The race to commercialize graphene is on
Graphene, composed of pure carbon atoms and made into 1-atom-thick sheets, is one of the thinnest, strongest materials ever created. It may one day change the way microelectromechanical systems (MEMS) and sensors are made.
In awarding the 2010 Nobel Prize in Physics to Andre Geim and Konstantin Novoselov of the University of Manchester, The Royal Swedish Academy of Sciences described the attributes of graphene this way: “As a conductor of electricity, it performs as well as copper. As a conductor of heat, it outperforms all other known materials. It is almost completely transparent, yet so dense that not even helium, the smallest gas atom, can pass through it. Carbon, the basis of all known life on Earth, has surprised us once again.”
While skeptics may relegate graphene to perpetual residency in the land of R&D, the MEMS Industry Group, a trade association supporting the MEMS and sensors industry, as well as MEMS and electronics manufacturers STMicroelectronics, Nokia and VTT, beg to differ. The three companies, along with 73 other academic and industrial research groups in 17 European countries, comprise the Graphene Flagship consortium, which was recently established to support graphene commercialization.
According to its mission statement, the Graphene Flagship “is tasked with taking graphene from the realm of academic laboratories into European society in the space of 10 years, thus generating economic growth, new jobs and new opportunities for Europeans as both investors and employees.”
While this work is not without its challenges, the promise of an advanced material that could change the composition of MEMS and sensors, as well as myriad electronic devices, is well worth the investment.
Chemical vapor deposition is the most promising method for the production of high-quality graphene. Graphene is grown on a catalytic metal surface, such as copper (left). After transfer to a silicon or polymer substrate, graphene can be patterned into components (center) just like any other thin-film material. Another route for the production of thin graphene films is printing with graphene inks (right). Images courtesy VTT.
There are several ways to manufacture graphene. According to VTT, 2D, large-area graphene films can be grown via chemical vapor deposition (CVD) on catalytic surfaces such as copper, platinum or germanium. The process requires high temperatures, roughly 1,000° C, and a gaseous source of carbon, such as methane.
Using this method, the graphene produced must be transferred from the catalytic growth surface to the desired substrate, typically via a thin polymer film.
Two-dimensional graphene also forms when silicon sublimates from SiC surfaces at 1,300° C and above, but because of the cost of the SiC substrates, this method seems to hold limited commercial promise.
In addition to the CVD process, graphene sheets and platelets also can be produced using different mechanical and chemical exfoliation routes from graphite—i.e., selectively removing sheets of single-atom-thick graphene from a multi-carbon-layer-thick graphite parent.
Aixtron SE, a Herzogenrath, Germany-based provider of semiconductor and compound-semiconductor deposition equipment and services, is one of the equipment suppliers offering turnkey systems for growing graphene in quantity. Its processes accommodate up to 300mm wafers.
Graphene’s two main commercial advantages are its flexibility and transparency. The ability to utilize these attributes by deploying graphene in flexible substrates makes it ideal for the coming transition from rigid to flexible electronics.
Sanna Arpiainen, senior scientist at VTT, Espoo, Finland, said graphene is an ideal material for sensor applications due to its high surface area and flexibility. Graphene-based biosensors can be compared to silicon-nanowire sensors in that they both have high sensitivity and both require additional functionality to achieve selective detection of chemical components in liquids or gases, for example. But, unlike silicon nanowires, functional graphene elements for sensing applications can be flexible and transparent. And, as essentially 2D surfaces, they do not require deep, submicron-line-width patterning skills in fabrication, as do round, 3D silicon nanowires with diameters on the order of 10s of nanometers.
These mechanical properties give graphene essential advantages over silicon for some MEMS applications. For instance, the high piezoresistivity and strength of graphene make it ideal for MEMS pressure sensors and MEMS microphones. It is also suited for generating sound in applications such as MEMS microspeakers and MEMS ultrasonic transducers. The latter (sans graphene) are already being used for gesture recognition, said to be one of the next important MEMS apps.
To be sure, commercializing graphene in 10 years is fast-track thinking. In the past, the average time-to-market for MEMS components, including developing and integrating them into commercial products, has been 20 years or more.
It might seem improbable, but the 10-year target is realistic. First, Graphene Flagship’s research plans cover the entire graphene value chain, in parallel efforts, from material production to components to system integration.
Second, current graphene-based R&D applications include flexible electronic devices; devices and solutions for energy storage and harvesting; devices for environmental and biological sensing; wireless communications gear; and flexible user interfaces.
Plus, a major step toward using graphene in consumer products—and one a little closer to our home in MEMS—may be Samsung’s foldable touchscreen phone, scheduled for release in 2015 or 2016.
Evidence like this suggests that the race to commercialize graphene is on, and that the MEMS industry will need to lace up its running shoes. µ