Development of High-Temperature Electronic Device by Microstructure Control of Composite Ceramics of Silicon Carbide

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SiC-BN composite particles were prepared by a fluidized-beb CVD method, in which BN was deposited on SiC particles (paticle size : 0.3mum) from BCl_3-NH_3-H_2 gas phase. The composite particles formed spherical agglomerates with sizes of about 50mum. Although BN tended to segregate on the agglomerate surface, the homogeneous distribution of BN inside the agglomerates was achieved by control of preparation conditions. SiC-TiC composite particles were also prepared by deposition of TiC from TiCl_4-CH_4-H_2 gas phase, in which TiC was deposited on agglomerated SiC particles.The sintered composites were fabricated by hot-pressing of the composite particles. The SiC-BN composite had an excellent thermal-shock resistance because of the relaxation of thermal stress by uniformly-dispersed h-BN particles. The electrical resistivity of semiconductive SiC was lowered by addition of small smount of BN,whereas the resistivity became large at large BN content, because BN is insulator. The sintered body of SiC-TiC composite particles exhibited the low resistivity. Since TiC is metallic conductor, TiC on the agglomerate composite particles seemed to form the network structure which worked as electrical conduction path.TiC electrode was formed on semiconductive SiC.The stable bonding of TiC to SiC was achieved by grading composition at the interface. The electrical connection between SiC and TiC was ohmic, indicating that the gradiently-bonded TiC electrode was useful for high-temperature SiC electronic device.