Optimization of Microstructure to Improve Si3n4 Ceramics with Thermal Conductivity and Mechanical Properties: Effect of Si and Α-Si3n4 Powder Composition

Abstract

The heat dissipation capacity and mechanical reliability of silicon nitride (Si3N4) ceramic substrates determine the service life of power devices. In this work, a two-step sintering method was designed to produce Si3N4 ceramics with excellent performance using Si and α-Si3N4 powders with different ratios as raw materials. The nitridation mechanism and the microstructural evolution mechanism were clarified. The in-situ-generated β-Si3N4 seeds regulated the microstructure of the post-sintered Si3N4 ceramics. The introduction of Si powder reduced the content of oxygen impurities and regulated the microstructure of Si3N4 ceramics, thereby improving thermal conductivity while maintaining excellent mechanical properties. When the mass ratio of Si powder nitridation to α-Si3N4 was 0.75, its thermal conductivity was 120 W·m-1·K-1, fracture toughness was 11.92±0.36 MPa·m1/2, and bending strength was 712±20.6 MPa. This study provides a strategy to reduce the introduction of oxygen impurities while optimizing the microstructure to prepare Si3N4 ceramics with excellent performance.

Keywords: Silicon nitride, Microstructure, nitridation mechanism, Thermal conductivity