High sensitivity conducting polymer sensors

The sensitivity and response speed of the resistance changes of conducting polymer films when exposed to gases is increased if the film is thin and if the measurement of the response excludes the polymer-to-metal contact resistance at the electrodes of the sensor. A method is described whereby the resistance of electrodeposited films can be measured as they are grown, enabling films of pre-determined resistances to be produced. The principal cause of film resistance variation is differences in the time taken to bridge the gap between electrodes, The experiments reported here involve four-terminal measurements, which enable the effect of electrode contact resistance to be estimated and eliminated. The contact resistance between the polymer and metal electrodes is found to be up to 50% of the total resistance of the sensor, and less affected by exposure to a gas than is the polymer resistance, Four-terminal measurements of resistance therefore give the greatest sensitivity.