Logic devices and circuits based on giant magnetoresistance

In this paper, a new paradigm of performing logic operations is proposed. This new approach is based on the submicrometer giant magnetoresistance (GMR) effects. The key enabling features are nonvolatility, high GMR ratio, and control over the switching fields. The possible advantages of the new approach include ultrahigh density (because of the small device size), ultrahigh speed, nonvolatility, and radiation hardness. Key limitations are also identified. Several possible ways to surmount the limitations are also discussed. The proposed approach can, in principle, be applied to other material systems with similar characteristics     

Role of semiconducting and metallic tubes in P3HT/carbon-nanotube photovoltaic heterojunctions: density functional theory calculations

A density functional theory approach is employed to investigate poly-3-hexylthiophene (P3HT) interfaced with both a semiconducting and metallic carbon nanotube (CNT). For the semiconducting CNT, a type-II heterojunction can form, making such an interface desirable as a photovoltaic heterojunction. In contrast, with the metallic CNT, substantial charge redistribution occurs and the interaction is strongly enhanced. The built-in-potential is, however, quite small, and P3HT becomes electrostatically more attractive for electrons. These observations together indicate that, in a photovoltaic heterojunction based on a mixed CNT distribution, the majority of interfaces are with metallic CNTs and inefficient.     

Logic devices based on inductive Josephson logics

Inductive Josephson logic (IJL) is realized by using Josephson junctions as a kind of nonlinear inductance. The operational principle of inductive Josephson logic is studied from a very simple example and generalized to multiple Josephson inductive logic devices. Concepts offorward andbackward are introduced to describe the states of the operations. IJLs operate in terms of current or flux; they are suitable to be used in connection with other flux-control Josephson circuit devices such as DC SQUID or DCFP. Some circuit devices based on the principle of inductive Josephson logic are given as examples of IJL logic functions.     

Routes towards separating metallic and semiconducting nanotubes

Separation of single-walled carbon nanotubes (SWNTs), according to their electronic characteristics, is essential to the development of molecular electronics, including field-effect transistors. Recent efforts by many groups have used non-covalent and covalent sidewall chemistry to probe differential reactivity in metallic and semiconducting nanotubes. These chemically based methods may more easily effect the bulk separation of tubes, as compared with physical techniques associated with (i) alternating current dielectrophoresis as well as (ii) the current-induced oxidation of metallic nanotubes, that have recently been reported as alternative methods of achieving chiral separations of nanotubes. Exploration of these types of reactions is critical for the development of interesting chemical and physical properties at the interface between molecules and materials as well as for establishing protocols for the selective functionalization of nanotubes.     

Fabrication and electrical characterization of circuits based on individual tin oxide nanowires

Two-?and four-probe electrical measurements on individual tin oxide (SnO(2)) nanowires were performed to evaluate their conductivity and contact resistance. Electrical contacts between the nanowires and the microelectrodes were achieved with the help of an electron-?and ion-beam-assisted direct-write nanolithography process. High contact resistance values and the nonlinear current-bias (I-V) characteristics of some of these devices observed in two-probe measurements can be explained by the existence of back-to-back Schottky barriers arising from the platinum-nanowire contacts. The nanoscale devices described herein were characterized using impedance spectroscopy, enabling the development of an equivalent circuit. The proposed methodology of nanocontacting and measurements can be easily applied to other nanowires and nanometre-sized materials.     

Intrinsic metallic and semiconducting cubic boron nitride nanofilms

We show by density functional theory calculations with both hybrid and semilocal functionals that cubic boron nitride (111) nanofilms are intrinsically metallic and even turn into semiconductors once the thickness is less than 0.69 nm, which is in sharp contrast to the known insulating nature of boron nitride materials. The exceptional metallic or semiconducting band gap is due to a combined effect of thickness-dependent inbuilt electric polarization and labile near-gap states unique in the polar nanofilms. The band gap and dipole moment of the nanofilms can be further significantly tuned by applying an in-plane strain. These distinguished features of the boron nitride nanofilms are robust to surface passivation and can be enhanced by hybridizing with diamond films, thereby opening an exciting prospect of using the versatile cubic nanofilms in future electronic and piezoelectric devices.     

Magnetic nanoparticle-based separation of metallic and semiconducting carbon nanotubes

We report a simple and scalable method for the separation of semiconducting single-walled carbon nanotubes (SWNTs) from metallic SWNTs using magnetic nanoparticles (MNPs) functionalized with polycationic tri-aminated polysorbate 80 (TP80). MNPs-TP80 are selectively adsorbed on acid-treated semiconducting SWNTs, which makes the semiconducting SWNTs be highly concentrated to over 95% under a magnetic field. Almost all the field effect transistor network devices, which were fabricated using separated semiconducting SWNTs, exhibited a p-type semiconducting behavior with an on/off ratio of higher than 10(4).     

金属型和半导体型单壁碳纳米管的分离研究进展

单壁碳纳米管(SWNTs)有优良的电学性能,但是目前制备的单壁碳纳米管都是金属型(met-)和半导体型(sem-)SWNTs的混合物,极大地限制了SWNTs进一步的应用。以物理法和化学法概述了近年来met-和sem-SWNTs的分离方法,并对各方法进行了机理分析和优劣比较。     

Backgating in GaAs devices and integrated circuits

This paper reviews current understanding of backgating in GaAs integrated circuits and discusses approaches used to predict and mitigate its effect. Current theoretical approaches to explain backgating are reviewed and the impact of materials, process techniques, and design on backgating are also discussed. A standard backgating test structure and test proposed at the 1990 GaAs IC Symposium are described.     

