Structures and dielectric performances of Mn/Y alternately doped BST films prepared by a novel preheating process

Mn (2%, 5%, 8%)/Y (1%) alternately doped BST multilayer thin films have been prepared by a modified sol-gel method on Pt/Ti/SiO2/Si substrates. The effects of Mn doping contents on the structures and dielectric properties of the films are studied by XRD, XPS, FESEM, EDS, and C-V. Meanwhile, a graded preheating (GP) process is designed to modify the conventional preheating (CP) process. It is found that for the two processes, the doped Mn2+ ions first enter into Ti sites and then into Sr sites with an increase of doping content, but the GP process mainly promotes Mn2+ ions to enter into Ti sites independence of the doping content. Therefore, the GP process leads to a more obvious enhancement on nonlinear dielectric properties, in particular a more marked increase in tunability and a more evident decrease in dielectric loss of the BST films. It is implied that the GP process is an effective route to improve the dielectric properties of BST films for the applications of tunable microwave devices. The effects of the CP process with different temperatures on the BST films and the modified mechanisms are also discussed.