Evaluation of Disorder Introduced by Electrolyte Gating through Transport Measurements in Graphene

We evaluate the degree of disorder in electrolyte gating devices through the transport measurements in graphene. By comparing the mobility in ion- and standard metal-gated devices, we show that the deposition of the ionic liquid introduces charged impurities with a density of approximately $6\times 10^{12}$ cm$^{-2}$; setting the upper limit of the mobility in graphene to 3000 cm$^2$/Vs. At higher temperature, phonons in the ionic liquid further reduce the mobility, making its upper limit 2000 cm$^2$/Vs at room temperature. Since the degree of disorder is independent of the base material, these results are valuable towards understanding disorder effects in general devices using electrolyte gating.