NpjComput.Mater.：HfO₂的超晶格設計：解決鐵電材料穩定性瓶頸

海歸學者發起的公益學術平臺

分享資訊，整合資源

交流學術，偶爾風月

HfO₂最早因其高介電常數在半導體工業中備受關注。自2011年被發現具有鐵電性以來，其研究熱點逐步轉向這種鐵電材料在CMOS相容裝置中的應用。然而，HfO₂的極性相在熱力學上具有亞穩特性，體相圖中並沒有極性相，主要以非極性的單斜相為基態。這種特性嚴重限制了HfO₂作為功能性鐵電材料的實際應用，因為只有在特定的動力學條件或外延應變作用下才能穩定極性鐵電相。因此，如何穩定鐵電相HfO₂，一直是該領域的一大挑戰。文章中已有諸多有關如何穩定鐵電相HfO₂的報道，包括氧空位、摻雜劑的種類和濃度、表面能最小化、猝滅動力學和力學效應等，但結果都不盡人意。

Fig. 1 | Structures of the considered 2/2
X/Hf oIII SL’s superlattices.

來自盧森堡科學技術研究所（LIST）材料研究與技術系的Binayak Mukherjee等人，提出了一種創新的超晶格設計，將HfO₂與其他簡單氧化物構成多層超晶格，透過調節超晶格的成分和堆疊方向，實現了鐵電相的熱力學穩定性。透過第一性原理計算，作者發現，可以透過組合選擇極性、反極性或混合極性結構，在實現熱力學穩定性的同時，提升材料的極化表現。

Fig. 2 | Structure and sublayer polarization
of Ge/Hf and Ti/Hf mixed SLs.

這一工作為未來的鐵電薄膜器件提供了重要的設計思路，併為開發新一代高效穩定的鐵電材料鋪平了道路。該文近期發表於npj Computational Materials10: 153 (2024)，英文標題與摘要如下，點選左下角“閱讀原文”可以自由獲取論文PDF。

First-principles predictions of HfO2-based ferroelectric superlattices

Binayak Mukherjee, Natalya S. Fedorova & Jorge Íñiguez-González

The metastable nature of the ferroelectric phase of HfO2 is a significant impediment to its industrial application as a functional ferroelectric material. In fact, no polar phases exist in the bulk phase diagram of HfO2, which shows a dominant non-polar monoclinic ground state. As a consequence, ferroelectric orthorhombic HfO2 is stabilized either kinetically or via epitaxial strain. Here, we propose an alternative approach, demonstrating the feasibility of thermodynamically stabilizing polar HfO2 in superlattices with other simple oxides. Using the composition and stacking direction of the superlattice as design parameters, we obtain heterostructures that can be fully polar, fully antipolar or mixed, with improved thermodynamic stability compared to the orthorhombic polar HfO2 in bulk form. Our results suggest that combining HfO2 with an oxide that does not have a monoclinic ground state generally drives the superlattice away from this non-polar phase, favoring the stability of the ferroelectric structures that minimize the elastic and electrostatic penalties. As such, these diverse and tunable superlattices hold promise for various applications in thin-film ferroelectric devices.