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

(K-x,Na1-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 sys tem. The lattice constant of the c-axis increased with in creasing concentrations of potassium. The KNN thin films showed typical ferroelectric behavior; the relative dielectric constant Er was 270 similar to 320. The piezoelectric properties were measured from the tip displacement of the KNN/MgO unimorph cantilevers; the transverse piezoelectric coefficient e(31)* (= d(31)/S-11(E)) of KNN (x = 0) thin films was calculated to be -0.9 C/m(2). 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 e(31)* = -2.4 C/m2.