Ferroelectric properties of BiFeO3 thin films by Sr/Gd/Mn/Co multi-doping

Bi0.97-xSr0.03GdxFe0.94Mn0.04Co0.02O3 (BSGxFMC) thin films were fabricated by sol-gel method. It is found that the formation of oxygen vacancies of BSGxFMC thin films is restrained by multi-doping, leading to the decrease of built-in electric field in depletion layer formed between Au electrode and BFO ferroelectric layer. Hence, the shift phenomena of coercive fields are weakened and the better symmetry of hysteresis loops can be observed in the thin films. Among all the films, BSG0.09FMC thin film exhibits real and excellent ferroelectric properties with a giant remnant polarization of Pr ∼108 μC/cm2, a large switching current of 1.4 mA and a high squareness ratio of 1.18. And the BSG0.09FMC film displays a symmetric-well narrow butterfly curve, which suggests its great ferroelectric behavior. Meanwhile, the remnant polarization of BSG0.09FMC film exhibits the flattest slope with the increase of applied voltages compared with other samples, indicating the greatest ferroelectric stability at different applied voltages. Ferroelectric properties of BSGxFMC thin films have been improved significantly due to the coefficient contributions from the reduced oxygen vacancies ratio, the increased resistance and the structure transition with multi-doping.