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

移动设备和计算机产生的数据迅速增加，需要研究和开发先进的固态数据存储技术。铁电效应，一种可切换的极化电荷，发生在某些材料中，与先进的存储设备概念结合在一起，为实现非易失性存储技术的革命性改进提供了一种有前途的方法。2011年在无铅二氧化铪薄膜中发现铁电性，为进一步扩大下一代可制造、低功耗和高性能非易失性存储器铁电器件的规模提供了一条可持续的途径。在本项目中，将使用铁电二氧化铪薄膜研究一种称为铁电隧道结（FTJ）的先进器件概念。在FTJ中，隧穿电阻通过改变极化方向（内部电场）在高、低值之间切换。数值研究表明，基于二氧化铪的FTJ可以大大降低存储数据所需的电量。在一个双管齐下的方法，实验和数值模拟将进行测试的数值模型和推进基本的理解和最先进的非易失性FTJ存储技术使用二氧化铪薄膜。该项目的首要目标是了解和定制薄膜电容器中二氧化铪铁电相的原子结构，从而实现互补金属氧化物半导体（CMOS）兼容的ftj。一项评估二氧化铪基铁电薄膜沉积和加工条件的全面和方法研究将提供有关杂质、掺杂剂、薄膜生长和退火温度以及界面稳定性对铁电性能影响的关键见解。这些研究将为研究铁电二氧化铪薄膜的物理极限和实现cmos兼容和可扩展的ftj铺平道路。近年来对掺杂剂浓度的宏观变化和二氧化铪中掺杂剂混合单层的原子分层的研究表明，掺杂二氧化铪薄膜的铁电性能有极好的微调可能性。CMOS兼容和可扩展铁电二氧化铪的发现为通过仔细耦合的理论和实验研究CMOS兼容二氧化铪FTJ的性能潜力提供了一个独特的机会。数值研究表明，在特征尺寸为F=20nm的锗衬底上，铁电二氧化铪FTJ可以接近亚飞焦耳/位。通过实验调整不同厚度的铁电二氧化铪薄膜的特性，再加上先进的从头算材料和器件模拟，使得研究在锗上使用铁电二氧化铪的FTJ器件的性能极限成为可能。

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.