▎ 摘　　要

The dc and microwave experiments on a top-gate field effect transistor based on graphene, at and far from the Dirac point, are reported. Far from the Dirac point the transistor behaves as an active device, while at the Dirac point the transistor becomes a passive device, its amplification being suppressed due to a reduction in the carrier density. Microwave switches can be implemented using this property. The maximum stable gain of the transistor is preserved up to 5 GHz. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3358124]