A high-mobility dual-gated graphene field-effect transistor (FET) with an Al₂O₃ dielectric is reported. The device uses a thin Al nucleation layer to enable atomic layer deposition (ALD) of Al₂O₃ on graphene. The fabricated devices exhibit a carrier mobility of over 8,000 cm²/V·s at room temperature, indicating that the top-gate stack does not significantly increase carrier scattering. A device model incorporating quantum capacitance is developed and agrees well with experimental data, extracting mobility, initial charge density, and contact resistance. Graphene, a single- or few-layer sp²-bonded carbon, has been studied for its high electron mobility and potential in electronic devices. The fabrication of graphene-based FETs requires a uniform gate dielectric with high dielectric constant and low interface state density. While SiO₂ has been used for silicon-based devices, ALD of high-κ dielectrics like Al₂O₃ on graphene is challenging due to the hydrophobic nature of the graphene basal plane. Surface treatments and nucleation layers are used to enable ALD growth of Al₂O₃ on graphene. The Al₂O₃ dielectric is deposited using a thin Al nucleation layer, which is oxidized before ALD. The resulting devices show minimal carrier mobility degradation compared to graphene without a top dielectric. The transport characteristics are measured at room temperature, with the top-gate electrode and Si substrate acting as local and global gates, respectively. The device shows a high dielectric quality with a low interface state density. The model for the device characteristics is based on carrier concentration and quantum capacitance. The extracted mobility is 8,600 cm²/V·s, and the residual carrier concentration is 2.3×10¹¹ cm⁻². The mobility is primarily determined by fixed impurity scattering, with minimal temperature dependence. These results demonstrate the potential of Al₂O₃ as a high-κ dielectric for graphene-based FETs, enabling high-speed devices and novel designs.A high-mobility dual-gated graphene field-effect transistor (FET) with an Al₂O₃ dielectric is reported. The device uses a thin Al nucleation layer to enable atomic layer deposition (ALD) of Al₂O₃ on graphene. The fabricated devices exhibit a carrier mobility of over 8,000 cm²/V·s at room temperature, indicating that the top-gate stack does not significantly increase carrier scattering. A device model incorporating quantum capacitance is developed and agrees well with experimental data, extracting mobility, initial charge density, and contact resistance. Graphene, a single- or few-layer sp²-bonded carbon, has been studied for its high electron mobility and potential in electronic devices. The fabrication of graphene-based FETs requires a uniform gate dielectric with high dielectric constant and low interface state density. While SiO₂ has been used for silicon-based devices, ALD of high-κ dielectrics like Al₂O₃ on graphene is challenging due to the hydrophobic nature of the graphene basal plane. Surface treatments and nucleation layers are used to enable ALD growth of Al₂O₃ on graphene. The Al₂O₃ dielectric is deposited using a thin Al nucleation layer, which is oxidized before ALD. The resulting devices show minimal carrier mobility degradation compared to graphene without a top dielectric. The transport characteristics are measured at room temperature, with the top-gate electrode and Si substrate acting as local and global gates, respectively. The device shows a high dielectric quality with a low interface state density. The model for the device characteristics is based on carrier concentration and quantum capacitance. The extracted mobility is 8,600 cm²/V·s, and the residual carrier concentration is 2.3×10¹¹ cm⁻². The mobility is primarily determined by fixed impurity scattering, with minimal temperature dependence. These results demonstrate the potential of Al₂O₃ as a high-κ dielectric for graphene-based FETs, enabling high-speed devices and novel designs.