Ambipolar-to-unipolar conversion of carbon nanotube transistors by gate structure engineering

The switching behavior of carbon nanotube field-effect transistors (CNFETs) can be improved by decreasing the gate oxide thickness. However, decreasing the oxide thickness also results in more pronounced ambipolar transistor characteristics and higher off-currents. To achieve high-performance unipolar CNFETs as required for CMOS logic gates, we have fabricated partially gated CNFETs with an asymmetric gate structure with respect to the source and drain electrodes. With our gate structure engineering concept, p-type CNFETs have been fabricated from an ambipolar CNFET. It is also found that fringing fields from source and drain are important in determining the CNFET behavior as the device size decreases.