A wearable flexible humidity sensor with high-density and large-thickness interdigital electrodes and sensitive CQD bundles for urination monitoring in diapers

This work proposes a fabrication technique that can achieve wafer-level preparation of flexible interdigital electrodes (IDEs) with high-density and large-thickness (HD&LT). Utilizing these HD&LT flexible IDEs, we developed a flexible humidity sensor that employs a composite material made of nanowire bundles with carbon quantum dots (CQDBs) for humidity sensitivity. In this device, the composite material facilitates high absorption and capillary condensation of water molecules across various relative humidity (RH) conditions, while the HD&LT IDEs enhance the effective sensing area. Consequently, we achieve a flexible humidity sensor with exceptional performance. This sensor not only boasts key attributes such as low cost, easy fabrication, and straightforward operation but also establishes a foundation for extensive humidity sensing applications. In comparison to other devices utilizing small-thickness and low-density IDEs, our sensor demonstrates remarkable 2.5-fold and 5.8-fold increase in sensitivity across humidity ranges of 7%–59% RH and 59%–97% RH, respectively. To explore the practical applications of the device, we demonstrate its functionality in diaper humidity detection. With characteristics of wearability and durability, the sensor shows significant potential for humidity monitoring in wearable electronics.