Towards fully printed capacitive gas sensors on flexible PET substrates based on Ag interdigitated transducers with increased stability

Interdigitated capacitive transducers have been inkjet printed onto flexible substrates and optimized for gas sensing applications. Their characteristics have been improved by tuning the annealing/sintering conditions and making use of additional passivation procedures, such as Ag electroplating with Ni or Parylene-C coating of the whole device surface. The as-prepared transducers printed with Ag ink could be utilized in capacitive gas sensing structures up to 70% relative humidity only. Higher humidity levels irreversibly altered the nominal capacitance and conductance of the devices, limiting their practical application. This drawback could be eliminated through the upgrading routes specified above and stable operation over wide temperature ranges has been achieved. From the acquired data a quite accurate description of the sorption processes, involving the printed conducting layers and the supporting material, has been inferred. Furthermore the parasitic sensitivity to test vapours from the class of Volatile Organic Compounds in the concentration range of Threshold Limit Value - Time-Weighted Average as possible interfering analytes has been estimated. Test gas sensors obtained from the optimized transducers by additional coating with gas sensing films poly(ether urethane) successfully passed the laboratory evaluations and seem to be appropriate for use in real devices. (C) 2012 Elsevier B. V. All rights reserved.