Ferroelectric HfO2 on Germanium Tunnel Junctions Towards Sub-Femto Joule Switching

移动设备和计算机产生的数据的快速增长需要研究和开发先进的固态数据存储技术。在某些材料中出现的铁电效应，即可切换的极化电荷，与先进的存储器件概念相结合，为实现非易失性存储技术的变革性改进提供了一种有前途的方法。2011年在无铅二氧化汞薄膜中发现了铁电性，为下一代可制造、低功耗和高性能的非易失性存储铁电器件的进一步扩展提供了可持续的途径。在这个项目中，一种先进的器件概念被称为铁电隧道结(FTJ)，它将使用铁电二氧化汞薄膜进行研究。在FTJ中，通过切换极化方向(内部电场)在低和高值之间切换隧道电阻。数值研究表明，基于二氧化汞的FTJ可以大幅减少存储数据所需的功率。通过双管齐下的方法，将通过实验和数值模拟来检验数值模型，并促进对使用HfNO2薄膜的非易失性FTJ存储技术的基本理解和最新技术。该项目的首要目标是了解和定制薄膜电容器中HfNO2铁电相的原子结构，从而实现互补的金属氧化物半导体(CMOS)兼容FTJ。对HfO2基铁电薄膜的沉积和加工条件进行全面和方法学的研究，将对影响铁电性能的杂质、掺杂、薄膜生长和热处理温度以及界面稳定性的影响提供重要的见解。这些研究将为研究铁电二氧化汞薄膜的物理极限以及实现与CMOS兼容和可扩展的FTJ铺平道路。最近对掺杂浓度的宏观变化以及混合单层掺杂在二氧化汞中的原子分层的研究表明，微调掺杂二氧化汞薄膜的铁电性能是非常有可能的。通过仔细的理论和实验研究相结合的方法，发现了与CMOS兼容的可伸缩铁电材料HfO_2，为研究COS兼容Hf_2O_2 FTJ的性能潜力提供了一个难得的机会。数值研究表明，当特征尺寸为F=20 nm时，在Ge衬底上的铁电HfO2 FTJ可以接近亚飞托焦耳/比特。这种通过实验调节不同厚度的铁电薄膜特性的能力，结合先进的从头计算材料和器件模拟，使我们能够研究在Ge上使用铁电HfO2的FTJ器件的性能极限。

The rapid increase in data generated by mobile devices and computers necessitates research and development of advanced solid-state data storage technologies. The ferroelectric effect, a switchable polarization charge, which occurs in certain materials combined together with an advanced memory device concept provides a promising approach to achieve a transformative improvement in non-volatile memory technologies. The discovery of ferroelectricity in lead-free hafnium dioxide thin films in 2011 offers a sustainable route for further scaling of the next generation of manufacturable, low-power, and high performance nonvolatile memory ferroelectric devices. In this project, an advanced device concept known as a ferroelectric tunnel junction (FTJ) will be investigated using the ferroelectric hafnium dioxide thin films. In a FTJ, the tunneling electroresistance is switched between a low and a high value by switching the polarization direction (internal electric field). Numerical studies indicate that the hafnium dioxide-based FTJ can yield substantial reductions in the amount of power required to store data. In a two-pronged approach, experiments and numerical modeling will be conducted to test the numerical models and to advance the fundamental understanding and state-of-the-art in nonvolatile FTJ memory technology using hafnium dioxide thin films.The overriding goal of the project is to understand and tailor the atomic structure of the ferroelectric phase of hafnium dioxide in thin film capacitors, thereby enabling complementary metal-oxide-semiconductor (CMOS)-compatible FTJs. A comprehensive and methodological study evaluating the deposition and processing conditions of hafnium dioxide-based thin film ferroelectrics will provide critical insights about the effect of impurities, dopants, film growth and annealing temperatures, and interfacial stability that influence the ferroelectric properties. These studies will pave the way toward investigating the physical limits of ferroelectric hafnium dioxide-based films and the realization of CMOS-compatible and scalable FTJs. Recent studies on macroscopic variation of the dopants concentration as well as the atomic layering of mixed mono-layers of dopants in hafnium dioxide suggest extreme possibilities in fine-tuning ferroelectric properties of doped hafnium dioxide thin films. The discovery of CMOS compatible and scalable ferroelectric hafnium dioxide offers a unique opportunity to investigate the performance potential of CMOS compatible hafnium dioxide FTJ through carefully coupled theoretical and experimental investigation. Numerical studies indicate that ferroelectric hafnium dioxide FTJ on germanium substrate can approach sub-femto Joule/bit for a feature size of F=20nm. This ability to experimentally tune the characteristics of the ferroelectric hafnium dioxide thin films of varying thickness coupled with advanced ab initio material and device simulation enable this investigation of the performance limits of FTJ devices employing ferroelectric hafnium dioxide on germanium.