Drain-engineered carbon-nanotube-film field-effect transistors with high performance and ultra-low current leakage

A small bandgap and light carrier effective mass (m₀) lead to obvious ambipolar transport behavior in carbon nanotube (CNT) field-effect transistors (FETs), including a high off-state current and severe degradation of the subthreshold swing (SS) with increasing drain bias voltage. We demonstrate a drain-engineered method to cope with this common problem in CNT-film FETs with a sub-μm channel length, i.e., suppressing the ambipolar behavior while maintaining high on-state performance by adopting a feedback gate (FBG) structure to extend the drain region from the CNT/metal contact to the proximate CNT channels to suppress the tunneling current. Sub-400-nm-channel-length FETs with a FBG structure statistically present a high on/off ratio of up to 10⁴ and a sub-200 mV/dec SS under a high drain bias of up to -2 V while maintaining a high on-state current of 0.2 mA/μm or a peak transconductance of 0.2 mS/μm. By lowering the supply voltage to 1.5 V, FBG CNT-film FETs can meet the requirement of standard-performance ultra large scale integrated circuits (ULSICs). Therefore, the introduction of the drain engineering structure enables applications of CNT-film-based FETs in ULSICs and could also be widely extended to other small-bandgap semiconductor-based FETs for an improvement in their off-state property.