Interface-controlled uniaxial in-plane ferroelectricity in Hf0.5Zr0.5O2(100) epitaxial thin films
Kai Liu, Feng Jin, Tianyuan Zhu, Jie Fang, Xingchang Zhang, E Peng, Kuan Liu, Qiming Lv, Kunjie Dai, Yajun Tao, Jingdi Lu, Haoliang Huang, Jiachen Li, Shouzhe Dong, Shengchun Shen, Yuewei Yin, Houbing Huang, Zhenlin Luo, Chao Ma, Shi Liu, Lingfei Wang, Wenbin Wu
Abstract
Hafnium oxide-based ferroelectric thin films are widely recognized as a CMOS-compatible and highly scalable material platform for next-generation non-volatile memory and logic devices. While out-of-plane ferroelectricity in hafnium oxide films has been intensively investigated and utilized in devices, purely in-plane ferroelectricity of hafnium oxides remains unexplored. In this work, we demonstrate a reversible structural modulation of the orthorhombic phase Hf0.5Zr0.5O2 films between (111)-oriented [HZO(111)O] multi-domain and (100)-oriented [HZO(100)O] single-domain configurations by altering perovskite oxide buffer layers. Unlike conventional out-of-plane polarized HZO(111)O films, the HZO(100)O films exhibit uniaxial in-plane ferroelectric polarization, sustained even at a thickness of 1.0 nm. Furthermore, the in-plane ferroelectric switching achieves an ultralow coercivity of ~0.5 MV/cm. The HZO(100)O phase is stabilized by a staggered interfacial reconstruction, driven by the delicate interplays between symmetry mismatch and surface energy. These findings pave the way for innovative device designs and strategies for modulating the functionalities of hafnium oxide-based ferroelectrics. Moving beyond the widely studied (111)-oriented Hf0.5Zr0.5O2 films, the authors demonstrate purely uniaxial in-plane ferroelectricity in orthorhombic (100)-oriented Hf0.5Zr0.5O2 films, sustained even at a thickness of 1 nm.