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Graphene-based bulb brings light to semicon ICs

Posted: 03 Aug 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Columbia University? graphene? electrode? light emitter? LED?

Researchers from a number of universities have showcased an on-chip visible light source that uses graphene as a filament. They attached small strips of graphene to metal electrodes, suspended the strips above the substrate, and passed a current through the filaments.

"We've created what is essentially the world's thinnest light bulb," said James Hone, professor at Columbia Engineering, part of Columbia University (New York). "This new type of broadband light emitter can be integrated into chips and will pave the way towards the realisation of atomically thin, flexible and transparent displays, and graphene-based on-chip optical communications."

The study was led by Young Duck Kim, a postdoctoral research scientist in Hone's group, with teams from Seoul National University (SNU) and Korea Research Institute of Standards and Science (KRISS).

A graphene-based lightbulb was announced earlier this year based on filament-shaped LED coated in graphene designed at Manchester University. The dimmable light bulb claims to cut energy use by 10 per cent.

On-chip visible light is crucial for developing fully integrated "photonic" circuits that do with light what is now done with electric currents in semiconductor ICs, the release noted. Until now, researchers have yet to put an incandescent bulb onto a chip because the temperature required to light the blub isn't suitable for micro-scale metal wires.

The graphene was able to reach temperatures above 2,500°C, hot enough to glow to the naked eye without magnification. Researchers also found that graphene becomes a poorer conductor of heat at higher temperatures, meaning heat would be confined to a "hot spot" in the centre of the chip. Suspended graphene can be heated to half the temperature of the sun and is 1,000 times more efficient than graphene on a solid substrate, a researcher said.

The spectrum of emitted light also peaked at specific wavelengths due to interference between the light emitted directly from the graphene and light reflecting off the silicon substrate and passing back through the graphene.

"This is only possible because graphene is transparent, unlike any conventional filament, and allows us to tune the emission spectrum by changing the distance to the substrate," said Young Duck Kim, a postdoctoral research scientist in Hone's group and study co-author.

Researchers are also studying the scale of their technique with arrays of chemical-vapour-deposited (CVD) graphene light emitters and characterizing the performance of these devices to develop integration techniques for flexible substrates.

Graphene research was also conducted by scientists from Konkuk University, Sogang University, Sejong University, University of Illinois at Urbana-Champaign and Stanford University.

- Jessica Lipsky
??EE Times

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