Development of high-performance CaCu₃Ti₄O₁₂/NaCl humidity sensors via microstructural processing during aerosol...

CaCu₃Ti₄O₁₂ (CCTO) is a promising material for humidity sensing applications owing to its advantageous characteristics such as high dielectric constant. However, the low surface porosity induced during the preparation of pellet-based CCTO sensors results in poor sensitivity and minimal variation in capacitance in low-humidity environments. Notably, combining NaCl with CCTO is expected to enhance its sensing performance, surface hydrophilicity, and internal porosity, thereby solving the low sensitivity and poor linearity issues associated with low-humidity environments. Therefore, a high-performance humidity sensor, based on a CCTO/NaCl composite, was developed for environmental monitoring, with potential applications in healthcare, industry, agriculture, and daily-life humidity tracking. The sensor utilized CCTO/NaCl composite films prepared via aerosol deposition. The film performance was optimized by varying the carrier gases and pretreatment protocols. Air, as the carrier gas, enhanced the surface roughness, facilitating efficient water molecule adsorption. Post-annealing at 400 °C further improved the dielectric and sensing properties of the film. The incorporation of NaCl enhanced charge transport in low-humidity environments, thereby improving the sensitivity of the sensor. The NaCl milling time and particle size were controlled to precisely tune the film microstructure and porosity, and consequently, high sensitivity (2561 pF/%RH) and fast response times (1 s/2 s) were achieved. The proposed sensor has great potential for high-performance humidity detection and respiratory monitoring.