Team reports scalable fabrication of self-aligned graphene transistors, circuits

Jun 17, 2011 By Mike Rodewald
Self-aligned graphene transistor array

(PhysOrg.com) -- Graphene, a one-atom-thick layer of graphitic carbon, has the potential to make consumer electronic devices faster and smaller. But its unique properties, and the shrinking scale of electronics, also make graphene difficult to fabricate and to produce on a large scale.

In September 2010, a UCLA research team reported that they had overcome some of these difficulties and were able to fabricate transistors with unparalleled speed. These transistors used a nanowire as the self-aligned gate — the element that switches the transistor between various states. But the scalability of this approach remained an open question.

Now the researchers, using equipment from the Nanoelectronics Research Facility and the Center for High Frequency Electronics at UCLA, report that they have developed a scalable approach to fabricating these high-speed graphene transistors.

The team used a dielectrophoresis assembly approach to precisely place nanowire gate arrays on large-area chemical vapor deposition–growth graphene — as opposed to mechanically peeled graphene flakes — to enable the rational fabrication of high-speed transistor arrays. They were able to do this on a glass substrate, minimizing parasitic delay and enabling graphene transistors with extrinsic cut-off frequencies exceeding 50 GHz. Typical high-speed graphene transistors are fabricated on silicon or semi-insulating silicon carbide substrates that tend to bleed off electric charge, leading to extrinsic cut-off frequencies of around 10 GHz or less.

Taking an additional step, the UCLA team was able to use these graphene transistors to construct radio-frequency circuits functioning up to 10 GHz, a substantial improvement from previous reports of 20 MHz.

The research opens a rational pathway to scalable fabrication of high-speed, self-aligned graphene and functional circuits and it demonstrates for the first time a graphene transistor with a practical (extrinsic) cutoff frequency beyond 50 GHz.

This represents a significant advance toward graphene-based, radio-frequency circuits that could be used in a variety of devices, including radios, computers and mobile phones. The technology might also be used in wireless communication, imaging and radar technologies.

The research was recently published in the peer-reviewed journal Nano Letters.

The UCLA research team included Xiangfeng Duan, professor of chemistry and biochemistry; Yu Huang, assistant professor of materials science and engineering at the Henry Samueli School of Engineering and Applied Science; Lei Liao; Jingwei Bai; Rui Cheng; Hailong Zhou; Lixin Liu; and Yuan Liu. Duan and Huang are also researchers at the California NanoSystems Institute at UCLA.

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More information: Scalable Fabrication of Self-Aligned Graphene Transistors and Circuits on Glass, Nano Lett., Article ASAP, DOI: 10.1021/nl201922c

Abstract
Graphene transistors are of considerable interest for radio frequency (rf) applications. High-frequency graphene transistors with the intrinsic cutoff frequency up to 300 GHz have been demonstrated. However, the graphene transistors reported to date only exhibit a limited extrinsic cutoff frequency up to about 10 GHz, and functional graphene circuits demonstrated so far can merely operate in the tens of megahertz regime, far from the potential the graphene transistors could offer. Here we report a scalable approach to fabricate self-aligned graphene transistors with the extrinsic cutoff frequency exceeding 50 GHz and graphene circuits that can operate in the 1–10 GHz regime. The devices are fabricated on a glass substrate through a self-aligned process by using chemical vapor deposition (CVD) grown graphene and a dielectrophoretic assembled nanowire gate array. The self-aligned process allows the achievement of unprecedented performance in CVD graphene transistors with a highest transconductance of 0.36 mS/μm. The use of an insulating substrate minimizes the parasitic capacitance and has therefore enabled graphene transistors with a record-high extrinsic cutoff frequency (> 50 GHz) achieved to date. The excellent extrinsic cutoff frequency readily allows configuring the graphene transistors into frequency doubling or mixing circuits functioning in the 1–10 GHz regime, a significant advancement over previous reports (20 MHz). The studies open a pathway to scalable fabrication of high-speed graphene transistors and functional circuits and represent a significant step forward to graphene based radio frequency devices.

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User comments : 6

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Pharago
5 / 5 (3) Jun 17, 2011
welcome to the future
travisr
5 / 5 (2) Jun 17, 2011
It doesn't say what the feature size is though. If its self assembling I would suppose its small, but how small?

I think either way, this is a monumental break through though. If a semiconductor company takes serious interest in this you could see the graphene races in just a few years that you currently see in semiconductors. It would be easy to spot on a flop/t graph. A straight-line up and down showing desktop computers soaring upwards in capability at 90 degrees compared to the moore line.
El_Nose
3.3 / 5 (4) Jun 17, 2011
there will be no graphene race of any type --

silicon is the most understood material on the planet. Until the amount of research hours that have been put into graphene get close to the hours put into silicon there will be no change.

Semiconductor manufacturers are ready to go 7 more years with silicon and have developed research goals that go for the next 10 - 12 years with silicon -- until graphene becomes more well known it will be a decade probably before we see a graphene based microprocessor.
Vendicar_Decarian
4 / 5 (3) Jun 17, 2011
There will be some high end applications for graphene devices, probably military, satellite communications, and perhaps the 2020 iFad from Apple.
SemiNerd
5 / 5 (4) Jun 17, 2011
there will be no graphene race of any type --

silicon is the most understood material on the planet. Until the amount of research hours that have been put into graphene get close to the hours put into silicon there will be no change.

Semiconductor manufacturers are ready to go 7 more years with silicon and ... until graphene becomes more well known it will be a decade probably before we see a graphene based microprocessor.

Hmmm... not necessarily. Many thousands of research man-hours were spent decreasing the feature size and increasing the scale of current devices. Since current graphene transistors and other devices are already smaller than any existing silicon device and have other speed and current advantages, all that's really necessary at this point is to develop large scale manufacturing processes for these devices.

At this point, I estimate we are 4-6 years out before we see amazing graphene devices on the market.
Intensero
not rated yet Jun 18, 2011
Sweetness. Someone invest a couple hundred billion in graphene please and save the world by advancing things like this. I can't wait until they learn to deal with the entropy issues with 3D computing, still at a lost here. Can anyone say nano neural net processing with speeds 50,000-100,000 times faster than today?

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