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 p O 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.