Effects of Pt Bottom Electrode Layers and Thermal Process on Crystallinity of Alkoxy-Derived (Na,K)NbO3 Thin Films

Lead-free ferroelectric (Na 0.5 K 0.5 )NbO 3 (NKN) thin films were fabricated by a sol–gel process on two types of Pt/Ti/SiO 2 /Si substrate at different deposition temperatures, that is, a room temperature and 300 °C, for Pt/Ti layers. The Pt layer deposited at room temperature had a large variation in 111 d -space, and many hillocks were formed on the surface of the Pt layer owing to the relaxation of compressive stress with the elevation of annealing temperature. On the other hand, the variation in 111 d -space and the generation of hillocks in the Pt layer deposited at 300 °C were improved. By using the Pt layer deposited at 300 °C and a low heating rate (10 °C/min) during sintering, highly oriented NKN thin films were obtained at 500 °C. The P – E hysteresis loop of the NKN thin films showed a relatively good shape, and the remanent polarization P r was estimated to be about 0.98 µC/cm 2 at 120 kV/cm. The leakage current density of the NKN thin films on the Pt layers deposited at 300 °C was 4.0 × 10 -6 A/cm 2 at 60 kV/cm.