Additive Nanomanufacturing of Flexible Hybrid Electronics

Abstract

There is always great interest in finding new advanced manufacturing techniques to pave the way for realization of future flexible and wearable electronics. Direct printing of functional materials, structures, and devices on various platforms such as flexible to rigid substrates are of interest for applications ranging from electronics to energy and sensing to biomedical devices. Current additive manufacturing (AM) at micro scale processes are either limited by the available sources of functional materials or require to be in the form of precisely designed inks. In addition, the existence of surfactants/additives in inks add further printing complexity and contamination issues to the process. Here, for the first time, we report a novel laser-based additive nanomanufacturing (ANM) system capable of in-situ and on-demand generations of nanoparticles that can serve as nanoscale building blocks for real-time sintering and printing a variety of multifunctional materials and patterns at atmospheric pressure and temperature. We show the ability to print different materials, including titanium dioxide (TiO2), barium titanate (BTO), and indium tin oxide (ITO), on various rigid and flexible platforms such as silicon dioxide (SiO2), paper, polydimethylsiloxane (PDMS), and polyethylene terephthalate (PET) substrates. This nonequilibrium process involves a pulsed laser for the ablation of targets and in-situ formation of pure amorphous nanoparticles in atmospheric pressure and temperature. These amorphous nanoparticles are then guided through a nozzle via an inert carrier gas onto the surface of the substrate, where they are sintered/crystallized in real-time. We further show the process-structure relationship of the printed materials from nano to microscale. We demonstrated the dry printing and additive nanomanufacturing of flexible hybrid electronics and sensors on flexible polyimide and PET substrates. The electrical and mechanical characterization of the printed lines are studied, and different flexible hybrid electronics designs are printed and the performance of the devices are tested. Silver is the 68th most abundant element in the earth while copper is the 25th, which makes copper cheaper (1% of the price of silver). Therefore, printing copper has attracted more attention because of its huge potential. Using this technique, we were able to get the 12 µΩ.cm resistivity. Resistance of printed Cu measured in 5 months showed negligible variation, confirming the good stability of printed Cu in long time. 5B classification of ASTM adhesion test confirmed the good adhesion between the sintered Cu and polyimide kapton substrate. We upgraded the ANM printer to a multimaterial additive nanomanufacturing (M-ANM), allowing the printing of lateral and vertical hybrid structures and devices. By using M-ANM technique, various multimaterial devices such as silver/zinc oxide (Ag/ZnO) photodetector and hybrid silver/aluminum oxide (Ag/Al2O3) circuits has been printed and tested. The formation of a trench can increase the mechanical interlocking and interfacial region of the printed material, which can improve its reliability. We demonstrated a facile technique for simultaneously creating trench into polyimide substrates via laser etching process, followed by printing and sintering the laser-ablated silver (Ag) nanoparticles onto the embedded trench in the polyimide substrate. The irradiated areas is evaluated by mean of optical microscopy, and the relationship between laser beam fluence, pulse repetition rate and number of scanning path to the depth of created trench is described.