HfLaOxHigh-k Dielectric Based, Fully Solution Processed OFET H2S Gas Sensor at Sub-ppm Regime, Using Photoirradiated-SVA Annealed PCPDTBT/MoS2 Nanocomposite Thin Film

Abstract

We have reported a highly efficient, low-voltage, and cost-effective H2S gas sensor utilizing the nanocomposite thin film of conjugated organic polymer Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b; 3,4- b'] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and inorganic material (MoS2) as an active sensing layer. To enhance the molecular ordering of the polymer chains in a composite solution, a photoirradiation method has been employed. A facile, inexpensive, and solution-processed floating film transfer method (FTM) is used to fabricate the nanocomposite thin film of PCPDTBT/MoS2. Furthermore, the state-of-the-art annealing method known as 'solvent vapor annealing' (SVA) provides improved crystallinity and excellent charge transfer throughout the polymer chain, which substantially enhances the gas sensing performance. High- {k} dielectric film of HfLaOx was deposited using the precursors of Hf and La, and spin coating deposition method. The dielectric film exhibited a smooth, pin-hole free, and uniform nature with a very low rms roughness of 0.18 nm and excellent dielectric properties such as high bandgap (5.2 eV), low leakage current density (100 nA/cm2 at -5 V), and high- {k} (24.8). To evaluate the thin film's electrical and gas detecting capabilities for harmful and dangerous H2S gas, a top contact bottom gate (TCBG) organic field effect transistor (OFET) was fabricated. The device was exceptionally responsive to the presence of hydrogen sulfide gas at concentrations even lower than 1 ppm and operated at room temperature (RT). The developed OFET device exhibits outstanding air stability, excellent response-recovery behavior, outstanding gas response repeatability, and a sensor response of 93.2% at 1 ppm exposure of H2S gas. Response/recovery times are 4/55 s, respectively. © 2001-2012 IEEE.