Solution-Based Fabrication of High-Performance K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ Thin Films for Surface Haptics

Abstract

K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ is among the most promising lead-free piezoelectrics. While its sputtered films match the performance of the champion piezoelectric Pb(Zr,Ti)O${}_3$, reproducible processing of high-quality and time-stable solution-processed K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ films remains challenging. Here, we report 1 $\mu$m-thick Mn-doped K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ films prepared through a chemical solution deposition process, which have perfectly dense microstructure and uniform composition across their thickness. The films exhibit a high transverse piezoelectric coefficient ($e_{31,f}=-15.4$ C/m${}^2$), high dielectric permittivity (${\epsilon }_r\approx 920$), low dielectric losses ($\tan \delta =0.05$) and can withstand electric fields up to at least 1 MV/cm. The functional properties show excellent stability over time, and the synthesis process is reproducible. Furthermore, a surface acoustic haptic device is demonstrated by using K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ thin-film actuators. The results demonstrate the high potential of Mn-doped K${}_{0.5}$Na${}_{0.5}$NbO${}_3$ films to become a replacement for lead-based Pb(Zr,Ti)O${}_3$ films in piezoelectric applications.