12-03 :: March/April 2012

nanotimes News in Brief

Rice’s transparent memory is based upon the 2010 discovery that pushing a strong charge through standard silicon oxide, an insulator widely used in electronics, forms channels of pure silicon crystals less than 5nm wide. The initial voltage ap- pears to strip oxygen atoms from the silicon oxide; lesser charges then repeatedly break and reconnect the circuit and turn it into nonvolatile memory. A smaller signal can be used to poll the memory state without altering it.

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Single-layer graphene in solution used for making flexible transistors on a polyimide substrate (thermostable polymer). © CEA

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The research teams from CEA, CNRS, Université de Lille 1 (FR) and Northwestern University (US) developed the first ever process for making flexible transistors from solubilized graphene on polyimi- de (a thermostable polymer) substrates. They then made an in-depth study of high-frequency perfor- mance of these transistors. In the process developed by the researchers, sheets of graphene in solution are deposited on the substrate with an alternating electric field applied between electrodes made in advance. This technique, known as dielectrophore- sis or DEP, is used to guide the graphene deposition process so as to obtain a high density of deposited sheets in certain spots. This density is essential for achieving outstanding high-frequency performance. The charge mobility in the transistors is in the region of 100 cm2

/V.s, a far higher value than that ob-

tained with semiconductor molecules or polymers. These transistors thus achieve very high frequen- cies – around 8 GHz – a level of performance

never before obtained in organic electronics! The results show that “conductive ink” graphene is a highly competitive material for making flexible electronic applications in a high-frequency range (GHz) that is completely out of reach for conventi- onal organic semiconductors. This new generation of transistors offers excellent prospects for many applications, including flexible screens (folding or roll-up), electronic devices built into fabrics or other everyday objects, such as RFID tags, capable of pro- cessing and transmitting information.

Cedric Sire, Florence Ardiaca, Sylvie Lepilliet, Jung-Woo T. Seo, Mark C. Hersam, Gilles Dambrine, Henri Hap- py, and Vincent Derycke: Flexible Gigahertz Transistors Derived from Solution-Based Single-Layer Graphene, In: NANO Letters, Volume 12, Issue 3, March 14, 2012, Pages 1184-1188, DOI:10.1021/nl203316r: http://dx.doi.org/10.1021/nl203316r