A frequency tunable device includes a substrate, and a capacitor structure supported by the substrate and including a ferroelectric film and first and second electrodes. The ferroelectric film has two opposite sides, and is made from a ferroelectric material having a formula of Pb.sub.1-xBa.sub.xZrO.sub.3, where x is a positive number greater than 0.3 and less than 0.6. The first and second electrodes are respectively formed on the sides of the ferroelectric film. The dielectric constant of the ferroelectric film varies with a voltage applied to the first and second electrodes. |