Scientists from NPL, in collaboration with Instituto Nazionale di Ricerca Metrologica (Italy), Graphenea SA (Spain), Das-Nano (Spain), delivered the EMPIR Grace project with the aim of developing novel metrology for electrical characterisation of graphene, to enable standardisation electrical measurements of future graphene-based electronics.
Graphene has become the focus of extensive research efforts to harness the potential for disruptive applications. Advances in manufacturing mean that the material can now be produced on a wafer scale up to 6’’. To harness the opportunity for the development of next generation graphene-based electronic components using wafer scale materials, electrical characterization of graphene is imperative and requires the measurement of work function, sheet resistance, carrier concentration and mobility on a variety of scales (i.e. macro-, micro- and nano-scale).
The Industry pull to incorporate graphene in RF electronics, integrated circuits and optoelectronics has triggered manufacturing progress for the scale up of production. However, in this emerging industry there is a lack of standardised electrical measurements to extract useful parameters such as carrier concentration, mobility and sheet resistance, all of which are often presented as figures-of-merit of the graphene quality.
In recognition of the challenges posed, a consortium of National Measurement Institutes, Universities and Industries ( producing both the material and the advanced instrumentation) worked together to collaboratively deliver the EMPIR Grace project with the aim of developing novel metrology for electrical characterisation of graphene, to enabling standardized electrical measurements of future graphene-based electronics.
Currently, the most widely used method for electrical characterisation are slow, requiring off-line measurements. The method is not suitable for high throughput characterisation and often the measured graphene is significantly altered due to contamination associated with the microfabrication processes. Commercial applications of graphene require fast and large-area mapping of electrical properties, rather than obtaining a single point value, which should be ideally achieved by a contactless measurement technique.
The consortium developed a comprehensive and metrologically accurate methodology for measurements of the electrical properties of graphene that ranges from nano- to macro- scales, while balancing the acquisition time and maintaining the robust quality control and reproducibility between contact and contactless methods. The results exhibit excellent agreement between the different techniques. A further outcome of the research is the need for standardized electrical measurements in highly controlled environmental conditions and the application of appropriate weighting functions.
The impact of this research has been to bring together the emerging supply chain to understand the challenges for the scale up of production and trial new Quality Control instrumentation against precision laboratory measurements This paper marks significant progress not only for the EMPIR GRACE project but also for the emerging industry. As the next step, the consortium will release two metrological best practice guides for electrical measurements of graphene.
To read the article in full : https://www.nature.com/articles/s41598-020-59851-1
To learn more about EMPIR GRACE: http://empir.npl.co.uk/grace/
23 Mar 2020