Graphene Devices Processing Using Direct Writing Laser Lithography and Electrical Properties Characteristics
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Graphene Devices Processing Using Direct Writing Laser Lithography and Electrical Properties Characteristics J. A. Leon*, E. S. Alves, D. C. Elias, L. M. Moreira, T. C. Barbosa, M. A. Pimenta, and F. O. Plentz Department of Physics, Federal University of Belo Horizonte, 30161-970, Belo Horizonte, MG, Brazil
ABSTRACT In this work, we establish the use of lithography technique by laser direct writing for fabricating bilayer graphene devices. This technique, which is based on direct laser writing on graphene coated with a photoresist is simple to implement, versatile, and capable of achieving good throughput. Double-layer graphene flakes were obtained by micromechanical cleavage of graphite producing large graphene samples up to 40µm in size. The presence of a bilayer of graphene on SiO2/Si substrate was verified by optical microscopy and resonant Raman spectroscopy. We have measured the four-terminal resistance as a function on the back-gate voltage and found initially p-type doping in graphene, but annealing inside cryostat at 127C° in He atmosphere, the samples become n-type. Our measurements show electron mobility reached values around ~1,900 cm2/V.s at high electron concentration.
INTRODUCTION So far, many graphene devices reported in the literature were fabricated by e-beam lithography (EBL). EBL is convenient since it delivers very high resolution, up to 10nm line width, and also devices with arbitrary shape can be directly written over the irregular graphene flakes. On the other hand it requires alignment marks to be previously patterned over the substrate or the e-beam resist, can subject graphene to unwanted irradiation by energetic electrons and, in general, require a separate step to define larger structures such as bonding pads. Multiple steps can also subject graphene to unwanted contamination and disorder and is also time consuming. Conventional photolithography is difficult to apply to make graphene devices. Although it is not difficult to achieve 1µm or better resolution, conventional photolithography requires the use of photomasks and it is not practical to make many different masks to suit graphene flakes with various shapes or different device structures. Therefore it is desirable to pursue alternative graphene device fabrication. In this work we describe the application of direct write laser lithography (DWL) to the fabrication of bilayer graphene devices (BGL). DWL is a maskless lithography technique that uses the combination of a tightly focused laser beam that is properly modulated and scanned over the substrate, and a high precision XYZ stage to write the patterns directly on the substrate. Devices fabricated were characterized by resistivity
measurements as a function on the gate voltage before and after an annealing step in He atmosphere.
EXPERIMENTAL DETAILS For the deposition of BLG we used p-type Si substrates with a 300nm of thermal SiO2. This SiO2 thickness makes BLG readily observed under the optical microscope [1]. To exfoliate the graphite we used a method similar to
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