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

采用流化床CVD法，在BCl_3-NH_3-H_2气相中，将BN沉积在粒径为0.3 μ m的SiC颗粒上，制备了SiC-BN复合颗粒。复合颗粒形成尺寸约为50 μ m的球形团聚体。虽然BN倾向于在团聚体表面上偏聚，但通过控制制备条件实现了BN在团聚体内部的均匀分布。采用TiCl_4-CH_4-H_2气相沉积法，将TiC沉积在团聚的SiC颗粒上，制备了SiC-TiC复合颗粒，并通过热压烧结制备了复合材料。由于均匀分散的h-BN颗粒缓解了热应力，SiC-BN复合材料具有优异的抗热震性。少量BN的加入降低了SiC陶瓷的电阻率，但由于BN是绝缘体，当BN含量增加时，SiC陶瓷的电阻率增大。SiC-TiC复合颗粒的烧结体具有较低的电阻率。由于TiC是金属导体，TiC在团聚体复合颗粒上形成了网状结构，起到了导电通路的作用，TiC电极在SiC基体上形成，TiC与SiC的稳定结合是通过界面成分的梯度化实现的。SiC和TiC之间的电连接是欧姆的，表明梯度结合的TiC电极适用于高温SiC电子器件。

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.