Electrochemically Gated Single Molecule FETs

Moore's Law, the observation that the number of components that can be placed on a silicon chip approximately doubles every two years, with commensurate increases in the processing and data storage capacities of devices, and decreases in the unit cost of components, has driven technological achievement and new materials science for 40 years. Devices featuring <45 nm feature sizes are now in production, and close-to-market chips with 22 nm feature sizes are being disclosed. However, to achieve these remarkable device sizes, top-down scaling is giving way to more complex and lithographically challenging 3-D designs, and conventional materials superseded. Although 'More Moore' remains an important driver for the semiconductor industry, the concept of 'More than Moore', in which added value is packaged into devices by adding functionalities that themselves do not necessarily scale in line with Moore's Law is growing as a design strategy. The integration of smaller and faster device technology with innovative total systems packaging is now seen as the most feasible route to improve device performance, recognising the increasing difficulties in following traditional top-down scaling. With or without More than Moore augmentation, if pace of electronic device development is to continue along a Moore's Law projection in the longer-term further reductions in feature size will be required. Two consequences flow from this proposition. The first is that, in the medium-long term, feature sizes will approach molecular dimensions. The second, more practical and more immediate consequence, is that new materials must now be integrated into silicon-based devices. In the present generation 45 nm chips , a SiO2 gate would be so thin as to leak too much current when the transistor is in the 'off' state. This problem was recognised, and the solution (a high-dielectric alternative insulator) apparent, long before the exact materials solution was conceived. HfO2 is now used as the transistor gate insulator despite the technical challenges inherent in depositing HfO2, a highly refractory and expensive material. Thus, while 'molecular electronics' is commonly perceived to be very difficult to implement, the continued development of 'traditional' silicon technology also faces profound and difficult challenges, which industry adapts to meet.

The term 'molecular electronics' is generally applied to structures designed to involve a single molecule, a small bundle of molecules, or a single layer of molecules, oriented between two contacts (which may be metals or semiconductors), with the critical dimension between the contacts therefore lying in the nanometer size range. Circuit components at the molecular level could exploit the small size of molecules and their enormous potential variation in structure and properties, controlled using the tools of synthetic chemistry, to increase device density and to incorporate new functionality into existing or new microelectronic architectures. Primary objectives in this research phase are (a) to identify classes of molecular materials, and their contacts, which display promising attributes for molecular electronics, (b) to identify and understand mechanisms by which the electrical properties can be exploited, (c) to further develop defined metrological techniques for reliably determining the electrical behaviour of molecular devices. To convey future practical relevance our focus will be on room temperature operation and condensed matter interfaces.

Organic electronics exploits the bulk properties of organic materials to achieve useful electronic function, for instance in polymer LEDs, an area in which in the UK is world-leading. Molecular electronics, in which small ensembles of molecules perform distinct electronic functions, is at a much earlier stage, a point highlighted by the International Roadmap on Semiconductors (ITRS). The Roadmap, which is followed closely by academics and cutting-edge industrialists working towards the next generation of electronic device platforms, has identified "Molecular State Device Materials" as attractive candidates for application in the next generation of sub-20 nm devices.

The microelectronics industry has evolved over the last 50 years in a spectacular manner though the continuous development of semiconductor fabrication technologies and is a key long-term (>10 years) beneficiary of molecular electronics research. The use of molecules within these platforms is clearly a major departure off this track. For this reason any first technological breakthroughs are likely to come through the deployment of molecular components within well-established semiconductor micro-fabrication technologies, where molecules might lend new electronic characteristics. The microelectronics industry has a long track record of using wet-chemical processes (e.g. silicon etching, photoresist processing, electroplating etc.) providing a viable route to the integration of molecular-scale electronic technologies into processing streams. Nevertheless, this integration of molecules into semiconductor devices will require difficult technological challenges to be overcome and much groundwork, primarily in universities since applications are currently too far from market. Through the present project we aim to demonstrate viable device behaviour with an electronically active molecular component in line with ITRS technology milestones.

The communication of new results will help build awareness of the field of molecular electronics in related areas of science and technology (sensors, electrochemistry, surface science, etc.) with technologists and with the general public. Since molecular electronics is at an earlier development stage than related technologies, such as organic electronics, it is important to engage actively with possible industrial beneficiaries to explore potential impact. The investigators have experience in both academic publication and the translation of academic results to industrial settings. For example, Higgins has a series of patented discoveries concerning detector and sensor technology, catalysis and organic materials with Merck Chemicals (Chilworth) and Philips (Eindhoven). In collaboration with Akzo Nobel Coatings in (Sassenheim, NL) Hartl has a worldwide patent for novel catalysts of oxidative drying of alkyd paints, and has contributed to development of new detergents in collaboration with Unilever Research Laboratory (Vlaardingen, NL). Low has supervised industry sponsored PhD students with Avecia Ltd (hole transport materials) and Sony MSL (LCD technology). The independent knowledge transfer team at Chemistry Innovation (the Knowledge Transfer Network, KTN) helps develop and manage collaborative research projects with UK industries, whilst each of the partner institutions has an administrative unit devoted to Business, Innovation and Exploitation of research results, offering legal and business support to academic researchers to aid collaboration with industry and develop new commercial opportunities.

In addition to longer term (>10 year) industrial benefit, the project will directly benefit the early career researchers who will be appointed, as their specific and generic training (e.g. synthetic chemistry/STM/spectroelectrochemistry) and experience will help develop the skills necessary to contribute to development of commercial opportunities in molecular electronics and related areas of chemical science in the UK economy.