Combinational and sequential logic with transistors based on individual carbon nanotubes

Field-effect transistors (FETs) that utilize an individual semiconducting carbon nanotube (CNT) as the channel are potentially useful for the realization of logic circuits with high integration densities that can be fabricated on transparent, large-area substrates, such as glass or flexible plastics. While FETs based on individual CNTs have already demonstrated excellent static characteristics [1,2], the realization of logic circuits with good static and dynamic performance based on individual-CNT FETs remains a challenge. Bachtold et al. realized 2-input NOR gates by connecting p-channel CNT FETs to external load resistors using coaxial cables and reported a signal delay of 30 msec per stage for a 3-stage unipolar ring oscillator [3]. Javey et al. realized complementary 2-input NAND, AND, NOR and OR gates by connecting p- and n-channel CNT FETs using coaxial cables and measured a delay of 750 µsec for a 3-stage ring oscillator [4]. The only monolithically integrated circuit based transistors utilizing individual carbon nanotubes was reported by Chen et al. who measured a signal delay of 1.9 nsec per stage in a complementary ring oscillator realized on a very long (19 µm) carbon nanotube [5].