[en] BiFeO₃ is a multiferroic material with physical properties very sensitive to its stoichiometry. BiFeO₃ thin films on silicon substrate are prepared by the sol–gel method combined with layer-by-layer annealing and final annealing schemes. X-ray diffraction and scanning electron microscopy are employed to probe the phase structures and surface morphologies. Using Rutherford backscattering spectrometry to quantify the nonstoichiometries of BiFeO₃ thin films annealed at 100 °C–650 °C. The results indicate that Bi and Fe cations are close to the stoichiometry of BiFeO₃, whereas the deficiency of O anions possibly plays a key role in contributing to the leakage current of 10⁻⁵ A/cm² in a wide range of applied voltage rather than the ferroelectric polarizations of BiFeO₃ thin films annealed at high temperature. (paper)