Cold spray-based rapid and scalable production of printed flexible electronics

Flexible electronics (FE) is attracting great attention from both scientific and industrial communities, and plays a crucial role in smart device applications. Despite great promise, traditional printing approaches (e.g., screen printing, ink-jet printing, etc.) often need a high-temperature post-sintering process to produce FE with desired electrical conductivity and adhesion strength. The post-sintering processes, however, often lead to fast oxidation of the functional coating while limiting the use of low-thermal budget substrates. Exponential advance of FE in a large-scale and energy-efficient manner relies on rationally eliminating the post-sintering processes. To this end, with the aim of uncovering process-structure-properties relationships, we employ the emerging cold spray (CS) technique for rapid and scalable production of FE without a need for high-temperature post-sintering. In this regard, micron-scale Tin (Sn) particles are directly written on a flexible polymer substrate (PET) by cold spraying under ambient conditions. The effect of CS process parameters on the resultant coatings is comprehensively characterized in terms of microstructure, film thickness, electrical conductivity, linewidth, and adhesion strength. The resulting electrodes show excellent electrical conductivity (6.98 x 105 S m-1), adhesion strength, long-term stability, and flexibility without significant conductivity loss after 1000 bending cycles. By leveraging the CS operational settings, a resistive macro-heater (12 x 15 cm2) and an LED circuit (2.5 cm x 18 cm) are fabricated to demonstrate the applicability of the CS in printed FE. Moreover, to address the low-spatial reso-lution of CS writing, a case study on sequential CS and femtosecond laser machining is performed, which further led to ultra-high resolution (i.e., 30 mu m linewidth) custom-designed flexible electrodes. Thus, the present study reveals the immense potential of the CS technique for rapid and scalable production of FE without the need for post-sintering.