Current density is the amount of electrical current per cross-sectional area at a given point. As transistors in integrated circuits become smaller and smaller, they need higher and higher current densities to perform at the desired level. Most conventional electrical conductors, such as copper, tend to break due to overheating or other factors at high current densities, presenting a barrier to creating increasingly small components.

Microscopy image of an electronic device made with 1D ZrTe3 nanoribbons. The nanoribbon channel is indicated in green; the metal contacts are shown in yellow. Because of the nanometer-scale thickness, the yellow metal contacts appear to be under the green channel, when they are actually on top.

The electronics industry needs alternatives to silicon and copper that can sustain extremely high current densities at sizes of just a few nanometers. The advent of graphene resulted in a massive, worldwide effort directed at investigation of other two-dimensional (2D) layered materials that would meet the need for nanoscale electronic components that can sustain a high current density. While 2D materials consist of a single layer of atoms, 1D materials consist of individual chains of atoms weakly bound to one another, but their potential for electronics has not been as widely studied.

Prototype devices were developed that are made of an exotic material that can conduct a current density 50 times greater than conventional copper interconnect technology. Zirconium tritelluride (ZrTe3) nanoribbons were found to have an exceptionally high current density that far exceeds that of any conventional metals like copper. Conventional metals are polycrystalline — they have grain boundaries and surface roughness that scatter electrons. Quasi-one-dimensional materials such as ZrTe3 consist of single-crystal atomic chains in one direction. They do not have grain boundaries, and often have atomically smooth surfaces after exfoliation.

In principle, such quasi-1D materials could be grown directly into nanowires with a cross-section that corresponds to an individual atomic thread, or chain. The level of the current sustained by the ZrTe3 quantum wires was higher than reported for any metals or other 1D materials, almost reaching the current density in carbon nanotubes and graphene.

Electronic devices depend on special wiring to carry information between different parts of a circuit or system. As developers miniaturize devices, their internal parts also must become smaller, and the interconnects that carry information between parts must become smallest of all. Depending on how they are configured, the ZrTe3 nanoribbons could be made into either nanometer-scale local interconnects or device channels for components of the tiniest devices.

The experiments were conducted with nanoribbons that had been sliced from a pre-made sheet of material. Industrial applications need to grow nanoribbon directly on the wafer. This manufacturing process is already under development.

For more information, contact Holly Ober at This email address is being protected from spambots. You need JavaScript enabled to view it.; 951-827-5893.

Tech Briefs Magazine

This article first appeared in the November, 2018 issue of Tech Briefs Magazine.

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