Preparation of sputtered (Ba _x′Sr _1-x)TiO ₃ thin films directly on copper

(Ba _0.6,Sr _0.4)TiO ₃ (BST) films were deposited on copper foils by radio frequency magnetron sputtering. By the use of controlled pO ₂ high-temperature anneals, the films were completely crystallized in the absence of substrate oxidation. X-ray diffraction and transmission electron microscopy (TEM) revealed an abrupt Cu/BST interface. The deposited BST films exhibit a zero bias permittivity and loss tangent values of 600 and 0.018, respectively. An electrical tunability ratio of 3.5:1 is observed on these metal-insulator-metal devices. Devices show leakage currents of 10 ^-8 A/cm ² at ±10 V/μm, and loss tangents as low as 0.003 in fields approaching 40 V/μm.