Recently, flexible electronics has attracted increasing attention, including batteries, displays, conformal antenna arrays, radio-frequency identification tags, electronic circuits fabricated in clothing, and biomedical devices, with new characteristics like large area, nonplanar forms, low manufacturing cost, disposable and wearable style, environmentally sustainable production methods, recycling, lightweight, lower energy consumption, and the integration of electronics as a part of other structures[6–10].
Traditionally, etching silicon technology is widely adopted in the microfabrication of conductive patterns in flexible electronics[11–14]. This method involves not only a complicated process but also much pollution. In recent years, many new manufacturing techniques have been improved, such as screen printing, gravure, inkjet printing, dip-pen nanolithography, nanoimprint lithography, etc.
Though the new technologies have shown great advantages compared with amorphous silicon technologies for flexible electronics, there still exist many problems, for example, some pollution and waste still cannot be avoided during screen printing, printer setups are also very expensive, the defective products produced by these methods are hard to repair, etc. Therefore, more practical technologies need to be studied.
Herein, an unusual strategy was designed to fabricate conductive patterns with high reproducibility for flexible electronics by drop or fit-to-flow method. In this strategy, firstly, silver nanowire (SNW) was synthesized and used to prepare SNW ink. Compared with silver nanoparticle ink, SNW ink provides low sintering temperature and low resistivity, guaranteeing good performance of the conductive pattern, because the continuous conductive track was fabricated by the contact of silver nanowires, not the melt of silver nanoparticles. Though the new emerging organic silver conductive ink can avoid high sintering temperature, but as for conductive track with more narrow line width, there exist many tiny bubbles by this method, resulting in bad performance. Secondly, polymer template (polydimethylsiloxane (PDMS), polymethyl methacrylate, etc.) on polyester (PET) substrate can be easily obtained by spin coating, baking, and laser etching. Thirdly, the prepared SNW ink can flow along the trench of the PDMS pattern spontaneously by drop, especially after plasma treatment with oxygen.
Clearly, compared with the current technologies, the drop or fit-to-flow method shows the following advantages: it decreases the pollution to a lower level and the setups used here are also very cheap. Besides, before the PDMS layer was peeled off, if there exist some defects in the conductive patterns, it can be easily repaired. So, this paper will attempt to describe the strategy. In addition, the feasibility of the approach was also testified by the preparation of an antenna pattern[20–23].