Comparison between stamping method and one-by-one dry-transfer method for the fabrication of h-BN sandwiched graphene FET in the quantum Hall regime

We have fabricated a dual-gate graphene field-effect-transistor (FET) for the study of integer Quantum Hall Effect in terms of its edge-state transport. The graphene was encapsulated by hexagonal boron-nitride (h-BN) flakes without any interlayer residues using the `stamping-transfer' method, which is critical for the observation of graphene's intrinsic transport properties. Using the poly propylene carbonate (PPC) and Polydimethylsiloxane (PDMS), initially top h-BN flake is picked up and then graphene flake is picked up by van der Waals' force between graphene and top h-BN. These two layers are dropped down on the bottom h-BN flake to complete the encapsulated formation. To make the source/drain (S/D) and top-gate electrodes, whole area of graphene is not covered by top h-BN flake. The open areas of graphene, located at both ends, are covered by S/D metal electrodes, which made whole graphene channel region sandwiched by top and bottom hBN. We compared this method with the old one which put the two-dimensional flakes one by one using `dry-transfer'' method, and found out a significant difference in the device quality especially at low temperatures and high magnetic fields in the quantum Hall regime.