Network Transistors Research Articles

Site‐Specific Self‐Assembled Liquid‐Gated ZnO Nanowire Transistors for Sensing Applications

A scalable bottom-up solution-based approach for the site-specific realization of ZnO nanowire (ZnO-NW)-based field-effect transistors for sensing applications in liquids is reported. The nanowires are grown across predefined electrodes patterned by photolithography. Site specificity is attained by the use of nanoparticles acting as seeds. Using integrated on-chip microchannels and microfabricated gate electrodes, electrochemically gated ZnO-NW network transistors functioning in liquids are demonstrated. The optimized devices are rendered sensitive to pH through chemical functionalization. The unique combination of the sensitivity, site specificity, scalability, and cost effectiveness of the technique opens up avenues for the routine realization of one-dimensional nanostructure-based chemical and biosensors for analytical and diagnostic applications.

Gate dielectric effects on subthreshold transport of carbon nanotube network transistors grown by plasma-enhanced chemical vapor deposition

Gate dielectric effects on subthreshold transport of carbon nanotube network transistors grown by plasma-enhanced chemical vapor deposition

Aligned Tin Oxide Nanonets for High-Performance Transistors

Highly oriented tin oxide (SnO2) nanowire network (nanonets) based devices fabricated through photolithography-free techniques are studied. These nanowire networks are studied at submillimeter scales for their utilization as the active material in thin film transistors for macroelectronics. The SnO2 nanowire network transistors show excellent device characteristics and possess electron mobilities of ∼7.5 cm2 V−1 s−1 and on/off ratios between 106 and 108 with channel lengths ranging from 75 to 175 μm. Exposure of the SnO2 nanonet transistors to the ambient results in positive threshold voltage shifts due to electron trapping by oxygen at the nanowire surface. On the contrary, the electrical properties of the devices remained unchanged upon passivation by a polystyrene (PS) layer, which demonstrates a practical way to enhance the device performance in air. These results suggest that SnO2 nanonets that offer fault tolerance, flexibility, and high transparency due to low areal coverage could be a suitable can...

Directed Assembly of SWNTs by Electrostatic Interactions and its Application for Making Network Transistors

Single-wall carbon nanotubes (SWNTs) are promising building blocks for the fabrication of nanoelectronic devices. However, achieving control over their assembly on substrates has been challenging and is still a bottleneck to their utilization. Herein, we present a general method for directing the chemical assembly of SWNTs on substrates through electrostatic interactions. By covalently functionalizing both the nanotube sidewalls and the SiO(2) substrate with charged groups, dense networks of SWNTs were produced. The method is selective and highly efficient to process network field-effect transistors.

Toward High-Performance Solution-Processed Carbon Nanotube Network Transistors by Removing Nanotube Bundles

Reported solution-processed field-effect transistor (FET) devices based on single-walled carbon nanotube (SWNT) networks have either high mobility but low on/off ratio or vice versa. Recently, Arnold et al. (Nat. Nanotechnol. 2006, 1, 60−65) have made significant improvements in obtaining semiconductor-enriched SWNTs by using density-gradient ultracentrifugation. Here, we report that removing the SWNT bundles using organic−aqueous interfacial purification can further enhance the electrical performance of SWNT-FETs. The on/off ratio of the SWNT-FET is improved by ∼1 order of magnitude. By combining density-gradient ultracentrifugation and interfacial purification, it is possible to obtain high on/off ratio and high mobility of solution-processed SWNT-FETs at a promising yield.

Noise characteristics of single-walled carbon nanotube network transistors

The noise characteristics of randomly networked single-walled carbon nanotubes grown directlyby plasma enhanced chemical vapor deposition (PECVD) are studied with field effecttransistors (FETs). Due to the geometrical complexity of nanotube networks in the channelarea and the large number of tube–tube/tube–metal junctions, the inverse frequency,1/f, dependence of the noise shows a similar level to that of a single single-walled carbonnanotube transistor. Detailed analysis is performed with the parameters of number ofmobile carriers and mobility in the different environment. This shows that the change inthe number of mobile carriers resulting in the mobility change due to adsorption anddesorption of gas molecules (mostly oxygen molecules) to the tube surface is a key factor in the1/f noise level for carbon nanotube network transistors.

