Barium Strontium Titanate Thin Film for Electrically Tunable THz Metasurface

Barium strontium titanate (BST) thin films are distinguished for their ferroelectric behavior which makes them highly promising for optical and microwave applications, but there is a lack of studies in the important terahertz (THz) frequency range. In this work, we report the deposition of high‐quality BST films by physical vapor deposition at high temperatures and its application in tunable THz metadevices. The Ba 0.6 Sr 0.4 TiO 3 film exhibits a full width at half maximum of 0.57° in high‐resolution X‐ray diffraction (HR‐XRD) spectroscopy, a real dielectric constant of 140 at 0.2 THz. By integrating interdigitated electrodes (IDEs) of varying periodicities, we systematically investigated their impact and identified a 100 µm electrode separation as the optimal electrode separation for maximizing THz response modulation. A metasurface using Ba 0.6 Sr 0.4 TiO 3 thin film as the active material working in reflection mode has been designed using finite‐difference time‐domain (FDTD) simulation, and the fabricated metadevice experimentally demonstrated a remarkable resonance shifts of up to 5.5 GHz under applied voltage. These findings underscore the potential of BST for reconfigurable intelligent metasurfaces and future electrically tunable THz device applications.