Low-cost conductometric transducers for use in thin polymer film chemical sensors

Low-cost conductometric transducers have been designed and characterised with a view to their potential use as chemiresistors in mobile sensor applications. Four different geometries of transducer have been evaluated by two different measurement techniques. Devices were fabricated by etching planar gold electrodes on low-cost glass-fibre substrates (FR-4) using a standard printed circuit board (PCB) photolithography, wet etching and electroless plating method. Thin films of the P-type semiconducting polymer poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate), PEDOT-PSS, were cast onto the electrodes by spin-coating. The conducting polymer films were electrically characterised by measuring the film resistance from the underlying gold electrodes using a digital multimeter, and also by determination of the film's current–voltage transfer characteristic (I–V curve) measured with a precision laboratory 4-point probe instrument. This allowed the relative contribution of the contact resistance at the Au/PEDOT-PSS interface to be determined as a proportion of the overall measured resistance. Contact resistance is known to affect the analytical performance of chemiresistor type devices, so in this work the combined effects of electrode geometry, polymer film composition and ageing of the film on bulk film and contact resistances have been investigated. The applicability of the chemiresistor transducers for chemical sensing is demonstrated using a PEDOT-PSS thin film as an ethanol vapour sensitive coating in a simple vapour exposure test, where a reversible conductometric response was observed. Due to the simplicity, low-cost and ultra low-power requirements of these transducers, they may be particularly suited to battery powered mobile and wireless sensing applications, or to applications dependant upon energy harvesting.