Piezoelectric and Dielectric Properties of Multilayered BaTiO₃/(Ba,Ca)TiO₃/CaTiO₃ Thin Films

Highly oriented multilayered BaTiO₃–(Ba,Ca)­TiO₃–CaTiO₃ thin films were fabricated on Nb-doped (001) SrTiO₃ (Nb:STO) substrates by pulsed laser deposition. The configurations of multilayered BaTiO₃–(Ba,Ca)­TiO₃–CaTiO₃ thin films are designed with the thickness ratio of 1:1:1 and 2:1:1 and total thickness ∼300 nm. Microstructural characterization by X-ray diffraction indicates that the as-deposited thin films are highly c-axis oriented and large in-plane strain is determined in BaTiO₃ and CaTiO₃ layers. Piezoresponse force microscopy (PFM) studies reveal an intense in-plane polarization component, whereas the out-of-plane shows inferior phase contrast. The optimized combination is found to be the BaTiO₃–(Ba_0.85Ca_0.15)­TiO₃–CaTiO₃ structure with combination ratio 2:1:1, which displays the largest domain switching amplitude under DC electric field, the largest room-temperature dielectric constant ∼646, a small dielectric loss of 0.03, and the largest dielectric tunability of ∼50% at 400 kV/cm. These results suggest that the enhanced dielectric and tunability performance are greatly associated with the large in-plane polarization component and domain switching.