Carbon Nanotube Single-electron Transistors Research Articles

An analytical approach to model capacitance and resistance of capped carbon nanotube single electron transistor

The single electron transistor (SET) as a nanoscale transistor operates according to the electron tunneling via two tunnel junctions. Since selecting a suitable island material plays a key role in electron transfer through the tunnel junctions, in this research capped Carbon NanoTube (CNT) is utilized for the SET island which produces the quantum capacitance (CQ). Its low value decreases the total capacitance (CT). Subsequently the coulomb blockade (CB) energy and the critical temperature are reduced. Moreover the resistance of the capped CNT as a two dimensional material is very low thus its effect on the total resistance can be neglected. The result of an investigation on the capped CNT SET tunnel junction shows that the tunneling time of electron into or out of island decreases therefore the operation speed of capped CNT SET increases. Furthermore both the resistance and the quantum capacitance are modeled and analyzed. Comparison studies of proposed models indicate that the capped CNT length and applied bias voltage play effective roles on the resistance. Additionally the capped CNT SET is simulated and the capped CNT SET stability diagrams are analyzed. The simulation result shows that the lower capped CNT length exhibits a smaller coulomb diamond regions. The lower CB range leads to faster capped CNT SET and a better reliability can be achieved.

Carbon nanotube single-electron transistors with single-electron charge storages

Carbon nanotube single-electron transistors (CNTSETs) with single-electron charge storages were fabricated to detect single-electron charges from a CNT channel to a charge storage. A single-electron charge storage is composed of Au floating dots between tunneling and blocking layers of Al2O3. Electrons were injected into a Au floating dot by sweeping gate voltage, and the Coulomb peak was shifted owing to the effect of electrons inside the Au floating dot. In addition, a staircase relationship between the charging voltages and the peak positions was observed. The calculation based on this staircase relationship revealed that the single-electron charging into the Au floating dot was obtained. Therefore, our devices are one of the candidates for CNTSET-based single-electron memories, which can be used for digital operating and ultralow-power consumption devices.

Low temperature electron transport spectroscopy of mechanically templated carbon nanotube single electron transistors

We report electronic transport investigations of mechanically templated carbon nanotube single electron transistors (SETs). The devices were fabricated on a Si/SiO2 substrate by controllably placing individual single walled carbon nanotubes (SWNTs) between the source and drain electrodes via dielectrophoresis with a 100 nm wide local Al/Al2O3 bottom gate in the middle. From the low temperature electronic transport measurements, we show that a quantum dot is formed whose charging energy can be tuned from 10 to 90 meV by varying both the local gate and Si backgate. The temperature dependent measurements show that the Coulomb oscillations persist up to 250 K. The transport properties can be explained by a simple potential configuration, which suggests that two tunnel barriers are formed due to the bending of the SWNT at the local gate edges and that the size of the dot and tunnel barrier transparency can be tuned by the gates allowing the operation of SET in a wide temperature range and thereby realizing a controllable and tunable SET. Our simple fabrication technique and its tunability over a large temperature range could facilitate large scale fabrication of SET for practical applications.

Asymmetric magnetoconductance and magneto-Coulomb effect in a carbon nanotube single electron transistor

We report single step-like asymmetric magnetoconductance from a double-walled carbon nanotube single electron transistor contacted by ferromagnetic cobalt electrodes. The device conductance changed significantly when the direction of the applied magnetic field was reversed, but did not show the spin-valve-type double extrema feature near the coercive field of the electrodes. The magnetoconductance also showed quasi-periodic sign-reversing oscillations with respect to the applied bias. The bias-dependent oscillation of the magnetoconductance was compared with the quantum dot stability diagram for the device. As a result, it was confirmed that the asymmetric magnetoconductance was caused by the magneto-Coulomb effect.

Room-Temperature Carbon Nanotube Single-Electron Transistors Fabricated Using Defect-Induced Plasma Process

We propose and demonstrate the “defect-induced plasma process” for the fabrication of the room-temperature-operated carbon nanotube single-electron transistors (CNT-SETs) with the SiO2 protection films on the CNT channels. After introducing of defects in the CNT channels by O2 plasma irradiation through the SiO2 protection films, multi-quantum dots were fabricated in the CNT channels. The electrical properties of the CNT-SETs suggested that the oscillation in the drain currents as a function of the gate voltage was observed at room temperature, as a result of the Coulomb blockade effect. Moreover, we report that the yield of the CNT-SETs depended on the thickness of the SiO2 protection films on the CNT channels for the purpose of obtaining a high yield of CNT-SETs. The results indicate that the high yield of the CNT-SETs is as high as approximately 35% when the SiO2 protection film thickness is 60 nm. Consequently, the defect-induced plasma process is useful for obtaining the high yield efficiency of CNT-SETs operating at room temperature.

Improved temperature characteristics of single-wall carbon nanotube single electron transistors using carboxymethylcellulose dispersant

Single-wall carbon nanotube (SWNT) based single electron transistors were fabricated by the dispersion method using carboxymethylcellulose (CMC) as a dispersant to make SWNT suspension. The temperature characteristics were improved compared to the one fabricated with a Triton X-100/water SWNT suspension, so that the regular Coulomb oscillations were observed up to 80K. This could be due to the increased barrier height, which may be originated from extra dipoles induced by the adsorbed CMC molecules at the SWNT/metal interface.

Fabrication Technique for Carbon Nanotube Single-Electron Transistors Using Focused Ion Beam

We have proposed a technique for fabricating carbon nanotube single-electron transistors using a focused ion beam (FIB). Wiring to a multiwalled carbon nanotube was formed by the ion-beam-assisted deposition of tungsten. Tunneling barriers were formed in the nanotube by ion beam etching. A drain current oscillation originating from the Coulomb blockade effect was observed at 23 K.

Localized states and conductance gaps in metallic carbon nanotubes

We have found that a purely metallic carbon nanotube consisting of a nanometer-size metallic island connected to another two metallic leads gives rise to discrete energy levels, thus behaving as metallic quantum dot. Remarkably, we find discrete levels not only when the constituent tubes have a symmetry gap, but also in structures made of tubes without a common symmetry. In the latter case, the states are actually sharp resonances; we attribute these quantum size effects to the wave-vector mismatch between the available states of the constituent tubes. When there is a symmetry gap, the conductance vanishes for a wide energy window. Otherwise, nonzero conductance values occur for a series of resonances coupled to the leads continua, yielding interesting transport characteristics that may be exploited for carbon nanotube single-electron transistors.

Observing 2-channel Kondo physics in a carbon nanotube single-electron transistor

Recently, Coulomb blockade physics was observed at room temperature in a carbonnanotube single-electron transistor (Postma et al 2001 Science 293 76). In thiswork, we suggest that these devices may be promising for observing 2-channelKondo physics, and allow for a detailed investigation of the 2-channel Kondo fixedpoint. Experimental signatures of the Kondo effect in these systems are discussed.