Guidelines for the optimization of hafnia-based ferroelectrics through superlattice engineering

Abstract: Hafnia-based ferroelectrics are revolutionizing the data storage industry and the field of ferroelectrics, with improved materials and devices being reported monthly. However, full understanding and control has not been reached yet and the ideal material still needs to be found. Here we report ferroelectric hafnia-zirconia superlattices made out of zirconium-substituted hafnia (Hf$_{1-x}$Zr$_x$O$_2$) sublayers of varying stoichiometries alternating with pure ZrO$_2$ sublayers. It is observed that the ZrO$_2$ layers in these superlattices act as a booster for the total remnant polarization (P$_r$). By combining the benefits of the ZrO$_2$ layers and the added interfaces, which help prevent breakdown, we fabricate superlattices with a total 87.5% ZrO$_2$ content, exhibiting record polarizations with a 2P$_r$ value of 84 $\mu$C/cm$^2$ that can be cycled 10$^9$ times, while maintaining a 2P$_r$ > 20 $\mu$C/cm$^2$. Next to these attractive properties, substitution of HfO$_2$ by the much more abundant ZrO$_2$ offers a significant step towards the sustainable application of these devices.