Performance improvement of organic field-effect transistor ammonia gas sensor using ZnO/PMMA hybrid as dielectric layer

Ammonia (NH₃) gas sensors based on organic field-effect transistor (OFET) using poly(methyl methacrylate) (PMMA) blending with zinc oxide (ZnO) nanoparticles as a gate dielectric layer were fabricated. Compared to those with the pure PMMA dielectric layer, the sensing properties of these devices using ZnO/PMMA hybrid as the gate dielectric layer were significantly improved when the sensors exposed to various concentrations of NH₃, and the percentage response was nearly 10 folds higher than that using pure PMMA under 75 ppm NH₃. Also, the results showed that there was a remarkable shift in the threshold-voltage as well as a change in field-effect mobility after exposed to NH₃ gas. By analyzing the morphologies of the dielectrics and pentacene films and the electrical characteristics of OFET, it was found that ZnO/PMMA hybrid gate dielectric layer was responsible for the enhanced sensing properties. Also, the decreased grain size of pentacene was formed on the ZnO/PMMA hybrid dielectric, facilitating NH₃ to diffuse into the conducting channel and then interact with the ZnO nanoparticles. Moreover, the environmental stability of the OFET sensors was measured after storing the sensors under ambient atmosphere for 40 days.