Epitaxial growth of ferroelectric Ba_1-xSr_xTiO₃ thin films for room temperature tunable microwave devices

This paper will review the recent progress of the Texas Center for Superconductivity concerning the epitaxial growth of ferroelectric Ba_1-xSr_xTiO₃ thin films on various substrates using pulsed laser ablation. Microstructure studies from X-ray diffraction and electron microscopy suggest that the as-grown films on (001) LaAlO₃ and (001) MgO are c-axis oriented with excellent single crystallinity. The Rutherford Back-Scattering Spectroscopic studies indicate that the films have excellent epitaxial behavior. Microwave property measurements showed that the room temperature dielectric constant could be tuned up to 33% at 2.33 V/μm applied electric field. The coupled microwave phase shifter has achieved a phase shift of over 200° at 23.675 GHz and a figure of merit of about 55°/dB at room temperature. These results demonstrate that the epitaxial Ba_1-xSr_xTiO₃ thin films are close to becoming used in the practical applications for the wireless rf communications.