Resistance characteristics of conducting polymer films used in gas sensors

The measurement of the resistance of thin films of conducting polymer deposited between microelectrodes is discussed. Attention is drawn to the severity of self-heating effects which may perturb the measurement unless the measuring power is kept low. The conduction mechanism is nonohmic at frequencies below 1 MHz, but considerably more ohmic at frequencies of tens of MHz. Noise measurements show that the passage of d.c. current generates a high level of excess noise with a 1/f characteristic. This result, taken with the high-frequency data, is consistent with a model picture of a film conductivity which is dominated by intergranular contact at low frequencies although electrode contact effects cannot be completely excluded. Due to the 1/f noise, accurate resistance measurements are best made using a.o. techniques. (C) 1997 Elsevier Science S.A.