Ferroelectric and dielectric properties of Ca2+-doped and Ca2+–Ti4+ co-doped K0.5Na0.5NbO3 thin films

Abstract

Chemical solution deposition (CSD) of K_0.5Na_0.5NbO₃ (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.