Polarization switching in ferroelectric films triggered by charge injection/extraction at interfaces

A new mechanism is proposed for polarization switching in metal-ferroelectric-metal (MFM) structures. The switching is triggered by charge injection at electrode or grain interfaces under an external field, opposite to the initial direction of polarization. Such injection destabilizes the compensation of the polarization, and is favored by disappearance of Schottky barriers at interfaces, leading to a resistive like behavior. At the coercive voltage the depolarization field is no longer compensated and the polarization change orientation parallel to the applied field. After switching, the Schottky barriers are restored and the current start to decrease although the voltage continues to increase. This leads to a differential negative resistance until the barriers are totally restored, polarization saturated on the new direction and the depolarization field annihilated by the injected charges. In a perfect structure the switching takes place homogeneously, while the defects presence induces domains via local nucleation and fields. The model is supported by theory, showing that at switching the MFM structure has a resistive like behavior, and by experiments, showing that the voltage dependence of the current during switching is linear and that the phase change at switching, in PFM measurements performed on high quality epitaxial films, is abrupt. The analysis was performed on MFM structures based on different ferroelectric layers (e.g. Pb( Zr , Ti )O 3 , BaTiO 3 , BiFeO 3 or (HfZr)O 2 ), different metal electrodes and different structural qualities. It appears that polarization switching triggered by charge injection at interfaces is a mechanism that can be applied to all MFM structures based on oxide ferroelectrics. • Polarization switches due to charge injection at interfaces in ferroelectric oxides. • The ferroelectric has a resistive like behavior during polarization switching. • No domains form during polarization switching in perfect ferroelectric structures. • Domains occurs due to structural imperfections in the ferroelectric structures.