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

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.

The recent report by Committee on Climate Change recommended that the UK commit to net zero carbon emission by 2050. A key consumer of energy is electronics - accounting for consumption of nearly 10% of the total generated energy and likely to grow in the coming decade to approximately 20%. A recent Foresight report has highlighted the importance of novel materials and devices for meeting the broad industrial and societal energy needs. Our work will create such new materials and energy efficient electronics using industrially relevant processes to leverage significant impact in strategic areas such as Energy, Quantum Technologies, Information and Communication Technologies (ICT), the Internet of Things (IoT), batteries. catalysis, ultra-precision manufacturing, with a return for UK plc, in innovation and exploitation. The long term impact of our project will be significant because it underpins important future developments in quantum materials, metrology of ideal metal-semiconductor interfaces, electronics and other diverse applications.

Our project addresses key questions pertinent to industrial materials development for transition metal dichalcogenide (TMD) ATB semiconductors, in particular development of low-cost, scalable, reproducible synthesis and CMOS compatible fabrication process for device integration. This will allow development of pathways for their industrial exploitation, and to enable commercial dividends to be paid on the substantial investment that the UK has already made in low dimensional materials research. Our proposal covers the whole value chain and we bring together market-leading industrial partners (Aixtron and Cambridge Microelectronics) and key stakeholder such as NPL and national programmes such as SHRI, hence supporting the whole developing market. Our partner companies will directly benefit from the research results and will be natural exploitation pathways. Industrially relevant TMD growth processes and target applications will open new opportunities and markets for Aixtron UK and new device concepts will be integrated to platforms designed by Cambridge Microelectronics. We infer that the technology IP created will yield long-term economic benefits to the UK that will multiply and grow with time. The realization new ATB semiconductors and processes for their implementation into high performance electronics will provide a particularly fertile ground for creating of intellectual property and generation of spin-out companies, and help to sustain the world-leading innovation, resilience and competitiveness of UK science parks, incl. the Cambridge Cluster of Companies that support more than hundred thousand jobs across the UK.

The societal impact of our project will be significant and long lasting through the development of wide range of applications of low electrical resistance contacts and novel ATB semiconductors, particularly in new form factors in life style energy efficient electronics, long lasting batteries with low series resistance, secure and faster communication technology, mass sensing applications in healthcare, security and environmental protection, new energy generation and storage solutions, and development of technologies which will benefit the nation's health through reductions in harmful emissions over the coming decades. Our proposal targets new type of devices that operate at exceptionally low power to enable sustainable electronics. These devices have significant potential to help reducing the carbon footprint of our society and assist policy-makers and government agencies in meeting internationally-agreed ambitious emissions obligations and in building a sustainable economy to tackle pressing long-term challenges such as climate change.