A new fabrication technology for stretchable electrical interconnections is presented. This technology can be used to connect various non-stretchable polyimide islands hosting conventional electronic components. The interconnections are realized by patterning a 200 nm thick sputter-deposited gold film into meandering horseshoe shapes, functioning as 'two-dimensional springs' when embedded in a silicone elastomer. Polyimide support is introduced around the meandering conductors as a means to improve the mechanical performance. Processing is done on a temporary carrier; the islands and interconnections are embedded in polydimethylsiloxane in a final stage. To this end, a release technique compatible with high temperatures up to 350• C based on the evaporation of a 400 nm thick layer of potassium chloride is developed. Test structures consisting of stretchable interconnections with a varying polyimide support width were fabricated. These were strained up to twice their original length without compromising their functionality. Also cyclic mechanical loading at various strains was performed, indicating the influence of the polyimide support width on the lifetime. At strains of 10%, a minimum lifetime of 500 000 cycles is demonstrated. The presented technology thus provides a promising route towards the fabrication of stretchable electronic circuits with enhanced reliability.
A stretchable platform with spherical-shaped electronics based on thermo-
plastic polyurethane (TPU) is introduced for soft smart contact lenses. The
low glass transition temperature of TPU, its relatively low hardness, and its
proven biocompatibility (i.e., protection of exterior body wounds) fulfill the
essential requirements for eye wearable devices. These requirements include
optical transparency, conformal fitting, and flexibility comparable with soft
contact lenses (e.g., hydrogel-based). Moreover, the viscoelastic nature of
TPU allows planar structures to be thermoformed into spherical caps with a
well-defined curvature (i.e., eye’s curvature at the cornea: 9 mm). Numerical
modeling and experimental validation enable fine-tuning of the thermo -
forming parameters and the optimization of strain-release patterns. Such
tight control is proven necessary to achieve oxygen permeable, thin, nonde-
velopable, and wrinkle-free contact lenses with integrated electronics (silicon
die, radio-frequency antenna, and stretchable thin-film interconnections). This
work paves the way toward fully autonomous smart contact lenses potentially
for vision correction or sensing applications, among others
Conformable electronics, i.e., electronics that can be applied on curved surfaces, is demanded nowadays in place of conventional rigid printed circuit board (PCB) based electronics for a number of applications. In the field of stretchable electronics there has been a swift progress in recent years. In this paper we are presenting our contribution to this ever growing topic, including thin-film based polyimide (PI), supported Au stretchable meanders as well as PCB based Cu meanders. These meanders are supported by PI or poly(ethylene naphthalate)/poly(ethylene terephthalate) (PEN/PET) films. Thin-film based stretchable interconnects is targeting mainly the biocompatible environments with demands for strong miniaturization while the PCB based technology is used more for large area applications. Both approaches are reviewed in this paper in terms of fabrication processes, materials and cyclic fatigue reliability. For each technology fabricated demonstrators are presented as well.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.