Structure–property relationships in pure and acceptor-doped Ba1−xSrxTiO3 thin films for tunable microwave device applications

The influence of low concentration (1 mol %) Mg doping on the structural, microstructural, surface morphological, and dielectric properties of Ba1−xSrxTiO3 (BST) thin films has been measured and analyzed. The films were fabricated on MgO and Pt–Si substrates via the metalorganic solution deposition technique using carboxylate–alkoxide precursors and postdeposition annealed at 800 °C (film/MgO substrates) and 750 °C (film/Pt–Si substrates). The structure, microstructure, surface morphology, and film/substrate compositional quality were analyzed by glancing angle x-ray diffraction, field emission scanning microscopy, atomic force microscopy, and Auger electron spectroscopy studies. Dielectric properties of unpatterned films were measured at 10 GHz using a coupled, tuned split dielectric resonator system, and at 100 kHz using metal–insulator–metal capacitors. The Mg-doped BST films exhibited improved dielectric and insulating properties compared to the undoped Ba0.6Sr0.4TiO3 thin films. The improved dielectric properties, low leakage current, and good dielectric tunability of the low level Mg-doped BST thin films merits strong potential for utilization in tunable microwave devices.