Researchers develop transistor with high on/off switching ratio

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Researchers at Southampton University have developed a graphene transistor with an on/off switching ratio that is 1,000 times higher than in previous devices.

A new transistor made from graphene — the world’s thinnest material — has been developed by a research team at the university.

The new transistor is claimed to achieve a record high switching performance, which will make future electronic devices — such as personal digital assistants and computers — more functional and high performance.

In a paper published in Electronics Letters, Dr Zakaria Moktadir of the Nano research group at the university’s School of Electronics and Computer Science (ECS), described how his research into graphene led to the development of graphene field-effect transistors (GFETs) with a channel structure at the nano scale.

According to Moktadir, in the context of electronics, graphene could potentially replace — or at least be used side by side with — silicon integrations.

‘CMOS [silicon complementary metal-oxide semiconductor] downscaling is reaching its limits and we need to find a suitable alternative,’ he said. ‘Other researchers had looked at graphene as a possibility, but found that one of the drawbacks was that graphene’s intrinsic physical properties make it difficult to turn off the current flow.’

Moktadir discovered that by introducing geometrical singularities (such as sharp bends and corners) in bilayer graphene nanowires, the current could be turned off efficiently.

According to Prof Hiroshi Mizuta, head of the Nano group, this engineering approach has achieved an on/off switching ratio that is 1,000 times higher than previous attempts.

‘Enormous effort has been made across the world to pinch off the channel of GFETs electrostatically, but the existing approaches require either the channel width to be much narrower than 10nm or a very high voltage to be applied vertically across bilayer graphene layers,’ he said. ’This hasn’t achieved an on/off ratio that is high enough, and is not viable for practical use.’

Moktadir developed this transistor using the new helium-ion beam microscope and a focused gallium-ion beam system in the Southampton Nanofabrication Centre.

‘This is a breakthrough in the quest to develop advanced transistors as we progress beyond our current CMOS technology,’ said Prof Harvey Rutt, head of the ECS school. ‘It will have major implications for next-generation computer, communication and electronic systems. Introducing geometrical singularities into the graphene channel is a new concept that achieves superior performance while keeping the GFET structure simple and therefore commercially exploitable.’

Having created the transistor, Moktadir is now undertaking further research to understand the mechanism that causes the current to stop flowing in the channel, testing its reliability and performance under various noise and temperature conditions.