Effect of Anneal Conditions on Electrical Properties of Mn-Doped (Na0.85K0.15)0.5Bi0.5TiO3 Thin Films Prepared by Sol-Gel Method

Mn-doped (Na0.85K0.15)(0.5)Bi0.5TiO3 (NKBT-Mn) thin films were fabricated on Pt(111)/Ti/SiO2/Si substrates via an aqueous sol-gel method and annealed at different temperatures from 550 degrees to 800 degrees C. Two different crystallization processes, i.e., single crystallization and multiple crystallizations, were used. The structures of the films were analyzed using X-ray diffraction, which shows that the NKBT-Mn thin film prepared by multiple crystallizations crystallize into the pure perovskite phase, while pyrochlore phase formed in the film prepared by the single crystallization. Ferroelectric and dielectric properties of NKBT-Mn thin films are quite dependent on the anneal temperature. The P-r value was a maximum for the 700oC-annealed thin film and decreased with both decreasing and increasing anneal temperature. The NKBT-Mn thin film annealed at 700 degrees C had the largest epsilon(r) of 426 and the lowest tan delta of 0.061. At the same time, the temperature-dependent ferroelectric property was also investigated from room temperature to -150 degrees C. It is found that P-r of the film sample increases as temperature decreases, which can be well explained by a temperature-dependent charged carriers-domain wall interaction. Current density measurement indicates that the change in morphology with increasing anneal temperature and the volatility of Bi and Na/K at high temperature may responsible for the change in leakage current density and the NKBT-Mn thin film annealed at 700 degrees C has the lowest leakage current of 7.6 x 10-5 A/cm2.