Recent advances in flexible and stretchable electronics have led to a surge of electronic skin (e-skin)–based health monitoring platforms. Conventional wireless e-skins rely on rigid integrated circuit chips that compromise the overall flexibility and consume considerable power. Chip-less wireless e-skins based on inductor-capacitor resonators are limited to mechanical sensors with low sensitivities. We report a chip-less wireless e-skin based on surface acoustic wave sensors made of freestanding ultrathin single-crystalline piezoelectric gallium nitride membranes. Surface acoustic wave–based e-skin offers highly sensitive, low-power, and long-term sensing of strain, ultraviolet light, and ion concentrations in sweat. We demonstrate weeklong monitoring of pulse. These results present routes to inexpensive and versatile low-power, high-sensitivity platforms for wireless health monitoring devices.

Energy-harvesting technology utilising mechanical energy sources is a promising approach for the sustainable, independent, and permanent operation of a variety of flexible electronics. A new concept of a fully-flexible light-emitting system, self-powered by a high-performance piezoelectric thin-film energy harvester has been first established by manipulating highly-robust, flexible, vertically structured light emitting diodes (f-VLEDs). The f-VLEDs fabricated by anisotropic conductive film bonding and entire wafer etching show stable and durable performances during periodic mechanical deformations. A high-output energy harvester capable of generating up to 140 V and 10 μA can be fabricated via laser lift-off (LLO) process widely used in industries, in a safe and robust manner. In particular, this LLO process is of great benefit for the fabrication of mechanically stable, flexible piezoelectric devices, without causing any degradation of piezoelectric properties. In this process, self-powered all-flexible electronic system with light emittance can be spontaneously achieved by the electricity produced from flexible thin-film generator by applying slight biomechanical energy without any externally applied energy storage. This conceptual technology of self-powering based on the conversion of mechanical energy to electrical energy can open a facile and robust avenue for diverse, self-powered, bio-implantable applications, as well as commercial display applications.

Artificial auxetic sweat ducts enable electronic skin sensors to perform reliable and noninvasive health monitoring over a week.