(221e) Direct-Write Printing of Metal-Carbon Nanotube Composites for High-Performance Electronics

Bulk conductors for high-performance electronics rely on metals. However, research efforts to advance the technology increasingly seek to incorporate nanomaterials such as carbon nanotubes (CNTs) due to exceptional electrical transport properties at high frequencies (>10 GHz), elevated temperatures (>200 C) and small scales (e.g., natively avoiding eddy currents through a phenomenon similar to litz wire). In this presentation, we demonstrate the development of a 3D printing process based on simultaneous electrochemical deposition of metal and dispersed CNTs within a small liquid capillary bridge between a printing nozzle and conductive substrate. This novel process can create freestanding conductors with composition and CNT alignment controlled by the applied electric field. This technique builds upon our recent development of an electrodeposition process whereby homogeneous nucleation of Cu into a CNT mesh has been used to create bulk composites in sequential processing. This has enabled control of the final conductivity of a bulk composite over several orders of magnitude up to 2 MS/m for a lightweight composite with density up to 0.8 g/cm3, and identifying the process control parameters for the nucleation of copper within CNT meshes in aqueous and organic electrolytes.

Here, we first describe the requirements to formulate a suitable printing ink, including choice of metal ions, leveling agent, base solvent and CNT functionalization to balance dispersibility in solution with final part conductivity. We further develop the process by control of the applied current in galvanostatic operation to form printed lines and 3D structures with suitable conductivity (>1 MS/m), good part homogeneity (assessed via scanning electron microscopy and electron dispersion spectroscopy) and mechanical strength (able to survive dewetting of the capillary bridge of the ink). We finally discuss the size limits to form homogeneous, conductive structures and the next steps to convert our printing method into scalable processes.

Future directions may include scalable printing of microstructured antennas and wiring onto circuit boards, and for incorporation of our CNT-laden electrochemical deposition ink into standard metal-based semiconductor electronics production.