Dec 23, 2011
Graphene amplifies voltage
The first graphene device capable of significant voltage amplification (more than 10 dB) has been fabricated by researchers in Italy. The result confirms that the "wonder material" could compete head-on with silicon as the material of choice in electronics and is not simply limited to niche, low-voltage gain, high-frequency applications as currently thought.
The voltage amplifier (a device capable of amplifying small alternating voltage signals) is the main building block in analogue electronics. Thanks to its unique electrical and mechanical properties, graphene (a sheet of carbon atoms arranged in a honeycomb-like lattice just one atom thick) should be ideal for use in a host of technological devices – such as high-speed transistors – and in photonics. However, many scientists believe that it cannot compete with silicon in applications requiring voltage amplification, like analogue amplifiers and digital logic gates.
"Without voltage amplification though, graphene electronic devices will be mostly limited to high-frequency (>100 GHz) analogue mixers," explained team leader Roman Sordan of the Politecnico di Milano. "This is a niche application that reinforces the general perception of graphene as a material only used in 'exotic' applications without any real value in the everyday world."
Worse still, because analogue electronics cannot exist without voltage amplifiers, graphene devices would need to be integrated with silicon transistors for this most important task of signal amplification, he adds. "Such an eventuality is frowned upon by the semiconductor industry, which in general, is not very fond of such expensive hybrid technologies."
Even though it is their first graphene amplifier, it already shows "remarkable performance", according to Sordan and colleagues – with a flat frequency response well exceeding the audio range (>20 kHz) and a very low total harmonic distortion (<1%).
Until this work, there was only one previous report of voltage amplification in a graphene device, which itself proved difficult to fabricate. The device was not integrated either and so required external metal inductors and capacitors to operate. Moreover, the voltage gain achieved was not large enough for general use.
Indeed, it is no easy task to obtain signal amplification in graphene devices. A good example in point is the triple-mode single-transistor graphene amplifier recently made by researchers at the University of California – Riverside and Rice University. This device had an amplification of 0.02 (that is -34 dB), which made it, strictly speaking, an attenuator and not an amplifier, says Sordan. "Our device is a real amplifier since it has an amplification of 3.7 (+11.4 dB)." Amplification (or voltage gain) must be larger than 1 (0 dB) if the device is to be called an amplifier.
"This work is a paradigm shift for graphene because it shows that the material can challenge silicon head-on in this respect," he told nanotechweb.org. "It is a strong message to the scientific community that graphene should not just be confined to specialist, low-voltage gain, high-frequency applications."
Amplification of audio signals (in audio voltage amplifiers – the main components of home-theatres and iPods, for example), could now be possible using graphene, he adds.
The work was published in Small.
About the author
Belle Dumé is contributing editor at nanotechweb.org