Preparation and dielectric properties at high frequency of AlN-based composited ceramic

摘要

Pressureless sintering of AlN-SiC and AlN-ZrO_2 systems with Y_2O_3 as a sintering aid was carried out in a nitrogen atmosphere. The effects of SiC grain size and molding methods on the sinterability and microstructure were characterized and high-frequency dielectric properties of AlN-SiC ceramic in different bands were investigated. The dielectric constant decreased as the increase of frequency, but the dielectric loss (tgδ) showed the opposite trend. The tgδ values of AlN-SiC ceramic reached a maximum rang of 0.44-0.57 in the 75-110 GHz region (W band). Besides, the thermal conductivity at room temperature was 41.414 W/(m·K). To improve the thermal conductivity of AlN-SiC ceramic, the ZrO_2 spherical attenuator was selected as the substitute for SiC. The microstructure, high-frequency dielectric properties in W band and thermal conductivity of AlN-ZrO_2 ceramic were investigated. By adding ZrO_2 spherical attenuator in A1N substrate material, the thermal conductivity can be greatly improved up to 138 W/(m·K). At the same time, high microwave loss ability was obtained for the AlN-ZrO_2 ceramic: tgδ = 0.3-0.5 in W band. The relatively high thermal conductivity and high dielectric loss in W band would make AlN-ZrO_2 microwave absorbing materials promising for application.