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

当今场效应晶体管（fet）的高性能和相对较低的能量成本，是通过数十年来对电触点的优化实现的，这使得半导体通道的小型化达到了纳米级尺寸。然而，器件尺寸的减小会导致关闭状态下的功耗（漏电流）和其他统称为短通道效应的有害后果。新兴的半导体，如二硫化钼，是天然的原子薄，原则上可以减轻与短通道效应有关的几个问题。在具有原子薄体（ATB）通道的场效应管中，电荷载流子被限制在亚1nm厚的半导体内，因此栅极电压的施加均匀地影响所有载流子。这可以防止漏电流，并允许场效应管迅速打开或关闭。事实上，原子薄的块层材料的单个层可以被隔离，这就需要在二维半导体中没有悬垂键，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材料可能是通往未来节能电子产品的一条途径，这种电子产品可以使用当前的CMOS制造平台工作到毫伏。虽然2D半导体fet在解决短通道效应方面的优势是显而易见的，但由于高接触电阻，与最先进的硅和III-V半导体类似物相比，它们的性能仍然较低。为了获得超短通道（低于10nm节点）和隧道场效应管的优势，必须将接触电阻降低到量子极限。接触电阻作为一个严重的源扼流圈。这导致晶体管的性能下降，因为电流非常强烈地依赖于源注入点的有效栅极电压。金属与二维半导体之间的高接触电阻是其在高性能短通道电子器件中实现的主要障碍。该提案旨在开拓原子薄体（ATB）过渡金属二硫化物（TMD）半导体上的低电阻接触，以探索目前受不良接触限制的基本现象，并了解支撑短通道和隧道场效应晶体管行为的关键过程，从而实现具有前所未有的能源效率和性能的器件。该提案建立在我们最近在《自然》（2019年4月）上发表的ATB半导体的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大学对节能ICT主题材料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触点，这将使广泛的器件社区能够解决和克服在低维材料上制造良好电触点的长期挑战。拟议的工作将支持和影响与EPSRC几个优先领域一致的正在进行的计划和倡议。这包括使用微电化学电池和有机半导体和钙钛矿的低电阻触点来适应电池材料的操作特性。该提案旨在为基于ATB半导体的高性能电子产品提供低电阻触点，并建立国际领先的计划，这将增加价值并连接广泛的社区。拟议的工作将为实现基于ATB材料的新型设备的深入物理基础知识开辟新的途径，以加速其向技术准备和高附加值产品商业化的发展。

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.