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(a) Schematic of the metal back-gate device layout. (b) SEM and (c) AFM images of the active area. Note the wrinkles in the graphene due to transfer. (d) Ratio of Ids to Ids 0 vs. Vg . The drain voltages Vds 0 at the minimum drain currents Ids 0 are indicated by the legend. (e) Ids vs. Vds for various Vg . (f) Current gain vs. frequency extracted from as-measured (green squares) and de-embedded (blue circles) S-parameters. The achieved maximum transit frequencies are fT = 6.4 GHz and 60 GHz, respectively. The ideal 1/f dependence is indicated by black lines. The inset shows the rf transconductance vs. Vg .
(a) Schematic of the graphene nanoribbon back-gate device layout. (b)-(g) Optical micrographs of the sample fabrication steps: (b) Exfoliation of graphene (few layer of ∼2 nm thickness) for back-gate defined by EBL and etched using reactive ion etching (c). (d) Transfer of a thin layer of h-BN covering the gate fingers. (e) Transfer of a monolayer graphene flake (channel). (f) Patterning of the contacts and gate electrode by EBL. (g)Metal evaporation Ti/Al.
Graphene back-gate device: (a) Current ratio vs. back-gate voltage Vg . (b) Ids vs. Vds for varying back-gate voltages Vg . (c) At Vg = 0.48 V and Ids = 8.5 mA, maximum transit frequencies of fT = 4.8 GHz (extrinsic) and 30 GHz (intrinsic) are found (green squares and blue circles, respectively). The red curve corresponds to the fit with our small-signal model. (d) The rf transconductance at 10 MHz is comparable to the first metal-gate device but decreases with increasing frequency. (e) small-signal model used to fit our GFET current gain .
Polar plot of the S-parameters before de-embedding of (a) the metal back-gate and (b) graphene back-gate device. The frequency range from 10 MHz to 40 GHz has to be read clockwise.
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