High-Mobility Dual-gated Graphene Field-Effect Transistors with Al$_{2}$O$_{3 }$Dielectric*

The carrier mobility in graphene field-effect transistors (GFETs) is primarily dominated by the extrinsic impurity scattering, such as charged impurities in the dielectric. Therefore, the impact of a top-gate dielectric stack on the transport characteristics of graphene represents a key issue for high-performance GFETs. Here, we present the fabrication and characterization of dual-gated graphene FETs and dual-gated graphene devices with Hall bar geometry using Al$_{2}$O$_{3}$ as top-gate dielectric. We use a thin Al film as a nucleation layer to enable the atomic layer deposition of Al$_{2}$O$_{3}$. Our FETs show mobility values of over 6,000 cm$^{2}$/Vs at room temperature, a finding which indicates that the top-gate stack does not significantly increase the carrier scattering, and consequently degrade the device characteristics. We propose a device model to fit the experimental data with a single mobility value.