Epidermal electronics for seamless monitoring of biopotential signals

Medical deployment of electronics is often hampered by boxy and rigid packaging. Biological tissues are soft and curved, while electronic components are hard and angular. The mechanical mismatch can be improved by re-packaging electronics in radical new form factors. We present a technology platform using ultra-thin components linked with conformal interconnects and embedded in low modulus polymers to provide an excellent match to biological tissues. This technology platform builds on the pioneering work by Prof. John Rogers @ UIUC. [1, 2] Rather than developing novel semiconducting, conducting and insulating materials, the platform exploits the concept that only the top 5-15 μm of a silicon IC contributes to functional behavior. Similar considerations apply to other high performance components such as LEDs and photodiodes. The thin active layer can be removed and transferred to polymer by various processes, which we discuss below. The resulting thin and flexible silicon islands can be interconnected using metallization patterned to permit substantial macro-scale deformation while experiencing minimal micro-scale deformation, just as a coiled spring can stretch several times its own length while keeping the local metal strain within the elastic limit. On-body and in-body applications are both well suited to the technology platform. Epidermal electronics are skin-mounted systems that resemble electronic tattoos, and can be worn for extended periods without discomfort while providing continuous monitoring. In this paper, we discuss in detail, the following technologies and concepts that enable epidermal electronics: (1) Advanced die preparation methodologies that allow for thinning, placement, and attachment of sub-50μm commercial IC devices (COTS); (2) die embedding methods in flexible polymer substrates; (3) use of conformal metal interconnects to connect components; and (4) elastomer stacking optimized for application strain and compatibility with biological tissue. We present data of thinned COTS ICs embedded in flex test circuits to demonstrate the technology.