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Abstract:
To keep up with the demands of next generation electronics that are multi-functional as well as highly responsive, lighter, thinner, flexible, foldable and even wearable and printable on different substrates, we need materials that are as highly conductive as copper, robust as steel, light-weight as plastics, and flexible enough to be applied for curved, 3-D, foldable or wearable products.
November 25th, 2013
Graphene - Enabling Next Generation Multi-functional Electronics
Graphene has been considered as one of the most appealing materials for next generation electronics especially since the Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov (from University of Manchester) "for groundbreaking experiments regarding the two-dimensional material graphene". Today graphene is making the transition from research journals to commercial applications driven by its superior properties and cost-effective manufacturing in volume.
Graphene is known to be strong and flexible, 200 times stronger than steel, conducts heat 10 times more effective than copper and can carry 1,000 times the density of electrical current of copper wire, yet its density is four times lower compared to that of copper, and surface area is twice that of carbon nanotubes. These amazing properties have been utilized by scientists and engineers in realizing multifunctional materials such as conductive and stronger plastics for ESD protection and thermal dissipation; fast charging and long cycle life supercapacitors and batteries; and flexible and transparent electrodes used in touch screens, OLEDs, thin film solar cells and the emerging flexible electronics industry. In this article, we will share the most excited examples of graphene adoption today, and barriers for commercialization.
Charcoal and pencil - the discovery and application of graphite can be traced back to the ancient times and everywhere in our daily life. If we look through the history of the carbon family, diamond was the first to be found in 1770s and at that time it is valued due to its hardness and brilliance. 20 years later, soft graphite materials came to people's life and are widely used in pencils. After two centuries, the nano capsule fullerene was discovered in laboratory and has been used in cosmetics and high performance composite industries. Since 1991 when Prof Iijima reported the discovery of single-wall carbon nanotubes (SWCNT), the focus was on carbon nanotubes which could be conductive or semiconducting by tuning chirality. Multi-walled carbon nanotubes (MWCNT) have been commercialized in batteries, electrically and thermally conductive plastics and high performance composites. Nanocyl, CNano, Showa Denko, Hanwha Chemicals, Hodogaya, Future Carbon and others are the key players capable of annual production capacity of 200 tons. Nanocyl claims to sell over 100 tons of CNT powders and masterbatch, and their killer product NC7000 is sold at the price of 90 Euro per kilogram. Nanocyl is one of the few key "winners" in CNT space as it not only supply CNT materials but also application solutions.
The focus has shifted to graphene and expectations for commercial applications soar up especially since Andre Geim & Konstantin Novoselov were awarded the 2010 Nobel Prize in Physics for their discovery of graphene - the 2D atomic layer form of carbon atoms with superior mechanical, optical, electrical and thermal conductive properties. Being the strongest material ever measured, even stronger than diamond, graphene is 200 times stronger than steel at only one quarter of its weight. These superior properties enable its applications for sporting goods, automotive, boats and aerospace. A company named Head launched in 2013 graphene-infused tennis rackets. The weight reduced yet strongest central part of racket allows players to generate more power with less effort. Graphene is highly conductive. Its electrical conductivity is similar to copper, yet carries 1,000 times the density of electrical current than that of copper wire, and its thermal conductivity is over 10 times that of copper. Graphene could be 8-10 times more flexible than ITO. Beyond this, graphene is the thinnest and most transparent film in the world. The monolayer graphene is only 0.335 nm thick and its transparency is up to 97.7%. Graphene has the largest surface area in the world which is twice that of carbon nanotubes, and the electronic mobility is 100 times faster than that in silicon. This unique combination of superior properties makes graphene an ideal candidate for printed electronics, touch panels, OLED, batteries, solar cells and heat dissipation applications. You can see how stretchable and durable Vorbeck's graphene printed circuits are to go through the harsh conditions in your washer and dryer on Youtube. LG's G Flex and Samsung's Galaxy Round smartphones were just launched Oct. 2013. Although only curved OLED display is featured and no graphene technology is mentioned in these two products, Samsung, Nokia and Apple have filed many patents recently for graphene or graphene related applications for touch screens and heat dissipation in mobile phones, which indicates industries are moving closer in adopting graphene as a key component of their mobile phones. Integrating the mechanical, electrical and optical functionalities, graphene enables new generation of multifunctional devices and will reduce the world metal consumption in electronics and other industries as well.
