Realization of high tunability barium strontium titanate thin films by rf magnetron sputtering

Ferroelectric thin films are currently being used to develop tunable microwave circuits based on the electric-field dependence of the dielectric constant. $({\mathrm{Ba}}_{\mathrm{0.5}}{\mathrm{Sr}}_{\mathrm{0.5}}){\mathrm{TiO}}_{\mathrm{3}}$ (BST) films prepared by sputtering on ${\mathrm{Pt/TiO}}_{\mathrm{2}}/{\mathrm{SiO}}_{\mathrm{2}}/\mathrm{Si}$ substrates are found to exhibit a capacitance change (tunability) of nearly 4:1. Higher tunability has been attributed to the (100) texturing of the BST films and is a result of the biaxial tensile stress imposed by Si on BST making the polar axis oriented in plane. Electrical characterization shows that the dielectric permittivity increases with increase in film thickness (up to ∼200 nm).