Bismuth zinc niobate pyrochlore dielectric thin films for capacitive applications

Bi₂O₃-ZnO-Nb₂O₅ pyrochlore thin films were prepared on platinum coated Si wafers using a metalorganic deposition process. The structures, morphologies, and dielectric properties of films with two compositions: (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O ₇ and Bi₂(Zn_1/3Nb_2/3)₂O₇, were investigated. Thin films of (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O ₇ have a cubic pyrochlore phase when crystallized at 550°C or higher. The crystal structure of Bi₂(Zn_1/3Nb_2/3)₂O₇ thin films was dependent on the firing temperature; the films showed the cubic pyrochlore phase at temperatures below 650°C, and a pseudo-orthorhombic pyrochlore structure at 750°C. A mixture of cubic and pseudo-orthorhombic structures was found in thin films crystallized at 700°C. (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O ₇ films fired at 750°C had a dielectric constant of ∼ 150 and a negative temperature coefficient of capacitance of -400 ppm/°C. Bi₂(Zn_1/3Nb_2/3)₂O₇ thin films fired at 750°C had a smaller dielectric constant of ∼80 and a positive temperature coefficient of capacitance of 150 ppm/°C. The dielectric constants of the thin films are composition, structure, and firing temperature dependent. The loss tangents of both types of films were smaller than 0.008. Bias voltage dependence of dielectric constant showed that the cubic (Bi_1.5Zn_0.5)(Zn_0.5Nb_1.5)O ₇ films fired at 750°C were tunable, while the pseudoorthorhombic Bi₂(Zn_1/3Nb_2/3)₂O₇ films were nearly field independent. The relatively large dielectric constants, small loss tangents, controllable temperature coefficients of capacitance, and tunability of the dielectric constant suggests that Bi₂O₃-ZnO-Nb₂O₅ thin films have potential applications for integrated microwave components and decoupling capacitors.