Electrical conductor

Abstract: Optically transparent oxides tend to be electrical insulators, by virtue of their large electronic bandgap (⩾3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO—all n-type (electron) conductors—which are widely used as the transparent electrodes in flat-panel displays1,2. On the other hand, no transparent oxide exhibiting high p-type (hole) conductivity is known to exist, whereas such materials could open the way to a range of novel applications. For example, a combination of the two types of transparent conductor in the form of a pn junction could lead to a ‘functional’ window that transmits visible light yet generates electricity in response to the absorption of ultraviolet photons. Here we describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency. We illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p-type conductivity up to 1 S cm−1. Although the conductivity of our candidate material is significantly lower than that observed for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.

Abstract: To avoid electrostatic charging of an insulating matrix an electrical conductivity above σ=10−6 Sm−1 is needed. At present, the most common practice to achieve this conductivity is to use a conductive filler such as carbon black. In this work, untreated catalytically-grown carbon nanotubes were dispersed in an epoxy matrix. After curing the epoxy, the electrical properties of the composite were measured in order to relate the filler volume fraction to the electrical conductivity. The intense stirring process used to disperse the carbon nanotubes has made it possible to achieve a matrix conductivity around σ=10−2 Sm−1 with filler volume fractions as low as 0.1 vol.%. These figures represent an advance on best conductivity values previously obtained with carbon black in the same epoxy matrix. These low filler fractions ensure that the mechanical properties of the matrix are not compromised.

Abstract: By using an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, we uniformly dispersed single-walled carbon nanotubes (SWNTs) as chemically stable dopants in a vinylidene fluoride-hexafluoropropylene copolymer matrix to form a composite film. We found that the SWNT content can be increased up to 20 weight percent without reducing the mechanical flexibility or softness of the copolymer. The SWNT composite film was coated with dimethyl-siloxane-based rubber, which exhibited a conductivity of 57 siemens per centimeter and a stretchability of 134%. Further, the elastic conductor was integrated with printed organic transistors to fabricate a rubberlike active matrix with an effective area of 20 by 20 square centimeters. The active matrix sheet can be uniaxially and biaxially stretched by 70% without mechanical or electrical damage. The elastic conductor allows for the construction of electronic integrated circuits, which can be mounted anywhere, including arbitrary curved surfaces and movable parts, such as the joints of a robot's arm.

Abstract: Recently, electromigration has been identified as a potential wear-out failure mode for semiconductor devices employing metal film conductors of inadequate cross-sectional area. A brief survey of electromigration indicates that although the effect has been known for several decades, a great deal of the processes involved is still unknown, especially for complex metals and solute ions. Earlier design equations are improved to account for conductor film cross-sectional area as well as film structure, film temperature, and current density. Design curves are presented which permit the construction of high reliability "infinite life" aluminum conductors for specific conditions of maximum current and temperature stress expected in use. It is also shown that positive gradients, in terms of electron flow, of temperature, current density, or ion diffusion coefficient foreshorten conductor life because they present regions where vacancies condense to form voids.

Abstract: Large-scale superconducting electric devices for power industry depend critically on wires with high critical current densities at temperatures where cryogenic losses are tolerable This restricts choice to two high-temperature cuprate superconductors, (Bi,Pb)2Sr2Ca2Cu3Ox and YBa2Cu3Ox, and possibly to MgB2, recently discovered to superconduct at 39 K Crystal structure and material anisotropy place fundamental restrictions on their properties, especially in polycrystalline form So far, power applications have followed a largely empirical, twin-track approach of conductor development and construction of prototype devices The feasibility of superconducting power cables, magnetic energy-storage devices, transformers, fault current limiters and motors, largely using (Bi,Pb)2Sr2Ca2Cu3Ox conductor, is proven Widespread applications now depend significantly on cost-effective resolution of fundamental materials and fabrication issues, which control the production of low-cost, high-performance conductors of these remarkable compounds