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 ${\mathrm{Ba}}_{\mathrm{0.7}}{\mathrm{Sr}}_{\mathrm{0.3}}{\mathrm{TiO}}_{\mathrm{3}}$ 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 $\text{(∼300\hspace{0.17em}}\mathrm{K}\mathrm{),}$ 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.