Piezoelectric properties of (K,Na)NbO3 thin films deposited on (001)SrRuO3/Pt/MgO substrates

(K_x,Na_1-x)NbO₃ (KNN) thin films were deposited on (001)SrRuO₃/(001)Pt/(001)MgO substrates by RF-magnetron sputtering, and their piezoelectric properties were investigated. The X-ray diffraction measurements indicated that the KNN thin films were epitaxially grown with the c-axis orientation in the perovskite tetragonal system. The lattice constant of the c-axis increased with increasing concentrations of potassium. The KNN thin films showed typical ferroelectric behavior; the relative dielectric constant epsiv_r was 270 ~ 320. The piezoelectric properties were measured from the tip displacement of the KNN/MgO unimorph cantilevers; the transverse piezoelectric coefficient e₃₁* (= d₃₁/s₁₁ ^E) of KNN (x = 0) thin films was calculated to be -0.9 C/m². On the other hand, doping of potassium caused an increase in the piezoelectric properties, and the KNN (x = 0.16) films showed a relatively large transverse piezoelectricity of e₃₁* = -2.4 C/m².