Interface-related thickness dependence of the tunability in BaSrTiO3 thin films

The thickness dependence of the tunability of Ba0.7Sr0.3TiO3 thin films is investigated. The capacitance-voltage curves, revealing the tunability of the films with thickness from 30 to 370 nm, show a strong thickness dependence. This is attributed to a bias-independent interface capacity. The interface suppresses the permittivity of the film with increasing influence for decreasing film thickness, whereas the tunability of the bulk of the film remains constant. Calculations are performed from a thermodynamic model based on the Landau-Ginzburg-Devonshire theory leading to the assumption of the bias-independent interface capacity. The bias dependence of the bulk of the films derived from measurement data are in very good agreement with the theoretically derived values. (C) 2004 American Institute of Physics.