Optical Control of Ferroelectric Imprint in BiFeO₃

Achieving reliable performance in advanced ferroelectric thin-film devices depends on effectively controlling ferroelectric imprint—an internal electric field that can cause polarization fatigue and retention loss challenges. This imprint arises from factors such as charged defects, strain, and electrostatic boundary conditions, and thus can be influenced by the chemical environment, growth conditions, and external stimuli like temperature and light. In this work, dynamic optical control of imprint behavior in high-performance BiFeO₃ (BFO) thin films fabricated via low-cost, scalable spray pyrolysis, using above-bandgap light irradiation at room temperature is achieved. Through X-ray photoelectron spectroscopy, transmission electron and scanning probe microscopy, it is revealed that the distribution of charged defects, including Fe²⁺ ions and oxygen vacancies at the interface and bulk, corresponds to the real-space mapping of the “frozen-in” imprint patterns and pristine polarization. Interestingly, while the electrical reversal of the polarization direction leaves the imprint behavior unchanged, it can be finely tuned using the above-band-gap light. This light stimulus generates non-equilibrium photocarriers with much faster kinetics, reducing the internal electric field and enabling polarization reorientation. These results pave the way for optically controlled polarization switching at room temperature, offering exciting possibilities for the development of ferroelectric optoelectronic memory and sensing devices.