Effect of Substrates on the Structure and Ferroelectric Properties of Multiferroic ${\hbox {BiFeO}}_{3}$ Films

Structure and ferroelectric properties of multiferroic BiFeO₃ (BFO) films prepared by pulse laser deposition (PLD) with different substrates of Pt/Ti/SiO₂/Si(100) and Pt/glass have been studied. Isotropic perovskite BFO phase is obtained in the 200-nm-thick BFO films deposited on both substrates at reduced substrate temperature T_s = 400-500°C. Uniformly finer grains and smoother surface are obtained for BFO films grown on Pt(111)/glass as compared to Pt/Ti/SiO₂/Si(100) substrate. This difference may be related to the distinct BFO/Pt interface morphology. After postannealing, the Pt layer grown on glass substrates has very smooth surfaces consisting of (111) grains, while it contains cracks in the Pt/Ti/SiO₂/Si(100). As a result, lower leakage current density and better ferroelectric properties of 2P_r = 15.1-78.6 μC/cm² and E_c = 383-514 kV/cm are obtained in the BFO films deposited on Pt(111)/glass substrates. Nevertheless, high deposition temperature of 550°C leads to the formation of large amount of BFO into Bi₂O₃, Bi₂Fe₄O₉, and Fe₂O₃ phases, and therefore, no ferroelectric behavior is observed.