Improvement in Thermal Conductivity of Silicon Nitride Ceramics via Microstructural Control and Their Application to Heat Dissipation Substrates

Abstract

Silicon nitride is well known as a typical structural ceramic material which exhibits excellent mechanical and heat resistance properties. In addition, β-Si₃N₄ single crystal is expected to possess a high intrinsic thermal conductivity over 200 Wm⁻¹K⁻¹. This makes silicon nitride a serious candidate as a substrate material for power devices.

However thermal conductivity of commercially available silicon nitride substrates is as low as 90 Wm⁻¹K⁻¹, and therefore extensive research works have been conducted for improving its thermal conductivity while retaining good mechanical properties. This paper reviews the microstructural factors affecting thermal conductivity of sintered silicon nitrides and investigations so far for improving their thermal conductivity. Recently it has been demonstrated that reaction bonding process followed by post-sintering process is a superior method for increasing thermal conductivity of Si₃N₄. Silicon nitride with high thermal conductivity of about 180 Wm⁻¹K⁻¹ with moderate bending strength of 600 MPa and high fracture toughness of 11 MPa·m^1/2 has been developed by this method. Application of the developed Si₃N₄ to metalized substrates is also introduced.