Charge-Gradient-Induced Ferroelectricity with Robust Polarization Reversal

Developing a ferroelectric tunnel junction with a robust polarization reversal is essential for errorless data storage, but it remains challenging since the second-order phase transition dominates the reversal and introduces intermediate states. This investigation has proposed a charge-gradient-induced ferroelectricity, which is featured with the first-order phase transition. As an order parameter, a charge-gradient-induced polarization is achieved by modulation of stoichiometric oxygen along the Bi₂O₂Se/Bi₂Se₃O₉ bilayer during pulsed laser deposition. At room temperature, this polarity points out-of-plane and shows an abrupt reversal in the ferroelectric hysteresis loop. The coercive field only increases by 0.04 V/nm after 300 reversals. Fabricated into the ferroelectric tunnel junction, the bilayer ferroelectric exhibits a comparable electroresistance of 100. The ON/OFF state can be switched repeatedly or after a 360 s retention. Characterizations of scanning capacitance microscopy and the current-voltage relation demonstrate that the ON/OFF switching is based on an injection exchange between the tunnelling and the thermionic emission.