Structural and Ferroelectric Transition in Few-Layer HfO 2 Films by First Principles Calculations

• Published in: Chinese physics letters Vol. 41; no. 8; p. 87701
• Main Authors: Gao 高, Ruiling 瑞灵, Liu 刘, Chao 超, Shi 施, Bowen 博文, Li 李, Yongchang 永昌, Luo 罗, Bing 兵, Chen 陈, Rui 睿, Ouyang 欧, Wenbin 阳文彬, Gao 高, Heng 恒, Hu 胡, Shunbo 顺波, Wang 王, Yin 音, Li 李, Dongdong 东栋, Ren 任, Wei 伟
• Format: Journal Article
• Language: English
• Published: 01.08.2024
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/41/8/087701

The discovery of ferroelectricity in HfO 2 -based materials with high dielectric constant has inspired tremendous research interest for next-generation electronic devices. Importantly, films structure and strain are key factors in exploration of ferroelectricity in fluorite-type oxide HfO 2 films. Here we investigate the structures and strain-induced ferroelectric transition in different phases of few-layer HfO 2 films (layer number N = 1–5). It is found that HfO 2 films for all phases are more stable with increasing films thickness. Among them, the Pmn 2 1 (110)-oriented film is most stable, and the films of N = 4, 5 occur with a P 2 1 ferroelectric transition under tensile strain, resulting in polarization about 11.8 μC/cm 2 along in-plane a -axis. The ferroelectric transition is caused by the strain, which induces the displacement of Hf and O atoms on the surface to non-centrosymmetric positions away from the original paraelectric positions, accompanied by the change of surface Hf–O bond lengths. More importantly, three new stable HfO 2 2D structures are discovered, together with analyses of computed electronic structures, mechanical, and dielectric properties. This work provides guidance for theoretical and experimental study of the new structures and strain-tuned ferroelectricity in freestanding HfO 2 films.