Study On SiC Ceramic Capacitor

SiC was normally considered not suitable for the application as capacitors due to its low intrinsic dielectric constant (～10). Recently it was tried to be used in grain boundary barrier layer capacitor because of the good semiconductivity and high coefficient of thermal conductivity. Huge dielectric constant was obtained, which was much higher than that of conventional titanates dielectrics. However, the high dielectric loss would limit its practical applications.In this experiment,α-SiC particles (China White Dove Group) were commercially available. Double coating processes were carried out to prepare composite particles. Conventional sintering, hot-press sintering and microwave sintering were used to prepare the compacts, respectively. The surface composition of different samples was confirmed through the zeta potential measurement. The microstructure was observed using SEM. The thermodynamic behavior of the SiC-SiO₂-Cu(OH)₂ composite particles was analyzed using DSC-TG technique. Phases in the sintered compacts were identified by XRD. The dielectric properties were tested by HP4192 frequency spectrograph. The effect of sintering temperature, sintering method, boundary content on dielectric properties was studied. The influence of temperature and frequency on dielectric properties was analyzed.The results showed that good core-shell structure can be constructed by the two-step coating method. SiC would react with Cu to form Cu_6.69Si at high temperature. Cu_6.69Si will change into Cu₃Si at higher temperatures due to the decomposition of SiO₂. The best sintering temperature was at 1300℃. When it was lower than 1300℃, many pores and Cu existed; when it was higher than 1300℃, a lot of glass phase was observed. The dielectric constant of the sample sintered at 1300℃was much higher than that sintered at other temperatures, and the dielectric loss was the lowest. The capacitor had a good frequency-dispersion effect. A turning point at 60℃was observed on the curve of dielectric constant/dielectric loss versus temperature, which may be associated with the space charge polarization. The dielectric constant of the sample containing 35%(vol%) grain boundary was much lower than that of the sample containing 25% grain boundary, and the loss of the former was lower than the latter. No turning point was observed, which implied that space charge polarization didn't occur. Pores and glass phase were disadvantageous for the formation of the space charge polarization. The microwave sintering sample had much higher dielectric constant and lower dielectric loss. The reason may be fine microstructure and small defect size can be obtained by microwave sintering.