Humidity sensors fabricated with polyelectrolyte membrane using an ink-jet printing technique and their electrical properties

Humidity-sensitive membranes made of ionene oligomer have been fabricated on the electrode substrate using a commercial drop-on-demand ink-jet printing system using a 15 μm diameter nozzle driven by a piezoelectric device. After deposition and evaporation of the solvent, the humidity sensors have been cross-linked by heating. Their humidity-sensitive properties have been determined by using a thermostatic humidity chamber. Electrical measurements under various relative humidity were performed. The humidity-sensitive characteristics of sensors obtained by ink-jet printing technique were compared with that of dip-coating method. Humidity sensors showed a decrease in impedance as an increase of relative humidity and their impedance characteristics are in a close agreement.