Improved Mechanisms for Excellent Tunable Microwave Ce and Mn Codoped Ba0.6Sr0.4TiO3 Thin Films

Smooth and dense preheated cerium (Ce) and manganese (Mn) codoped barium strontium titanate (CeMn-BST) films with various thicknesses have been prepared by improved sol-gel method. Capacitance-voltage curves show that with increasing film thickness, combination of dielectric properties are significantly improved with optimized values of about 1300 moderate permittivity, less than 0.007 dielectric loss, more than 58% tunability and hence near 180 figure of merit (FOM) for eight-layer CeMn-BST film. The objective of this paper is to study the improved mechanisms for such excellent dielectric properties. XRD shows that the films layered-grow mainly along (110) orientation and exhibit ABO(3) cubic perovskite structure. As film thickness increases, Ce3+ and/or Mn2+ ions are showing doping modes from donor doping to acceptor doping, the crystallization of films is enhancing, but the average grain sizes of the films show gradually decreased trend from about 45nm to 25nm in terms of the intensities of (110) diffraction peaks. AFM indicates that the films are getting smoother with smaller roughness with increasing thickness. XPS reveals that the films reveal decreased non-perovskite structure, element core levels and Fermi levels with increasing thickness. Leakage current densities are significantly decreased almost at two orders of magnitude with increasing thickness. Pure BST films are compared.