Interface Engineering Using Multiple La-Doped HfO ₂ Epitaxial Subnanolayers To Improve the Ferroelectric Properties of Hf _0.5 Zr _0.5 O ₂ Films

The fabrication of ferroelectric multilayer systems based on hafnia represents a promising approach for achieving high-performance ferroelectric devices. Electrical cycling instability is, in this regard, a key barrier to commercialization. Here, we report on the incorporation of La:HfO₂ subnanolayers into an epitaxial Hf_0.5Zr_0.5O₂ film, forming multilayer heterostructures. Ferroelectric properties of multilayers are compared with single-layer structures. We observe that wake-up and fatigue are not present up to 10⁵ cycles in the multilayers. The improved stability is enabled by the ≈25% reduction of coercive field together with the lower leakage resulting from the columnar microstructure throughout the entire thickness without phase discontinuity at interfaces and negligible presence of structural defects. This improvement on endurance response is obtained while the polarization is maintained in comparison with single Hf_0.5Zr_0.5O₂ films; there is negligible loss of the polarization throught time and there is a fast response time lower than 100 ns, limited by the measurement circuit. In addition, dielectric permittivity and large resistive switching up to 10⁸%, not related to the ferroelectric response, are also observed. These findings underscore multilayer architecture as an interesting approach to improve properties while also showing that careful selection of interlayer composition is critical to improve device performance.