Rf-magnetron sputtered ferroelectric (Na,K)NbO3 films

Sodium potassium niobate (Na,K)NbO₃ (NKN) thin films were grown by rf-magnetron sputtering from stoichiometric Na_0.5K_0.5NbO₃ target on LaAlO₃ (LAO) single crystals and polycrystalline Pt₈₀Ir₂₀ (PtIr) substrates. NKN films on polycrystalline PtIr substrates were found to be preferentially (00l) oriented while XRD measurements reveal epitaxial quality of NKN/LaAlO₃ film structures. The ferroelectric state in NKN/PtIr films at room temperature is indicated by polarization loops with polarization as high as 33.4 μC/cm² at 700 kV/cm remnant polarization of 9.9 μC/cm², and coercive field of 91 kV/cm. I-V characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties. For NKN IDC the leakage current density was in the order of 30 nA/cm² at 400 kV/cm. Rf dielectric spectroscopy demonstrates low loss, low frequency dispersion, and high voltage tunability both for vertical Au/NKN/PtIr and planar interdigital Au/NKN/LAO capacitors.