Stretchable printed circuit board integrated with Ag-nanowire-based electrodes and organic transistors toward imperceptible electrophysiological sensing

Abstract

Wearable devices with excellent mechanical stretchability, comparable to that of human skin, are highly desirable for preventing discomfort and dermatitis. Composite material systems that use metal particles and elastomers are promising for realizing intrinsic stretchable electrodes with high conductivity and enhancing mechanical flexibility of wearable devices. However, it is challenging to achieve stable device performance under mechanical deformation using stretchable electrodes. In this study, stretchable electrodes with enhanced conductivity and stretchability are developed and integrated with organic transistors to fabricate a stretchable printed circuit board (PCB) that acts as a voltage amplifier under large strains. The stretchable electrodes are composed of silver microparticles, a small quantity of silver nanowires (AgNWs), and an elastomer matrix, which demonstrated a conductivity of 8.5 × 103 S cm−1 at a curing temperature of 100 °C. The observed conductivity was 3.6 times higher than that of electrodes without AgNWs. Owing to the addition of AgNWs, the durability strain in cyclic stretching increased from 10% to 75%; the increment can be attributed to the suppression of microcrack propagation. Moreover, the proposed stretchable PCB was applied to fabricate a voltage amplifier, which enabled stable amplification by 14 times under 0% and 75% strain owing to a mechanical rigid-soft patterning designed into the substrate according to the rigidness of the mounted components. The stabilization technologies in the proposed stretchable PCB can contribute to the development of wearable devices for long-term usage to assist the early detection of diseases.