Single-walled Carbon Nanotube Field-effect Transistors Research Articles

P–n homo-junction arrays of aligned single walled carbon nanotubes fabricated by selectivepatterning of polyethyleneimine film

We describe the fabrication and electrical performance of p–n homo-junctiondiode arrays of horizontally aligned single walled carbon nanotubes (SWCNTs).Horizontally aligned SWCNTs grown on stable temperature-cut quartz with a density of ∼ 6 SWCNTsµm − 1 were transferredonto a SiO2/Si substrate. After the electrical breakdown, aligned SWCNT field effecttransistors (FETs) showed unipolar p-type characteristics with a large currenton/off ratio of106 at 1 V and a holemobility per tube of 1500 cm2 V − 1 s − 1. Spin-coating of polyethyleneimine (PEI) onto p-type SWCNT FETs showedthe n-type transfer characteristics. Patterning of spin-coated PEI film enabledthe fabrication of p–n homo-junction arrays of aligned SWCNTs in an easyway, where the rectifying behavior was observed with a rectification ratio of ∼ 104 at ± 2 V. A comparative study with a p–n homo-junction of random networks of SWCNTsconfirmed the advantage of aligned SWCNTs for applications in high performanceelectronic devices.

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.

Network single-walled carbon nanotube biosensors for fast and highly sensitive detection ofproteins

Detection of proteins is powerfully assayed in the diagnosis of diseases. A strategy for thedevelopment of an ultrahigh sensitivity biosensor based on a network single-walled carbonnanotube (SWNT) field-effect transistor (FET) has been demonstrated. MetallicSWNTs (m-SWNTs) in the network nanotube FET were selectively removed orcut via a carefully controlled procedure of electrical break-down (BD), and leftnon-conducting m-SWNTs which magnified the Schottky barrier (SB) area. Thisnanotube FET exhibited ultrahigh sensitivity and fast response to biomolecules. Thelowest detection limit of 0.5 pM was achieved by exploiting streptavidin (SA) or abiotin/SA pair as the research model, and BD-treated nanotube biosensors had a2 × 104-fold lower minimum detectable concentration than the device without BD treatment. Theresponse time is in the range of 0.3–3 min.

Self‐Aligned Sub‐10‐nm Nanogap Electrode Array for Large‐Scale Integration

A novel approach to creating a gap on the nanometer scale between two adjacent electrodes of the same or different metals is described. The gap size can be well controlled through sidewall coverage in a self-aligned manner and it can be tuned from 60 nm down to 5 nm with high reproducibility. This technique is fully compatible with traditional microfabrication technology and it is easily implemented to fabricate a nanogap electrode array for integration purposes. An array of short-channel single-walled carbon nanotube field-effect transistors is demonstrated.

Piperidine induced polarity conversion in single-walled carbon nanotube field effecttransistors

Piperidine is found to be an efficient electron doping agent that converts as-preparedp-type single-walled carbon nanotube (SWCNT) field effect transistors (FETs)into n-type SWCNT-FETs. Electron transfer from the amine group in piperidineto the SWCNTs is suggested to be the origin of the p- to n-type conversion.The effect of electron doping is further supported by the Raman tangentialG + andG − -peak downshiftup to 3 cm − 1 without the peak broadening. No detectable change in the Raman D-peak suggestsnon-covalent attachment of piperidine to the SWCNTs. A low temperature (110 °C)Si3N4 passivation layer is used to maintain the long term air stability of the converted n-typedevices. A complementary SWCNT inverter is demonstrated through integrating the n- andp-type SWCNT-FETs.

Electronic Sensitivity of Carbon Nanotubes to Internal Water Wetting

We have constructed devices in which the interior of a single-walled carbon nanotube (SWCNT) field-effect transistor acts as a nanofluidic channel that connects two fluid reservoirs, permitting measurement of the electronic properties of the SWCNT as it is wetted by an analyte. Wetting of the inside of the SWCNT by water turns the transistor on, while wetting of the outside has little effect. These observations are consistent with theoretical simulations that show that internal water both generates a large dipole electric field, causing charge polarization of the tube and metal electrodes, and shifts the valence band of the SWCNT, while external water has little effect. This finding may provide a new method to investigate water behavior at nanoscale. This also opens a new avenue for building sensors in which the SWCNT simultaneously functions as a concentrator, nanopore, and extremely sensitive electronic detector, exploiting the enhanced sensitivity of the interior surface.