As the most amazing and versatile substance which can be derived from cheap and naturally abundant graphite, graphene has rapidly attracted significant attention from researchers, industries, investors and government policy makers. The European Union (EU) just launched Europe's first ten-year 1 billion Euro Graphene Flagship last month. Britain decided to invest over 50 million pounds for the graphene development. South Korea plans to spend over 360 million US dollars in the next 6 years to support companies in developing graphene for electronic devices. While in China, billions of RMB has been invested by government owned corporations and private investors to build up the graphene production lines and support the application development for batteries and touch panels. Hundreds of venture companies have come out in recent years in China, and some of the venture companies started by Chinese oversea returnees from US, Europe, Japan, and elsewhere.
Graphene is now in the early stage of commercialization. Companies are generally selling three kinds of graphene products: graphene films, graphene nanoplatelets and reduced graphene oxide. Graphene films grown by CVD method on copper foil have the best quality and are promising for touch panel applications. South Korea and Japan-based manufacturers and research institutes are the pioneers of developing large-scale graphene films. Sungkyunkwan University (SKKU) and Samsung Techwin first synthesized the 30-inch monolayer graphene film by CVD method in 2010 and using layer-by-layer stacking to fabricate a doped four-layer transparent conductive film (TCF) which has a sheet resistance as low as 30 Ohm/sq at 90% transparency. Sony Corp. developed a machine and made the largest graphene sheet with a width of 23cm and a length of 100m using R2R CVD method. Its sheet resistance is around 200 Ohm/sq at 97% transparency. However, CVD method faces challenges in mass production due to its limited throughput and high production cost (It requires high temperature and vacuum operation) and additional cost involved in transfer.
Another prevailing product is graphene nanoplatelets produced by chemical exfoliation method which is easy to scale up. XG Sciences and Vorbeck are leaders in this business and they are moving up the value chain. Vorbeck is selling graphene inks for printedcircuits and high-end RFID. XG Sciences is applying their graphene nanoplatelets to batteries and high performance composites with various international partners. For supercapacitors and battery, the largest surface area and superfast electron transport in graphene help improve the energy density and power density. The charging time for commercial e-vehicles using lead acid batteries or lithium batteries is around 8 hours or longer, while Angstron Materials have demonstrated the graphene-enhanced supercapacitor can be charged in one minute and allows the e-vehicle to run the same distance as what present commercial e-vehicles can do. The American company Bluestone is sampling their films for touch screens, and Japanese company Incubation Alliance is applying their graphene flower dispersion for heat dissipation components. All these graphene enabled applications have amazing performance, but they are still at lab scale. We haven't seen actual adoption in marketplace.
There is hype and overselling for graphene and it is actually taking more time to commercialize this material than people anticipated. Given all those beautiful properties of graphene, practical challenges remain in translating the theoretical superior property into real products. The first barrier is cost. Companies sell 2-inch monolayer graphene on PET film at 800 US dollars. How can you image the touch panel manufacturers to adopt it if they have to control the budget for a touch module within 30 dollars or less? The cost could be reduced dramatically with a breakthrough synthesis technology to efficiently ramp up in volume. However, scale up takes time. Another important issue is application engineering. For example, if we want to use the graphene infused composites, we must disperse graphene uniformly in the matrix materials. As for the application in touch screens, OLEDs and solar cells, we need to coat or transfer graphene onto required substrates including PET, polycarbonate (PC), silicon and glass, make patterns, make connections and do integration. Last but not the least, there is the issue of reliability. How about the adhesion when it is coated, printed or transferred onto different substrates? How's the electrical continuity after patterning? Is there any compatibility issue of this carbon material with all the existing processes and equipment for building up the devices? These engineering and reliability hurdles have to be overcome before it is adopted in real products.
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