Low Temperature Sintering Of AlN Ceramics With Organized Structure Optimization

With rapid development of electronic technique, integration and power density of the electronic devices are increased, therefore, requirement of heat dissipation of the device substrates is improved to higher level. Al2O3 and other traditional ceramic substrate materials can not meet the requirement, however, AIN will certainly become the new ceramic substrate materials used in power devices, due to its excellent properties, such as high thermal conductivity, high dielectric constant, high strength and so on.It is known that sintering activity of AIN is rather poor due to the main Al-N covalent bonding in the compound. In order to implement low-temperature sintering AIN ceramics, the key is to choose suitable sintering additives and adding style. In this work, the Sm2O3-Y2O3-CaO ternary sintering additives is employed to develop the low-temperature sintering technique of AIN ceramics. Effects of adding style and amount of the sintering additives on microstructures and properties of the AIN ceramics were studied. Microstructural optimization of low-temperature sintering AIN ceramics was also fulfilled.Based on the Y2O3-CaO sintering additive system, co-adding of Sm2O3 and Y2O3 has a higher sintering-improvement effect, the sintering additive added in dehydrated nitrates can distribute more uniform, which is beneficial to the densification of the AIN ceramics. When 2 wt% rare-earth metal oxides is added, secondary phases in the AlN ceramics are CaYAl3O7 and CaSmAl3O7. However, when content of the rare-earth metal oxides is increased to 4 wt%, YAG and SmA103 may be formed in the AIN ceramics, except CaYAl3O7 and CaSmAl3O7. The AIN ceramics sintered at 1700℃ have an even microstructure and an intergranular and cleavage mixing fracture mode, when the sintering additives of 1 wt%Sm2O3,1 wt% Y2O3 and 2 wt% CaO is added. Bending strength and the thermal conductivity of the ceramics were tested to be 321.4 MPa and 123.8 W/(m-K), respectively.Densification of the ceramics and phase, amount and distribution of the secondary phases are key factors to influence microstructures and properties of the low-temperature sintered AIN ceramics. On the condition that the nearly fully-dense AIN ceramics are achieved, as the sintering additive reduced in amount and preferentially distributed at triple AIN grains, properties of the AIN ceramics should be further improved. When the sintering additives of 2 wt% Sm2O3,2 wt% Y2O3 and 1 wt% CaO is added, the AlN ceramics sintered at 1750℃ has higher bending strength and thermal conductivity, which are 402.1 MPa and 153.7 W/(m·K), respectively.