  We demonstrate ambipolar graphene field effect transistors individually
controlled by local metal side gates. The side gated field effect can have
on/off ratio comparable with that of the global back gate, and can be tuned in
a large range by the back gate and/or a second side gate. We also find that the
side gated field effect is significantly stronger by electrically floating the
back gate compared to grounding the back gate, consistent with the finding from
electrostatic simulation.
