Low-Cost Flexible Graphene Oxide Humidity Sensor Fabricated Using Inkjet Printing and Aerosol Deposition

Flexible humidity sensors play a critical role in medical diagnostics and industrial control systems. In this study, a low-cost flexible humidity sensor is presented. The humidity sensor is developed by printing silver interdigitated electrodes (IDE) on a polyethylene terephthalate (PET) substrate using an Epson Stylus C88+ inkjet printer. The sensing layer of the humidity sensor was fabricated using graphene oxide (GO) ink, which is deposited onto the electrodes using an aerosol deposition technique. The GO humidity sensor achieves excellent sensing performance over a wide range of humidity levels from 11% to 97% RH range, with a fast response time of 2 seconds and recovery time of 17 seconds. The sensor also exhibits ultra-high sensitivity (243 kΩ/%RH), low hysteresis (2.16%), excellent repeatability, long-term stability, and high flexibility (tested at bending radiuses of 4 cm, 3.5 cm, 3 cm, and 2.5 cm). The humidity sensing mechanism of the proposed GO humidity sensor was also discussed. Furthermore, the sensor exhibited excellent capabilities in monitoring human respiration, distinguishing between nose and mouth breathing, detecting finger movements without physical contact, and even recognising basic spoken words. These features of the sensor possess significant potential for various applications in human healthcare.