Surface-Functionalized Hafnia with Bespoke Ferroelectric Properties for Memory and Logic Applications

In this work, we, for the first time, provide an atomic-level understanding of the surface functionality of ferroelectric (FE) hafnia in relation to their FE properties from thorough first-principles calculations. We devise a new algorithm that automatically finds the stable geometries of various functionalized surfaces of FE hafnia, which overcomes the previous challenges in modelling the formidably complicated bonding chemistry between Hf, O, H atoms and other functional groups at the surfaces. Using our method, we demonstrate that preferred crystallographic orientations in thin film hafnia can be extensively engineered by a combination of hydroxyl (-OH) and fluorine (-F) functionalization at the surface. This enables the control of remnant polarization (Pr) as well as coercive field (Ec) of FE hafnia for targeted applications, where, for instance, Pr can be tuned from zero (in-plane polarization) to the theoretical maximum limit (Pr = 52 µC/cm2). Our results not only explain the recent observations of an enhanced Pr in highly-Textured ultrathin hafnia, but also provide practical guidelines for the design and fabrication of FE hafnia-based advanced memory and logic devices.