Effect of Rb-doping on the dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin films prepared by sol-gel

Abstract

There is growing interest in BaxSr1−xTiO3 (BST) thin films due to their dielectric tunability and low dielectric loss. Doping small concentrations of elements is an effective way to increase the dielectric tunability and decrease the dielectric loss of BaxSr1−xTiO3 thin films. Many doping elements have been studied to date, but this does not include the use of rubidium (Rb). In this study, we reported here the effect of Rb-doping on the surface morphology, dielectric and tunable properties of Ba0.6Sr0.4TiO3 thin films prepared by the sol-gel method. It was observed that the tunability of Ba0.6Sr0.4TiO3 thin films was increased greatly from 46.53% to 63.37% at 377kV/cm when Rb was doped at a concentration of 4mol%. The observed improvements originate from increased grain size. Doping effects included occupation of the A site of the composites by Rb+ ions, and also enhanced grain growth during the annealing process, due to the relatively low melting point of rubidium oxide. (Ba0.6Sr0.4)96%Rb4%TiO3 thin films exhibited the largest grain size and a surface root-mean-square roughness (RMS) of 2.409nm, the smallest among the various doping concentrations of rubidium used. They also exhibited the best dielectric characteristics (figure of merit value 31.53 at 2MHz). Thus, Rb doping can be considered a promising way to optimize the dielectric properties of BST thin films for their potential application in microwave tunable devices.