High Frequency Top-Gated Graphene RF Ambipolar FETs Using Large-Area CVD Graphene and Advanced Dielectrics
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HIGH FREQUENCY TOP-GATED GRAPHENE RF AMBIPOLAR FETs USING LARGE-AREA CVD GRAPHENE AND ADVANCED DIELECTRICS Osama M. Nayfeh and Madan Dubey United States Army Research Laboratory, Sensors and Electron Devices Directorate, 2800 Powder Mill Road, Adelphi, MD 20783, USA ABSTRACT Ambipolar top-gated field effect transistors (FETs) based on large area Cu catalyzed CVDgrown monolayer graphene interfaced to advanced dielectrics have been constructed and examined both for their material and electrical qualities. Interfacing of the graphene with novel insulators/substrates could be tailored for the particular application and provide for enhanced device functionality. In contrast to graphene FETs using SiO2-based top-gate dielectric, which show asymmetric electron/hole mobility (with larger hole mobility), and Dirac point shifted to positive levels, FETs constructed using advanced AlN show Dirac point almost near neutral levels and near symmetric electron/hole mobility. The DP is shifted likely due to compensation of the intrinsic p-type doping by n-type doping introduced by the AlN deposition and potentially via a contribution of polarization-induced carrier density. Finally, we demonstrate a top-gated graphene FET with the first observation of RF operation with GHz cut-off frequency based on large area CVD graphene. INTRODUCTION Graphene is a unique 2D material of atomic thickness that exhibits excellent transport characteristics for both electrons and holes. Wafer-scale graphene synthesized by chemical vapor deposition has the potential to enable new extremely scalable advanced electron device and sensors [1-12]. Also, due to the ability to transfer CVD graphene to substrates of choice and to deposit dielectrics directly to graphene, the design space of graphene FETs via interfacing of the graphene with novel insulators/substrates could be tailored for the particular application and provide for enhanced functionality. LARGE-AREA CVD GRAPHENE: MATERIAL CHARACTERIZATION Graphene is grown by Cu catalyzed LPCVD and subsequently transferred to device quality SiO2 and other advanced dielectrics for device processing. Figure 1 shows Raman mapping, AFM and XPS measurements. Raman shows a high quality monolayer graphene film with good large area uniformity with a small level of defects, as evidenced by the ratio of the intensities of the measured D and G peaks. AFM measurements show films with good uniformity with some disruptions due to wrinkles. XPS measurements show the characteristic 1s peak dominated by sp2 hybridized C bonding, and a smaller sp3 bonding peak at higher binding energies due to the presence of some disruptions to the graphene lattice.
1000
G
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2D Measured measured Lorentzian f it to f it2D SingleLorentzian 2D Peak
D
40
2.5 2.0 1.5 1.0 0.5
D
500
0.0 1500
2000
2500
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30 nm (d)
(b)
c/s (x105) arb. units
4500 wrinkles
-O 1s
0
-C KLL
2640
3.0
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800 600 400 Binding Energy (eV)
-Si 2s -Si 2p -O 2s
1500
2645
-O KLL
G
2000
3.5
2650
-C 1s
Counts
2500
(c) 4.0 26
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