Enhanced polarization and reduced leakage current in BiFeO3 thin films fabricated by chemical solution deposition

BiFeO3 (BFO) thin films were fabricated by chemical solution deposition on Pt/Ti/SiO2/Si(100) and Pt/sapphire(0001) structures. In order to reduce leakage current density in BFO films, the stoichiometric BFO chemical solution of 0.1-0.2 mol/l concentration was used to deposit approximately 10-20-nm-thick films at one step in the spin-coating method. The optimized conditions for preannealing were determined to be at 350 degrees C for 10 min in air, and those for annealing were at 550 degrees C for 5 min in nitrogen atmosphere. It was found from x-ray diffraction analysis that the obtained films on both Si and sapphire substrates were mostly composed of polycrystalline BFO grains with a perovskite structure. It was also confirmed from x-ray photoelectron spectroscopy that the origin of low leakage current was due to the presence of Fe3+ valance state. In the P-E (polarization versus electric field) measurements for BFO films on both Si and sapphire substrates we observed nonsaturate and saturated hysteresis loops at room temperature and 80 K, respectively. At 80 K, the remanent polarization and coercive field in the film on sapphire were approximately 100 mu C/cm(2) and 0.4 MV/cm at 2 MV/cm electric applied field, respectively, and the polarization was about 10% smaller in the film on Si. Improved ferroelectric properties of BFO films on sapphire substrates are considered to be due to the improved BFO/Pt interface. (c) 2006 American Institute of Physics.