Research Progress of High Thermal Conductivity Silicon Nitride Ceramics Prepared by Non-oxide Sintering Additives

The development trend of high voltage, high current and high-power density of power semiconductor devices has raised the requirement for the heat dissipation capability and reliability of ceramic substrates in devices.Silicon nitride（Si3N4） ceramics, known for their high thermal conductivity and excellent mechanical properties, have emerged as a preferred thermal dissipation substrate material for high-power electronic devices. However, there is a significant gap between experimental and theoretical values of thermal conductivity in Si3N4 ceramics. The long period of heat preservation during preparation leads to excessive grain growth, compromising mechanical properties and increasing costs, which hinders large-scale application. Lattice oxygen defects act as main factor limiting thermal conductivity of Si3N4 ceramics. Now, researchers are exploring ways to promote removal of lattice oxygen and full development of bimodal morphology formation of Si3N4, by selecting non-oxide sintering additives to reduce the oxygen content in the system, adjusting the composition and properties of the liquid phase, constructing a "nitrogen-rich-oxygen-deficient" liquid phase, and regulating the dissolution and precipitation process in the liquid phase. These efforts aim to the synergistic optimization of thermal conductivity-mechanical properties of Si3N4 ceramics. Based on the elemental classification, we review the non-oxide sintering additives developed at domestic and abroad, explain how they improve the thermal conductivity of Si3N4 ceramics from liquid-phase modulation and microscopic morphology control, analyze the grain development and morphology evolution laws, and discusse the mechanism of lattice oxygen removal. The out look on future development of high thermal conductivity Si3N4ceramics is also prospected.