We discuss a fabrication process for making graphene devices based on encapsulated graphene for reducing contaminations during individual processing steps. A 3–5 nm alumina layer is deposited directly after exfoliating graphene, protecting it during the entire processing. We show that the visibility of the encapsulated graphene is sufficient to identify graphene flakes and Raman spectra exhibit the characteristic finger print. We perform transport measurements to study the sample quality and compare the results with graphene samples processed without an alumina layer. In particular we observe a higher yield and significantly reduced contact resistances for devices fabricated with the here presented method.
Graphene flake with metal (Cr/Au) contacts covered with an ultra-thin (3–5 nm) oxidized aluminum layer (left) and without the layer (right).