Induction of ferroelectricity in nanoscale ZrO₂/HfO₂ bilayer thin films on Pt/Ti/SiO₂/Si substrates

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• 作者：Y.W. Lu ; J. Shieh ; ^{jayshieh@ntu.edu.tw" class="auth_mail" title="E-mail the corresponding author} ; F.Y. Tsai
• 关键词：Hafnia ; Zirconia ; Ferroelectricity ; Bilayer thin films ; TEM
• 刊名：Acta Materialia
• 出版年：2016
• 出版时间：15 August 2016
• 年：2016
• 卷：115
• 期：Complete
• 页码：68-75
• 全文大小：3689 K

文摘

Large ferroelectricity has been demonstrated in nanoscale bilayer thin films consisting of undoped ZrO₂ and HfO₂ layers on conventional Pt/Ti/SiO₂/Si substrates for the first time. The bilayer thin films had thicknesses between 7.5 and 18 nm and their crystalline phases, symmetry groups, polarization hystereses and composition depth profiles were characterized to understand the influence of the stacking order and thickness of the ZrO₂ and HfO₂ layers on ferroelectricity. Two factors: (1) effective confinement of the HfO₂ layer by the ZrO₂ layer and Si substrate to promote the ferroelectric orthorhombic phase and (2) reduction of the bulk characteristics of the ZrO₂ and HfO₂ layers to minimize the paraelectric monoclinic phase are the key to stable ferroelectricity with a large remanent polarization. These factors can be manipulated by the stacking order and thickness of the layers, and consequently, producing ferroelectric behaviors ranging from minor to fully developed hystereses. The undoped ZrO₂/HfO₂ bilayer thin film is a simpler design and can be fabricated more easily compared to the doped HfO₂ or solid solution Hf_xZr_1-xO₂ thin films reported in the literature, which require not only precise composition control but also the less available TiN electrodes for stable ferroelectricity. The chosen Pt/Ti/SiO₂/Si substrate for the ZrO₂/HfO₂ bilayer thin films is readily available and has been widely used in MEMS applications. These advantages make the ZrO₂/HfO₂ bilayer thin films favorable for silicon-based device integration.