Developments of high performance n-type carbon nanotube field-effect transistors

As scaling down with Moore's law, the modern silicon complementary metal­oxide­semiconductor (CMOS) technology is facing great challenges and people are looking for alternatives. Carbon nanotube (CNT), due to its novel structure and properties, has been regarded as one of the most promising building blocks for the future integrated circuits. Since the first CNT field­effect transistor (CNTFET) was designed in 1998, device performance hasbeen continually improved. By using palladium (Pd) electrodes and high­k materials (which are less prone to current leakage) as gate dielectrics, p­type CNTFETs have now surpassed the capabilities of state­of­the­art silicon p­MOSFETs. However, the development of n­type CNTFETs has lagged behind. This is mainly due to the difficulty of fabricating a Schottky barrier­free contact between metal electrodes and the conduction band of the CNT. The slow progress in producing n­CNTFETs has greatly hindered the development of CNT­based integrated circuits. We Recently discovered that scandium (Sc) can be used to generate an ohmic contact with the conduction band of a CNT and high performance n­type CNTFETs can be easily fabricated. Based on this discovery, we proposed an CNT­based doping­free CMOS technology and pushed the limits of n­ type CNTFETs. We also demonstrated a design of whole carbon nanotube circuits by integrating Multi­Walled CNTs with the Single­Walled CNTFETs which serve as interconnects. All of our results show a prospective future of CNT­based integrated circuits. ----