▎ 摘　　要

An improved cut-off frequency model of a modified equivalent circuit of graphene field-effect transistors, which incorporates the additional capacitive effect physically present due to dipole layer between the metal and the graphene, is proposed. The original equivalent circuit is not accurate for a large separation distance dipole layer. Based on the improved equivalent circuit model, a more accurate parameter extraction by two-port analysis is possible, and the cut-off frequency will be more accurate particularly for largely separated dipole layer near the Dirac point. Considering the dipole layer, the equivalent circuit is never investigated before, and the cut-off frequency model shows good agreement with experiments.