11-11/12 :: November/December 2011

nanotimes News in Brief

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The paper reports an extrinsic cut-off frequency of 24 GHz in transistor performance, the highest reported so far in a real-world epitaxial graphene de- vice, the authors believe. (Extrinsic cut-off frequency is a measure of device speed under operating con- ditions, and is typically a fraction of intrinsic speeds often reported.)

The hydrogenation technique, which was first de- veloped by a group in Germany (Riedl, et al.; Phys. Rev. Lett. 2009, 103, 246804), involves turning the buffer layer into a second, free-floating one-atom- thick layer of graphene by passivating dangling carbon bonds using hydrogen. This results in two free-floating layers of graphene. Penn State resear- chers, led by Joshua Robinson and David Snyder, have implemented an additional process step to their wafer-scale graphene synthesis process that fully con- verts the buffer layer to graphene.

With this hydrogenation technique, the epitaxial graphene test structures showed a 200-300% incre- ase in carrier mobility, from 700-900 cm2 average of 2050 cm2 in vacuum.

/(V s) in air and 2375 cm2

/(V s) to an /(V s)

Optical image of transistors and structures to test device performance on hydrogenated epitaxial graphene. © Joshua Robinson, Penn State EOC

Matthew J. Hollander, Michael LaBella, Zachary R. Hughes, Michael Zhu, Kathleen A. Trumbull, Randal Cava- lero, David W. Snyder, Xiaojun Wang, Euichul Hwang, Su- man Datta, and Joshua A. Robinson: Enhanced Transport and Transistor Performance with Oxide Seeded High-k Gate Dielectrics on Wafer-Scale Epitaxial Graphene, In: NANO Letters, Vol. 11, Issue 9, September 14, 2011, Pages 3601-3607, DOI:10.1021/nl201358y: http://dx.doi.org/10.1021/nl201358y