Ferroelectric Polarization and Oxygen Vacancy Synergistically Induced an Ultrasensitive and Fast Humidity Sensor for Multifunctional Applications

With the arrival of the Internet of Things and artificial intelligence, humidity sensors monitoring water emissions from human metabolism have attracted great attention in the fields of smart wearable devices and noncontact human–machine interaction. However, their application is seriously limited by the trade-off between the sensitivity and response speed for traditional humidity sensors. Herein, to overcome it, a self-powered high performance humidity sensor is developed on the basis of the electric-poled and oxygen vacancy-rich BiFeO₃ (BFO) ferroelectric material. The synergistic effect of ferroelectric polarization and oxygen vacancy provides a strong driving force and active adsorption sites for an abundance of OH/H₂O adsorption, resulting in an ultrahigh response (∼10⁴) and ultrafast response/recovery speed (∼84/376 ms). Benefiting from its promising advantages, the wearable humidity sensor can accurately record the respiration rate/depth and recognize different human respiratory behaviors in real-time. Importantly, by utilizing the moisture from mouth-blowing and skin, the sensors are successfully applied to noncontact control of a robotic car, noncontact switch, and noncontact interface for visualization applications. This work provides an effective strategy for developing excellent humidity sensors that meet the requirement of noncontact interaction for next-generation intelligent electronics.