Growth behavior and dielectric properties of K/Mg alternately doped BST films

摘要

There has been no report on the influence of film growth behavior on the dielectric properties of BST films alternately doped with K and Mg up to now, thereby 1%K and 1%Mg alternately doped Ba0.6Sr0.4TiO3 (K/Mg-BST) films with various thicknesses were prepared by an improved sol-gel method, and their growth behaviors and dielectric properties were studied in this paper. The K/Mg-BST films were designed as KBST/MgBST/...multilayer films composed of 1 approximate to 8 layers with the first K doped BST layer (about 120nm/layer). 1, 3, 5 and 7-layer films were not annealed, while 2, 4, 6 and 8-layer films were annealed. 7 or 8-layer pure BST, Mg-BST, K-BST and Mg/K-BST (with the first Mg doped BST layer) films were compared. All films show ABO(3) cubic perovskite polycrystalline structures and grow mainly along (110) orientation. The K/Mg-BST films show enhancing crystallizations but fluctuant lattice constants with increasing film thickness. However, the not annealed films show larger lattice constants than the annealed films, and Mg2+ ions tend to replace Ti4+ ions and show acceptor doping mechanism. K+ ions in the not annealed films have a tendency to substitute for Sr2+ ions, and in the annealed films tend to replace Ba2+ ions. Increasing film thickness promotes K+ ions replacing Sr2+ ions and Ba2+ ions, and causes acceptor doping mechanism. The Mg/K-BST films show island growth with the fastest speed, while the other films show layer growth. The K/Mg-BST films reveal the slowest growing speed, and increasing film thicknesses gradually improve surface morphologies, thus show better comprehensive dielectric properties than K or Mg-BST films. 7-layer and 8-layer K/Mg-BST films display excellent comprehensive dielectric properties, but 7-layer film is more suitable for tunable microwave applications owing to smaller capacitance.