HIGH-SENSITIVITY CONDUCTING POLYMER SENSORS

The sensitivity and response speed of the resistance changes of conduc ting polymer films when exposed to gases is increased if the film is t hin and if the measurement of the response excludes the polymer-to-met al contact resistance at the electrodes of the sensor. A method is des cribed whereby the resistance of electrodeposited films can be measure d as they are grown, enabling films of pre-determined resistances to b e produced. The principal cause of film resistance variation is differ ences in the time taken to bridge the gap between electrodes, The expe riments reported here involve four-terminal measurements, which enable the effect of electrode contact resistance to be estimated and elimin ated. The contact resistance between the polymer and metal electrodes is found to be up to 50% of the total resistance of the sensor, and le ss affected by exposure to a gas than is the polymer resistance, Four- terminal measurements of resistance therefore give the greatest sensit ivity.