Effects of postannealing rate on dielectric/piezoelectric properties of sol‐gel (Na,K,Li)NbO₃ films for sensors

Abstract In this study, lead‐free (Na₀.₅K₀.₅)NbO₃ (KNN) piezoelectric films were prepared using the sol‐gel method. By adjusting the rapid thermal annealing (RTA) parameters, the crystallinity of the films was improved, and a strong (100) orientation was achieved when the annealing rate was set to 30°C/s. Lithium with different doping concentrations (0–6 mol%) was introduced into the A‐site of the lattice to further compensate for alkali ion vacancies caused by high‐temperature annealing. The resulting (Na₀.₅K₀.₅Li X )NbO₃ films (denoted as LKNN‐100x, with x = 0.06) exhibited a dielectric constant of 515.88, a dielectric loss of 4.93%, a remanent polarization of 23.85 µC/cm 2 , and a piezoelectric coefficient d₃₃ of 68.2 pm/V. Subsequently, the addition of an HfO₂ buffer layer improved interface defects and reduced stress accumulation in the films, further enhancing the piezoelectric performance to 76.81 pm/V. Finally, a piezoelectric force sensor was designed and fabricated using the optimized films on a stainless‐steel substrate. The sensor exhibited a sensitivity of 2.4 mV/g and was successfully applied to the detection of extension forces in unmanned aerial vehicles (UAVs).