Study On Fabrication And Properties Of High-thermal-conductivity AlN/Si₃N₄Composites

With the rapid development of technology and information, stricter and higher requirements for electronic equipment and supporting materials are presented especially in terms of high reliability, high performance and low price. Meanwhile, great progress has been made in the research and application in highly integration, high density, high speed and other aspects of semiconductor chips. Si3N4ceramic has the similar theoretical thermal conductivity with AlN, thermal expansion coefficient like Si, excellent mechanical properties as well as good electrical insulation and non-toxic and other characteristics, so it is considered to be promising heat dissipation and packaging material in high-speed circuits and power devices.This paper systematically studied the effects of sintering method, sintering temperature, AlN content and the type and amount of sintering aids on AIN/S13N4composite ceramic density, thermal conductivity, bending strength and flexural dielectric properties. Using three different sintering methods such as pressureless sintering, pressure sintering and hot pressing sintering method under N2atmosphere under the same conditions of sintering temperature and holding time, the relative density, the bending strength and thermal conductivity of the sample have increased significantly, while the dielectric constant have changed little. The sample prepared by hot press sintering could obtain the relative density of93.7%, the bending strength of372GPa, a thermal conductivity of33W·m-1·K-1and a dielectric constant of8.14when the sintering temperature reaches1750℃. When the content of AlN in the composite material was20wt.%, AlN/Si3N4composite ceramic sintered at1750℃,30GPa by hot pressing with La2O3as a sintering aid showed the best overall performance with the relative density of98%, and the flexural strength and thermal conductivity reached387GPa and35W·m-1·K-1respectively.In this study, AlN/Si3N4composite ceramics in high thermal conductivity have been prepared using hot pressing sintering method by adding AlN to improve the thermal conductivity of Si3N4ceramics. The study found that with the increase of AlN content, the density of the material dropped after the first increasing, mainly because a small amount of AlN added in the material played a role in promoting the composites densification as sintering aid while further increase of AIN content promoted the formation of a-sialon and β-sailon phases and then the increase of the grain boundary. As AIN content was15wt.%, the relative density of the material reached99.5%; as the content of AIN increased, the flexural strength and thermal conductivity of the composite ceramics both decreased mainly due to the decrease in density of the material. As AIN content was15wt.%, the thermal conductivity and the bending strength of the material reached32W·m-1·K-1and385MPa respectively, and when AIN content was30wt.%, the thermal conductivity of the material was only29W·m-1· K-1and the bending strength was345MPa.