Effect of film thickness on piezoelectric vibrator using hydrothermally synthesized epitaxial (K_0.88Na_0.12)NbO₃ film

<jats:title>Abstract</jats:title> <jats:p>Two types of vibrators using hydrothermally synthesized ferroelectric (K, Na)NbO<jats:sub>3</jats:sub> films were fabricated on SrTiO<jats:sub>3</jats:sub> substrates. Cantilever piezoelectric vibrators with film thicknesses of 3.5–22.3 <jats:italic>μ</jats:italic>m were used under low-frequency and no resonance drive. The obtained output displacement increased almost linearly as the film thickness increased under both unipolar and bipolar drives. The obtained transverse piezoelectric coefficient, <jats:italic>e</jats:italic> <jats:sub>31,f</jats:sub>, was almost independent of film thickness, ≈−5 C m<jats:sup>−2</jats:sup>. On the other hand, a longitudinal piezoelectric vibrator was used under the resonance of half-length longitudinal vibration. The electromechanical coupling factor, <jats:italic>k</jats:italic> <jats:sub>eff</jats:sub> <jats:sup>2</jats:sup>, and the mechanical quality factor, <jats:italic>Q</jats:italic> <jats:sub>m</jats:sub>, were evaluated. <jats:italic>k</jats:italic> <jats:sub>eff</jats:sub> <jats:sup>2</jats:sup> and <jats:italic>Q</jats:italic> <jats:sub>m</jats:sub> respectively increased from 0.14% to 1.23% and decreased from 556 to 224 as the film thickness increased from 2.5 to 26 <jats:italic>μ</jats:italic>m. By applying a large voltage of 50 V<jats:sub>0-p</jats:sub>, a large vibration velocity of 1.5 m s<jats:sup>−1</jats:sup> was obtained for the vibrator with a film thickness of 26 <jats:italic>μ</jats:italic>m.</jats:p>