Lenox Megan K, Islam Md Rafiqul, Hoque Md Shafkat Bin, Skidmore Chloe H, Salanova Alejandro, Fields Shelby S, Jaszewski Samantha T, Maria Jon-Paul, Hopkins Patrick E, Ihlefeld Jon F
Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, United States.
Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904, United States.
ACS Appl Mater Interfaces. 2024 Dec 18;16(50):69588-69598. doi: 10.1021/acsami.4c15934. Epub 2024 Dec 3.
The discovery of ferroelectricity in hafnia based thin films has catalyzed significant research focused on understanding the ferroelectric property origins and means to increase stability of the ferroelectric phase. Prior studies have revealed that biaxial tensile stress via an electrode "capping effect" is a suspected ferroelectric phase stabilization mechanism. This effect is commonly reported to stem from a coefficient of thermal expansion (CTE) incongruency between the hafnia and top electrode. Despite reported correlations between ferroelectric phase fraction and electrode CTE, the thick silicon substrate dominates the mechanics and CTE-related stresses, negating any dominant contribution from an electrode CTE mismatch toward the capping effect. In this work, these discrepancies are reconciled, and the origin of these differences deriving from electrode elastic modulus, not CTE, is demonstrated. Pt//TaN/HfZrO/TaN/Si devices, where is platinum, TaN, iridium, tungsten, and ruthenium, were fabricated. Sin(ψ)-based X-ray diffraction measurements of biaxial stress in the HZO layer reveal a strong correlation between biaxial stress, remanent polarization, and electrode elastic modulus. Conversely, a low correlation exists between the electrode CTE, HZO biaxial stress, and remanent polarization. A higher elastic modulus enhances the resistance to electrode elastic deformation, which intensifies the capping effect during crystallization, and culminates in the tandem restriction of out-of-plane hafnia volume expansion and preferential orientation of the polar -axis normal to the plane. These behaviors concomitantly increase the ferroelectric phase stability and polarization magnitude. This work provides electrode material selection guidelines toward the development of high-performing ferroelectric hafnia into microelectronic devices, such as nonvolatile memories.
基于氧化铪的薄膜中铁电性的发现推动了大量研究，这些研究聚焦于理解铁电性能的起源以及提高铁电相稳定性的方法。先前的研究表明，通过电极“盖帽效应”产生的双轴拉伸应力是一种疑似铁电相稳定机制。据普遍报道，这种效应源于氧化铪与顶部电极之间的热膨胀系数（CTE）不一致。尽管有报道称铁电相分数与电极CTE之间存在相关性，但厚硅衬底主导了力学和与CTE相关的应力，从而消除了电极CTE不匹配对盖帽效应的任何主要贡献。在这项工作中，这些差异得到了调和，并证明了这些差异源于电极弹性模量而非CTE。制备了Pt//TaN/HfZrO/TaN/Si器件，其中 分别为铂、氮化钽、铱、钨和钌。基于Sin(ψ)的HZO层双轴应力X射线衍射测量揭示了双轴应力、剩余极化和电极弹性模量之间的强相关性。相反，电极CTE、HZO双轴应力和剩余极化之间的相关性较低。较高的弹性模量增强了对电极弹性变形的抵抗力，这在结晶过程中增强了盖帽效应，并最终导致面外氧化铪体积膨胀的串联限制以及极轴垂直于平面的优先取向。这些行为同时提高了铁电相稳定性和极化幅度。这项工作为将高性能铁电氧化铪开发成微电子器件（如非易失性存储器）提供了电极材料选择指南。
