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Graphene in Telecommunications

There is a lot of talk about Graphene and how it will potentially change telecom network solutions, so we thought we would give you a brief summary of what it is all about.

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The wonder material

Graphene is composed of pure carbon with atoms arranged in a 2D regular hexagonal pattern, in a one-atom thick sheet. It is proven to provide, at minimum, 160 times higher electron mobility, 19 times higher intrinsic strength and 20 times higher thermal conductivity than silicon. Therefore, Graphene is perceived as an enabler to high-speed electronics and photonics, efficient energy generation, and storage, as well as in many other applications. Interest in Graphene is now in the forefront, ahead of silicon.

A look back

Although known since 1947 and first fabrication in 1962, it was not until 2004 that the interest in graphene exploded. This was when the 2010 Nobel Prize winners K.S. Novoselov and A. Geim from the University Of Manchester, UK, published a pioneering paper on the preparation of graphene. R&D has since increased, bringing up the exponential growth of patents and papers in the respective fields of applications.

Over the last decade, graphene moved from scientists’ speculations, to lab samples, to benchtop application setups, to commercialization process of large sheets of graphene fabrication, and in some rare cases, products.

Unique properties

Exact properties and application fields depend on the graphene quality, which in itself, is the result of the preparation technique. The study of graphene has triggered experiments on many other 2D atomic crystals, such as BN, NbSe2, TaS2, MoS2 and many others. It is possible to extend the range of applications for graphene, when used in combination with other materials, such as 2D-based heterostructures. For the telecom industry that relies on optics and electronics, high purity graphene is desired. Although cost-ineffective, this can be achieved through chemical vapor deposition (CVD) or for large volume production, synthesis on silicon carbide. Such quality graphene could be applied to touch screens, e-paper, foldable organic light-emitting diode-based components, transistors, a variety of laser types, photo-detectors, polarization controllers and optical modulators.

Graphene in Electronics

In theory, the very high electron mobility, high thermal conductivity, low optical absorption, and high current density of graphene would enable extreme high power, high bandwidth, and transparent, low noise, electrical components. However, there are also severe challenges, the most obvious being that carbon is not a semiconducting material,that is having no bandgap.

The first graphene MOSFET transistor was reported in 2007. In 2012, a graphene MOSFET, with a cut-off frequency (fT) exceeding 400GHz, has been demonstrated. This was in parity with Si MOSFET, but lower than GaAs mHEMT and InP HEMT. On the other hand, graphene MOSFETs behaves rather poorly in terms of the maximum frequency of oscillation (fmax).

So far, the highest fmax reported is only in the range of 30-40 GHz. This is in comparison to several hundreds of gigahertz for the competing FET types, with a record fmax above 1 THz for InP HEMT. The low fmax comes from a large drain conductance, caused by a poor current saturation characteristic, due to the lack of a bandgap. The missing bandgap also makes graphene transistors unsuitable for complex logic circuits due to insufficient on-off switching performance. Bi-layer graphene can be used to provide a small bandgap. This may improve fmax, but this would not be enough for logic applications.

Nevertheless, there is promising research in graphene, directed at transparent electrodes, replacing ITO, an expensive material. There is also research on devices for flexible and printable electronics, replacing organic semiconductors, which have low electron mobility.

Graphene in Photonics

Graphene has been proposed for photonic applications, such as photodetectors, optical modulators, mode-locked lasers, optical isolators, and polarization controllers. State-of-the art graphene photodetectors have shown a response up to 40 GHz, but at a very low responsivity of a few mA/W, compared to 1 A/W for conventional photodiodes. Optical modulators with 1 GHz bandwidth have been reported. However, research is in its early stage and competitive components, with bandwidths >100GHz, are not expected before 2020.

The Future Perspective

It is estimated that by 2020, the time for the first electronic application, based on medium quality graphen, the entire commercialized market for graphene will pass 1 billion USD. In the following 15 years, high quality graphene-based transistors, in parallel to optical components, should be available on the market.

Out of all the currently, on-going research projects, the EU Graphene Flagship attracts the most attention. It has a funding of over 1 Billion EUR EU over 10 years. The focus is on “Graphene-Driven Revolutions in ICT and Beyond”.

Arne Alping, Patryk Urban and Herbert Zirath Ericsson Research

Sources:
[1] K.S. Novoselov, et al, “A Roadmap to Graphene”, Nature, Vol.490, pp.192-200, Oct-2012
[2] Frank Schwierz, “Graphene Transistors: Status, Prospects, and Problems”, Proc. IEEE, Vol.101, No.7, pp.1567-1584, July-2013
[3] Fengnian Xia, “The Interaction of Light and Graphene: Basics, Devices, and Applications”, Proc. IEEE, Vol.101, No.7, pp.1717-1731, July-2013

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