A High-Performance Surface Acoustic Wave Humidity Sensor with Uniform Multiwrinkled Graphene Oxide Film

Humidity sensors were widely used in Internet of Things (IoT) applications. According to medical respiration monitoring, noncontact sensing, and human-computer interface requirements, fast response and high repeatability are important for efficient and precise signal acquisition. Previous research works mainly focus on sensitivity improvement with the scarification of response time, stability, and repeatability. In this paper, we proposed the surface acoustic wave (SAW) humidity sensors with comprehensive performance using the uniform multiwrinkled graphene oxide (GO) films as the sensing material obtained by vacuum filtration and liquid phase transfer method. The multiwrinkled GO films offered controllable thickness (thin to 29 nm), uniform wafer-level fabrication (2 in.), and abundant wrinkle, making them become effective sensitive films for SAW humidity sensors due to numerous adsorption sites and transfer channels for water molecules. The experimental results showed that the sensors can obtain high sensitivity (10.5 kHz/RH%@60 nm thick film), ultrafast response (∼45 ms), good stability (variation amplitude ∼0.1%), repeatability (variation amplitude ∼1%), and wafer-level fabrication capability demonstrating their practical applications for medical respiration monitoring, noncontact sensing, and human-computer interface.