Integrated graphene - based sensor devices via scalable microfabrication process development based on graphene - metal multilayer deposition

In spite of its challenging properties, the utilization of graphene for technical applications still demands considerable efforts in developing dedicated processing methods, which have a potential to be adapted and finally utilized for industrial scale device manufacturing. Among the processes which have been investigated so far, chemical vapour deposition of graphene on copper, where copper acts as a catalyst to facilitate the growth of single layered graphene - appears to be one the most promising approaches. Although extensively studied, there are issues with this process related to quality, reproducibility and yield, which are connected to the lack of control of the interface between copper and graphene. Within the process, which we will be able to tackle these issues in a more controllable way by a combined in-situ deposition system, where copper and other possible metals are deposited within one vacuum system together with the graphene CVD, i.e without exposing the sample to an ambient environment. Like for 2D Ga-Al-As semiconductor heterostructures, the control of the interfaces on an atomic length scale by means of an in-situ multilayer deposition process is expected to be the pathway which will enable the ultilization of graphene's unqiue properties within manufacturable device structures.

In spite of this potential, we feel the full integration of graphene into CMOS technology, although being extremely challenging on the long term - still has a very long way to go and may even be impossible without fundamentally different processing approaches. However, sensor technologies as a whole are mostly based on hybrid solutions, where the sensor itself - even chip based in some cases - is still separated from the CMOS digital electronic by flip chip, wire bonding or simple by conventional wiring. A widely used example of high indutrial impact are piezoelectric sensors, where the high processing temperature of the lead-zirconium-titanate ceramics are incompatible with CMOS processing conditions.

Based on this philosophy, we believe that the in-situ growing approach for metal-graphene multilayers, as envisaged to be developed within this project, will enable a significant improvement of existing sensor concepts and the realization and manufacturing of new sensor concepts. Based on the expertise of our scientific partners within Imperial College and NPL and our associated partners from industry, we will focus on biosensor applications, where graphene - as carbon based material - is particularly challenging as bio-interface. As - from the point of view of process technology -the most simple approach, graphene coated copper electrodes will have a potential for radiofrequency - microwave - terahertz biosensor, where copper will outperform gold due to lower conduction losses and graphene provides the interface to the biomolecules and cells. As a second step on a scale of increasing complexity of process technology, we believe that a sacrificial layer process for arbitrary shaped free standing graphene membranes and (sub)micro scale flexural beam is a realistic development goal. This technology will enable the development of arrays of nanomechanical sensors, based on the exceptional mechanical properties of graphene. Apart from sensor applications, graphene- based NEMS structures are challenging objects for the refinement and exploration of metrology for nanotechnology and biology, as being pursued by our collaborators from NPL.

The recently discovered confined plasmon-polariton excitations - originating from the unique electronic properties of graphene - are currently one of the hottest topic within the graphene research community. We believe, that the tailored free standing structures we will be able to manufacture with this deposition kit, will pave the way to explore and finally utilize this unique optical - infrared properties of graphene for novel sensor applications.

The proposal aims to develop a wafer scalable deposition technology for graphene based multilayers for industrial scale manufacturing of integrated sensor devices. As such, we are clearly addressing the most promising technological approach based on a combination of metal electron beam deposition and plasma enhanced chemical vapour deposition within one ultrahigh vacuum system, which is expected to enable the realization and finally the commercialization of graphene-based sensor products. This will open up the huge potential of graphene, in terms of its unique optical, electrical, and mechanical properties, for exploitation, putting the UK in a competitive position at a time when major international funding drives (e.g. Horizon 2020) have started to target graphene. Within the current work, we are targeting specifically transition towards the biosensors market, with its huge growth potential in areas such as healthcare, point-of-care monitoring, and environmental sensing.

In partnership with Agilent Technologies, which is currently expanding their life science business, and world class biosensor groups at universities within the UK and Europe, we will explore the potential of graphene-based biosensors based on the 3 most established sensor concepts: rf impedance spectroscopy, micro/nanomechanical sensor structures and optical / IR sensors based on plasmon-polariton excitations.

Beyond these established sensor approaches, we will investigate planar microwave transmission line microwave resonators based on functionalized graphene-coated patterned copper structures for possible sensor applications in partnership with EMISENS / Link Microtek ltd, based on the PI's successful development of the bottle scanner EMILI 2. Moreover, with NPL as partner we intend to look into graphene-based NEMS technology for applications in metrology.

It is very important that the deposition cluster system, which will be purchased by means of the requested funding, and the processes which will be developed and optimized for graphene films, free standing structures and devices, are carefully assessed in term of reproducibility, yield and scalability throughout the project, in order to establish impact on industrial manufacturing processes early on in the project.

During and after this project, we will utilize our unique technology to develop dedicated research proposals addressing specific biosensor applications - together with our academic and industry partners.