Mechanical Properties and Thermal Conductivity of Si3N4 Ceramics with Composite Sintering Additives

Si3N4 ceramics have become one of the most promising materials for third-generation semiconductor's ceramic substrates due to its excellent mechanical and thermal properties. In this work, seven rare earth oxides (RE2O3, RE=Sc, Lu, Yb, Y, Gd, Nd, La) and non-oxides (MgSiN2) were used as composite sintering additives to prepare Si3N4 ceramics with high strength and high thermal conductivity by hot pressing sintering and annealing. The effects of RE2O3 types in the composite additives on the phase composition, microstructure, mechanical properties, and thermal conductivity of Si3N4 ceramics were systematically studied. The mechanical properties of Si3N4 ceramics after hot pressing sintering were superior to that without hot pressing, and the bending strength of the sample with Nd2O3-MgSiN2 additive reached (1115 +/- 49) MPa. After annealing, the thermal conductivity of Si3N4 ceramics increased significantly, and gradually increased with the decrease of the rare earth ion's radius. The thermal conductivity of the sample with Sc2O3-MgSiN2 additive increased from 54.7 W.m(-1).K-1 to 80.7 W.m(-1).K-1 (increased by 47.6%) after annealing. The results indicate that Sc2O3-MgSiN2 is expected to be a new composite additive for the preparation of high strength and high thermal conductivity Si3N4 ceramics as compared to the internationally accepted combination of Yb2O3-MgSiN2 and Yb2O3-MgSiN2 additives.