Dielectric properties of Ba _0.6Sr _0.4TiO ₃ thin films with various strain states

We deposited epitaxial Ba0.6Sr0.4TiO3(BST) films having thickness of 400 nm on MgO(001) substrates, where a 10 nm thick Ba1-xSrxTiO3 (x = 0.1 - 0.7) interlayer was inserted between BST and MgO to manipulate the stress of the BST films. Since the main difference of those epitaxial BST films was the lattice constant of the interlayers, we were very successful in controlling the stress of the BST films. BST films under small tensile stress showed larger dielectric constant than that without stress as well as those under compressive stress. Stress relaxation was investigated using epitaxial BST films with various thicknesses grown on different interlayers. For BST films grown on Ba0.7Sr0.3TiO3 interlayers, the critical thickness was about 600 nm. On the other hand, the critical thickness of single-layer BST film was less than 100 nm.