Papers by Author: Hyeon Keun Lee

Abstract: The high thermal conductivity of Aluminum nitride, coupled with its high electrical resistivity and nontoxic nature, makes it a very promising material for electronic substrate. In this study, microstructural characterization on the thermal conductivity of AlN ceramics was investigated. An AlN ceramic was prepared with a dopant Y2O3 under a reducing nitrogen atmosphere with carbon. In order to obtain high thermal conductivity, cooling rate control and after-heat treatment was carried out. Morphology of the second phase was characterized using scanning electron microscopy (SEM). SEM studies showed that the microstructural change caused by after-heat treatment have a major influence on the thermal conductivity.

Abstract: The mechanical properties of brittle coating structures were characterized by various indentation techniques. The adhesion properties of the coatings were evaluated by in situ scratch and sphere indentation method. Physical vapor deposited TiN coatings on transparent substrates, sapphire, were scratched by diamond cone indenter and in situ observed through the transparent substrate. In situ scratch results reveal that the failure of coating is originated from the damage of the substrate and the plastic deformation of substrate is a primary factor for determining the adhesion breakage. The unique characterization technique for the strength measurement of brittle thin coating has been developed. The strength of the thin coating was evaluated by the sphere indentation on the trilayer structure. The CVD SiC coatings on graphite were characterized by the technique. It is concluded that the microstructure of SiC coatings influences the strength. In this paper, the various indentation technique were applied to evaluate the mechanical properties of TiN and SiC coatings and the effect of microstructure on the reliability of the brittle coating system was discussed.