Vergleich dielektrischer Gassensoren. CHEMFET's und Interdigitalkondensation

Dielectric sensors are nowadays widely investigated devices for gassensors (CHEMFETs or interdigital capacitors). If the adsorption of a gas changes the electric properties (dielectric permittivity, ion conductivity) of a dielectric material, it can be used as sensitive layer in a dielectric sensor. The change in the permittivity is the basis for the direct measurement of gases with dielectric sensors. In this paper organically modified silicates (heteropolysiloxanes) are used as sensitive layers (thickness about 0.6 mym) for SO2 and gas-concentrations from 1 ppm up to 6000 ppm. Sensor devices are CHEMFETs and interdigital capacitors. Both use the same electrical effect (change of the permittivity) to detect gases. Compared with interdigital capacitors CHEMFETs have lower impedance and detect as charge-sensitive devices the ionconcentration of the sensitive material. This paper describes the properties of CHEMFETs and interdigitated capacitors and shows their differences.