Imperceptible Circuits for Wearable and Wireless Reconfigurable Electronic Devices

For the past decades, soft/stretchable sensors and actuators have been developed with a high-degree of imperceptibility, in order to match biological tissues’ properties and seamlessly functionalize textiles, attach to the human body or directly on internal organs. Integrated functionalities require robust electronic circuitry for proper synchronization, processing and transmission of data. Therefore, a complete wearable device should embed silicon-based electronics that meet standard Printed Circuit Boards’ performances. It should also have mechanical properties as close as possible to the sensors/actuator parts in terms of flexibility and imperceptibility to the user. Additional efforts should focus on the connection method between the different elements of the circuit, as classic rigid wiring on soft substrates inherently create concentration of strains and therefore mechanical weakness in the system.<br/>Here we present a process for the fabrication of flexible and lightweight circuits, for imperceptible, wearable and reconfigurable electronic devices. Based on copperleaves and parylene layers, the circuit can be multilayered to meet standard circuit density, while keeping an overall thickness below 10 µm. The materials are suitable with off-the-shelves soldering methods and microelectronic components. The thinness of the layers allows both high flexibility and the integration of microcontroller package with a high-density of connections, like the Wafer-Level Chip Scale Packages (WLCSP) with a pitch of 400 µm. In order to eliminate tethers and rigid connectors, wireless transmission methods were investigated through capacitive coupling plots. This study presents the signal parameters for wireless data transmission, as well as fabrication methods for selective deposition of capacitive materials. Patterning of non-conductive materials were also investigated to create a strong temporary attach between the different functionnal layers. Final device features fully wireless connections for high versatility, robustness and further imperceptibility in integration.