Carbon nanotube field-effect transistors with molecular interface

We report on a study of molecular modifications of the electronic characteristics of single-walled carbon nanotube (SWNT) field-effect transistors (FETs) through insertion of different organic self-assembled monolayers (SAMs) between the SWNT and an electrode. The changes induced by the molecular interface were elucidated using a device structure created by directed assembly of a single SWNT over three prepatterned electrodes, one of which had a SAM deposited via dip-pen nanolithography. The resulting direct comparison of two FETs sharing the same SWNT revealed pronounced modification of the transfer characteristics, on/off ratio, and threshold voltages due to the SWNT/molecule/metal junction. The effects are attributed primarily to the alteration of the electronic bands in the Au electrode and the SWNT, and the resulting changes in the effective Schottky barrier height/thickness, by the ordered and well-aligned molecular SAM.

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.

Selective and Sensitive TNT Sensors Using Biomimetic Polydiacetylene-Coated CNT-FETs

Miniaturized smart sensors that can perform sensitive and selective real-time monitoring of target analytes are tremendously valuable for various sensing applications. We developed selective nanocoatings by combining trinitrotoluene (TNT) receptors bound to conjugated polydiacetylene (PDA) polymers with single-walled carbon nanotube field-effect transistors (SWNT-FET). Selective binding events between the TNT molecules and phage display derived TNT receptors were effectively transduced to sensitive SWNT-FET conductance sensors through the PDA coating layers. The resulting sensors exhibited an unprecedented 1 fM sensitivity toward TNT in real time, with excellent selectivity over various similar aromatic compounds. Our biomimetic receptor coating approach may be useful for the development of sensitive and selective micro- and nanoelectronic sensor devices for various other target analytes.

Investigation on Self-Heating Effect in Carbon Nanotube Field-Effect Transistors

Electrothermal modeling of single-walled carbon nanotube (SWCNT) field-effect transistor (FET) is performed in this paper, with special attention focused on its self-heating effect. The method of finite difference is implemented for solving a 1-D heat conduction equation in the semiconducting channel self-consistently, and its nonuniform temperature distribution is evaluated for 20-, 32-, and 45-nm technology nodes, respectively. The numerical results are presented to show the self-heating effect on the I -V characteristics, signal delay, and cutoff frequency of the carbon nanotube FET (CNTFET). It is further demonstrated that the maximum temperature rise, as well as the performance degradation of the CNTFET, is quite lower than that of the silicon-based FET counterpart. All these advantages are contributed by the excellent electrothermal properties of the SWCNTs, and they have great potential for the development of active devices with low power dissipation and good reliability at high-operating temperature.

Floating-potential self-assembly of singe-walled carbon nanotube field effect transistors by ac-dielectrophoresis

An improved method for self-assembly fabrication of single-walled carbon nanotube (SWCNT) field effect transistors (FETs) is presented, combining the unique design of biased/floating potential electrode geometry and the technique of aligning CNTs by pre-defined trenches in “Sandwich”-like resist layers. Super-aligned SWCNT FETs bridging biased/floating potential electrode pairs with precisely controlled location can be demonstrated. Moreover, SWCNT FETs fabricated by this method exhibit excellent electrical properties, such as Ion/Ioff ratio up to 105 and sub-threshold slope ∼130mV/dec. This novel technique provides a more effective and flexible way to solve the CNT assembly issue. It could also enable the fabrication of future CNT based complementary logic circuit and nano-electrical–mechanical-system (NEMS).

Patterned nano-sized gold dots within FET channel: from fabrication to alignment of single walled carbon nanotube networks

We have introduced patterned gold dots between the electrodes of single walled carbon nanotube (SWNT) network films, to effectively guide the path of randomly assembled nanotube networks. Direct visualization results show well-aligned SWNT networks across the gold dots, generating improved SWNT–FET performance with a high on/off ratio of 104 and 85 cm2 V−1s−1 mobility, a remarkable enhancement compared to SWNT–FET in the absence of patterned gold dots. Unlike previously reported alignment techniques used, the proposed method affords the selective alignment of SWNTs within electrodes at room temperature without any direct growth on the device surface, and without the need for further alignment procedures. Thus, this gold-dot pattern technique within FET channel has proven to be truly simple, reliable and cost-effective. We discuss the effect of the voltage, channel size and feature dimensions of the gold nanopatterns in field effect transistor (FET) structures.

