Graphene, a form of two-dimensional carbon, has many desirable properties that make it a promising material in many applications. However, its production, especially for high-end electronics such as touch screens, faces many challenges. This may soon change with a fresh approach developed by NUS (National University of Singapore) researchers that mimics nature.
Inspired by how beetles and tree frogs keep their feet attached to submerged leaves, the findings revealed a new method that allows both the growth and transfer steps of graphene on a silicon wafer. This technique enables the graphene to be applied in both photonics and electronics for devices such as optoelectronic modulators, transistors, on-chip biosensors and tunneling barriers.
Professor Loh Kian Ping, Head of the NUS Department of Chemistry, led a team that came up with the one-step method to grow and transfer high-quality graphene on silicon and other stiff substrates. This promises the use of graphene in high-value areas where no technique currently exists to grow and transfer graphene with minimal defects for use in semiconductors.
Prof Loh, who is also a Principal Investigator with the Graphene Research Centre at NUS Faculty of Science, explained: "Although there are many potential applications for flexible graphene, it must be remembered that to date, most semiconductors operate on ìstiffî substrates such as silicon and quartz." Thus, a transfer method with the direct growth of graphene film on silicon wafer is needed for enabling multiple optoelectronic applications, he said.
In the process called "face-to-face transfer", Dr Gao Libo, who is with the Graphene Research Centre, grew graphene on a copper catalyst layer coating a silicon substrate. After growth, the copper is etched away while the graphene is held in place by bubbles that form capillary bridges, similar to those seen around the feet of beetles and tree frogs attached to submerged leaves. The capillary bridges help to attach the graphene to the silicon surface and prevent its delamination during the etching of the copper catalyst. The novel technique can potentially be deployed in batch-processed semiconductor production lines, such as the fabrication of large-scale integrated circuits on silicon wafers.
The researchers will be fine-tuning the process to optimise the high throughput production of large diameter graphene on silicon, as well as target specific graphene-enabled applications on silicon. They are also looking at applying the techniques to other two-dimensional films.