Separation of metallic and semiconducting single-walled carbon nanotubes through fluorous chemistry

Separation of metallic from semiconducting single-walled carbon nanotubes has been a major challenge for some time and some previous efforts have resulted in partial success. We have accomplished the separation effectively by employing fluorous chemistry wherein the diazonium salt of 4-heptadecafluorooc tylaniline selectively reacts with the metallic nanotubes present in the mixture of nanotubes. The resulting fluoroderivative was extracted in perfluorohexane leaving the semiconducting nanotubes in the aqueous layer. The products have been characterized by both Raman and electronic absorption spectroscopy. The method avoids the cumbersome centrifugation step required by some other procedures. This article is published with open access at Springerlink.com     

A density-driven phase transition between semiconducting and metallic polyamorphs of silicon

Amorphous and crystalline forms of silicon are well-known, tetrahedrally coordinated semiconductors. High-pressure studies have revealed extensive polymorphism among various metallic crystal structures containing atoms in six-, eight- and 12-fold coordination. Melting silicon at ambient or high pressure results in a conducting liquid, in which the average coordination is greater than four (ref. 3). This liquid cannot normally be quenched to a glass, because of rapid crystallization to the diamond-structured semiconductor. Solid amorphous silicon is obtained by synthesis routes such as chemical or physical vapour deposition that result in a tetrahedrally bonded semiconducting state. It has long been speculated that the amorphous solid and the liquid could represent two polymorphic forms of the amorphous state that are linked by density- or entropy-driven transformations. Such polyamorphic transitions are recognized to occur among several different types of liquid and glassy systems. Here we present experimental evidence for the occurrence of a density-driven polyamorphic transition between semiconducting and metallic forms of solid amorphous silicon. The experiments are combined with molecular dynamics simulations that map the behaviour of the amorphous solid on to that of the liquid state.     

Gel-based separation of single-walled carbon nanotubes for metallic and semiconducting fractions

Common technique for biomaterials recovery in genetics is freeze-squeeze procedure. However, this method found a new application in carbon nanotubes field in a selective separation of metallic and semiconducting nanotubes. None-commercial agarose gel acts as a selective absorbent for semiconducting nanotubes and allows to separate them from metallic type of nanotubes. In this work we point out the great potential of freeze-squeeze technique in the field of separation of nanotubes and prove that the post-separation purification procedure is crucial to perform the quality and quantity estimation of the fractionated samples. Furthermore, the detailed quantitative analysis of the efficiency of this process is shown. Additionally, we emphasize that this technique can be used for high-scale separation of metallic counterparts of single-walled carbon nanotubes due to its simplicity and low cost.     

Conductive polymer composites based on metallic nanofiller as smart materials for current limiting devices

The influence of the structure and the temperature on the Conductive Polymer Composites (CPC) properties has been studied. The investigated CPC are based on homo- and heterogeneous polymer blends of high density polyethylene, polybutylene terephthalate and poly(m-xylene adipamide), filled with dispersed silver nanoparticles (Ag). It is shown that by the appropriate use of the immiscible polymers blends the percolation threshold can be decreased twice, what significantly reduces costs and keeps better mechanical properties. Additionally, it was found that depending on the choice of CPC structure the commutation temperature from a conducting state to an insulating state can be observed between 45 and 180 °C. The observed high intensity of Positive Temperature Coefficient (PTC) effect, i.e. a sharp (narrow temperature range) and strong (10 orders of magnitude) resistivity increase, makes such composites promising for current limiting devices and temperature sensors.     

Reliability problems in state-of-the-art GaAs devices and circuits

A review of the reliability status of GaAs discrete devices and integrated circuits is given. In the present survey of new devices and circuits it is shown that a significant number of reliability problems continue to persist.     

State-of-the-art technologies and devices for high-voltage integrated circuits

The current status of high-voltage power semiconductor devices and technologies for high-voltage integrated circuits is reviewed and the new trends in this field are discussed. The paper focuses on the concepts of the novel reduced surface field and state-of-the-art silicon technologies such as high-voltage silicon on insulator, which are expected to play an increasingly important role in power system on-chip manufacturing. Lateral devices such as LDMOSFETs, superjunctions and lateral insulated gate bipolar transistors are discussed. The paper also touches on emerging technologies such as unified MEMS-IC for enhanced breakdown capability and isolation. Finally, an overview of the fierce fight of technology survival in terms of specific on-state resistance against breakdown voltage is given.     

High sensitivity to humidity of an element based on a carbon-nanotube bundle

The results of development and studies of humidity-sensitive elements based on a carbon-nanotube bundle are presented. It has been demonstrated that arrays of nanotubes grown by the low-temperature plasma-chemical method on planar silicon structures have exceptional sensitivity to humidity. The ratio of the structure resistance in dry and humid states is more than 10⁵-fold. Such a high relative resistance change is caused by the character of changes in conductivity of the charge carriers between individual tubes of the bundle upon adsorption of water molecules.