Mar 26, 2008
Beating noise in nanodevices
Low-frequency noise is a big problem in nanoscale devices but researchers at IBM have now discovered that it can be suppressed in devices made from bilayer graphene. The result means that the material, which is quite different from the more well-known single-layer graphene, could be ideal for low-noise applications, such as sensors and communication devices.
With their discovery, Yu-Ming Lin and Phaedon Avouris at the IBM TJ Watson Research Center in New York have addressed one of the key problems in nanoelectronics involving graphene. The researchers have demonstrated that the random electric fluctuations, or noise, in bilayer graphene devices can be suppressed.
Ideally, the noise in a device – which is caused by electrical charges that move around in an unpredictable and uncontrolled way – should be negligible compared to the current signal. However, in nanoscale devices this noise varies inversely with the size of the device. This trend, described by Hooge's law, means that the noise gets larger as devices get smaller. "The noise in nanodevices containing only a few atoms can therefore greatly surpass the current signal and render the device useless," explained Lin.
"Our work shows that bilayer graphene is promising in the race to build nanoscale devices and circuits," he told nanotechweb.org. "Moreover, the results may provide insight on how to reduce the electrical noise in other nanoscale devices, thus extending their applicability and usefulness."
Lin and Avouris obtained their results by testing both single-layer and bilayer graphene devices that they had made. The graphene sheets were produced by mechanical exfoliation of highly oriented pyrolytic graphite – the same material that is used in pencils.
The duo confirmed that a field-effect device made of a single-layer graphene sheet followed Hooge's rule. This behaviour is also seen in silicon transistors and carbon nanotubes. However, the noise in the same device made of two stacked graphene layers was suppressed. According to Lin and Avouris, the noise is inhibited thanks to the strong electronic coupling between the two graphene layers. "This counteracts the influence of the noise sources and the system acts as a 'noise insulator'," explained Lin.
The result suggests that graphene bilayers could be used in devices where large signal-to-noise and high-speed operation is required. Examples include sensors and communication devices.
The team now hopes to better understand the noise inhibition phenomena that it has seen. "We would also like to utilize this low-noise feature in graphene to build electrical circuits," added Lin.
The work was reported in Nano Letters.
About the author
Belle Dumé is contributing editor at nanotechweb.org