Omnidirectional stretchability of freestanding interconnects for stretchable electronics

Abstract

Advanced stretchable electronics applications, such as health monitoring patches, high-density curvilinear detectors etc, not only require the interconnects in these devices to accommodate large uniaxial strains vvvvbut they should also be able to withstand complex multiaxial loading such as in-plane and out-of-plane shear loading for reliable and optimal device operation. However, only uniaxial stretchability of these stretchable interconnects is typically characterised and reported in the literature. Here, we compare three relatively similar and relatively simple freestanding interconnect geometries on the basis of their multiaxial stretchability to evaluate their feasibility for typical stretchable electronics applications. The three geometries include: (1) the (traditional) serpentine structure, that has been studied most extensively in the literature (2) the rotation out-ofplane elongation (ROPE) interconnect, designed to exploit buckling and out-of-plane rotation to enhance stretchability (Shafqat et al 2017 Micromachines 8 277) and the (3) the non-buckling inplane elongation (IPE) interconnect, designed to fit a maximum number of beam members within the footprint area. To evaluate the multiaxial stretchability of the three designs finite element (FE) simulations were performed by loading the interconnects in the xy-, yz-and xz-planes under a range of loading angles. Furthermore, multiaxial loading experiments were performed on the ROPE interconnect samples by loading the samples in uniaxial in-plane stretching, in-plane shear and out-of-plane shear loading cases and compared with the FE simulations.