Annealing effects on epitaxial (K,Na)NbO3 thin films grown on Si substrates

Epitaxial (K,Na)NbO3 (KNN) thin films were deposited on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering, and post-annealing effects on the as-deposited epitaxial KNN thin films were investigated. According to the findings, by annealing, the crystal system of these thin films changes from a tetragonal to an orthorhombic system because of the release of internal stress. The asymmetry of polarization–electric field hysteresis loops along the electric field changes from a positive to a negative side by annealing. This means that stable spontaneous polarization Ps changes from the upward to downward direction with an increase in the number of A-site vacancies. In addition, the displacement–electric field curves of epitaxial KNN/Si unimorph cantilevers exhibit asymmetric behaviors. A relatively high converse piezoelectric coefficient ∣e31,f ∣ = 6.4 C m−2 is obtained for 5 h annealed epitaxial KNN thin films.