Highly sensitive NO2 sensors based on organic field effect transistors with Al2O3/PMMA bilayer dielectrics by sol-spin coating

NO2 gas sensors based on organic field effect transistors (OFETs) with alumina/poly(methyl methacrylate) (Al2O3/PMMA) bilayer dielectrics were prepared by sol-spin coating method. The sensors with 0.8 mol/L Al2O3-sol dielectric layer show a high NO2 response, low baseline drift, stable sensing performance, and fast response/recovery time at room temperature. The sensitivity is over 129%/ppm and the limit of detection is below 1 ppm (134%). The results are comparable to most organic devices. The high sensor properties were attributed to the more ordered films on the dielectric layer and better electrical properties with bilayer dielectric devices than those with single dielectric devices. Compared to OFETs with PMMA single dielectric, the mobility was improved above 23 times, threshold voltage was reduced by 32.47 V, and both on-off current radio and saturation current were improved above an order of magnitude for OFETs with Al2O3/PMMA bilayer dielectrics at 0.8 mol/L Al2O3-sol. Moreover, the mechanism of organic film growth and the effect of bilayer dielectrics on sensing properties were analyzed. It is revealed that the highly electrical and NO2 sensing properties are closely relate. A simple and effective method, the sol-spin coating method, was provided to obtain high performance NO2 gas sensors based on OFETs.