Three-dimensional out-of-plane geometric engineering of thin films for stretchable electronics: a brief review

Abstract Recent progress in engineering approaches for stretchable electronics and electronic components, including strategies focused on materials science or structural engineering, offer high signal-to-noise detection of vital signs via systems that provide conformal, noninvasive contact to curvilinear skin and are unobtrusive during human activity, such as general motion, exercise, and respiration. Structural engineering strategies with flexible thin films, whose deformation can be categorized as two-dimensional (2D) in-plane or three-dimensional (3D) out-of-plane, provide a release of stress created by stretching, bending, or twisting. Beyond 2D in-plane structural engineering techniques, 3D out-of-plane structural engineering techniques effectively distribute nonlinear and multidirectional 3D strain. Here, we review recent advances in 3D out-of-plane engineering techniques, including wavy and wrinkled structures, pop-up structures, kirigami and origami structures, and nature-inspired structures, and describe the strain distribution mechanisms, fabrication processes, applications, and characteristics of these approaches. We conclude with perspectives on applications of stretchable electronic devices with multidirectional stretchability and the existing challenges for future research.