Researchers have succeeded in upscaling superior-quality graphene devices to the 100 micron scale and beyond.
Scientists from the University of Hamburg and Graphenea have perfected the production, transfer and patterning processes of CVD graphene to observe the quantum Hall effect in devices measuring longer than 100 µm, with electronic properties on par with micromechanically exfoliated devices.
Transfer Process of Graphene
The work, published in Applied Physics Letters, by Timothy Lyon and Co-Authors, started from graphene grown by chemical vapor deposition (CVD) on a copper substrate. CVD is considered to be the most successful technique for developing large-area high-quality graphene ideal for high-tech applications.
However, graphene on metal is not suitable for applications in electronics, and hence the material is generally transferred onto another substrate before use. The transfer process has been shown to be a tough nut to crack, in several cases leading to defects, cracks, and chemical impurities that bring down the quality of the graphene.
Researchers, in this most recent advance, have optimized every step of the transfer and patterning processes, which resulted in large-area graphene of extraordinary quality. Transfer from copper was carried out in eight consecutive steps, with three more steps added in order to develop electrical contacts.
Although a standard etching solution is used to remove copper, the bottom side of the graphene is cleaned with two reactive chemical etching steps to remove inorganic and organic contaminants. Additionally, standard chemicals are replaced at other steps of the process, such as polymer removal, by carefully chosen ones so as to prevent graphene damage.
Figure: Graphene devices and measurement.
Optimized Processing of Graphene
The optimized processing leads to tear-free graphene on the preferred Si/SiO2 substrate. Additional processing is carried out to implement metallic contacts for electrical measurements.
The electrical performance of the devices is measured at low temperature and in vacuum, revealing multiple quantum Hall levels. Large-scale quantum Hall effect makes room for the usage of graphene for universal electrical resistance standard measurements, hopefully leading to more precise measures of electron charge and the Planck constant.
The graphene devices have their charge neutrality point near zero gate voltage, which highlights extremely high material purity. Perhaps most importantly, the measured carrier mobility is as high as 3760 cm2/(Vs), which unambiguously shows that CVD graphene is an exceptional candidate for electronic applications.
Upscaling high-quality graphene device production beyond 100 microns is very important for commercial production. The Authors of the research believe that such devices will find uses in thermo-power couplers, THz-emitters and probably flexible thin-film sensors.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
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