Microstructure, Growth Kinetics and Formation Mechanism of Oxide Layers on AlN Ceramic Substrates

AlN ceramic substrates doped with 2 wt% Y2O3 were oxidized at temperatures ranging from 1000 degrees C to 1300 degrees C for various times in air. Microstructure, growth kinetics and formation mechanism of the oxide layers were studied. The results show that oxidation originates from the AlN grain boundaries and then extends into the AlN grains to form a core-shell structure composed of the unoxidized AlN core wrapped in the continuous nanocrystalline Al2O3 layer. A continuous pore network is distributed over the oxide layer and connected with the AlN reaction interface, which actually acts as the O-2/N-2 rapid diffusion path. As a result, oxidation of the AlN substrates follows reaction-ratecontrolled kinetics. An activation energy of 260.5 kJ mol(-1) of the oxidation process is then derived. Finally, a model involving the microstructure and mechanism of the oxide layer formation on the AlN substrates is established.