Dielectric properties of the BaTiO₃-AlN-additive system

The mixed system of BaTiO₃ and AlN has been investigated in terms of dielectric properties and microstructure. Two different types of additives, bismuth oxide and bismuth borosilicate glass, were used to lower sintering temperature. First, the addition of a fixed content (3 wt.%) of Bi₂O₃ provided densification at 1200°C where monotonous decreases of dielectric constant were found with increasing the content of AlN. On the other hand, the bismuth borosilicate glass was effectively used to decrease firing temperature to 850°C, which is suitable for thick film capacitor applications. A practical demonstration of thick film capacitors using a Ag electrode on a 96% alumina substrate indicated that the optimum composition of 76BaTiO₃-20AlN-4glass may be adequate for generating k of 79.4 and tan δ of 0.014 at 1 MHz as a result of the low temperature firing of 850°C in air atmosphere.