Chemical Uniformity in Ferroelectric K Na NbO Thin Films.

Potassium sodium niobate (KNN) has long been considered a viable candidate for replacing lead-based materials in piezo- and ferroelectric devices. The introduction of KNN on an industrial scale is highly awaited; however, processing challenges still remain to be solved. The main obstacle is lack of reproducible growth of uniform boules or thin films at temperatures that facilitate monolithic device integration. Herein, atomic layer deposition (ALD) of KNN thin films, exhibiting high chemical uniformity over large areas, is reported. The cation composition can be controlled at a 1% level, enabling fine-tuning of the film stoichiometry across the morphotropic phase boundaries of the KNbO-NaNbO solid solution. The films are obtained as highly oriented on Pt (111)||Si (100)-substrates after annealing at temperatures as low as 550 °C. They exhibit converse piezoelectric effects with magnitudes in accordance with literature. It is believed that the successful development of the described ALD process represents a major step toward achieving lead-free piezo- and ferroelectrics on an industrial scale.