Deterministic Orientation Control of Ferroelectric HfO<sub>2</sub> Thin Film Growth by a Topotactic Phase Transition of an Oxide Electrode.

Lee, Kyoungjun; Park, Kunwoo; Choi, In Hyeok; Cho, Jung Woo; Song, Myeong Seop; Kim, Chang Hoon; Lee, Jun Hee; Lee, Jong Seok et al. · ACS Nano · 2024

basic_science · Level V

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Abstract

The scale-free ferroelectricity with superior Si compatibility of HfO<sub>2</sub> has reawakened the feasibility of scaled-down nonvolatile devices and beyond the complementary metal-oxide-semiconductor (CMOS) architecture based on ferroelectric materials. However, despite the rapid development, fundamental understanding, and control of the metastable ferroelectric phase in terms of oxygen ion movement of HfO<sub>2</sub> remain ambiguous. In this study, we have deterministically controlled the orientation of a single-crystalline ferroelectric phase HfO<sub>2</sub> thin film via oxygen ion movement. We induced a topotactic phase transition of the metal electrode accompanied by the stabilization of the differently oriented ferroelectric phase HfO<sub>2</sub> through the migration of oxygen ions between the oxygen-reactive metal electrode and the HfO<sub>2</sub> layer. By stabilizing different polarization directions of HfO<sub>2</sub> through oxygen ion migration, we can gain a profound understanding of the oxygen ion-relevant unclear phenomena of ferroelectric HfO<sub>2</sub>.