Investigation Of Breakdown Power During Electrical Breakdown Of Aligned Array Of Carbon Nanotubes

Massively parallel arrays of single walled carbon nanotubes (SWNT) have attracted significant research interests because of their ability to (i) average out inhomogeneities of individual SWNTs, (ii) provide larger on currents, and (iii) reduce noise to provide higher cutoff frequency for radio frequency applications. However, the array contains both metallic and semiconducting SWNTs and the presence of metallic nanotube in an aligned array negatively affects the device properties. Therefore, it is essential to selectively remove metallic nanotubes to obtain better transistor properties. It was recently found that although such a selective removal can be effective for a low density array, it does not work in a high density array and lead to a correlated breakdown of the entire array giving rise to a nanofissure pattern. In order to obtain a deeper understanding of such a correlated SWNT breakdown, we studied the breakdown power in the successive electrical breakdown of both low ( \u3c 2 /um) and high density ( \u3e 10 /um) SWNT arrays. We show that the breakdown voltage in successive electrical breakdown increases for low density array while it decreases for high density arrays. The estimated power required for the breakdown remains constant for low density arrays while it decreases for high density arrays in successive electrical breakdowns. We also show that, while a simple model of parallel resistor network can explain the breakdown of low density array, it cannot explain the behavior for the high density array implying that the correlation between the closely spaced parallel nanotubes plays a big role in the successive breakdowns of the high density SWNTs

Principles of carbon nanotube dielectrophoresis

Dielectrophoresis (DEP) describes the motion of suspended objects when exposed to an inhomogeneous electric field. It has been successful as a method for parallel and site-selective assembling of nanotubes from a dispersion into a sophisticated device architecture. Researchers have conducted extensive works to understand the DEP of nanotubes in aqueous ionic surfactant solutions. However, only recently, DEP was applied to polymer-wrapped single-walled carbon nanotubes (SWCNTs) in organic solvents due to the availability of ultra-pure SWCNT content. In this paper, the focus is on the difference between the DEP in aqueous and organic solutions. It starts with an introduction into the DEP of carbon nanotubes (CNT-DEP) to provide a comprehensive, in-depth theoretical background before discussing in detail the experimental procedures and conditions. For academic interests, this work focuses on the CNT-DEP deposition scheme, discusses the importance of the electrical double layer, and employs finite element simulations to optimize CNT-DEP deposition condition with respect to the experimental observation. An important outcome is an understanding of why DEP in organic solvents allows for the deposition and alignment of SWCNTs in low-frequency and even static electric fields, and why the response of semiconducting SWCNTs (s-SWCNTs) is strongly enhanced in non-conducting, weakly polarizable media. Strategies to further improve CNT-DEP for s-SWCNT-relevant applications are given as well. Overall, this work should serve as a practical guideline to select the appropriate setting for effective CNT DEP

Manipulation of carbon nanoparticles in composites with electric fields for improved electrical properties

Die Dispersion elektrisch leitfähiger Nanopartikel in einer Polymermatrix ermöglicht die Herstellung einer nützlichen Materialklasse: elektrisch leitfähige Polymerkomposite. Die gezielte Einstellung der elektrischen Leitfähigkeit des leitfähigen Komposits ist jedoch nicht trivial, da viele Material- und Verarbeitungsparameter die Partikel-Netzwerkstruktur im Komposit beeinflussen die letztlich für die elektrische Leitfähigkeit ausschlaggebend ist. In dieser Arbeit werden die elektrischen Eigenschaften von Epoxid-Nanokompositen mit Kohlenstoff-Nanopartikeln als leitfähigem Füllstoff für verschiedene Verarbeitungsbedingungen untersucht. Im Unterschied zu einem klassischen Formgebungsverfahren für Epoxidmaterialien wird die Anwendung von elektrischen Feldern während des Aushärtungsprozesses als zusätzlicher Prozessparameter benutzt. Elektrische Felder werden während des Aushärtens an die Nanokomposite angelegt, wodurch die elektrischen Eigenschaften des Endmaterials durch Induktion von Polarisations- und Dipol-Wechselwirkungen zwischen den leitenden Partikeln (Dielektrophorese) beeinflusst werden. Diese führen zu einer neuen, und im Hinblick auf die elektrische Leitfähigkeit vorteilhaften Mikro- und Nanostruktur des leitfähigen Netzwerks. Dieses Phänomen wird für ein System von einwandigen Kohlenstoff-Nanoröhren in einer Epoxidharzmatrix im Hinblick auf den Einfluss verschiedener Verarbeitungsparameter auf die elektrische Leitfähigkeit des Systems untersucht. Darauf aufbauend wird ein skalierbares Verfahren auf der Grundlage des Harzinjektionsverfahrens zur Herstellung von Nanokompositen unter elektrischen Feldern entwickelt. Für ein besseres Verständnis der Mechanismen, die der Wirkung elektrischer Felder auf die Rotation und die Verschaltung von SWCNTs werden die eigenen Ergebnisse mit Simulationen kooperierender Wissenschaftler der Anáhuac Mayab Universit¨1t (Merida, Mexiko) und das Imperial College London (Vereinigtes Königreich) verglichen