Single-Walled-Carbon-Nanotube-Based Field-Effect Transistors with Biosensing Functions for Prostate-Specific-Antigen

Single-walled carbon nanotube (SWCNT) field-effect transistors (FETs) were fabricated on strontium titanate (SrTiO3) substrate through a wet-process by using amide-functionalized SWCNT. The SWCNT-FET exhibited good gate-modulation for drain current at low operating voltages (-3 V). The hole mobility was 0.19 cm2/Vs with an on/ off current ratio of 1.3. After immobilization of prostate-specific-antigen (PSA) antibody the SWCNT-FET clearly responded against the PSA. The drain current at -3 V of both drain and gate voltage almost linearly increased with increasing the concentration of the PSA.

Nanoelectronic Detection of Lectin-Carbohydrate Interactions Using Carbon Nanotubes

We have used single-walled carbon nanotube field-effect transistor (NTFET) devices to probe the interactions between carbohydrates and their recognition proteins called lectins. These interactions are involved in a wide range of biological processes, such as cell-cell recognition, cell-matrix interaction as well as viral and bacterial infections. In our experiments, NTFETs were functionalized noncovalently with porphyrin-based glycoconjugates synthesized using "click" azide-alkyne chemistry, and change in electrical conductance was measured upon specific binding of two bacterial lectins that present different carbohydrate preference, namely PA-IL, PA-IIL from Pseudomonas aeruginosa and a plant lectin Concanavalin A. However, no significant change in the device characteristics was observed when the devices were exposed to other lectins with different specificity. Detection of PA-IL binding to galactosylated NTFETs was highly sensitive (2 nM) with a measured dissociation constant (K(d) = 6.8 μM) corresponding to literature data. Fluorescence microscopy, atomic force microscopy, UV-vis-NIR spectroscopy, and several control measurements confirmed the NTFET response to selective interactions between carbohydrates and lectins.

Current on/off ratio enhancement through the electrical burning process in ambient with/without oxygen for the generation of high-performance aligned single-walled carbon nanotube field effect transistors

We present characteristics of the electrical burning process with/without oxygen-ambient for parallel aligned single-walled carbon nanotube field effect transistors (SWNT-FETs). High selectivity of metallic and semiconducting nanotubes is demonstrated by an electrical burning process through partial etching of the atomic layer deposited Al2O3 layer beneath the gate electrodes. Metallic nanotubes exposed to oxygen show electrical breakdown during the burning process, resulting in the SWNT-FETs having excellent performance. Specifically, 100 μm source/drain width p-type aligned SWNT-FETs through electrical burning with local oxidation show high Ion/Ioff ratios (>103), 10 μS at a drain bias of −1 V and −100 μA at a reverse gate bias of −8 V.

Single Nucleotide Polymorphism Detection Using Au-Decorated Single-Walled Carbon Nanotube Field Effect Transistors

We demonstrate that Au-cluster-decorated single-walled carbon nanotubes (SWNTs) may be used to discriminate single nucleotide polymorphism (SNP). Nanoscale Au clusters were formed on the side walls of carbon nanotubes in a transistor geometry using electrochemical deposition. The effect of Au cluster decoration appeared as hole doping when electrical transport characteristics were examined. Thiolated single-stranded probe peptide nucleic acid (PNA) was successfully immobilized on Au clusters decorating single-walled carbon nanotube field-effect transistors (SWNT-FETs), resulting in a conductance decrease that could be explained by a decrease in Au work function upon adsorption of thiolated PNA. Although a target single-stranded DNA (ssDNA) with a single mismatch did not cause any change in electrical conductance, a clear decrease in conductance was observed with matched ssDNA, thereby showing the possibility of SNP (single nucleotide polymorphism) detection using Au-cluster-decorated SWNT-FETs. However, a power to discriminate SNP target is lost in high ionic environment. We can conclude that observed SNP discrimination in low ionic environment is due to the hampered binding of SNP target on nanoscale surfaces in low ionic conditions.

