Flexible Hybrid Integration Enabled xsOn-Skin Electronics for Wireless Monitoring of Electrophysiology and Motion.

On-skin electronics are promising in human motion and vital sign monitoring, disease diagnosis and treatment. On-skin systems are soft and stretchable, and can maintain electrical performances during bending, stretching or twisting, etc. However, current integrated circuit based fabrication processes are not compatible with stretchable substrate, and recently proposed flexible hybrid integration methods typically involve complicated fabrication processes or structural design, and do not support high integration density. Herein, we report a series of flexible hybrid integration strategies which endow the on-skin electronics with advantages of high integration density of electric components, facile fabrications, high stretchability and reliability. Proposed strategies include: 1. High I/O density with highly stretchable and conductive composite materials as interconnects; 2. Multi-layer structures enabled by stretchable and conductive via-holes; 3. High reliability approach for chip attachment onto stretchable substrate; 4. Design and fabrication of strain separation structure. Based on these methods, an on-skin flexible hybrid electronic system (FHES) is fabricated to collect electrocardiogram (ECG) and acceleration data, wirelessly transmit and display the data in real time on a mobile phone application through Bluetooth communication. We also verify the accuracy and stability of the FHES through the measurements of ECG and acceleration data from human skin under various conditions. The flexible hybrid integration schemes proposed can be adopted for the development of a variety of on-skin systems for biomedical applications.