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Printed graphene transistors promise high-speed wireless communications

Researchers at the University of Texas fabricate record-breaking 25GHz graphene transistors printed on flexible plastic

21 Aug 2013 | Editor

Professor Deji Akinwande and University of Texas materials scientist Rodney Ruoff have published, in the journal ACS Nano, their recent work on fabricating "record-breaking" 25-gigahertz graphene transistors printed on flexible plastic.

For Bluetooth communications transistor circuits have to be able to switch on and off billions of times per second—2.4 GHz to be exact, and about 1 GHz for cellular communications. However for practical applications, the transistors in these circuits have to be rated about 10 times faster than that, says Prof. Deji Akinwande.

High-performance graphene field-effect transistors (GFETs)

Figure: University of Texas - High-performance graphene field-effect transistors (GFETs)

Prof. Deji Akinwande said his group is very focused on keeping costs down by making graphene from inexpensive starting materials and producing the devices over large areas. To make the transistors, the researchers first fabricate all the non-graphene-containing structures—the electrodes and gates that will be used to switch the transistors on and off—on sheets of plastic. Separately, they grow large sheets of graphene on metal, then peel it off and transfer it to complete the devices. Akinwande says they use this graphene-last approach because the material is very sensitive to all the processing needed to make the other components. Finally, they encapsulate the circuit to make protect it from moisture and oxygen.

Prof. Deji Akinwande said, "He is now working with industry partners, including glass maker Corning of New York and 3M of Saint Paul, Minnesota, to demonstrate printed graphene circuits on a larger, more practical scale. And the group is currently designing a printer for continuously manufacturing graphene circuits." Deji added, "All the building blocks are done."

Practical and commercially viable transistors circuit using this technique could be manufacturable in five to 10 years.

25 GHz Embedded-Gate Graphene Transistors with High-K Dielectrics on Extremely Flexible Plastic Sheets

Jongho Lee | Tae-Jun Ha | Huifeng Li | Kristen N. Parrish | Milo Holt | Ananth Dodabalapur | Rodney S. Ruoff | Deji Akinwande

ACS Nano, Article ASAP | DOI: 10.1021/nn403487y | Publication Date (Web): August 13, 2013

Abstract

Despite the widespread interest in graphene electronics over the past decade, high-performance graphene field-effect transistors (GFETs) on flexible substrates have been rarely achieved, even though this atomic sheet is widely understood to have greater prospects for flexible electronic systems. In this article, we report detailed studies on the electrical and mechanical properties of vapor synthesized high-quality monolayer graphene integrated onto flexible polyimide substrates. Flexible graphene transistors with high-k dielectric afforded intrinsic gain, maximum carrier mobilities of 3900 cm2/V·s, and importantly, 25 GHz cutoff frequency, which is more than a factor of 2.5 times higher than prior results. Mechanical studies reveal robust transistor performance under repeated bending, down to 0.7 mm bending radius, whose tensile strain is a factor of 2–5 times higher than in prior studies. In addition, integration of functional coatings such as highly hydrophobic fluoropolymers combined with the self-passivation properties of the polyimide substrate provides water-resistant protection without compromising flexibility, which is an important advancement for the realization of future robust flexible systems based on graphene.

www.ece.utexas.edu    www.technologyreview.com   

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