Binary Co-doped Bst Thin Film Dielectric Properties And Doping Mechanism

This thesis studied the dielectric properties and surface morphology of doped Barium strontium titanate (BST) films prepared by sol-gel method. The research was focused on the improvement of dielectric tunability properties and the reduction of dielectric loss of BST. According to the current research trend of performance optimization of BST, not only the single doping and the co-doping were studied, but also the new alternative doping method was analyzed. The as-prepared BST films are characterized by XRD, AFM and XPS. Meanwhile, the relationships between the Sol-gel method, film structure, film composition, and film properties have been examed and discussed.First, variance of microstructure of BST affected by cerium, yttrium, manganese doping was studied. The change of BST film surface roughness and surface composition was analyzed by AFM and XPS method. The results showed that the grain size of doped BST was closely related to doping elements. The proportion of perovskite structure of single doped BST also showed strong dependence on doping elements. Cerium and manganese were chosen as the objects of comparative study between single doping and co-doping. In general, the cerium-manganese-doped BST obtain competitive advantage of dielectric properties. Its dielectric loss can be reduced to as low as 0.014. Figure of merit (FOM) can reach 16.9 at 20V bias. The disadvantage of resistance to pressure in single doped BST was overcomed.Secondly, to further reduce the dielectric loss of BST thin films, the research attempt to investigate the alternative doping. The influence of doping concentration and the number of film layer on the dielectric properties of BST thin film was analyzed in the thesis. Introduction of alternative doping method can significantly reduce the dielectric loss. Additionally, the alternating doped BST films display high voltage-resistance and good loss tangent-voltage properties. In addition, when the test frequency was rised from 100KHz to 1MHz, the dielectric properties of alternative doped BST thin film exhibit little change. This phenomenon implied good frequency invariance of the alternative doped BST thin film.