Poling Sequence-Dependent Tunneling Electroresistance in HfO2-Based Ferroelectric Tunnel Junctions

The current-voltage (I-V) characteristics and ON/OFF ratio in hafnium oxide (HfO2)-based ferroelectric tunnel junctions (FTJs) were investigated under different poling sequences. When -5 V poling pulse is applied prior to +5 V pulse (-5 V-poling-first operation), both ON-state and OFF-state show relatively low currents, whereas the ON/OFF ratio is more than doubled, as compared to the reverse poling sequence (+5 V-poling-first operation, i.e., + 5 V pulse applied prior to -5 V). Interestingly, the ON-state I-V curves exhibit the Ohmic behavior, while the OFF-state curves are nonlinear that can be described by direct tunneling across a barrier, regardless of the poling sequence. The poling sequence-dependent tunneling electroresistance in our FTJs is explained by the evolution of domain structure in the ferroelectric films driven by the poling pulse, as supported by both I-V measurements and data fitting. This work provides a guidance to modulate the performance of FTJs, and further help understand the structure-property relationship of HfO2-based ferroelectric memories at the nanoscale.