Graphene field-effect transistors for RF applicatoins

There has been growing interest in graphene as a replacement for III-V materials in MMIC applications because of its high mobility, its potential for high saturation velocity, and its nearly perfect two-dimensional electrostatics. We present results from the first experimental high-frequency measurements of graphene field-effect transistors (GFETs), demonstrating an f$_{T}$ of 14.7 GHz for a 0.5-$\mu $m-length device with a 30-nm-thick HfO$_{2}$ top-gate. Despite I$_{on}$/I$_{off} \quad \sim $7, high transconductances ($>$833 $\mu $S/$\mu $m) and current saturation are achieved. We present detailed measurement and analysis of velocity saturation in GFETs, demonstrating the potential for velocities approaching 10$^{8 }$cm/sec and the effect of an ambipolar channel on current-voltage characteristics. We find that the saturation velocity is sheet-carrier dependent and limited by interfacial phonon scattering from the SiO$_{2}$ substrate upon which the graphene is fabricated.