The dielectric response as a function of temperature and film thickness of fiber-textured (Ba,Sr)TiO₃ thin films grown by chemical vapor deposition

The temperature- and field-dependent permittivities of fiber-textured Ba_0.7Sr_0.3TiO₃ thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness. These films display a nonlinear dielectric response under conditions representative of those encountered in dynamic random access memories or other integrated capacitor applications. This behavior has the exact form expected for a classical nonlinear, nonhysteretic dielectric, as described in terms of a power series expansion of the free energy in the polarization as in the Landau-Ginzburg-Devonshire approach. Curie-Weiss-like behavior is exhibited above the bulk Curie point (∼300 K), although the ferroelectric phase transition appears frustrated. Small-signal capacitance measurements of films with different thicknesses (24-160 nm) indicate that only the first term in the power series expansion varies significantly with film thickness or temperature. Possible origins for this thickness dependence are discussed.