Residual stress effects in doped barium strontium titanate thin films

Barium strontium titanate (BaxSri -xTiO3; BST) thin films are the principal materials of interest for microwave antenna design, primarily because of their low loss, high dielectric constant, and large tunability. The effects of acceptor (Mg) doping, added to further tune film properties, on the BST thin films were investigated in parallel to the annealing temperature. Films were deposited on MgO single-crystal substrates using metallorganic solution deposition. Residual stress, known to have a drastic effect on the mechanical, electrical, and dielectric properties, becomes of particular importance in thin-film materials, where the residual stress can be several orders of magnitude higher. The residual stress in the films was measured in three ways (reflective curvature, nanoindentation, and glancing angle X-ray diffraction). Measured stresses (as high as 2 Gp) were tunable by varying the dopant concentration and annealing temperature. The results from all three stress measurement techniques showed that the films had a highly compressive stress at the interface that transitioned to a significantly lower, but still nonzero, stress at the top surface (similar to 200 nm) as theory would suggest. In this paper, we evaluate and report the effects of residual stress on acceptor-doped BST as a function of postdeposition annealing conditions. (c) 2005 The Electrochemical Society.