Low Resistance Contacts on Atomically Thin Body Semiconductors for Energy Efficient Electronics (LoResCon)

在今天的场效应晶体管(FET)中，以相对较低的能源成本实现了高性能，这是通过数十年来对电接触的优化实现的，这使得半导体通道可以小型化到纳米级。然而，器件尺寸的减小会导致关断状态下的功率损耗(泄漏电流)和其他有害后果，这些后果统称为短沟道效应。新出现的半导体，如MoS2，自然原子很薄，原则上可以缓解与短沟道效应有关的几个担忧。在原子薄体(ATB)沟道的FET中，载流子被限制在厚度小于1 nm的半导体中，因此栅极电压的施加对所有载流子的影响是均匀的。这可防止泄漏电流，并允许FET急剧导通或关断。原子薄的体层材料的各个层可以被隔离的事实使得2D半导体中没有悬挂键，这意味着表面粗糙度的影响被最小化。最近对场效应管的研究表明，这种ATB材料可能是通向未来能效电子产品的一条途径，这种电子产品可以使用目前的cmos制造平台运行到毫伏。虽然2D半导体FET在解决短沟道效应方面的优势是显而易见的，但与最先进的硅和III-V半导体类似物相比，由于高接触电阻，它们的性能仍然较低。为了获得超短沟道(低于10 nm节点)和隧道FET的优势，必须将接触电阻降低到量子极限。接触电阻是一个严重的源-扼流圈。这会导致晶体管性能的下降，因为电流强烈地依赖于源极注入点处的有效栅极电压。金属与2D半导体之间的高接触电阻是其在高性能短沟道电子学中实现的主要障碍。这项提议旨在率先在原子薄体(ATB)过渡金属二卤化物(TMD)半导体上开发低电阻触点，以探索目前因接触不良而受到限制的基本现象，目的是了解支撑短沟道和隧道场效应晶体管行为的关键工艺，从而实现具有前所未有的能效和性能的器件。该提议建立在我们最近在《自然》杂志(2019年4月)上发表的ATB半导体范德华接触方面的突破以及通过亨利·罗伊斯爵士研究所在剑桥对节能ICT材料主题的战略投资的基础上。我们的目标是在ATB半导体上实现低电阻接触，这将使广泛的设备社区能够解决和克服在低维材料上制造良好电接触的长期挑战。拟议的工作将巩固和影响与EPSRC若干优先领域相一致的正在进行的方案和倡议。这包括使用微电化学电池对电池材料进行操作中表征的低阻触点的调整，以及有机半导体和钙钛矿的低阻触点的调整。这项提议旨在带来一大变化，并在基于ATB半导体的高性能电子产品的低电阻触点方面建立一个国际领先的计划，这将增加价值并连接广泛的社区。拟议的工作将为深入了解基于ATB材料的新型器件的物理基础知识开辟新的途径，以加速它们朝着技术准备和更高附加值产品的商业化方向发展。

The high performance, at relatively low energy cost in today's field effect transistors (FETs), is achieved by decades long optimization of electrical contacts that has allowed the miniaturization of the semiconductor channel down to nanoscale dimensions. However, decreasing dimensions of the devices leads to power dissipation in the off state (leakage current) and other detrimental consequences that are collectively referred to as short channel effects. Emergent semiconductors, such as MoS2, that are naturally atomically thin can in principle mitigate several concerns related to short channel effects. In FETs with atomically thin body (ATB) channels, the charge carriers are confined within the sub 1nm thick semiconductor so that application of gate voltage influences all the carriers uniformly. This prevents leakage currents and allows the FETs to be sharply turned on or off. The fact that atomically thin individual layers of bulk-layered materials can be isolated necessitates the absence of dangling bonds in 2D semiconductors, which means that surface roughness effects are minimized. Recent research in FETs suggests that such ATB materials could be one pathway towards future energy efficient electronics that can operate down to milli volts using the current CMOS manufacturing platform. While the benefits of 2D semiconductor FETs in addressing short channel effects are obvious, they still possess lower performance compared to state-of-the-art silicon and III-V semiconductor analogues due the high contact resistance. To reap the benefits of ultra-short channel (sub 10 nm node) and tunnel FETs, contact resistances must be reduced down to the quantum limit. The contact resistance acts as a severe source-choke. This leads to degradation in the performance of the transistor, because the current depends very strongly on the effective gate voltage at the source injection point. The high contact resistance between metals and 2D semiconductors is a major barrier to their implementation in high performance short channel electronics. This proposal aims to pioneer low electrical resistance contacts on atomically thin body (ATB) transition metal dichalcogenide (TMD) semiconductors to enable the exploration of fundamental phenomena that is currently limited by poor contacts - with the motivation to understand key processes that underpin the behavior of short channel and tunnel field effect transistors so that devices with unprecedented energy efficiency and performance can be realized. The proposal builds on the our recent breakthrough on van der Waals contacts on ATB semiconductors published in Nature (April 2019) and strategic investments in the Materials for Energy-Efficient ICT theme at Cambridge through the Sir Henry Royce Institute. Our ambition is to realize low resistance contacts on ATB semiconductors that will allow a broad range of device communities to address and overcome the long-standing challenge of making good electrical contacts on low dimensional materials. The proposed work will underpin and impact ongoing programmes and initiatives aligned with several EPSRC priority areas. This includes adaptation of low resistance contacts for in operando characterization of battery materials using microelectrochemical cells and low resistance contacts for organic semiconductors and perovskites. This proposal aims to bring a step-change and establish an internationally leading programme in low resistance contacts for high-performance electronics based on ATB semiconductors that will add value and connect a broad range of communities. The proposed work will open up new pathways for achieving in-depth fundamental knowledge of physics of novel devices based on ATB materials to accelerate their development towards technological readiness and commercialization in higher value-added products.