Monolayer Solid-State Electrolyte for Electric Double Layer Gating of Graphene Field-Effect Transistors

The electrostatic gating of graphene field-effect transistors is demonstrated using a monolayer electrolyte. The electrolyte, cobalt crown ether phthalocyanine (CoCrPc) and LiClO4, is deposited as a monolayer on the graphene channel, essentially creating an additional two-dimensional layer on top of graphene. The crown ethers on the CoCrPc solvate lithium ions and the ion location is modulated by a backgate without requiring liquid solvent. Ions dope the channel by inducing image charges; the doping level (i.e., induced charge density) can be modulated by the backgate bias with the extent of the surface potential change being controlled by the magnitude and polarity of the backgate bias. With a crown ether to Li+ ratio of 5:1, programming tests for which the backgate is held at −VBG shift the Dirac point by ∼15 V, corresponding to a sheet carrier density on the order of 1012 cm–2. This charge carrier density agrees with the packing density of monolayer CoCrPc on graphene that would be expected with one Li...