  We propose two schemes of field-effect transistor based on gapped armchair
graphene nanoribbons connected to metal leads, by introducing sidearms or
on-site gate voltages. We make use of the band gap to reach excellent
switch-off character. By introducing one sidearm or on-site gate to the
graphene nanoribbon, conduction peaks appear inside the gap regime. By further
applying two sidearms or on-site gates, these peaks are broadened to conduction
plateaus with a wide energy window, thanks to the resonance from the dual
structure. The position of the conduction windows inside the gap can be fully
controlled by the length of the sidearms or the on-site gate voltages, which
allows "on" and "off" operations for a specific energy window inside the gap
regime. The high robustness of both the switch-off character and the conduction
windows is demonstrated and shows the feasibility of the proposed dual
structures for real applications.
