The rapid development of wearable electronics and Internet of Things (IoT) is posing new challenges in a variety of technological fields.¹ Flexible and unconventional substrates as thin polymeric sheets and textiles will likely overcome the rigid substrates of conventional electronics, allowing a new generation of microdevices with luminescent, sensing and communication capabilities able to withstand a variety of mechanical deformations.^2,3 In this framework, the stiff and rigid metallic sheets should be replaced by lightweight and thin conductive film. Nowadays, Ag nanoparticles (NPs) are the reference choice in producing flexible conductive patterns and thin film on a variety of substrates though coating and printing technologies.^4,5 However, cheaper alternatives to the highly costing Ag-based ink are needed. in particular, Cu NPs could be the ideal candidate but the difficulties in their mass production as well as their high susceptibility to oxidation limited their application.^6–8

In this work, we propose an innovative method to produce conductive patterns of Cu NPs by reactive Aerosol Jet Printing (r-AJP) on different substrates. Cu NPs were in-situ reduced coupling two aerosol streams carrying the Cu precursor and a reducing agent, respectively. The process is fast, scalable and cheap. The electrical properties of the r-AJP Cu NPs metallization patterns were investigated, as well as their structure and morphology by x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis.

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