Ultra-thin and Skin-conformable Strain Sensors Fabricated by Inkjet Printing for Soft Wearable Electronics

Ultra-thin strain sensors have received vast attention due to their ultra-thin and ultra-soft skin-conformable nature with numerous applications in wearable electronics for soft robotics, health monitoring, and human-machine interfaces. With the most recent developments in printing technologies, printing electronics directly on ultrathin substrates is now more beneficial comparing with the conventional lithographic based electronic fabrication techniques, as printing offers several unique benefits in terms of wide-ranging material processability, process simplification, rapidness, and lower costs. Here, we report an ultra-thin and high performance strain sensor based on metal/polymer composite films, fully fabricated by inkjet-printing on a biocompatible decal transfer substrate (thickness approximate to 1 mu m). The sensor patches are consist of two inkjet printed layers i.e. a highly conductive metal bottom-layer made of silver nanoparticles and a polymer top-layer made of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The sensor patches exhibit the average gauge factor (GF) of around 12, and stretchability of up to 10%, with excellent durability (stretch/release tests up to 500 cycles). As application demonstrations, the strain sensors are employed to monitor the subtle human muscle movements, demonstrating excellent performance. The results show that our ultra-thin strain sensors have broad applications in next-generation smart wearable electronics.