The mass production and consequent commercial adoption of graphene-based devices is still held back by a few crucial technical challenges related to quality control. In the case of graphene produced by chemical vapor deposition (CVD), the transfer process represents a delicate step that can compromise device performance, thus hindering industrial production. In this context, the impact of poly(methyl methacrylate) (PMMA) – the most common support material for transferring graphene from the Cu substrate to any target surface – can be decisive in obtaining reproducible sample batches. Although effective in mechanically supporting graphene during the transfer, PMMA solutions needs to be efficiently designed, deposited, and post-treated to serve their purpose while minimizing potential contaminations. Here, we prepared and tested PMMA solutions with different average molecular weight (AWM) and weight concentration in anisole, to be deposited by spin coating. Optical microscopy and Raman spectroscopy showed that the amount of PMMA residues on transferred graphene is proportional to the AMW and concentration in the solvent. Meanwhile, the mechanical strength of the PMMA layer resulted proportional to the AMW. These tests served to design an optimized PMMA solution made of a mixture of 550k and 15k AMW PMMA in anisole at 3% concentration. In this design, PMMA-550k provided a suitable mechanical strength against breakage during the transfer cycles, while PMMA-15k promoted de-polymerization which allowed a complete removal of PMMA residues without the need for any post-treatment. An XPS analysis confirmed the cleanness of the optimized process. We validated the impact of the optimized PMMA solution in the mass-fabrication of arrays of electrolyte graphene field effect transistors operating as biosensors. On average, the transistor channel resistance decreased from 1860 Ω to 690 Ω when using the optimized PMMA. Even more importantly, the vast majority of these resistance values are distributed within a narrow range (only ~300 Ω wide), in evident contrast with the scattered values obtained in non-optimized devices (~30% showed values above 1 MΩ). These results prove that the optimized PMMA solution unlock the production of reproducible electronic devices over batch scale, key towards an industrial production.
Keywords: 2D materials, poly(methyl methacrylate), graphene transfer process, large-scale fabrication, microelectronics
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Liao, C.-D.; Capasso, A.; Queirós, T.; Domingues, T.; Cerqueira, F.; Nicoara, N.; Borme, J.; Freitas, P.; Alpuim, P. Beilstein Arch. 2022, 202242. doi:10.3762/bxiv.2022.42.v1
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