Conformal,Ultra-thin Skin-Contact-Actuated Hybrid Piezo/Triboelectric Wearable Sensor Based on AlN and Parylene-Encapsulated Elastomeric Blend

Flexible electronics based on piezoelectric/triboelectric devices is an attractive technology for human sensing. Their hybridization overcomes the limitations of single components, resulting in compliant skin sensors with enhanced performances and applicability. Such hybrid devices are typically based on wide-area scarcely durable polymers or lead-containing piezoelectric materials; they are often not biocompatible and poorly skin-adaptable, lacking in multifunctionality. In this work, a novel compliant, conformal hybrid piezoelectric-triboelectric ultra-thin wearable sensor made of biocompatible materials is reported. The device is in contact with skin through an ultra-soft patch covered on both sides by a thin friction parylene film. Its working principle is unprecedently based on three simultaneous, complementary and mutually enhancing effects: piezoelectric, skin-contact-actuation, and piezo-tribo hybrid contact. The device can detect, with high sensitivity and wide measurement range, both the impulsiveness of sudden motions and the slower micro-friction phenomena due to skin deformations, ensuring a stable and repeatable identification of bio-signals typical of body movements. The device multifunctionality is shown for identifying gait walking, distinguishing hand gestures with a 5-sensor system on the hand back, and monitoring human joints motions (neck, wrist, elbow, knee, ankle). The assessed energy harvesting capabilities demonstrate the suitability for fabrication of more complex self-powered sensing systems.