Understanding AlN sintering through computational thermodynamics combined with experimental investigation

Aluminum nitride (AIN) 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 (Y2O3) is the best additive for AIN sintering. Binary diagrams of Al2O3-Y2O3, AIN-Al2O3, and AIN-Y2O3 were thermodynamically modelled. The obtained Gibbs free energies of components, stoichiometric phases and solution parameters were used to build a thermodynamic database of AIN-Al2O3-Y2O3 system. Liquid-phase sintering of AIN with Y2O3 as an additive has been studied and compared with the thermodynamic results. Sintering was performed in the temperature range of 1750-1950° C for upto 4h under a N-2 atmosphere to optimise the sintering conditions for each composition. The relative density exceeded 95% for all the compositions sintered at 1850° C and full densification was achieved for all four compositions sintered at 1900° C. The microstructure and assemblage of the secondary phase have a significant effect on the final thermal conductivity of the sintered AIN. Thermodynamic modelling of AIN-Al2O3-Y2O3 system provided an important basis for understanding the sintering behaviour and interpreting the experimental results. © 2004 Elsevier B.V. All rights reserved.