Porous silicon or silicon carbide gas sensor, used to detect e.g. ammonia or nitrogen oxides in vehicle emissions, is covered by functional sealing layer
The detection zone (12a) of porous material, is covered by a functional layer (12b). This (12b) reacts sensitively to a medium under measurement. It interacts with the medium, causing a variation of its internal charge carrier concentration. This can be detected in the porous material. The functional layer has passivation properties. Functional layer (12b) comprises a basic and/or an acidic oxide. The functional layer (12b), especially an oxide, is applied as a coating of 0.1-10 monolayers, preferably 0.8-3 monolayers, on the porous material. It is 10-100 nm thick. It forms part of a field effect transistor (1) channel (8). The porous material is formed in the channel region of a field effect transistor, which not covered by a gate (10). The functional layer is applied by precipitation from solution.
