Understanding AlN sintering through computational thermodynamics combined with experimental investigation

摘要

Aluminum nitride (A1N) has attracted large interest recently as a suitable material for hybrid integrated circuit substrates because of its high thermal conductivity, high flexural strength, good dielectric properties, thermal expansion coefficient matches that of Si and non-toxic nature. Yttria (Y_2O_3) is the best additive for A1N sintering. Binary diagrams of Al_2O_3-Y_2O_3, A1N-Al_2O_3, and A1N-Y_2O_3 were thermodynamically modelled. The obtained Gibbs free energies of components, stoichiometric phases and solution parameters were used to build a thermodynamic database of AlN-Al_2O_3-Y_2O_3 system. Liquid-phase sintering of A1N with Y_2O_3 as an additive has been studied and compared with the thermodynamic results. Sintering was performed in the temperature range of 1750-1950 deg C for upto 4h under a N_2 atmosphere to optimise the sintering conditions for each composition. The relative density exceeded 95 percent for all the compositions sintered at 1850 deg C and full densification was achieved for all four compositions sintered at 1900 deg C. The microstructure and assemblage of the secondary phase have a significant effect on the final thermal conductivity of the sintered A1N. Thermodynamic modelling of AIN-Al_2O_3-Y_2O_3 system provided an important basis for understanding the sintering behaviour and interpreting the experimental results.