Contact-Electrode Insensitive Rectifiers Based on Carbon Nanotube Network Transistors

This letter presents rectifiers based on the diode connection of carbon nanotube network (CNN) transistors. Despite a low density of carbon nanotubes in the CNNs, the devices can achieve excellent performance with a forward/reverse current ratio reaching . By casting nanotube suspension on oxidized Si substrates with predefined electrodes, CNN-based field-effect transistors are readily prepared. By short-circuiting the source and gate terminals, CNN-based rectifiers are realized with the rectification characteristics independent of whether Pd or Al is employed as the contact electrodes. This independence is especially attractive for applications of CNN-based transistors/rectifiers in flexible electronics with various printing techniques.

High-performance carbon nanotube network transistors for logic applications

We report on the fabrication of carbon nanotube network field effect transistors, in which a submonolayer network is selectively and uniformly dispersed in the active region with individually addressable back gate. The high current on/off ratio (104) and good device-to-device uniformity were achieved by selective burnout of metallic pathways. The enhanced capacitive coupling between the gate and nanotube network reduces the subthreshold slope down to 180mV∕dec. The effective local gating allows us to implement logic circuits, such as an inverter and the two most important universal NOR and NAND gates.

Percolation in random networks of heterogeneous nanotubes

The electrical performance of random carbon nanotube network transistors is found by Monte Carlo simulation to strongly depend on the nature of the conduction path percolating the network. When the network is percolated only by semiconducting nanotube pathways (OSPs), the transistors can directly achieve both high on current and large on/off current ratio. Based on percolation theory, the present work predicts that there exist specific nanotube coverage domains within which OSP has the highest probability and becomes predominant. Simulation results show that the coverage domains depend on the network dimension, nanotube length, and the fraction of metallic nanotubes.

Heme-Enabled Electrical Detection of Carbon Monoxide at Room Temperature Using Networked Carbon Nanotube Field-Effect Transistors

The electrical detection of CO at room temperature is achieved using Cr-contacted single-walled carbon nanotube network transistors modified with thiolated heme molecules.

Theory of transfer characteristics of nanotube network transistors

Carbon nanotubes (CNT) nanocomposites used for thin-film transistors (TFTs) provide one of the first technologically-relevant test beds for two-dimensional heterogeneous percolating systems. The characteristics of these TFTs are predicted by considering the physics of heterogeneous finite-sized networks and interfacial traps at the CNT/gate-oxide interface. Close agreement between our numerical results and different experimental observations demonstrates the capability of the model to predict the characteristics of CNT/nanowire-based TFTs. Such predictive models would simplify device optimization and expedite the development of this nascent TFT technology.

Electronically Selective Chemical Functionalization of Carbon Nanotubes: Correlation between Raman Spectral and Electrical Responses

Single-walled carbon nanotubes (SWNTs) demonstrate remarkable electronic and mechanical properties useful in developing areas such as nanoelectromechanical systems and flexible electronics. However, the highly inhomogeneous electronic distribution arising from different diameters and chirality in any given as-synthesized SWNT samples imposes severe limitations. Recently demonstrated selective chemical functionalization methods may provide a simple scalable means of eliminating metallic tubes from SWNT transistors and electronic devices. Here, we report on combined electron transport and Raman studies on the reaction of 4-bromobenzene diazonium tetrafluoroborate directly with single and networks of SWNT transistors. First, Raman studies are carried out on isolated individual SWNTs grown on SiO2/Si substrates by chemical vapor deposition with and without metal contacts. Metallic tubes are found to have, on average, higher reactivity toward diazonium reagents. However, a considerable degradation of electrical properties of semiconducting tubes occurs if the reaction is carried out to the point where the conductivity of metallic tubes is significantly suppressed. Insights from single-tube studies are then applied to elucidate the electrical and the Raman responses of SWNT random network transistors of different channel lengths to chemical functionalization.

Flexible Nanotube Electronics

Nanotube network transistors have been transferred to polymer supports. The polymer-supported networks can be bent through at least 60° angles without changing their electronic properties. They operate as p-type field-effect transistors with mobilities of 12 cm2/V s, the highest reported values to date for flexible organic transistors. Finally, the networks can be modified chemically to produce n-type transistors. Taken together, these properties provide the basis for high-mobility flexible electronics.