Wall Carbon Nanotube Field Effect Research Articles

(Invited) Single Ion Adsorption on Individual Isolated Single Walled Carbon Nanotube Field Effect Transistors

The detection of single ions has, for many years, been the domain of large devices such as the Geiger counter, and to date, there have been no studies investigating the effects of ions on materials and devices at the single-ion level, despite the widespread use of gaseous ions to modify material surface properties, for instance by corona discharge. Here, we report on single gaseous ion adsorption onto individual carbon nanotube field effect transistors, which, due to the severely restricted one-dimensional current path, experience discrete, quantized resistance increases of over two orders of magnitude [1]. Switching events were observed during exposure to lightly ionized nitrogen, helium, oxygen, argon and air. This is in contrast to single neutral atom adsorption detection techniques, which have shown only small, barely detectable responses. Only positive ions cause changes, by the mechanism of ion potential induced carrier depletion, which is supported by density functional and Landauer transport theory. Our observations reveal a new single-ion/CNT heterostructure with novel electronic properties, and demonstrate a powerful new system for studying ion adsorption dynamics at the single-ion level. [1] Bushmaker, A. W. et al. Single-ion adsorption and switching in carbon nanotubes. Nature Communications, 7, 10475, DOI: 10.1038/ncomms10475 (2016).

Directed Assembly of Single Wall Carbon Nanotube Field Effect Transistors.

The outstanding electronic properties of single wall carbon nanotubes (SWCNTs) have made them prime candidates for future nanoelectronics technologies. One of the main obstacles to the implementation of advanced SWCNT electronics to date is the inability to arrange them in a manner suitable for complex circuits. Directed assembly of SWCNT segments onto lithographically patterned and chemically functionalized substrates is a promising way to organize SWCNTs in topologies that are amenable to integration for advanced applications, but the placement and orientational control required have not yet been demonstrated. We have developed a technique for assembling length sorted and chirality monodisperse DNA-wrapped SWCNT segments on hydrophilic lines patterned on a passivated oxidized silicon substrate. Placement of individual SWCNT segments at predetermined locations was achieved with nanometer accuracy. Three terminal electronic devices, consisting of a single SWCNT segment placed either beneath or on top of metallic source/drain electrodes were fabricated. Devices made with semiconducting nanotubes behaved as typical p-type field effect transistors (FETs), whereas devices made with metallic nanotubes had a finite resistance with little or no gate modulation. This scalable, high resolution approach represents an important step forward toward the potential implementation of complex SWCNT devices and circuits.

Effect of parametric variation on the performance of single wall carbon nanotube based field effect transistor

The effects of dielectric constant and gate insulator thickness on the performance of single wall carbon nanotube field effect transistors (CNTFETs) have been analyzed using a mathematical model based on FETToy simulator. Both the parameters are found to have significant effect on the device performance, particularly the on-current; while the on-current (ION) increases on scaling down the gate oxide thickness, the level of leakage current (IOFF) is not considerably affected. This is an advantage of CNTFET over conventional MOSFETs where the thickness of thin oxide layer causes drastic increase in gate leakage current. Our analysis results show that thinner gate oxide and larger CNT improve the performance of CNTFETs. Therefore, the performance of our simulated CNTFETs using this model has clear lead over those of conventional MOSFETs.

Ultra low power dual-gate 6T and 8T stack forced CNFET SRAM cells

In this paper, two ultra-low power Single Walled Carbon Nanotube Field-Effect Transistor (SWCNFET) based SRAM cells are proposed to minimize static power dissipation due to leakage. The proposed first cell consists of six transistors (6T) with dual-gate n-type CNFETs whose back gates are negatively biased and the second cell employs stack forcing in the pull down n-type transistors of the cell, resulting in a symmetric eight transistor (8T) SRAM cell structure. The cells are designed with dual chirality and analyzed through simulation at two different temperatures (25°C and 110°C). A 6T CNFET based SRAM with dual chirality presented in reference literature is taken as reference for benchmarking the performance of the proposed cells. The proposed cells are effective in reducing the leakage power by more than 35% at 25°C and more than 60% at 110°C during standby mode of operation. Write leakage and average write power are also minimized at the expense of minimal increase (less than 5%) in write delay.

A dual analyzer for real-time impedance and noise spectroscopy of nanoscale devices

This paper introduces a simple portable dual analyzer which allows real-time ac-impedance measurements and noise spectroscopic analysis simultaneously, employing one or two data acquisition systems together with a low noise current-to-voltage preamplifier. The input signal composed of numerous selected frequencies of sinusoidal voltages with a dc bias was applied to a device under the test (DUT): single walled carbon nanotube field effect transistors (SWCNT-FETs). Each frequency component, ranging from 1 to 46.4 kHz, was successfully mapped to a Nyquist plot using the background of the electrical noise power spectrum. It is, thus, clearly demonstrated that this dual analyzer enables the real-time ac-impedance analysis and the frequency response of the carrier transport in the SWCNT-FETs as a DUT.

