Uniaxial dielectric anisotropy in Ba0.5Sr0.5TiO3 films studied by evanescent-probe microscopy

The dielectric permittivity, tunability (Δe/e), and loss tangent of Ba1−xSrxTiO3 (BST) films grown by pulsed-laser deposition are studied by near-field microwave microscopy. Based on theoretical simulations, a method is developed to measure the uniaxial dielectric anisotropy, e⊥/e∥, in BST films grown at different oxygen pressures. The measured e⊥/e∥ decreases with the film-growth oxygen pressure, consistent with the structural anisotropy. The films prepared at 50 mT, with e⊥≈e∥, have the highest permittivity, tunability, and figure of merit.