Copper‐Leaf‐Based Process for Imperceptible Computational Electronics

Imperceptible electronics have a key role in tomorrow's wearable technologies. Individual elements such as ultra-thin sensors, batteries, solar cells, and actuators are well described in literature, but there is a lack of methods to build the computing circuit itself. A new process is presented for the fabrication of flexible and imperceptible circuits that reach standards of microelectronics associated with significant integration density of components and interconnections, as well as multilayering. The stack uses a commercialized decorative copper leaf with a thickness of 450 nm as the conductive layer and a parylene substrate of a few micrometers. The copper leaf shows both high compliance and conductivity of bulk copper (5.96 x 10(7) S m(-1)), with electrical resistance stable over 5000 cycles of complete folding. The process requires stencil-free laser patterning that reaches fine-pitch integration, conventional soldering methods, and a three-step via fabrication and assembly process for multilayered circuits. The functionality of an ultra-thin, multilayered, lightweight, electrocardiogram-monitoring device is demonstrated. This allows for direct transfer of microelectronic designs for rapid prototyping from rigid board to imperceptible electronics.