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Graphene based products become a commercial reality

Graphene is starting to filter onto the market. HEAD claims its tennis racquets that feature graphene in the shaft are lighter, have better weight distribution and offer more power. Flexible security tags are also starting to be used using graphene circuitry.

However, one of the most promising early applications of graphene is in touch screen panels and displays. One company leading the pack is Bluestone Global Tech, which recently announced its partnership with the National Graphene Institute (NGI), partly to contribute to the research effort, but also to enable commercialisation of promising projects.
Chief executive Dr Chung-Ping Lai observed: "Bluestone is the first company to be invited by the NGI to join this development, partly because we have excellent marketing capability in the Asian and American markets. We also have the capability to bring the laboratory technology into production – we have demonstrated we can bring graphene from tiny laboratory scale into production in six months."

The company's range of products includes graphene inks and oxides, the Grat-Power range of graphene enhanced electrode materials that is claimed to offer better performance in Li-ion batteries, and Grat-FET – graphene transistors. This last group of products is still in its infancy, but has the most significant implications in terms of electronics design. Dr Lai said: "Graphene is so fast that it can enable even terahertz operation in current modulation – most communications devices are typically in the gigahertz range. We are being approached already and have delivered transistors to R&D departments to be tested and evaluated." An interesting application using the resultant small packages at high frequency is medical diagnostics using 'millimetre wave' electromagnetic radiation – the technology used in airport security scanners.

Touchscreens
Graphene's key attributes – lightweight, conductive and transparent – make it ideal for use in touchscreen displays and so it is no surprise that this has emerged not just as a market ready application, but also the application for which the market is most ready. Dr Yu-Ming Lin, Bluestone's vp of technology, commented: "Graphene is a single layer of carbon atoms, so it is transparent and also very flexible. At the same time, it cab conduct electricity at very high efficiency so it makes it an ideal material to replace or to complement the transparent conductive electrode currently being used in touch panels and displays."

The main material it could replace is indium tin oxide (ITO). Dr Lai said: "The price [of graphene films] is a little higher than ITO, but the price is not determined by the process itself; it is determined by the current supply. It is at a different maturity stage compared to ITO, which has been used by industry for a decade or more. Also, indium is very expensive because it is a rare earth metal that is mainly produced in China, which is controlling the supply so the price is soaring."

In 2012, China produced 390tonne of the 680tonne produced globally and, over the past year, prices have risen by around $150 per kg to $650, which adds some credence to Dr Lin's claims, although the current prices are a long way down on 2004's peak of more than $1000. Graphene has no such price considerations as the main cost component, in terms of materials, is the copper that is used as a substrate.

The core technology that Bluestone uses is chemical vapour deposition – CVD. CVD graphene is a particular type of graphene produced by depositing graphene on copper and then using a CVD process to produce a large area highly uniform single layer carbon films. The Gat-Film range has a number of variants with different properties. "We know that, for electronics, customers would prefer high uniformity and high mobility of continuous films," said Dr Lai. "For certain display applications and for flexible electronics, they care more about sheet resistance. We have optimised Grat-Film so that its sheet resistance is low enough for it to be used in touchscreen and display applications."

The sheet resistance is a measurement of resistance in very thin films. Typically, the sheet resistance of an ITO film is in the range from 10 to 250?/square, while for Grat-Film R it is 300 to 600?/square when transferred to PMMA or PET substrates.

Currently, production is at 10m2 a day, but the capacity is in place to ramp this to 200m2. Dr Lai commented: "1m2 of film can make up to 250 phones, so if we produced 200m2 per day we could produce 50,000 touchpanels, or 1.5million a month. So it is important to understand this is not just at laboratory scale – it is industrial scale."

Films with GLADIATORS!
GLADIATOR is a research project funded in part by the European Commission that began in November 2013 and will run for three and a half years. GLADIATOR (Graphene Layers: Production, Characterisation and Integration) seeks to improve the quality and size of CVD graphene sheets and to reduce production costs in order to make the use of graphene more attractive in applications such as transparent electrodes for large area organic electronics.

GLADIATOR is targeting the global market for transparent electrodes (estimated to be worth more than $11billion by 2016) and intends to demonstrate that the performance and price of indium tin oxide can be matched by graphene.

CVD graphene production will be optimised using new diagnostic and process control instrumentation based on Raman spectroscopy and spectrometric ellipsometry; the quality of graphene layers post transfer will be assured using new non contact in line eddy current measurement and THz imaging.

CVD production costs per unit area will not only be reduced by process parameter optimisation, but also by developing methods to reuse the catalysts and by increasing the size of the reactor chamber. A critical issue for graphene, especially as a transparent electrode, is how to achieve homogenous large area coverage. GLADIATOR will extend the size of graphene layers beyond that of the CVD tools by implementing a novel patchwork process using a transfer process with high yields and negligible impact upon the properties of the graphene. Transfer processes will be developed for rigid and flexible substrates appropriate for organic large area electronics and substrate and barrier properties will be optimised for use with graphene.

Speaking on behalf of the project, Dr James Whitby, managing director of Amanuensis, said: "We think the main barrier to more widespread use of graphene as a transparent electrode is simply its price – one 4in diameter piece of monolayer graphene with a sheet resistance of about 200?/square currently costs about €700, or about €80,000/m2. GLADIATOR aims to prove production technologies that will ultimately result in graphene with a much lower sheet resistance for less than 1/1000 of this price per area. It is not expected that this production cost will be reached within the project!"

Author
Tim Fryer

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