RELAXOR FERROELECTRIC MATERIALS FOR MICROWAVE TUNABLE APPLICATIONS

Abstract

With strong dependences of dielectric constant on external applied electric fields, relaxor barium zirconium titanate ( BaZr x Ti 1-x O 3 or BZT) and barium stannate titanate ( BaSn x Ti 1-x O 3 or BTS), in both bulk ceramic and thin film forms, are increasingly being recognized as potential candidates of microwave tunable materials for device applications. This paper is aimed to review the recent progress in understanding the dielectric properties (such as tunability, dielectric loss and dielectric constant) of these relaxor materials. However, due to their relatively high dielectric constant and loss tangent, pure Ba(Zr,Ti)O3 and Ba(Sn,Ti)O3 do not fully satisfy the requirements of practical device applications. Therefore, various strategies have been developed to improve the dielectric properties of these two groups of relaxor materials. In this paper, we first discussed the dielectric tunability characteristics of pure Ba(Zr,Ti)O3 and Ba(Sn,Ti)O3 and then summarized the strategies that have been used, including (i) small amount acceptor or donor doping (such as rare-earth ions and transition metal ions) and (ii) forming composites with low loss and low dielectric constant microwave dielectric materials (such as MgO , MgTiO3 and so on). At the same time, the relationship between relaxor behavior and dielectric tunability was also discussed.