Study On Fabrication And Properties Of Silicon Nitride Ceramics With High Thermal Conductivity

With the development of electronic information technology, heat dissipation problems seriously restrict the electronic devices to the development of high-density, multifunction, high-speed and high-power. Silicon nitride ceramic is considered as a promising material in the field of high-speed circuits and electronic packaging materials, owing to its high intrinsic thermal conductivity (320W·m-1K-1) similar to AlN, low thermal expansion coefficient close to silicon crystal, excellent electrical insulating and mechanical properties.In this paper, using MgO, Y2O3and CeO2as mixed sintering aids, SisN4ceramics were fabricated by GPS process under1800℃for4h in4MPa N2gas. The effect of sintering aid systems on the relative density, thermal conductivity, flexural strength, and dielectric property was studied systematically. The results showed that, in the MgO-Y2O3sintering aid system, when the content of Y2O3was4wt%, the sintered sample had the optimum combination property with relative density of98.9%, thermal conductivity of52W·m-1·K-1, the flexural strength of798MPa, the dielectric constant of8.49, and the dielectric loss of5.49X10-3; In the MgO-Y2O3-CeO2sintering aids system, it was found that the relative density, the flexural strength and the thermal conductivity of the sintered samples decreased with the increase of CeO2content. Compared with MgO-Y2O3sintering aid system, the thermal conductivity of sintered samples added with CeC>2was much lower, even when the total amount of sintering aid was8wt%(4wt%MgO+3wt%Y2O3+1wt%CeO2), the thermal conductivity of the sintered samples was only44W·m-1·K-1.The samples were then annealed at1750℃after being sintered with4wt%MgO+4wt%Y2O3as sintering aids at1800℃for4h. It was demonstrated that the crystallization of glassy phase and abnormal grain growth happened in all the annealed samples. The results showed that the thermal conductivity increased with the increasing annealing time, the thermal conductivity of specimen reached81W·m-1·K-1after being annealed for6h; With the increase of annealing time, the change of dielectric constant was little, but the dielectric loss increased, the minimum value of the dielectric loss was4.92X10-3when the sample was annealed for2h.Exploratory experiments of adding AlN were performed to improve the thermal conductivity of Si3N4ceramics by GPS, but the results were not good. It was found that the density of the prepared samples decreased with the increase of AlN content, the main reason was that AlN constrained the phase change of a-Si3N4â†'β-Si3N4, when the content of AlN was30wt%, the porosity of the prepared sample was22.5%; with the increase of AlN content, the flexural strength and the thermal conductivity of the prepared samples reduced but the dielectric loss increased, owing to the decrease of the density. When the content of AlN was15wt%, the thermal conductivity the prepared sample was32W·M-1·K-1, the flexural strength was540MPa, the dielectric loss was6.36×10-3, when the content of AlN was up to30wt%, the thermal conductivity was only5.8W·m-1·K-1, the flexural strength was only241MPa, but the dielectric loss was up to7.85×10-3.