Carbon Nanotube Magnetic Nanowire Compounds to Replace Transparent Conductive Oxide Films

Applied Materials has developed compound magnetic nanowires from materials comprising two-dimensional networks of carbon nanotubes and silver nanowires that provide an optically transparent electrically conductive layer with a desirable combination of low electrical sheet resistance and good optical transparency that can be used as a replacement for transparent conducting oxides. The carbon nanotube and compound magnetic wires are disclosed in U.S. Patent Applications 20100101832,  20100101830 and 20100101829. 

The conductive layer comprises a multiplicity of compound magnetic nanowires in a plane, the compound nanowires being aligned roughly (1) parallel to each other and (2) with the long axes of the compound nanowires in the plane of the layer, the compound nanowires further being configured to provide a plurality of continuous conductive pathways, and wherein the density of the multiplicity of compound magnetic nanowires allows for substantial optical transparency of the conductive layer, according to inventors Steven Verhaverbeke, Omkaram Nalamasu, Victor L Pushparaj and Roman Gouk in U.S. Patent Applications 20100101832.

 A compound magnetic nanowire may comprise a silver nanowire covered by a layer of magnetic metal such as nickel or cobalt. Furthermore, a compound magnetic nanowire may comprise a carbon nanotubes (CNT) attached to a magnetic metal nanowire. A method of forming the conductive layer on a substrate includes: depositing a multiplicity of compound magnetic conductive nanowires on the substrate and applying a magnetic field to form the compound nanowires into a plurality of conductive pathways parallel to the surface of the substrate.

Optically transparent conductor layers are used in a variety of applications where a transparent conductor is either required or provides an advantage. Applications using transparent conductors include: liquid crystal displays, plasma displays, organic light emitting diodes, solar cells, etc. The transparent conducting oxides (TCOs), such as indium tin oxide and zinc oxide, are the most commonly used transparent conductor materials.

However, TCO films represent a compromise between electrical conductivity and optical transparency--as carrier concentrations are increased to improve electrical conductivity, the optical transparency is reduced, and vice-a-versa. Furthermore, as the thickness of the TCO film is increased to improve electrical sheet resistance, the optical transparency is reduced. There is a need for optically transparent conductors with a more favorable compromise between electrical conductivity and optical transparency.  

Embodiments of Applied Materials’ invention provide an optically transparent conductive layer with a desirable combination of low electrical sheet resistance and good optical transparency. The transparent conductive layer is comprised of magnetic nanowires and/or magnetic nanoparticles which are (1) at a low enough density to provide good optical transparency, and (2) arranged to optimize electrical conductivity.

The properties of the transparent conductive layer may be optimized to provide good optical transmission, greater than 90% over the wavelength range of 250 nm to 1.1 microns, and low sheet resistance, less than 20 Ohm/square at room temperature. The concepts and methods for producing magnetic nanowires allow for integration of the transparent conductive layer into devices such as solar cells, displays and light emitting diodes.

According to aspects of Applied Materials’ invention, a conductive layer comprises a multiplicity of magnetic nanowires in a plane, the nanowires being aligned roughly (1) parallel to each other and (2) with the long axes of the nanowires in the plane of the layer, the nanowires further being configured to provide a plurality of continuous conductive pathways, and wherein the density of the multiplicity of magnetic nanowires allows for substantial optical transparency of the conductive layer.

Furthermore, the conductive layer may include an optically transparent continuous conductive film, wherein the multiplicity of magnetic nanowires are electrically connected to the continuous conductive film; the continuous conductive film may be either coating the multiplicity of magnetic nanowires or the multiplicity of magnetic nanowires may be on the surface of the continuous conductive film.