Precise measurement of the dielectric properties of BaxSr1−xTiO3 thin films by on-wafer through-reflect-line (TRL) calibration method

Polycrystalline BaxSr1−xTiO3 (x = 0.3, 0.4, 0.5) (BST) thin films with a thickness of 200 nm were deposited on r-cut sapphire substrates by rf sputtering method. The permittivity and loss tangent of the films were successfully observed in the range of 1–3 GHz, by utilizing the on-wafer through-reflect-line (TRL) calibration method although the estimated relative permittivity depended on an applied power to waveguides and the loss tangent had the dispersion around 1 GHz even in the case of 2 μm-thick aluminum. Finally, we concluded that the BST thin film with x = 0.4 is the most suitable for microwave tunable devices because it had the lowest loss tangent and relatively high permittivity.