Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

Christos Melios,Nathaniel Huang,Oihana Txoperena,Amaia Zurutuza,Luca Callegaro,Sergiy Rozhko,Albert Redo-Sanchez,Alex Lopez,Olga Kazakova,Vishal Panchal,Alessandro Cultrera,Alvaro Cordon,Israel Arnedo,David Etayo,Alba Centeno,Montserrat Fernandez

doi:10.1038/s41598-020-59851-1

Abstract

Graphene has become the focus of extensive research efforts and it can now be produced in wafer-scale. For the development of next generation graphene-based electronic components, electrical characterization of graphene is imperative and requires the measurement of work function, sheet resistance, carrier concentration and mobility in both macro-, micro- and nano-scale. Moreover, 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. We demonstrate a comprehensive 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 electrical characterisation is achieved by using a combination of techniques, including magneto-transport in the van der Pauw geometry, THz time-domain spectroscopy mapping and calibrated Kelvin probe force microscopy. The results exhibit excellent agreement between the different techniques. Moreover, we highlight the need for standardized electrical measurements in highly controlled environmental conditions and the application of appropriate weighting functions.

Highlights

Graphene has become the focus of extensive research efforts and it can be produced in waferscale
The already happening use of graphene in RF electronics[12], integrated circuits[13] and optoelectronics[14] has triggered impressive progress in large-scale production, the community still lacks standardised electrical measurements to extract useful parameters such as carrier concentration, mobility and sheet resistance, all of those are often presented as figures-of-merit of the graphene quality
In contrast to the conventional Hall effect, where device fabrication is required for carrier concentration and mobility measurements, the van der Pauw method only requires thin uniform samples with relatively small Ohmic contacts[26]

Summary

Introduction

Graphene has become the focus of extensive research efforts and it can be produced in waferscale. The most widely used method for electrical characterisation involves magneto-transport measurements in lithographically patterned Hall bars to extract carrier concentration, mobility and resistance. This method is not suitable for high throughput characterisation and often the measured graphene is significantly altered due to the microfabrication processes, in which case the electrical properties of the pristine transferred graphene are different from the ones measured. In contrast to the conventional Hall effect, where device fabrication is required for carrier concentration and mobility measurements, the van der Pauw (vdP) method only requires thin uniform samples with relatively small Ohmic contacts[26]. The measurement is fast and can cover the entire area of a sample and can be used in all stages of a material development since the prototyping up to manufacturing scale[29,30,31]

Methods

Results

Conclusion