The development of lead-free ferroelectric and piezoelectric materials is required from the viewpoint of environmental preservation. Among various lead-free materials, (K$ _{0.5}$Na$ _{0.5}$)NbO$ _{3}$ (KNN) has attracted much attention due to its excellent ferroelectric and piezoelectric properties. In this study, high-quality Mn-doped (K$ _{0.5}$Na$ _{0.5}$)NbO$ _{3}$ (KNMN) films were deposited on Pt/TiO$ _{2}$/SiO$ _{2}$/Si substrates by using the sol-gel method. For various numbers of coating cycles; the KNMN films have thicknesses of around 0.8, 1.0, 1.5 and 2.0 $\mu$m, respectively. The effective piezoelectric coefficient ($d_{33,\text{eff}}$) of the KNMN films was analyzed using a home-made laser Doppler vibrometer that could measure large millimeter-scale areas. The average $d_{33,\text{eff}}$ of a 2-$\mu$m-thick KNMN film was measured to be around 120 pm/V, which is comparable to those of lead-based materials and higher than those of other lead-free piezoelectric film alternatives.

Keywords: Effective piezoelectric coefficient, Laser Doppler vibrometer, (K,Na)NbO$ _{3}$, Thick film, Lead-free