Recent Progress in Potassium Sodium Niobate Lead-free Thin Films

Lead-free potassium sodium niobate (KNN)-based thin films have attracted much interest in replacing current lead zirconate titanate (PZT)-based piezoelectric thin films in micro electromechanical (MEMS) devices due to the increasing awareness and legislation concerning lead oxide toxicity. Recently, promising piezoelectric performance has been achieved in KNN-based thin films by compositional modification. Over the last decade, our group has concentrated on the fabrication of KNN-based thin films using sol-gel and RF sputtering techniques and has obtained encouraging results. However, controlling the complex stoichiometric compositions in KNN-based thin films is still challenging due to volatilization of alkaline elements and the high leakage current density. In the current review, the available synthetic approaches, chemical modification strategies, and stabilizing agents used to try and overcome these challenges and improve the piezoelectric properties of KNN-based thin films are reviewed. Herein, we systematically describe the recent advancements of the ferroelectric and piezoelectric properties of KNN-based thin films and summarize the properties of KNN-based thin films fabricated by various techniques, such as sol-gel and RF magnetron sputtering