Transport properties of single-walled carbon nanotube transistors after gamma radiation treatment

Single-walled carbon nanotube field-effect transistors (CNT-FETs) were characterized before and after gamma radiation treatment using noise spectroscopy. The results obtained demonstrate that in long channel CNT-FETs with a length of 10 μm the contribution of contact regions can be neglected. Moreover, radiation treatment with doses of 1×106 and 2×106 rad allows a considerable decrease parallel to the nanotube parasitic conductivity and even the shift region with maximal conductivity to the voltage range of nearly zero gate voltage that improves the working point of the FETs. The Hooge parameters obtained before and after gamma radiation treatment with a dose of 1×106 rad are found to be about 5×10−3. The parameters are comparable with typical values for conventional semiconductors.

Performance of Zero-Schottky-Barrier and Doped Contacts Single and Double Walled Carbon Nanotube Transistors

Atomistic quantum simulation is performed to compare the performance of single walled (SW) and double walled (DW) carbon nanotube field effect transistors (CNTFETs) with two different types of contacts: zero-Schottky-barrier (SB) contacts and doped (DP) contacts. Both the DW and SW CNTFETs have better performance with doped contacts. The conduction band under the gate region is pushed down below the source Fermi level when the applied gate bias is ≥ Eg/2. Beyond this gate voltage, the current in SB CNTFETs becomes almost constant. This does not happen to the doped contacts devices and they have better on-state performance. With the same type of contacts, the SW and DW CNTFETs exhibit similar I–V characteristics. However, the switching delay and the unity current gain frequency are much better in DW CNTFETs for both types of contacts. The better switching performance of DW CNTFETs results from the smaller gate capacitance.

Investigations of niobium carbide contact for carbon-nanotube-based devices

Single-walled carbon nanotube (SWCNT) field effect transistors (FETs)with Nb contacts have been fabricated and upon annealing in vacuum at700 °C for 1 h, niobiumcarbide (Nb2C) is formed at the Nb/SWCNT interface. TheNb2C/SWCNT contacts demonstrate a very small Schottky barrier height of ∼ 18 meV(decreased by > 80% relative to that of pristine Nb/SWCNT contact of ∼ 98 meV) to p-type transport. This is attributed to the higher work function ofNb2C (∼5.2 eV) than Nb (∼4.3 eV) and better bondingbetween Nb2C and SWCNTs.The performance of Nb2C-contacted SWCNT FETs is as follows: the p-channel ON current is as high as0.5 µA atVDS = 0.1 V, theION/IOFF ratio is up to ∼ 105 and the subthresholdslope is ∼ 550 mV/dec, which is as good as that of titanium carbide (TiC-) and Pd-contacted SWCNT FETs. Compared withTiC, Nb2C contacts yield more unipolar p-type SWCNT FETs, as a result of theNb2Cs higher work function.More importantly, Nb2C contacts can form near-ohmic contacts to both large-(≥1.6 nm) andsmall-diameter (∼1 nm) SWCNTs, while Pd can only form near-ohmic contacts for large-diameter SWCNTs. Moreover,the Nb2C contacts demonstrate good stability in air.

Biomimetic Chemosensor: Designing Peptide Recognition Elements for Surface Functionalization of Carbon Nanotube Field Effect Transistors

Single-wall carbon nanotube field effect transistors (SWNT-FETs) are ideal candidates for fabricating sensors due to their unique electronic properties and have been widely investigated for chemical and biological sensing applications. The lack of selectivity of SWNT-FETs has prompted extensive research on developing ligands that exhibit specific binding as selective surface coating for SWNTs. Herein we describe the rational design of a peptide recognition element (PRE) that is capable of noncovalently attaching to SWNTs as well as binding to trinitrotoluene (TNT). The PRE contains two domains, a TNT binding domain derived from the binding pocket of the honeybee odor binding protein ASP1, and a SWNT binding domain previously identified from the phage peptide display library. The PRE structure in the presence of SWNT was investigated by performing classical all-atom molecular dynamics simulations, circular dichroism spectroscopy, and atomic force microscopy. Both computational and experimental analyses demonstrate that the peptide retains two functional domains for SWNT and TNT binding. The binding motif of the peptide to SWNT and to TNT was revealed from interaction energy calculations by molecular dynamics simulations. The potential application of the peptide for the detection of TNT is theoretically predicted and experimentally validated using a SWNT-FET sensor functionalized with a designer PRE. Results from this study demonstrate the creation of chemosensors using designed PRE as selective surface coatings for targeted analytes.