화학공학소재연구정보센터
Journal of the American Ceramic Society, Vol.98, No.3, 879-887, 2015
Microstructure, Thermal Conductivity, and Electrical Properties of In Situ Pressureless Densified SiC-BN Composites
The microstructure, thermal conductivity, and electrical properties of pressureless densified SiC-BN composites prepared from in situ reaction of Si3N4, B4C, and C were systematically investigated, to achieve outstanding performance as substrate materials in electronic devices. The increasing BN content (0.25-8wt%) in the composites resulted in finer microstructure, higher electrical resistivity, and lower dielectric constant and loss, at the expense of only slight degradation of thermal conductivity. The subsequently annealed composites showed more homogeneous microstructures with less crystal defects, further enhanced thermal conductivities and electrical resistivities, and reduced dielectric constants and losses, compared with the unannealed ones. The enhanced insulating performance, the weakened interface polarization, and the reduced current conduction loss were explained by the gradual equalization of dissolved B and N contents in SiC crystals and the consequent impurity compensation effect. The schottky contact between graphite and p-type SiC grains presumably played a critical role in the formation of grain-boundary barriers. The annealed composites doped with 8wt% BN exhibited considerably high electrical resistivity (4.11x10(11) Omega center dot cm) at 100V/cm, low dielectric constant (16.50), and dielectric loss (0.127) at 1MHz, good thermal conductivity [66.06W(m center dot K)(-1)] and relatively high strength (343MPa) at room temperature.