Tunable Dielectric Characteristics of (111)-Oriented Barium Strontium Titanate Thin Films Deposited on Platinized Si Substrates

We report the fabrication and characterization of Ba0.5Sr0.5TiO3 (BST5) thin films on Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. The x-ray diffraction (XRD) studies revealed that the BST5 films are highly oriented along (111) direction. The misfit strain in the films was about -0.68%, which is compressive in nature. The Root Mean Square roughness (RMS roughness) measured using dynamic force microscope (DFM) was about 2.4 nm. The low frequency (40 Hz - 1 MHz) dielectric properties measured using a Metal-Insulator-Metal structure show no dispersion either in dielectric constant or tan delta. The dielectric constant, loss tangent, tunability and figure of merit measured at 1 MHz were about 598, 0.008, 54% (at 200 kV/cm) and 66, respectively. Varactors of circular patch capacitor (CPC) structure were patterned on the BST5 layer using UV photolithography and metal lift off process. The microwave dielectric response of the parallel plate varactors, measured from 1.5 - 10 GHz showed a tunability of similar to 30% (at 12 V dc bias) and a quality factor of 23.5 (at 0 V dc bias).