Ferroelectric and dielectric properties of Ca2+-doped and Ca2+–Ti4+ co-doped K0.5Na0.5NbO3 thin films†
Chemical solution deposition (CSD) of K0.5Na0.5NbO3 (KNN) thin films on silicon-based substrates is an interesting technology for fabrication of lead-free ferroelectric thin films. Here, we report on improved ferroelectric and dielectric properties of KNN thin films prepared by CSD through Ca2+-doping and Ca2+–Ti4+ (CaTiO3) co-doping. Undoped KNN, 0.5 mol% Ca2+-doped and 0.5 mol% CaTiO3-doped KNN films were deposited on platinized silicon substrates by aqueous CSD. X-ray diffraction of the films as well as powders, prepared from the precursor solutions, confirmed that the three KNN materials were single phase solid solutions. A smaller grain size was observed for the doped relative to undoped KNN films. In contrast to the pure KNN films, the Ca2+- and CaTiO3-doping was observed to promote ferroelectric switching, with a low leakage current and remnant polarization of 6.37 ± 0.47 and 7.40 ± 0.09 μC cm−2 of the Ca2+- and CaTiO3-doped films, respectively. The dielectric constants of the films were among the highest measured for KNN films from CSD and span from 1800 to 3200 at 1 kHz.