Ba $\mathsf{_{0.1}}$Sr $\mathsf{_{0.9}}$TiO$\mathsf{_{3}}$-BaTi$\mathsf{_{4}}$O$\mathsf{_{9}}$ composite thin films with improved microwave dielectric properties

Abstract.

Ba_0.1Sr_0.9TiO₃-BaTi₄O₉ composite thin films with different BaTi₄O₉ concentrations were deposited on (100) LaAlO₃ (LAO) single crystal substrates via a pulsed laser deposition (PLD) using a combined target configuration of Ba_0.1Sr_0.9TiO₃ and BaTi₄O₉ ceramics. The Ba_0.1Sr_0.9TiO₃-BaTi₄O₉ thin films showed good crystal growth with c-orientation on (100) LAO substrates, which were characterized by X-ray diffraction (XRD). From scanning electron microscopy (SEM) measurements, we could see that the crystal grains of the Ba_0.1Sr_0.9TiO₃-BaTi₄O₉ thin films changed from small ordered clusters to big triangle clusters with the increase of BaTi₄O₉ concentration. The microwave dielectric properties of the Ba_0.1Sr_0.9TiO₃-BaTi₄O₉ thin films under low temperature range from 65 to 120 K were measured at 7.7 Ghz and the results showed that all the thin films were in the paraelectric state. The dielectric constant and loss tangent of the Ba_0.1Sr_0.9TiO₃-BaTi₄O₉ thin films were modified by the addition of BaTi₄O₉. Specifically, the loss tangent of the composite thin films was greatly decreased from 0.025 for pure Ba_0.1Sr_0.9TiO₃ to 0.020 for the 4.7% BaTi₄O₉ doped Ba_0.1Sr_0.9TiO₃, and finally to 0.010 for the 15.9% BaTi₄O₉ doped Ba_0.1Sr_0.9TiO₃ sample.