Recent studies have shown that conducting polymers are sensitivento a wide range of gases and vapours and may be used in gas-sensingnmicroelectronic devices. The authors present a basic model for polymerngas sensors which consists of a thin uniform polymer film lying on topnof a pair of either semi-infinite or finite coplanar electrodesnsupported by an insulating substrate. It is assumed that the gas, ornvapour, diffuses into the film and is, simultaneously, adsorbed at sitesnrandomly distributed throughout the film. The diffusion and adsorptionnequations are presented in terms of several fundamental dimensionlessnparameters which describe the underlying chemical and physicalnproperties of the system. Numerical solutions to the equations arencalculated for both the gas and adsorbate profiles within the films atnvarious times. These numerical solutions are compared with approximatenanalytical expressions previously derived for diffusion-rate limited,nreaction-rate limited and intermediate cases, and show good agreement.nFinally, a semiconductor model of electronic conduction in gas-sensitivenpolymer films is developed to calculate the theoretical device responsento the sorption of organic vapours. This model can be used toninvestigate the effects of device geometry on sensor response and isntherefore a useful design tool for evaluating novel device structures.nThe model may also be extended to cover other types of device, such asncapacitive or mass balance
展开▼
