Effect of film thickness on piezoelectric vibrator using hydrothermally synthesized epitaxial (K0.88Na0.12)NbO3 film

Abstract

Two types of vibrators using hydrothermally synthesized ferroelectric (K, Na)NbO3 films were fabricated on SrTiO3 substrates. Cantilever piezoelectric vibrators with film thicknesses of 3.5–22.3 μm 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, e 31,f, was almost independent of film thickness, ≈−5 C m−2. On the other hand, a longitudinal piezoelectric vibrator was used under the resonance of half-length longitudinal vibration. The electromechanical coupling factor, k eff 2, and the mechanical quality factor, Q m, were evaluated. k eff 2 and Q m respectively increased from 0.14% to 1.23% and decreased from 556 to 224 as the film thickness increased from 2.5 to 26 μm. By applying a large voltage of 50 V0-p, a large vibration velocity of 1.5 m s−1 was obtained for the vibrator with a film thickness of 26 μm.