Anisotropic sintering shrinkage and microstructural evolution of c-axis-oriented Si₃N₄ ceramics

Abstract

High-thermal-conductivity Si₃N₄ ceramics are desired for substrates in SiC power devices. We successfully fabricated highly c-axis-oriented Si₃N₄ ceramic by casting in a rotating-magnetic field and then sintered using a conventional gas pressure. As a result, the c-axis orientation of Si₃N₄ grains effectively improves the thermal conductivity. The sintering behavior of c-axis-oriented Si₃N₄ ceramics was investigated. The linear shrinkage ratio in the c-axis-oriented direction was smaller than that in the direction normal to the c-axis-oriented direction. Fine c-axis-oriented structures resulted from the orientation of β-Si₃N₄ seeds during the casting because they played as templates controlling the grain growth of β-Si₃N₄ nuclei and inducing the anisotropic sintering shrinkage.