Printed electronic switch on flexible substrates using printed microcapsules

Printed electronics, the manufacturing of electronic components on large, flexible, and low-cost substrates by printing techniques, can facilitate widespread, very low-cost electronics for consumer applications and disposable devices. New technologies are needed to create functional components in this field. This paper introduces a new method to create an all-additive printed switch on flexible substrate materials, such as polymer foils and paper substrates. The active layer of the switch component consists of neutral polyaniline (PANI), which can be doped by acid to induce a shift from a non-conductive to a conductive oxidation state. Monodisperse core-shell microcapsules containing an acidic aqueous core liquid were produced by a novel inkjet-based encapsulation technology. It was shown that unfavorable water evaporation from the microcapsules could be reduced by the addition of calcium chloride to the core liquid. A switch component was prepared, consisting of inkjet-printed interdigitated silver electrodes, PANI active layer and printed microcapsules. If an external pressure was applied, for instance with a finger, then the switch component changed its state from non-conductive to conductive with a simultaneous distinct color change. The results clearly demonstrate the feasibility of the presented approach to create either a visual or electronic signal for use in printed electronic applications.