials Vol. 301

Abstract: The UV-Vis absorption spectrum of ZrO2 precursor solution containing 4-(phenylazo)benzoic acid (C6H5N=NC6H4COOH) reversibly changed accompanied with reversible change of the spectrum of 4-(phenylazo)benzoic acid by light irradiation. However, the spectrum of ZrO2 precursor solution containing azobenzene (C6H5N=NC6H5) did not change accompanied with reversible change of azobenzene by light irradiation. Furthermore, the back reaction of ZrO2 precursor solution containing 4-(phenylazo)benzoic acid by visible light irradiation was suppressed even if the back reaction of 4-(phenylazo)benzoic acid has occurred by visible light irradiation, when the hydrolysis of ZrO2 precursor was suitably controlled.

Abstract: Thin films of lithium ion conductive ceramic Li4+xAlxSi1-xO4 were fabricated on Au substrate using sol-gel process. The sol of Li-Al-Si-O was spread on Au substrate using a spin coater, and it was gelated at room temperature. The gel was calcinated at 400 °C and heat-treated at high temperatures between 500 °C and 800 °C in air. The addition of poly(vinylpyrrolidone) (PVP) was effective in stabilizing the sol. Furthermore, the morphology of the obtained thin film was changed by the PVP additive. Li4+xAlxSi1-xO4 thin film prepared at 800 °C exhibited a Li+ ion conductivity of 10-8 S cm-1 at room temperature.

Abstract: An AlBN thin film with a boron content (B/(Al+B)) of 0.1 or 0.3 was obtained by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE) using EB-guns as group-III element sources and an RF radical source for nitrogen supply. We compared the characteristics of the film with those of AlN and BN films. By reflective high-energy electron diffraction (RHEED), we observed ring patterns in the AlBN film. The X-ray photoelectron spectroscopy (XPS) N1s peak of the AlBN film was observed at a binding energy between the peaks of AlN and BN. There was no evidence for phase separation in the film.

Abstract: Layered perovskite, K2NbO3F, includes rock-salt type KF blocks in a K2NiF4 type structure. After the KF blocks are dissolved selectively in water at room temperature, the resultant colloidal suspension consists of nanosheet forms. Positively charged K+ ions in colloidal suspension act as an inorganic binder in electrostatic self-assembly with an exfoliated perovskite nanosheet. In the present study, we synthesized a KNbO3 thin film on a quartz substrate using a self-assembly process. The thin film on a quartz substrate was characterized using XRD analysis. The molar extinction coefficient of the colloidal suspension and absorbance of the thin film were examined using UV-vis absorption spectra. Respective thicknesses of perovskite nanosheet aggregate thin films were examined using AFM. The UV-vis absorption spectra of the films showed an increase in absorbance with increasing immersion time, suggesting growth of a self-assembled multilayer comprising perovskite nanosheets and K+ ions.

Abstract: For high frequency packaging applications, LTCC materials are required to have a low loss tangent to reduce the total microwave loss. For multi-layered ceramic devices with embedded passive components, besides a loss tangent, a small temperature coefficient of resonance frequency (TCF) is an important factor. To meet these demands, we developed a new LTCC material with a smaller TCF, less than +/-3ppm/oC, and a low loss tangent, 0.0012 at 15GHz. We designed the glass composition to precipitate two low-loss crystal phases during firing at 900 oC. One phase has a plus TCF and the other phase has a minus TCF. We also controlled the amount of the two crystal phases, so these crystal phases and the fixed amount of alumina filler make the sum of TCF for the LTCC material close to zero.

Abstract: In order to improve the sinterability and controllability of dielectric properties, we focused on self-flux composition. In the case of Ba(Mg1/3Nb2/3)O3, we selected Ba(1-b)NbbOd as self-flux system and investigated correlations between Q-factor and the b value. Interestingly, high Q-value was obtained only at the
b=0.45. Moreover, the dielectric constant and tf change linearly by the quantity of Ba0.55Nb0.45Od under keeping up high-Q value. As a result, it was indicated that the dielectric properties could be controlled by the assumption of stoichiometric composition and liquid phase consisted by self-flux.

Abstract: It is found through simulation that electromagnetic wave absorbers made of composites of Ni-Zn ferrite and SiO2 particles, which are isolated in a continuous medium of Ni-Zn ferrite, show absorption in the frequency regions both below and above 1 GHz. The measured complex permeabilities are close to simulation values above 1 GHz. Both absorbing bandwidth and center frequency of the composites are close to the desired values expected from the simulation result.

Abstract: In order to fabricate a microstrip band pass filter in GHz region as a passive component of RF modules, Al2O3 thick films were prepared on Cu metal substrates by AD (Aerosol Deposition) process. The dimensions of the filters were determined by the high frequency electromagnetic analysis. The filters were successfully fabricated on AD-derived Al2O3 thick films by employing sputtering, photolithography, electroplating and chemical etching processes. Their filtering characteristics were examined by a Network Analyzer. Through this work, we suggest that the AD process will be important the fabrication technology for integrated RF modules.

Abstract: Microwave reflection intensity for microwave absorber, Cu-plate and Al2O3 (0001) single crystal substrate was measured from 8GHz to11GHz as a function of distance between single probe and sample at room temperature. The minimum reflection intensity was observed in the distance of 0.2mm between single probe and sample at 9.4GHz, although the reflection intensity was decreased with increasing distance in other measurement frequencies. The electromagnetic field analysis was hence carried out for simulation model that is defined with coaxial cable, probe and sample using finite differential time domain method. The reflection coefficient and impedance for simulation model were calculated, and compared to the experimental data. From results of electromagnetic analysis, the minimum point of reflection intensity was caused from an impedance matching.