Mar 19, 2009
Graphene makes good microwave switch
Graphene could be used to make ultrafast microwave switches, say scientists in Romania and France. The devices represent a low-cost alternative to switches widely used in communications applications, such as the internet and in mobile phones.
"Wonder material" graphene is one of the hottest topics in physics and materials science today thanks to its great potential for making future electronic devices. It is an excellent conductor of electricity because, as well as being extremely thin and a semiconductor, electrons travel ballistically through the material at extremely high speeds. This is because they behave like relativistic particles that have no rest mass. This, and other unusual physical properties, means that graphene is often touted to replace silicon as the electronic material of choice in the future.
Now, Mircea Dragoman of the IMT in Bucharest, Romania, Daniela Dragoman from the University of Bucharest and colleagues from CNRS-LAAS in Toulouse, France, have shown that graphene flakes can enable and disable the propagation of high-frequency electromagnetic fields up to 60 GHz when a DC voltage is applied. The switching time is very short at less than 1 ns, which is among the fastest ever observed in such a device.
The device is a microwave NEMS switch that comprises a coplanar waveguide and an array of metallic graphene sheets suspended over it. The waveguide is made from three gold metallic strips deposited on a 500 µm thick semi-insulating silicon substrate. The central strip propagates the microwaves while the other two strips act as ground electrodes. The graphene flakes remain suspended over the waveguide thanks to van der Waals forces, but they could also be attached via metallic contacts too, say the researchers.
The graphene switch is much simpler and more efficient than switches made from conventional materials, such as silicon, says Mircea Dragoman. The electromagnetic field in the device switches on and off simply by applying different DC biases. "The properties of the switch are good – it rejects the transmitted field when biased and has low losses of propagation when not biased," he told nanotechweb.org.
"Graphene has been seen in only limited applications until now and will remain at the stage of academic research if it is not applied to big markets like communications or health," added Dragoman. "The microwave switch demonstrated in our work is novel because it is simple, robust and based entirely on the material's unusual properties."
The work was published in J. Appl. Phys.
About the author
Belle Dumé is contributing editor at nanotechweb.org