Tracking intrinsic ferroelectric switching under electric field via operando second harmonic generation

Polarization hysteresis is the defining characteristic of ferroelectrics, though the measurement of ferroelectric hysteresis is often complicated by artifacts such as leakage current and not all materials with apparent electrical hysteresis are ferroelectric. In this Letter, we have set up an operando second harmonic generation (SHG) system to track intrinsic ferroelectric switches under electric field, which is free from leakage current interference, thus yielding a signature for intrinsic ferroelectricity. Taking representative PbZr0.2Ti0.8O3 (PZT) thin films with different thicknesses as examples, the operando SHG system can capture ferroelectric hysteresis not only for PZT films thicker than 50 nm, for which conventional hysteresis measurement works, but also for PZT film as thin as 26 nm, for which conventional measurement fails due to the presence of large leakage current. Different domain evolution processes in these films are also illustrated.