Conformable Electronics With Conductive Silver Structures by Electrohydrodynamic Printing

Recent advances in research and fabrication of flexible, stretchable, or rather conformable electronics with printed conductive structures have enabled a wide range of applications. Various fields such as consumer electronics or wearable devices for health monitoring are affected by these achievements. Owing to gradually increasing demands on enhanced functionalities and an excellent deformability of such electronics, an investigation of appropriate hyperelastic materials and progressive manufacturing techniques are mandatory. In this article, a cost-efficient approach for fabrication of conformable electronics based on vacuum thermoforming with printed microscaled silver structures is presented. The patterns in form of conductive line arrays and meanders are realized by the emerging electrohydrodynamic printing (EHD) technique which constitutes a promising alternative to established additive technologies due to the applicability of various printing media as well as its high material compatibility. Moreover, hyperelastic material models comprising the Mooney-Rivlin, Ogden, neo-Hookean as well as the Yeoh model for description of stretchable thermoplastic polyurethane (TPU) during deformation are contrasted and general capabilities for design optimization of conductive structures are derived by means of numerical simulations. Based on the EHD-printed metallic silver patterns on TPU with a subsequent transfer of the flat 100- $\mu $ m thick matrix toward a 3D-shaped electronic device by thermoforming, first demonstrators with a degree of deformation up to 57% are realized.