Thin-film electronics on active substrates: review of materials, technologies and applications

In the last years, the development of new materials as well as advanced fabrication techniques have enabled the transformation of electronics from bulky rigid structures into unobtrusive soft systems. This gave rise to new thin-film devices realized on previously incompatible and unconventional substrates, such as temperature-sensitive polymers, rough organic materials or fabrics. Consequently, it is now possible to realize thin-film structures on active substrates which provide additional functionality. Examples include stiffness gradients to match mechanical properties, mechanical actuation to realize smart grippers and soft robots, or microfluidic channels for lab-on-chip applications. Composite or microstructured substrates can be designed to have bespoke electrical, mechanical, biological and chemical features making the substrate an active part of a system. Here, the latest developments of smart structures carrying thin-film electronics are reviewed. Whereby the focus lies on soft and flexible systems, designed to fulfill tasks, not achievable by electronics or the substrate alone. After a brief introduction and definition of the requirements and topic areas, the materials for substrates and thin-film devices are covered with an emphasis on their intrinsic properties. Next, the technologies for electronics and substrates fabrication are summarized. Then, the desired properties and design strategies of various active substrate are discussed and benchmarked against the current state-of-the-art. Finally, available demonstrations, and use cases are presented. The review concludes by mapping the available technologies to innovative applications, identifying promising underdeveloped fields of research and potential future progress.