Inkjet-Printed Graphene-based Flexible Humidity Sensor for Environmental Applications

In this study, a fully flexible inkjet-printed graphene-based capacitive humidity sensor is investigated using graphene oxide (GO) as sensing material mixed with Polyacrylic Acid, PAA. The printed humidity sensor consists of i) an optimally designed interdigitated electrode (IDE) made from reduced graphene oxide conductive ink material decorated with silver nanoparticle (rGO/Ag), ii) inkjet-printed GO as sensing material and iii) polyethylene terephthalate, PET as flexible substrate. The conductive ink is synthesize in house with a stable and consistent temperature setting which has successfully improve the yield performance of the graphene-based inkjet and the method of preparation has prevent the ink from agglomeration during printing. The multilayer inkjet-printed GO on top of the rGO/Ag IDE is employ to increase the contact area between the sensing layer and water vapor, thus leading to a high sensitivity sensor. The results shows that as the relative humidity is varies in the range of 30%RH to 90%RH, the proposed humidity sensor is able to achieve a highest sensitivity of 0.15pF/%RH at 50°C. The sensor show a stable capacitance value with a linear output at low humidity and increase exponentially at above 60%RH. The developed sensor also show a good temperature dependence at temperature below 60°C and humidity lower than 70%RH.