Characterization of Electrical Properties and Gating Effect of Single Wall Carbon Nanotube Field Effect Transistor

We attempted to fabricate carbon nanotube field effect transistor (CNT-FET) using single walled carbon nanotube(SWNT) on the heavily doped Si substrate used as a bottom gate, source and drain electrode were fabricated bye-beam lithography on the 500 nm thick <TEX>$SiO_2$</TEX> gate dielectric layer. We investigated electrical and physical properties of this CNT-FET using Scanning Probe Microscope(SPM) and conventional method based on tungsten probe tip technique. The gate length of CNT-FET was 600 nm and the diameter of identified SWNT was about 4 nm. We could observed gating effect and typical p-MOS property from the obtained <TEX>$V_G-I_{DS}$</TEX> curve. The threshold voltage of CNT-FET is about -4.6V and transconductance is 47 nS. In the physical aspect, we could identified SWNT with phase mode of SPM which detecting phase shift by force gradient between cantilever tip and sample surface.

Enhanced Subthreshold Slopes in Large Diameter Single Wall Carbon Nanotube Field Effect Transistors

The performance of single wall carbon nanotube field effect transistors (SWNT FETs) is greatly affected by the quality of its contacts. The presence of Schottky barriers imposes a strong scaling of the gate dielectric thickness. Here, we employ large diameter SWNTs in order to fabricate ohmically contacted FETs when a lower work function but higher adhesion strength metal such as Cr is used. A subthreshold slope as low as 113 mV/dec is obtained even when employing a thick, 200 nm SiO2 dielectric. The result is examined in light of the positive effects of exposure to air and underlines the possibility for less stringent device fabrication techniques.

Electronic transport characteristics of a single wall carbon nanotube field effect transistor wrapped with deoxyribonucleic acid molecules

A SWCNT-FET device wrapped with DNA molecules was fabricated and the electronic transport properties were investigated. The gate modulated current-voltage characteristics of a bare SWCNT-FET device showed a p-type conduction behavior, which was consistent with generally characteristics in previous studies. However, the characteristics of the DNA-wrapped SWCNT-FET showed clear staircase structures. In addition, the conduction type was changed from p-type to n-type and the transconductance of the DNA-wrapped SWCNT-FET became smaller than that of the bare SWCNT-FET. All these observations provided the evidences of DNA wrapping on the surface of SWCNTs. Especially, the observed type conversion was interpreted as a result of oxygen transport from the surface of SWCNT to DNA molecules across the SWCNT-DNA interface.

One-step grown suspended n-type semiconducting single wall carbon nanotube field effect transistors with carbon nanotube electrodes

The authors report on the in situ formation of n-type ferromagnetic single wall carbon nanotube field effect transistors for the first time using a rapid heating process with a continuous flow of H2 gas under a vacuum of millitorr and their electromagnetic transport properties. The suspended n-type single wall carbon nanotube (SWNT) bridge including nanosized Fe catalyst impurities also shows gate controlled magnetic field dependent field effect behavior. The interesting features of these devices can be understood qualitatively based on the influence of the nonoxidant interface and nano Fe residing at the growth site of the SWNT bridge.

Carbon contacted nanotube field effect transistors

The authors demonstrate that multiwalled carbon nanotube forests make exceptionally good source and drain contacts for single walled carbon nanotube field effect transistors. Fabrication is straightforward, involving only a single step of photolithography, followed by chemical vapor deposition. Bridging nanotubes are identified either by conventional scanning electron microscopy or by global photoluminescence imaging using only white light illumination. Gate voltage sweeps show that these devices are similar to conventional nanotube transistors but with surprisingly high on currents from the viewpoint of simple models of the contact-channel interface.

Self-assembled single wall carbon nanotube field effect transistors and AFM tips prepared by hot filament assisted CVD

The ability of the HFCVD to synthesize SWNTs using cobalt as catalyst has been applied to the preparation of self-assembled single wall carbon nanotube field effect transistor and tips for AFM imaging. This self-assembling batch process fabrication technique has allowed us to fabricate carbon nanotube-based devices that are directly usable without any post-treatment.

Single Stranded DNA Decorated Carbon Nanotube Transistors for Chemical Sensing

ABSTRACTWe demonstrate that single walled carbon nanotube field effect transistors (swCN-FET) decorated with single stranded DNA (ss-DNA) form a new, versatile, and highly sensitive class of nanoscale chemical sensors. These sensors are based on ss-DNA as the chemical recognition site and swCN-FET as the electronic read-out component. The ss-DNA decorated swCN-FETs are sensitive to chemical species (odors) that do not cause a detectable response in bare, as-fabricated swCN-FETs. Furthermore, odor responses ss-DNA decorated FETs differ in sign and magnitude for different odors, and the response characteristics depend on the base sequence of the ss-DNA used to decorate the swCN. The sensor surface is self-regenerating: samples maintain a constant response with no need for sensor refreshing through at least several dozens gas exposure cycles. These remarkable attributes suggest that DNA-decorated swCN-FET sensors could be created with sensitivity to a large variety of compounds, as required for “electronic-nose” and “electronic tongue” applications in medicine and homeland security.

Self-Assembly Fabrication of High Performance Carbon Nanotubes Based FETs

AbstractWe describe the realization of high quality self-assembled single wall carbon nanotube field effect transistors (CNTFET). A method using self-assembled monolayers (SAMs) is used to obtain high yield selective deposition placement of single wall carbon nanotubes (SWNTs) on predefined regions of a substrate. This is achieved with individual or small bundles of SWNTs and with high densities suitable for fabrication of integrated devices. We show that such positioned SWNTs can be electrically contacted to realize high performance transistors, which very well compare with state-of-the-art CNTFETs. We therefore validate the self-assembly approach to reliably fabricate efficient carbon nanotube based devices.