Resonant Tunnel Field Effect Transistors Based on Vertical 2D Crystal Heterostructures

这项拟议的跨学科研究结合了二维(2D)材料、大脑启发的网络计算和共振隧道二极管(RTD)的进步，创造了一个新的器件概念：2D共振隧道场效应晶体管(RTFET)。基于2D晶体的RTFET将解决III-V半导体RTD的晶格匹配/位错问题。这些设备中强大的负差分电阻和高频响应将被用于图像识别应用中执行类似于神经元突触的“比较”功能。基于RTFET的突触与传统的基于互补金属氧化物半导体(CMOS)的电路相比，可以潜在地降低能源消耗十倍以上。RTFET的超高工作频率将使其在高速无线通信、太赫兹成像和光谱学中得到应用。此外，RTFET还可以作为探测2D/2D界面的灵敏工具，为2D异质结构中的面外输运提供科学的见解。这一研究项目不仅将推进二维晶体、共振隧道器件和类脑电路中的量子隧道效应的知识，而且将对图像识别、非传统计算和高频无线通信产生直接的技术影响。将这项研究与小学课外计划、本科生/研究生新课程以及招收/留住女性学生相结合，将培养学生对纳米技术的兴趣，同时扩大他们的知识基础，从而对世界级和多样化的科学技术工作者的教育产生积极而持久的影响。本项目的目标是了解2D垂直异质结构中的层间共振隧道效应，并展示在室温下具有明显负微分电阻的高速RTFET，用于神经突触图像识别应用。PI将进行以下四项工作：(1)制备各种垂直二维异质结，包括黑磷/氮化硼/黑磷，二硒化钨/二硫化钼/二硒化钨异质结，并精确控制旋转角和层数；(2)评估旋转角度、带偏移、隧道势垒厚度和界面质量对垂直二维异质结中共振隧道电流的影响；(3)展示在室温下具有明显负阻的高速RTFET；(4)展示基于2D RTFET的突触，作为用于图像识别的神经突触芯片的基本元件。该项目的成功实施将扩大在2D异质结构、共振隧道器件和神经网络计算中的共振量子隧道的知识。更具体地说，这项研究将阐明旋转角排列、能带极值位置、带隙和能带偏移对RTFET中层间共振隧穿的影响。这也将提供对由于RTFET中的界面陷阱和缺陷而引起的非弹性隧道和散射的洞察。本研究对二维异质结中的共振隧穿有了基本的认识，这将使基于平面外输运的新型纳米电子器件能够取代传统的二维晶体的面内输运。这项研究还将为超越CMOS的新功能器件铺平道路，并提供基于RTFET的神经网络电路的实验演示。RTFET的负差分电阻和快速响应可能使一种超越传统冯·诺伊曼体系结构的新计算范式成为可能。

The proposed interdisciplinary research combines advances in two dimensional (2D) materials, brain-inspired network computing, and resonant tunnel diodes (RTDs), to create a new device concept: 2D resonant tunnel field-effect-transistor (RTFET). RTFETs based on 2D crystals will solve the lattice matching/dislocation issues of III-V semiconductor based RTDs. The strong negative differential resistance and high frequency response in these devices will be used to perform "comparison" functions, similar to synapses in neurons, for image recognition applications. RTFET-based synapses can potentially reduce energy consumption by more than ten times compared to the circuits based on traditional complementary metal-oxide-semiconductor (CMOS). The ultra-high operating frequencies of RTFETs will enable their applications in high speed wireless communication, THz imaging, and spectroscopy. In addition, RTFETs can also serve as sensitive vehicles to probe 2D/2D interfaces, providing scientific insights on the out-of-plane transport in 2D heterostructures. This research project will not only advance the knowledge of quantum tunneling in 2D crystals, resonant tunneling devices, and brain-like circuits, but also have direct technology impact on image recognition, non-traditional computing, and high frequency wireless communications. The integration of the proposed research with after-school programs in elementary schools, new courses for undergraduate/graduate students, and recruiting/retaining women students, will foster students' interest in nanotechnology while broadening their knowledge base, thus having a positive enduring impact on the education of a world-class and diverse science and technology workforce.The objective of this project is to understand the interlayer resonant tunneling in 2D vertical heterostructures and demonstrate high speed RTFETs with pronounced negative differential resistance at room temperatures for neurosynaptic image recognition applications. The PI will pursue the following four thrusts: (1) fabrication of a variety of 2D vertical heterostructures, including black phosphorus/boron nitride/black phosphorus, tungsten diselenide/molybdenum disulfide/tungsten diselenide heterostructures, with precise control of rotation angles and layer numbers; (2) evaluate the impact of rotation angle, band offsets, tunneling barrier thickness, and interface qualities, on the resonant tunneling currents in the vertical 2D heterostructures; (3) demonstrate high speed RTFETs with pronounced negative differential resistance at room temperatures; (4) demonstrate synapses based on 2D RTFETs, as basic elements in neurosynaptic chips for image recognition applications. The successful execution of this project will expand the knowledge of resonant quantum tunneling in 2D heterostructures, resonant tunneling devices, and neural-network computing. More specifically, this research will elucidate the effect of rotation angle alignment, band extrema location, bandgap, and band offsets on the interlayer resonant tunneling in RTFETs. This will also provide insight into inelastic tunneling and scattering due to interface traps and defects in RTFETs. The fundamental understanding of the resonant tunneling in 2D heterostructures gained in this research project will enable a new class of novel nanoscale electronic devices based on out-of-plane transport instead of the traditional in-plane transport of 2D crystals. This research will also pave the way for new functional devices beyond CMOS and provide an experimental demonstration of neural-network circuits based on RTFETs. The negative differential resistance and fast response in RTFETs can potentially enable a new computing paradigm beyond the traditional von Neumann architecture.