A New Transfer Technique for Graphene Deposited by CVD on Metal Thin Films
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A New Transfer Technique for Graphene Deposited by CVD on Metal Thin Films G. Amato1, E. Simonetto1,3, L. Croin1,3, E. Vittone2 1
The Quantum Research Laboratory, INRIM, strada delle Cacce 91, I-10135, Torino, Italy
2
Physics Dept. and NIS center, University of Turin, Via Pietro Giuria 1, I-10125, Torino, Italy.
3
Dept. of Applied Science and Technology, Polytechnic of Turin, Corso Duca degli Abruzzi 24, I-10129, Torino, Italy ABSTRACT Chemical Vapor Deposition of graphene on metallic substrates is one of the most attracting techniques for large area graphene production. The technique widely employed for transferring graphene to other substrates involves deposition of a polymer support with subsequent etching of the metal substrate. Here we report a safer transfer process, which requires a two-step PMMA deposition and bonding under pressure. Sheets of graphene before and after transfer have been both characterized by Raman spectroscopy, and show comparable quality, indicating that the proposed technique does not introduce additional defects in graphene. INTRODUCTION Graphene can be obtained by Chemical Vapor Deposition (CVD) by means of a catalytic Cu substrate and large area production, ideally along the entire surface of the metal catalyst, is achievable. The need of a stable and reproducible transfer technique is therefore becoming increasingly important since, for electrical measurements or device fabrication, an insulating substrate is required. The simplest graphene transfer method consists in the wet etching of the underlying Cu substrate using for example ferric chloride, ferric nitrate, or acids (usually nitric acid) and the consecutive collection of the graphene layer with the new substrate from the solution. The most popular improvement of this method consists in coating graphene by an insulating and non-reactive polymer like polymethyl-methacrylate (PMMA) or polydimethylsiloxane (PDMS), acting as a support, and then to etching away the Cu substrate. The graphene-polymer system, floating in the etching solution, is then picked up and laid onto the desired substrate, e.g. SiO2. Finally the PMMA support is dissolved in a suitable solvent [1], [2]. Another transfer solution, promising for its industrial implications is the roll-to-roll technique. It has been proposed firstly in 2010 [3] showing a 30-inch transfer from a Cu foil to a PET film. A similar method, integrating the CVD growth, has also been proposed by Kobayashi et al [4]. These promising transfer methods are all oriented toward the integration of graphene onto flexible substrates. However, for microelectronics applications, interest is growing for transfer techniques to rigid substrates, like Si wafers. A method proposed leads to avoid the use of a polymeric support layer and to transfer graphene directly on silanized SiO2 [5]. Recently, the growth of graphene on copper thin films has been underlined to be advantageous because it
allows for a face-to-face process that accomplishes for both growth and transfer on the same SiO2/Si wafer [6].
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