Papers by Author: Song Min Nam

Abstract: Direct observations for high frequency microscopic dielectric distributions in cross sections of a multi-layer ceramic capacitor were carried out using non-contact type microwave probe. The measured data were imaged from the raw data and rounding data process. Using microwave reflection intensity mappings from cross sections of multi-layer ceramic capacitor, the dielectric permittivity distribution in micro-region of a multi-layer ceramic capacitor was measured at room temperature. The spatial resolution was experimentally estimated to be about 10 μm from mappings of the dielectric and inner electrode layers in a multi-layer ceramic capacitor.

Abstract: To induce fine engineered domain configurations into potassium niobate (KNbO3) single crystals, two kinds of methods were performed, i.e., (1) high DC electric field exposure along the opposite direction of polarization of KNbO3 single-domain crystals at room temperature, and (2) introduction of randomly oriented fine domain configuration by heat treatment at 700 °C and then high DC electric field exposure along [001]c direction of KNbO3 multidomain crystals at room temperature. When the method (1) was performed, finally, the poled KNbO3 crystals became to single-domain state again through the formation of multidomain state. On the other hand, the KNbO3 multidomain crystals were obtained by using the method (2), and an enhancement of piezoelectric-related properties was observed.

Abstract: The microwave reflection intensity was measured at room temperature for Cu-plate, Al2O3 and SrTiO3 single crystals using a un-contact probe as a function of distance between sample and probe. The difference of reflection intensity for Cu-plate, Al2O3 and SrTiO3 single crystals was observed in the region where the distance of 0.2mm between sample and probe, and it was caused from dielectric permittivities of samples. The reflection coefficient of sample was estimated in comparison with results of electromagnetic simulation using finite differential time domain method. The reflection intensity for Cu-plate, Al2O3 and SrTiO3 single crystals was transformed to dielectric permittivity at reflection intensity minimum point. The dielectric permittivity mapping was also examined at reflection intensity minimum point.

Abstract: For potassium niobate (KNbO3) single crystal, the 31 resonators with the highest piezoelectric constant d31 were designed using transformation of axis. We confirmed that the engineered domain configurations with maximum d31 of –55.1 pC/N was caused by a combination between two polarization with polar directions along [101]c and [-101]c directions. Moreover, if there are larger piezoelectric constants from domain wall region, we can expect the much higher piezoelectric properties. To induce the above domain configuration, a new poling method using patterning electrode was investigated. In this study, the two methods on the basis of temperature-induced phase transition at 207 °C and electric-field-induced phase transition at room temperature were investigated.

Abstract: Dielectric permittivity of BaTiO3 powders was determined by measuring permittivity of slurries prepared from BaTiO3 powder and propylene carbonate as dispersion medium followed by analyzing with a finite element methods (FEM). The permittivity of powders depended on their characters such as tetragonality (c/a ratio), density, particle size and specific surface area. In order to extract the effect of each character, a statistical analysis was carried out to represent the permittivity of powders with an empirical equation where the c/a ratio, density and particle size were used as parameters. A fairly good agreement between observed data and those estimated from the relation was obtained and the contribution of each character to the permittivity could be determined.

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.