Piezoelectric properties of (K,Na)NbO 3 thin films deposited on (001)SrRuO 3/Pt/MgO substrates

(K<sub>x</sub>,Na<sub>1-x</sub>)NbO<sub>3</sub> (KNN) thin films were deposited on (001)SrRuO<sub>3</sub>/(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<sub>r</sub> was 270 ~ 320. The piezoelectric properties were measured from the tip displacement of the KNN/MgO unimorph cantilevers; the transverse piezoelectric coefficient e<sub>31</sub>* (= d<sub>31</sub>/s<sub>11</sub> <sup>E</sup>) of KNN (x = 0) thin films was calculated to be -0.9 C/m<sup>2</sup>. 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<sub>31</sub>* = -2.4 C/m<sup>2</sup>.

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