Large-area electronics based on two-dimensional atomically thin materials

Novel forefront technological products such as, paper like displays, stretchable sensor skin, electronic textiles, and robotic sensors require high speed processing on unconventional form factor substrates, which can be bendable, flexible, stretchable and that they can assume different geometries. Therefore, field effect transistors with performances on a par with the wafer-based conventional electronics and at the same time flexible, compatible with sensitive substrates (plastic/rubber) are required. As the performance figures of FETs are intrinsically related to the ultimate electronic properties of the channel material and its interfaces, the need is to have materials responsive to all aforementioned demands.

At present, large area electronics on plastic and unusual format electronics use low performing materials such as organic conductors or metal oxide or alternatively newly emerging Si-like materials shaped into thin membranes, which are fabricated by multi step process exploiting the existing industry infrastructure with the related high costs. Graphene has been identified as a suitable electronic material for all kind of electronic technologies, owing to its mechanical, electrical, optical, chemical properties. Although graphene is the ideal material as a transparent electrode, it does not have a band gap hindering its use as a channel material. Here I propose studying a new range of 2D atomically thin materials, which share optical and mechanical properties of graphene, but in addition they are semiconducting with a band gap (1.1-1.9 eV).

Moreover, their high carrier mobility, uniquely distinguishes them from graphene as channel material for development of heterogeneous electronics. These materials are practically appealing as they offer realistic pathways to manufacture devices due to their 2 dimensional geometry facilitating integration, they do not have dangling bonds on the basal plane, allowing manipulation as individual particles in solution and they have unique mechanical features, with effects related to shape distortions and folding. Simultaneously, they present quantum and other size-dependent effects leading to a wealth of electronic, phonon dynamics and optical properties, not found in zero- and one-dimensional materials, offering opportunities to extend the frontiers of their applications to spintronics, photovoltaic, catalysis etc. The main objective is to demonstrate low-voltage n/p-type FETs operating in logic inverters, which are the elemental units of logic electronics.

Toward this end, the aim is to develop novel solution phase processing necessary to isolate monolayer flakes with preserved atomic and electronic structure, from their 3D counterpart and create stable inks of these platelets. These inks will be then exploited to establish a reliable array of scalable deterministic assembly techniques of the flakes onto any substrates in the form of highly uniform ultrathin films over large areas. These materials will be interfaced with the atomically thin organic dielectrics, which secure low-power operation. In addition both, 2D membranes as well as the organic components are transparent in the optical range due to their ultimately thin thickness leading to semitransparent devices.
The solution based processing at room temperature will ensure low cost manufacturing and compatibility with any plastic/rubber substrates, and reduction of energy employed for fabrication addressing also worldwide need for energy saving. The raw materials cost is also competitive in comparison with the existing materials for electronics. Overall the proposed research can lead to new economic benefits, extend the frontiers of the present electronic technology, and open new scenarios in fundamental science in respect to new quantum and other size-phenomena.

A vision for future electronics is to develop methods and materials that can enable high-performance circuits to be fabricated on unconventional substrates and geometries for paperlike displays, curvilinear electronics, electronic textile, stretchable solar cells, and biointegrated sensors. These technologies can have a huge impact in the society, revolutionising human-electronics interfaces and medical diagnostics. The vision is to overcome the commonly referred to as large-area electronics that traditionally presents lower performance figure than Silicon technology, to reach a wafer-like technology on flexible/stretchable substrates. The potential societal impact of the emerging Plastic Electronics and Conformal Electronics is enormous as reflected by predictions [IDTechEx (www.idtechex.com)] of growth for the global market from current $5bn in 2012 to over $300bn by 2027. However, at present there are no straightforward methodologies to produce materials with electrical characteristics comparable to silicon and that are also mechanically flexible/stretchable, inexpensive and, processable on polymeric substrates at temperature below 100 C. Here, I aim to develop foundational work on a new two-dimensional (2D) atomic materials system (WSe2, WS2, MoS2) which retains the facile solution processing commonly associated with organic electronics and concurrently presents Si-like electrical properties and mechanical flexibility, for use in large-area electronics on unconventional substrates/geometries. These materials are 2D atomically thin layers and share many properties with graphene, such as: high thermal stability, chemical inertness, transparency, mechanical flexibility high surface area, high carrier mobility, controllable doping. However, there is a key difference that underlies the novelty in this work and which is of critical importance; they are semiconductors with a band gap (1.1-1.9 eV).
This additional attribute will be exploited for the manufacturing of environmentally stable channel materials for field effect transistors (FET). Colloidal chemistry necessary to produce high yield of monolayer in solution with high structural and electrical quality to implement room temperature scalable deterministic deposition techniques onto flexible/stretchable substrates for integration in FETs will be developed. By the end of the project this technology will be implemented in prototype n/p-channel FET and logic inverters on flexible/stretchable substrates will be demonstrated. UK companies, many of which are already at the leading edge of plastic electronics, will benefit from opportunities to broaden their product portfolio overcoming the limited performance of the present technology. These new product families will support these companies to grow from leading technology companies to major manufactures, as well as creating a new UK position in 2D manufacturing routes for active electronic components on diverse substrates. The products, themselves, have the potential to become ubiquitous as they offer energy savings, due to the low-cost associated with room temperature processing, from material development to devices fabrication, and impact from health care to new ambient electronics. The development of new 2D atomic layers will also provide innovative products to UK chemicals manufacturers as ink feedstock materials allowing establishing worldwide suppliers from early stage of field development following the model of graphene. The highly innovative nature of the proposed research on a field, which is still at its infancy, gives extensive opportunities for patents. Lastly, the project will create a leading team that will complement the already present graphene expertise. The staff trained during the project, which will also benefit from the environment within the Centre for Plastic Electronics and London Centre for Nanotechnology, will be highly qualified to translate the emerging technologies into commercial opportunities.