Incipient ferroelectrics based on hafnium oxide

铁电（FE）材料由于其非凡的介电，电光，热电和压电性能而引起了高度的技术兴趣。它们的应用领域从执行器和传感器到数据和能量存储。传统的铁电体通常具有所谓的Percent结构，并且是铁电复合氧化物，如作为最重要的例子之一的锆钛酸铅（PbZrxTi 1-xO 3，PZT）所证明的。这一发现特别令人惊讶，因为人们对HfO 2作为陶瓷材料以及半导体技术中的高介电常数陶瓷进行了大量研究。这种铁电性的起源仍然不清楚。提出了一种正交相Pca 21相来解释这种行为。到那时为止还不能提供实验证据。掺杂和机械应力进行了讨论，以潜在地占FE相的稳定。因此，实验和理论研究对齐沿着的工作假设，即纯HfO 2是一个初期的铁电体，可以克服固有的小障碍之间的帕拉和铁电状态促进上述杠杆。报告部分包含以下讨论：I）Pca 21相的稳定性和实验证明; II）不同制备方法的适用性，重点是成本效益高、灵活的化学溶液沉积; III）不同掺杂剂的表现和适应性; IV）先前仅稀疏地考虑HfO 2的场循环行为。扩展提案的目标是加深对铁电相的稳定以及对占基于HfO 2的薄膜中的场循环行为的机制的物理和理论理解。这对基础材料科学和未来应用都具有重要意义。拟议研究的起点是第一个资助期的研究结果，它允许明确识别系统HfO 2/ZrO 2的物理多尺度模型的相关因素。与经典的钙钛矿铁电体相比，特定方面旨在进行批判性讨论。这里，类比将是有益的，但也应该强调差异。工作包围绕以下子目标进行安排：I）理解表面能的影响; II）分析相变和极化反转; III）研究尚未使用的掺杂剂; IV）阐明氧空位的作用; V）计算出与经典钙钛矿铁电体的差异。

Ferroelectric (FE) materials are of high technological interest because of their extraordinary dielectric, electro-optic, pyro- and piezoelectric properties. Their fields of application range from actuators and sensors through to data and energy storage. Conventional ferroelectrics usually possess a so-called Perovskite structure and are comparably complex oxides as evidenced by lead zirconate titanate (PbZrxTi1-xO3, PZT) as one of the most important examples.Prior to the first funding period, the first observation of FE properties in 10 nm thin Si-doped HfO2 films was published by the applicants. This finding was especially surprising given the intense research devoted to HfO2 as ceramic material as well as for ultrathin high-permittivity dielectrics in semiconductor technology. The origin of this ferroelectricity remained unclear. An orthorhombic Pca21 phase was proposed to explain the behavior. The experimental proof could not be provided up to that point. Doping and mechanical stress were discussed to potentially account for the stabilization of the FE phase. Therefore, the experimental and theoretical investigations were aligned along the working hypothesis that pure HfO2 is an incipient ferroelectric which could overcome the inherently small barrier between the para- and the ferroelectric state promoted by the abovementioned levers. The report section contains a discussion of I) the stabilization and the experimental proof of the Pca21 phase; II) the suitability of different preparation methods with focus on the cost-efficient, flexible chemical solution deposition; III) the manifestation and aptitude of different dopants; IV) the previously only sparsely considered field cycling behavior of HfO2-based ferroelectrics.Goal of the extension proposal is to deepen the physical and theoretic understanding of the stabilization of the ferroelectric phase as well as of the mechanisms that account for the field cycling behavior in HfO2-based thinfilms. This is of outstanding relevance for both fundamental material science and future applications. Starting point for the proposed studies are the findings of the first funding period, which allowed a clear identification of relevant factors toward a physical multiscale model of the system HfO2/ZrO2. Particular aspects are intended to be critically discussed in comparison to the classic Perovskite ferroelectrics. Here, analogies will be helpful but also differences shall be emphasized. The work packages are arranged around the following subgoals: I) an understanding of the influence of surface energy; II) analysis of the phase transitions and the polarization reversal; III) study of dopants not utilized yet; IV) elucidation of the role of oxygen vacancies; V) working out the differences to classic perovskite ferroelectrics.