Frequency dependence of dielectrophoretic fabrication of single-walled carbon nanotube field-effect transistors

A new theoretical model for the dielectrophoretic (DEP) fabrication of single-walled carbon nanotubes (SWCNTs) is presented. A different frequency interval for the alignment of wide-energy-gap semiconductor SWCNTs is obtained, exhibiting a considerable difference from the prevalent model. Two specific models are study, namely the spherical model and the ellipsoid model, to estimate the frequency interval. Then, the DEP process is performed and the obtained frequencies (from the spherical and ellipsoid models) are used to align the SWCNTs. These empirical results confirm the theoretical predictions, representing a crucial step towards the realization of carbon nanotube field-effect transistors (CNT-FETs) via the DEP process based on the ellipsoid model. © 2020, The Author(s)

Modeling of Nano-Transistor Using 14-Nm Technology Node

Latest process technologies in transistor development demonstrate massive changes in the size of transistor chip. In this chapter, a 14-nm technology node is used to model nanosize transistor. The 14-nm technology node consists of multiple numbers of carbon nanotube. Carbon nanotube is a very good energy efficient and low-cost material. Carbon nanotube demonstrates excellent characteristics in metallic and semiconducting characteristics by analyzing electrical properties. At first, the nanotube device physics and material properties are briefly explained in this chapter. Further, a nanotube device is designed for semiconducting properties. The gate length of nanotube is 14 nm which is placed on the gate channel. Finally, the model of 14-nm nano-transistor will be demonstrated for low-energy consumption which can be considered as a better replacement of CMOS

Single-Walled Carbon Nanotube Arrays for High Frequency Applications

This dissertation presents a thorough analysis of semiconducting Single-Walled Carbon Nanotube-based devices, followed by a test structure fabrication and measurements. The analysis starts by developing an individual nanotube model, which is then generalized for many nanotubes and adding the parasitic elements. The parasitic elements appear when forming the device electrodes degrade the overall performance. The continuum model of an individual nanotube is developed. A unique potential function is presented to effectively describe the electron distribution in the carbon nanotube subsequently facilitating solving Schrödinger\u27s equation to obtain the energy levels, and to generalize the model for many nanotubes. It is shown that the overall energy band gap is inversely proportional to the number of nanotubes due to the coupling between the nanotubes. The coupling is then enhanced by applying an external transverse electric field, which controls the energy band gap. The electric field is represented as a function of the number of nanotubes per device showing that the higher the number of nanotubes, the lower the value of the electric field needed to alter the energy band gap. An electromagnetic model is developed for the contact where a detailed parametric study of the length, thickness, and conductivity of the contact area is presented. The overlap length between the nanotube and the metal of the contact appears to be the dominating factor.There is a clear inverse proportionality between overlap length and contact resistance to reach a minimum value after an effective overlap length. An equation is developed to describe the conductance as a function of the number of nanotubes per device. A four-electrode test structure is fabricated using both photolithography and electron-beam-lithography. The carbon nanotubes are deposited using the dielectrophoresis method for many devices simultaneously to provide a sheet resistance as low as 10 K/. The I-V characteristics are measured with and without change in the transverse electric field. It shows a change in the current reflecting the changes in the energy band gap discussed earlier. There are many applications for the results presented in this dissertation such as optimizing devices operating in the THz frequency range

Spin-state-dependent electrical conductivity in single-walled carbon nanotubes encapsulating spin-crossover molecules

Spin crossover (SCO) molecules are promising nanoscale magnetic switches due to their ability to modify their spin state under several stimuli. However, SCO systems face several bottlenecks when downscaling into nanoscale spintronic devices: their instability at the nanoscale, their insulating character and the lack of control when positioning nanocrystals in nanodevices. Here we show the encapsulation of robust Fe-based SCO molecules within the 1D cavities of single-walled carbon nanotubes (SWCNT). We find that the SCO mechanism endures encapsulation and positioning of individual heterostructures in nanoscale transistors. The SCO switch in the guest molecules triggers a large conductance bistability through the host SWCNT. Moreover, the SCO transition shifts to higher temperatures and displays hysteresis cycles, and thus memory effect, not present in crystalline samples. Our results demonstrate how encapsulation in SWCNTs provides the backbone for the readout and positioning of SCO molecules into nanodevices, and can also help to tune their magnetic properties at the nanoscale.Marie Skłodowska-Curie Actions 74657Programa de Atracción del Talento Investigador 2017-T1/IND-5562Ministerio de Economia, Industria y Competitividad CTQ2017-86060-P, PID2019-111479GB-100, MAT 2017-8225, GC2018-101689-B-I00Consejo Europeo de Investigación ERC-StG-307609, ERC-PoC-842606Comunidad Autónoma de Madrid MAD2D-CM S2013/ MIT-3007, PEJD-2017-PRE/IND-4037, Y2018/NMT- 4783NANOMAGCOST P2018/ NMT-432