A highly sensitive, biodegradable capacitive humidity sensor with aerosol jet printed electrodes on a self-standing CMC film

Abstract

The increasing demand for sustainable, flexible and high-performance humidity sensors is driving the search for biodegradable alternatives to conventional electronic sensors. In this study, we report a highly sensitive capacitive humidity sensor fabricated on a self-standing carboxymethyl cellulose (CMC) bioplastic film, thus eliminating the need for additional substrates or sensing layers. The sensor design, including interdigitated electrode (IDE) geometry and film thickness, was optimized using COMSOL Multiphysics software's simulations to maximize sensitivity and ensure reliable performance. The CMC film was prepared via a dispersion-casting technique, and silver IDEs were directly deposited using aerosol jet printing, thus enabling a low-cost and scalable fabrication process. Comprehensive material characterization confirmed the film's smooth surface, robust electrode adhesion, and excellent flexibility, which allowed it to withstand repeated mechanical deformation. Electrical performance testing of the sensor revealed a marked increase in capacitance with increasing relative humidity (35–100% RH). The sensor achieved a sensitivity of 7110 pF/%RH, significantly outperforming a comparable paper-based reference. The sensor also exhibited a rapid response time of 5.3 s and a recovery time of 9.2 s, while maintaining stable performance under cyclic mechanical stress. The sensor also showed low hysteresis, confirming reversibility and operational stability. Biodegradability assessments under soil burial conditions indicated substantial weight loss and material disintegration, underscoring the environmental compatibility of the sensor. Owing to its high sensitivity, mechanical robustness, eco-friendliness, and cost-effective fabrication, the proposed CMC-based humidity sensor therefore holds significant potential for a scalable, broad spectrum of applications, including smart packaging, environmental monitoring, food safety, health care and wearable electronics.