Structural and Electrical Characterization of Highly Oriented (KxNax)NbO3 (KNN) Thin Films By Chemical Solution Deposition

Abstract

(K0.5Na0.5)NbO3 (KNN) perovskite materials have been developed as promising lead-free piezoelectric materials for environmentally and biologically benign piezoelectric devices. To date, however, there are few reports on the growth of good KNN thin films by chemical solution deposition (CSD) and on their properties for device applications. Excellent crystallinity at low temperatures with a uniform and controllable microstructure is required for improvement of the electrical properties, including piezoelectric properties. KNN thin films were fabricated on SiO2/Si(100) and Pt(111)/SiO2/Si(100) substrates by chemical solution deposition. By applying different annealing conditions, highly oriented KNN was attained at 550 °C and above. The effects of the substrates on crystallographic orientation were not distinguishable in these films. However, the thickness of pyrolized film strongly affects film orientation. For thinner pyrolized layers, KNN showed textured orientation due to the influence of interfaces between the Pt(111) layer and KNN, which served as heterogeneous nucleation sites. For thicker layers, homogeneous nucleation and growth were prevalent, thus resulting in random orientations. For (K0.5Na0.5)NbO3, typical P-E hysteresis loops could not be obtained due to the leakage current. Since the leakage current could stem from volatilization of Na and K ions at a higher temperature, the excessive Na and K were added in order to compensate for the volatile ones and sustain MPB composition of KNN. K0.6Na0.5NbO3 could endure higher applied electric fields over 800 kV/cm showing reasonably typical P-E hysteresis curves. The maximum 2Pr and 2Ec values are approximately 17.5 µC/cm2 and 150 kV/cm, respectively.