Tunability of Bi-rich BZN Cubic Pyrochlore Thin Films by Reactive Sputtering

Abstract

ABSTRACT(Bi3xZn2−3x)(ZnxNb2−x)O7 thin films (x=1/2 and 2/3) have potential great for tunable RF and microwave devices due to medium dielectric constant and low dielectric loss. The tunable dielectric properties of Bi-rich, (Bi1.5 Zn0.5)(Zn0.5 Nb1.5)O7 thin films were investigated. To make Bi-rich cubic pyrochlore thin films, Bi2O3–ZnO–Nb2O5 monoclinic pyrochlore ceramic targets were used in reactive RF magnetron sputtering process. Substrate heating was employed to improve surface morphology and tunability. As-deposited films were crystallized or amorphous state depending on substrate temperature. All films were annealed at 600°C ∼ 800°C for 3 hours in the air. There were no zinc niobate secondary phases in the films before and after post-annealing, while quite significant amount BZN thin films were found in sputtered using cubic pyrochlore ceramic targets, especially after post-annealing. It was found that Bi-rich BZN films have much larger tunability when as-deposited phase are amorphous. The maximum tunability 38% was obtained when substrate is heated to 350°C and composition of films is close to exact stoichiometric cubic BZN.