High stable dielectric permittivity and low dielectric loss in sol–gel derived BiFeO3 thin films

BiFeO3 (BFO) thin films were prepared on (111)Pt/Ti/SiO2/Si substrates via a sol–gel spin-coating method, and the influence of the annealing temperatures on the phase formation, the microstructure and the electrical properties was systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and an HP 4294A precision impedance analyser and a ferroelectric material test system, respectively. The XRD analysis revealed the films to be well-crystallised, and those annealed at approximately 700 °C were well-formed in the perovskite phase. The SEM images confirmed that the BFO films had a uniform and dense microstructure with an average thickness of 300 nm. As the frequency increased to 1 MHz, the dielectric constant of the BFO films remained stable and exhibited only a slight decrease. The film annealed at 715 °C exhibited the best dielectric properties with a high dielectric permittivity (εr=194 at 100 kHz) and a low dielectric loss (tanδ=0.02 at 100 kHz). The leakage current density of the BFO thin films was also notably low, i.e., 10−6 A/cm2, under an applied electric field of 200 kV/cm for the film annealed at 715 °C. The excellent electrical properties obtained in the sol–gel-derived BFO films are attributed to the improved phase purity and microstructure.