Electroresistance in All-Oxide RuO2/Hf0.5Zr0.5O2/ITO Ferroelectric Tunnel Junctions

Ferroelectric tunnel junctions (FTJs) have attracted significant interest for applications ranging from nonvolatile memories to neuromorphic devices. After ferroelectricity was discovered in doped hafnium dioxide (HfO2), research on FTJs shifted from perovskite oxide to HfO2-based ferroelectrics because of their compatibility with silicon processing technology. The presence of an asymmetric potential distribution in the ferroelectric barrier induces resistive switching [i.e., tunnel electroresistance (TER)] in FTJs. In this study, we demonstrated that the use of different oxides for the top and bottom electrodes is effective in inducing an asymmetric potential distribution in a HfO2-based FTJ and the resultant electroresistance. In ruthenium dioxide (RuO2)/Hf0.5Zr0.5O2 (HZO)/indium tin oxide (ITO) junctions, the difference in the work functions between the RuO2 and ITO electrodes tilts the energy band of the HZO layer, resulting in a shift in the polarization–voltage (V) hysteresis loop toward a positive V of approximately 1 eV. RuO2/HZO (2.6 nm)/ITO FTJs showed electroresistance with a switching ratio of ∼75 and a high current density (J) of >130 A/cm2 at 0.5 V for a low resistance state. These results offer a promising solution to the challenge of a low current density (high junction resistance), which hinders the high-density integration of FTJs.