(186b) Particle Atomic Layer Deposition of Yttrium Oxide for Hydrolysis Protection and Sintering of Aluminum Nitride Particles

Aluminum nitride (AlN) has a high thermal conductivity and electrical resistivity, making it an attractive material for high power LED heat sinks. However, AlN particles hydrolyze in the presence of water, forming aluminum oxide (Al₂O₃) impurities which reduce the thermal conductivity of the material. Consequently, AlN powder must be processed in organic solvents which increases the cost of AlN heat sinks. Typically, AlN parts are densified by adding a small amount of secondary phase (ie, sintering aid) to enable liquid phase sintering and scavenge Al₂O₃ impurities at the grain boundaries to enhance thermal conductivity. Sintering aids are usually added by mechanical mixing, where primary ceramic particles (AlN) are mixed with a small quantity of secondary phase particles which can lead inhomogeneities in the final microstructure. In this work, particle atomic layer deposition (ALD) was used to conformally coat AlN particles with a thin film of yttrium oxide (Y₂O₃) to protect the AlN particle surface from hydrolysis and to enable liquid phase sintering. Transmission electron microscopy was used to characterize the as-deposited Y₂O₃ film. Investigation of the hydrolysis behavior of uncoated and coated AlN powders showed that the Y₂O₃ nanofilm effectively hindered hydrolysis of the AlN particles. The densification behavior of the powders was investigated by push-rod dilatometry and showed that the addition of Y₂O₃ by particle ALD increased the final relative density by ~30% relative to pure-AlN. Scanning electron microscopy and X-ray diffraction were used to determine the microstructural homogeneity and secondary phase formation of the dense AlN ceramics. The addition of Y₂O₃ by particle ALD homogeneously disperses the Y₂O₃ prior to densification and may benefit both the hydrolysis and densification behavior of AlN powders.