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Optimization of the tunability of barium strontium titanate films via epitaxial stresses

Summary: Optimization of the tunability of barium strontium titanate films
via epitaxial stresses
Z.-G. Ban and S. P. Alpaya)
Department of Metallurgy and Materials Engineering and Institute of Materials Science,
University of Connecticut, Storrs, Connecticut 06269
Received 2 July 2002; accepted 6 October 2002
The tunability of epitaxial barium strontium titanate films is analyzed theoretically using a
phenomenological model. The relative dielectric constant of Ba0.5Sr0.5TiO3 BST 50/50 films as a
function of the applied external electric field is calculated and an electric field­misfit strain phase
diagram is developed to assist in the interpretation of the behavior. On the basis of these results, the
tunability of BST 50/50 films as a function of the misfit strain is provided and compared with the
experimental data in the literature. Analysis shows that a high tunability can be achieved by
adjusting the misfit strain especially in the vicinity of a structural phase transformation. The misfit
strain in epitaxial films can be controlled with the selection of a substrate material or variations in
the film thickness. The film thickness dependence is due to misfit dislocation formation at the film
growth temperature. A critical thickness to attain the maximum tunability can be defined for BST
50/50 films on MgO 90 nm and LaAlO3 120 nm substrates. It is suggested that the selection
of the substrate and/or the film thickness can be chosen as design parameters to manipulate the strain
state in the film to achieve optimum tunability. © 2003 American Institute of Physics.
DOI: 10.1063/1.1524310


Source: Alpay, S. Pamir - Department of Materials Science and Engineering, University of Connecticut


Collections: Materials Science