A wafer-scale graphene circuit was demonstrated in which all circuit components, including graphene field-effect transistor and inductors, were monolithically integrated on a single silicon carbide wafer. The integrated circuit operates as a broadband radio-frequency mixer at frequencies up to 10 gigahertz. These graphene circuits exhibit outstanding thermal stability with little reduction in performance (less than 1 decibel) between 300 and 400 kelvin. These results open up possibilities of achieving practical graphene technology with more complex functionality and performance.
When epitaxial graphene layers are formed on SiC͑0001͒, the first carbon layer ͑known as the "buffer layer"͒, while relatively easy to synthesize, does not have the desirable electrical properties of graphene. The conductivity is poor due to a disruption of the graphene bands by covalent bonding to the SiC substrate. Here we show that it is possible to restore the graphene bands by inserting a thin oxide layer between the buffer layer and SiC substrate using a low temperature, complementary metal-oxide semiconductor-compatible process that does not damage the graphene layer.
Up to two layers of epitaxial graphene have been grown on the Si-face of 2 in. SiC wafers exhibiting room-temperature Hall mobilities up to 2750 cm 2 V −1 s −1 , measured from ungated, large, 160 ϫ 200 m 2 Hall bars, and up to 4000 cm 2 V −1 s −1 , from top-gated, small, 1 ϫ 1.5 m 2 Hall bars. The growth process involved a combination of a cleaning step of the SiC in a Si-containing gas, followed by an annealing step in argon for epitaxial graphene formation. The structure and morphology of this graphene has been characterized using atomic force microscopy, high resolution transmission electron microscopy, and Raman spectroscopy. Furthermore, top-gated radio frequency field-effect transistors ͑rf-FETs͒ with a peak cutoff frequency f T of 100 GHz for a gate length of 240 nm were fabricated using epitaxial graphene grown on the Si-face of SiC that exhibited Hall mobilities up to 1450 cm 2 V −1 s −1 from ungated Hall bars and 1575 cm 2 V −1 s −1 from top-gated ones. This is by far the highest cutoff frequency measured from any kind of graphene.
Abstract-This letter presents a detailed study of transport in graphene field-effect transistors (GFETs) with various channel lengths, from 5 μm down to 90 nm, using transferred graphene grown by chemical vapor deposition. An electron-hole asymmetry observed in short-channel devices suggests a strong impact from graphene/metal contacts. In addition, for the first time, we observe a shift of the gate voltage at the Dirac point in graphene devices as a consequence of gate length scaling. The unusual shift of the Dirac point voltage has been identified as one of the signatures of short-channel effects in GFETs.
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