Improvement of piezoelectric properties of epitaxial (K,Na)NbO3 thin films grown on Si substrates

Abstract

Lead-free epitaxial (K0.47Na0.53)NbO3 (KNN) thin films were fabricated on (001)SrRuO3/Pt/ZrO2/Si substrates by RF magnetron sputtering at 650 °C and were post-annealed at the same 650 °C by a rapid thermal annealing (RTA) process. The crystal structure of epitaxial KNN thin films were changed by RTA, i.e. the lattice parameter c in the out-of-plane direction decreased instead of an increase of the parameter a in the in-plane direction. The displacement–electric field curve of the RTA-annealed KNN thin films was symmetrical and the shift of the polarization reversal field was smaller than in the KNN thin films annealed by a conventional furnace. This means that RTA is effective in compensating for oxygen vacancies as well as suppressing the generation of A-site vacancies at the interface between the thin film and the substrate. The converse piezoelectric coefficient ∣e 31,f ∣ of the epitaxial KNN/Si unimorph cantilever was found to improve by up to 7.7 C m−2 due to the decrease in defect density resulting from RTA.