Interface Engineering for Expanded Stable Polarization Regime Upon Cycling in Ferroelectric Hf_0.5Zr_0.5O₂

Interfaces have a significant influence on the functional properties of ferroelectric devices, and their optimization is necessary to accelerate the path toward applications. Interface engineering has been extensively investigated in polycrystalline HfO₂, but research on epitaxial films is scarce. In this work, we use epitaxial La-doped HfO₂ (LHO) in a Pt/LHO/La_0.67Sr_0.33MnO₃ capacitor grown on SrTiO₃(001) and SrTiO₃(110) substrates and we investigate the impact of ZrO₂ nanolayers when inserted as top layers, bottom layers, or simultaneously in both positions. It is found that the position of the ZrO₂ nanolayers and the substrate orientation influence the formed phases and functional properties. In the multilayers on SrTiO₃(110) polarization is larger, but there is pronounced wake-up. Multilayers on SrTiO₃(001) with a ZrO₂ nanolayer at the bottom interface exhibit presence of monoclinic phase and low polarization, as well as wake-up effect. However, inserting ZrO₂ solely as a capping layer on SrTiO₃(001) results in high polarization, minimal wake-up effect, long endurance of 10¹¹ cycles, retention beyond 10 years, leakage current less than 10^-7 A/cm² at 1 V and switching time shorter than 90 ns.