▎ 摘　　要

We demonstrate a 500-nm graphene frequency doubler with a record 3-GHz bandwidth, exceeding the device transit frequency by 50%, a previously unobserved result in graphene, indicating that graphene multiplier devices might be useful beyond their transit frequency. The maximum conversion gain of graphene ambipolar frequency doublers is determined to approach a near lossless value in the quantum capacitance limit. In addition, the experimental performance of graphene transistor frequency detectors is demonstrated, showing responsivity of 25.2 mu A/mu W. The high-frequency performance of these gigahertz devices is enabled by top-gate device fabrication using synthesized graphene transferred onto low capacitance, atomically smooth quartz substrates, affording carrier mobilities as high as 5000 cm(2)/Vu.s.