Microwave properties of ferroelectric strontium(0.16) barium(0.39) niobate thin films fabricated by pulsed laser deposition

This report presents work towards the fabrication, characterization and measurement of the low and high frequency properties of ferroelectric Strontium Barium Niobate (Sr_xBa_1−xNb₂O₆ ; SBN) thin films. A high ferroelectric coefficient and low dielectric losses make SBN a promising material for microwave tunable devices. Strontium Barium Niobate thin films were fabricated on MgO (100) and LaAlO₃ (100) substrates by the Pulsed Laser Deposition technique. Samples were characterized by X-ray diffraction (XRD), Rutherford Back-scattering Spectroscopy (RBS), and Atomic Force Microscopy (AFM). Coupled microstrip phase shifters were fabricated over the SBN samples using a photolithography technique. Results at low frequency indicate different phase transition temperatures for samples on both substrates, varying widely from the bulk. Samples grown over the LaAlO ₃ substrates showed moderate phase shift but high losses, while those grown over the MgO substrates showed poor phase shift but very low losses. The high losses in the SBN/LaAlO₃ samples can be explained because of the mismatch in lattice parameters. For the SBN/MgO samples, on the other hand, there is excellent lattice matching.