Their paper was published in Nature in just two days before.
They used a Co2Si–Al2O3 core–shell nanowire as a top gate electrode which is able to apply an electric field across the thin layer of Al2O3 that serve as a gate dielectric. Apparently, the gating effect would be far more large than that of back-gated configuration, since the dielectric layer is extremely thin and possess higher dielectric constant than SiO2. To fulfill the requirements of microwave measurement, they replaced the degenerate silicon substrate with highly resistive ones that could effectively reduce the dielectric loss at microwave frequency. And they found that the cutoff frequency could be up to 300GHz, which increases the usability of graphene transistor at high frequency.
