Uncovering the atomic origins of thin film ferroelectricity

非技术摘要存储器是笔记本电脑和手机等消费电子产品的关键规格。例如，硬盘驱动器将信息存储为一系列“1”和“0”，这些“1”和“0”在物理上被实现为微小的磁铁。新的“铁电”材料可能会成为下一代数字存储的基础，而不是硬盘驱动器中的磁性材料。在这个项目中，研究小组使用先进的电子显微镜在原子水平上探测这些新材料的物理结构（原子在哪里）和电子结构（它们如何响应电场）之间的关系。该奖项资助的研究生和本科生将从事微电子器件制造和测试，并精通电子显微镜。这些技能可以直接应用于半导体行业。学生们不仅在加州大学洛杉矶分校的本土机构接受培训，而且还在诺福克州立大学和刘易斯堡学院的少数族裔服务机构接受培训，这是与美国国家科学基金会资助的材料研究和教育合作伙伴关系（PREM）合作的量子和纳米系统的教育和进步伙伴关系（PEAQS）的合作。技术总结：当以非常特殊的非平衡晶体状态制备时，铪（HfO2）可以表现出铁电性。诸如铪酸盐之类的材料在微处理器中已经很常见，并且是铁电场效应晶体管（fefet）和铁电随机存取存储器（FRAM）等新兴技术的基础。该团队制造了纳米级、电子透明的铁电铪离子器件，并在原位对铪离子进行热和电循环。这些刺激使沉积时呈无定形的铪通过其不同的结晶相。利用电子束感应电流（EBIC）成像和电子能量损失光谱（EELS）对每个相的半氟体进行成像，该团队产生了近原子分辨率的结构图、电子图和温度图。将这些地图与同时获得的运输数据相关联，可以提供这些活动的、可切换的设备的完整图像。特别是，在热和电循环之前和之后对电子特性的差分测量，使团队能够直接解决诸如铁电相的起源和稳定性等开放性问题。开发测量这些材料的电学和热学特性的技术有助于合理设计紧凑、低功耗和坚固的存储元件。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Summary Memory is a key specification in consumer electronics like laptop computers and cell phones. For instance, a hard disk drive stores information as a series of “1”s and “0”s that are physically realized as tiny magnets. Instead of the magnetic materials in hard disk drives, new “ferroelectric” materials might form the basis of next-generation digital storage. In this project the research team uses advanced electron microscopy to probe the relationships between physical structure (where the atoms are) and electronic structure (how they respond to electric fields) in these new materials at the atomic level. Graduate and undergraduate students sponsored by this award will perform microelectronic device fabrication and testing, and become proficient at electron microscopy. These skillsets are directly applicable in the semiconductor industry. Students are being trained not only at the home institution of UCLA, but also at the minority-serving institutions of Norfolk State University and Fort Lewis College via a collaboration with the Partnership for Education and the Advancement of Quantum and nanoSystems (PEAQS), which is part of the NSF-funded Partnership for Research and Education in Materials (PREM).Technical SummaryHafnia (HfO2), when prepared in a very specific, non-equilibrium crystalline state, can exhibit ferroelectricity. Materials such as hafnia specifically are already commonplace in microprocessors, and underlie the emerging technologies of ferroelectric field effect transistors (FeFETs) and ferroelectric random access memory (FRAM). The team fabricates nanoscale, electron-transparent ferroelectric hafnia devices, and cycles the hafnia thermally and electrically in situ. These stimuli bring the hafnia, which is amorphous as deposited, through its various crystalline phases. Imaging the hafnia in each phase with electron beam-induced current (EBIC) imaging and electron energy loss spectroscopy (EELS), the team produces near-atomic resolution structural, electronic, and temperature maps. Correlating these maps with transport data acquired simultaneously provides a complete picture of these live, switchable devices. In particular, differential measurements of electronic properties, both before and after thermal and electrical cycling, enable the team to directly address such open problems as the origin and stability of the ferroelectric phase. Developing techniques for measuring the electrical and thermal properties of such materials contributes to the rational design of compact, low-power, and robust memory elements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.