Humidity Sensor Using Subthreshold Regime of Flexible Organic Field Effect Transistor: Concomitant Effect of Gate Leakage Current and Semiconductor Conductivity

In this study, we fabricated a humidity sensor using top gate field effect transistor working in subthreshold regime with a dielectric deposited onto the pentacene semiconductor acting as encapsulation layer too. The device is characterized at room temperature with different humidity rate (RH). The results showed that the subthreshold current (Ioff) level depends on the humidity rate especially due to the concomitant change of dielectrique leakage current and semiconductor conductivity. From 10% – 90% of humidity rate, we observe an increase of subthreshold current after 25% of RH, and this increase was found to be reversible by pumping down. However, the electrical parameters such as mobility and threshold voltage remain unchanged under humid environment. The results obtained in this work show for the first time, to our knowledge this kind of behavior in OFET top gate devices, pointing out the combination effects of both leakage current and conductivity increasing.