Electrical properties of lead-free KNN films on SRO/STO by RF magnetron sputtering

Highly (001) oriented (K,Na)NbO3 lead-free piezoelectric films were fabricated on SrRuO3 buffered SrTiO3(001) single crystal substrates by RF magnetron sputtering. The films showed a stable frequency dependence of dielectric permittivity and loss tangent in the range of 1 kHz–1 MHz. A fairly high tunability of 69.7% (@400 kV/cm) was obtained in the films. Well saturated P–E hysteresis loops were obtained at E=250 kV/cm, the remnant polarization Pr was 8 μC/cm2, and coercive field Ec was only 40 kV/cm. These films showed a fatigue-free behavior up to 1010 switching cycles. The decreased coercive field, improved dielectric and fatigue properties may be related to SRO bottom electrodes, which can efficiently suppress the “dead layer” near the ferroelectric-electrode interface. The leakage current density of the films was only 3.48×10−6 A/cm2 at the electric field of 250 kV/cm, which is even lower than that of Mn-doped KNN films. In addition, the piezoelectric constant d33 was estimated to be 36 pm/V.