Wireless communications today consist of a wide range of standards available on a host of different devices - mobile phone, GPS devices, computers, bluetooth sensors, all operating in different frequency bands. To work across multiple platforms, connected objects have to be compatible with a whole range of frequencies without being weighed down by excessive hardware. Most portable, wireless systems currently come equipped with reconfigurable circuits that can adjust the antenna to transmit and receive data in the various frequency bands. The only problem is that the technologies currently available like MEMS and MOS, using silicon or metal, do not work well at high frequencies. And that's where data can travel much faster.
EPFL researchers have come up with a tunable graphene-based solution that enables circuits to operate at both low and high frequencies with unprecedented efficiency. This new graphene-based solution, which was developed in the Nanoelectronic Devices Laboratory, is designed to replace tunable capacitors, which can be found in all wireless devices. This new device "tunes" the circuits to different frequencies so that they can operate across a wide range of frequency bands. It also meets other needs that neither MEMS nor MOS capacitors can: good performance at high frequency, miniaturization and the ability to be tuned using low energy.
Researchers overcame these obstacles with a graphene-based capacitor that is compatible with traditional circuits. It consumes very little energy and has a miniaturized design. When operating above 2.1 GHz it outperforms its competitors. According to Clara Moldovan, the lead author of the article, the surface area of a conventional MEMS system would have to be a thousand times greater to get the capacitance value.
How does it work?
This breakthrough is based on a clever sandwich structure that takes graphene's unique characteristics into account. Graphene is a very good electrical and thermal conductor and it is flexible, lightweight, transparent and sturdy. But researchers discovered that it was difficult to integrate into electronic systems because its atomic thickness gives it high effective resistance.
The sandwich-shaped structure takes advantage of the fact that a two-dimensional gas of electrons in a quantum well can behave like a quantum capacitance. This is because it follows the Pauli Exclusion Principle, according to which a certain amount of energy is needed to fill a quantum well with electrons. Quantum capacitance can be easily measured in a single-atom layer of graphene, and the key advantage is that it is tunable by varying the charge density in graphene with a very low voltage. This voltage that is applied allows the capacitors to be tuned to a given frequency.
Many advantages
This device, which is only several hundred micrometers (around 0.05 cm) long and wide, can be stiff or flexible, is easily miniaturized, and uses very little energy. Potential applications are numerous. In addition to improving the flow of data between connected devices, it could extend battery life and lead to ever more compact devices. In its flexible state, it could be easily used in sensors placed in clothes or directly on the human body. Their results confirm that graphene could truly revolutionize the future of wireless communications.
The end technology will be a hybrid in which graphene will be paired with advanced silicon technologies. Some have claimed that graphene will one day replace silicon technology. However, graphene is most effective in the realm of electronics when it is combined with functional silicon blocks.
The paper on this research was published here.
