▎ 摘　　要

The effect of source-gate spacing on graphene filed effect transistors has been investigated. Reducing the source gate spacing allows for a significant improvement on both the direct current and radio frequency (RF) performances. Instead of the generally considered output conductance, our results suggest that the access resistances at the un-gated region contribute more to the maximum oscillation frequency (f(max)). Further analysis reveals that the ratio of cut off frequency (f(T)) to f(max) is also sensitive to the resistances at source-gate spacing. This work can be used to guide the further optimization of graphene-based RF devices. (C) 2015 AIP Publishing LLC.