Ion Gel Coated Graphene Field Effect Transistor for Humidity Sensing Applications

Humidity sensors are crucial for weather forecasting, instrumentation and industrial processes, agriculture and real-time respiratory monitoring. Nevertheless, the sensitivity and response time are the key parameters, particularly, for the clinical applications. Here, we demonstrate an ion gel coated graphene field effect transistor (GFET) for humidity sensing. The ion gel, in addition to being a gate dielectric, acts also as a humidity sensing layer. Indeed, water molecules from the surrounding attach onto the surface of the ion gel due to the presence of the hydrophilic poly(ethylene glycol) diacrylate (PEGDA) monomer in it. The water molecules, being polar, act as a gate bias thereby modulating the current transport in the GFET. The sensor's sensitivity, in terms of the normalized current change per percent relative humidity (RH), is 0.0014 in the low sensitivity regime (<; 71% RH) and 0.0135 in the high sensitivity regime (>71% RH). The sensor swiftly detects the human respiration with a response time of 350 ms. Moreover, a stable response over an extended period of four weeks demonstrates the sensor's stability.