  We fabricate and characterize dual-gated graphene field-effect transistors
(FETs) using Al2O3 as top-gate dielectric. We use a thin Al film as a
nucleation layer to enable the atomic layer deposition of Al2O3. Our devices
show mobility values of over 8,000 cm2/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 using a single mobility value.
