Microwave properties of epitaxial (111)-oriented Ba0.6Sr0.4TiO3 thin films on Al2O3(0001) up to 40 GHz

Perovskite Ba0.6Sr0.4TiO3 (BST) thin films have been grown on Al2O3(0001) substrates without/with inserting an ultrathin TiOx seeding layer by rf magnetron sputtering. X-ray diffraction and pole figure studies reveal that the film with the TiOx layer (12-Å-thick) is highly oriented along the (111) direction and exhibits a good in-plane relationship of BST(111)∥Al2O3(0001). The high frequency dielectric measurements demonstrate that the complex permittivity (ε=ε′−jε″) is well described by a Curie–von Scheidler dispersion with an exponent of 0.40. The resulting epitaxial BST films show high permittivity (∼428) and tunability (∼41%, at 300 kV/cm and 40 GHz) and their microwave properties (1–40 GHz) potentially could be made suitable for tunable devices.