Interconnected nanowire clusters in polyimide for flexible circuits and magnetic sensing applications

TLDR: In this paper, a 3D flexible circuit was fabricated by combining nano-and microtechnology, where clusters of nanowires form the vertical via connections. But the circuit structure is in essence a magnetic field sensor since the wires are made of nickel, a magnetoresistive material.

Abstract: By combining nano- and microtechnology we have fabricated three-dimensional (3D) flexible circuits, where clusters of nanowires form the vertical via connections. The nanowires, embedded in foils of polyimide plastic, are interconnected with two lithographically structured metallic surface layers. As the wires are defined by ion track technology they are stochastically distributed with a uniform density in macro-scale. In addition they are highly parallel in well-defined directions in the foil. The key structural element is a junction where overlapping lateral interconnection lines on the surface intersect with clusters of perpendicular or tilted wires. The demonstrated circuit structure is in essence a magnetic field sensor since the wires are made of nickel, a magnetoresistive material. The essential fabrication process comprises: ion track generation by means of heavy ion irradiation, selective ion track etching, electrodeposition of nanowires, and double-sided photolithography. The polyimide, employed commercially in, e.g. flexible printed circuit boards, is for the first time evaluated as a carrier for nanowires. The chemical properties and temperature stability makes the polyimide an appropriate material for implementation of electronic circuitry by ion- and photolithography.