High tunability barium strontium titanate thin films for rf circuit applications

Large variations in the permittivity of rf magnetron sputtered thin-film barium strontium titanate have been obtained through optimization of growth conditions for maximum dielectric strength and zero-field permittivity in a parallel-plate capacitor structure. Using nominal target compositions of Ba0.5Sr0.5TiO3, and Pt electrodes on c-plane sapphire substrates, adjustment of the O2 partial pressure during deposition was used to vary the excess Ti incorporation into the films, which influenced the low-field permittivity, loss tangent, and dielectric strength. By balancing the benefits of a high permittivity with dielectric strength and loss, we have produced films capable of sustaining short-duration fields greater than 4MV∕cm with over 13:1 (>90%) change in dielectric constant, and greater than 5:1 tunability in bias fields under 1MV∕cm.