Carbon nanotubes (CNTs) exhibit several technologically important characteristics such that metallic nanotubes can carry extremely large current densities; semiconducting nanotubes can be electrically switched on and off as field effect transistors (FETs), and so on CNT FETs with characteristics comparable to or exceeding state of the art Si based transistors have been demonstrated using a conventional FET design with high-κ <sup>1)</sup> and SiO<sub>2</sub> dielectric <sup>2)</sup>. In addition, CNTs have been successfully demonstrated as biological sensors with high sensitivity. It has been reported that the real time detection of single viruses <sup>3)</sup>, small molecules <sup>4)</sup>, and proteins <sup>5)</sup>, <sup>6)</sup> becomes is possible with biosensors that use CNT transistors as the active transducer. For these applications of CNTs, the control of the number of CNT between electrodes is quite important technology. However, it is quite difficult and has not been realized yet. It is therefore, indispensable to control it for the future applications of CNT. In the present study, we have established the new technology to control the number of the CNT one by one during the growth of CNT by monitoring the electrical current between electrodes, which is named as "Digital Growth Process".
Proc. SPIE. 6127, Quantum Sensing and Nanophotonic Devices III
KEYWORDS: Carbon, Atomic force microscopy, Scanning electron microscopy, Capacitance, Measurement devices, Transistors, Atomic force microscope, Field effect transistors, Temperature metrology, Carbon nanotubes
We successfully fabricated single electron transistors (SETs) operating at room temperature with carbon nanotube (CNT) channel having different island sizes. The fabrication of the CNT SETs is performed by electrical manipulation using non-contact mode atomic force microscope (AFM). We carried out cutting or nicking of CNTs by applying negative voltage between a metal-coated AFM tip and CNT. A precise control over the CNT dot size was achieved by changing the nicking distance and CNT SETs with a dot size of 15 and 22 nm were fabricated. By changing the size of the dot we could arbitrarily change the operation characteristics of the device where the period of oscillations increases as the dot size decreases.
We have succeeded in observing the coexistence of the Coulomb charging effect and the coherent transport of the hole in a single-walled carbon nanotube (SWNT) with a length of 4.5 μm at 8.6 K. SWNT channel field-effect transistor (FET) structures were prepared with two different channel lengths of 4.5 and 1.4 μm. The samples showed p-type semiconductor characteristics under large gate and drain biases at 8.6 K. At 8.6 K, on the other hand, single-hole transistor characteristics with different Coulomb charging energies corresponding to the length of the channel were observed in each sample. Drain current peaks with different periods corresponding to the length of the channel were also observed outside of the Coulomb blockade area for the higher drain voltages in each sample. The drain current peaks are attributed to resonant tunneling of the hole through the separation of the quantum energy levels originating from coherent transport of the hole in the entire semiconductive SWNT.