Phase equilibria in the AIN-AIO-YO system : utility in AIN processing

The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to its high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability and chemical stability. Yttria (Y2O3) is the best additive for AlN sintering, which undergoes densification through a liquid phase mechanism. The surface oxide, Al2O3, reacts with the oxide additive, Y2O3, to form a Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is becoming essential for further development of AlN.Binary diagrams of A2O3-Y2O3, AlN-Al2O3, and AlN-Y2O3 were thermodynamically modeled in this work. The obtained Gibbs free energies of the components, stoichiometric phases and solution parameters were used for the calculation of the isothermal sections and liquidus surface of the AlN-Al2O 3-Y2O3 system. Phase evolutions, melting and solidifications in the Al2O3-Y2O3 phase diagram were investigated using x-ray diffraction and in situ high temperature neutron diffractometry. The phase diagram of AlN-Y2O 3 system was established and verified experimentally. The predicted ternary phase diagram for AlN-Al2O3-Y2O 3 was also verified experimentally using in situ high temperature neutron diffractometry and it has been constructed for the first time in this work.A self-consistent thermodynamic database including all the phases in the AlN-Al2O3-Y2O3 system was developed during the course of this project. This database was used to explain the experimental results of AlN sintering. It has been found that the samples with high densities had lower liquid formation temperatures, and low thermal conductivity was related to the residual Al2O3 and high YAP (Al2O3.Y2O3) content