Highly Sensitive Humidity Sensor Based on NaCl-BiFeO3 for Noncontact Sensing

The development of advanced humidity sensors is becoming increasingly essential for the progression of various industries, particularly for integration with IoT devices. Consequently, the creation of high-performance humidity sensors is of paramount importance. In this study, we present a highly sensitive humidity sensor based on the ferroelectric oxide BiFeO3, which is further enhanced by the incorporation of the hydrophilic inorganic salt NaCl. By optimizing the NaCl content and the thickness of the sensing film, the 15 wt % NaCl-BiFeO3 sensor with a film thickness of 68 μm demonstrated an exceptional response of 10,073 as the relative humidity was varied from 13 to 86% RH at room temperature, representing a 46.3-fold enhancement compared to pure BiFeO3-based sensors. The sensor also exhibited rapid response and recovery times of 0.27 and 5.73 s, respectively. The excellent humidity sensing performance can be attributed to the increased electrical conductivity, which results from the generation of free ions due to NaCl dissolution in adsorbed water under high humidity conditions. Furthermore, this highly sensitive sensor is well-suited for noncontact applications, such as human respiratory monitoring and contactless control. This work underscores the potential of NaCl-BiFeO3 as a highly promising material system for high-performance humidity sensors in smart sensing applications.