Sensor array and sigma-delta converters for carbon monoxide monitoring

In this paper a smart sensor system for carbon monoxide (GO) monitoring is described. A fabrication technology suitable for the realisation of a micromachined integrated microstructure, as physical support of the thin film gas sensors operating at high temperatures, has been developed. The thin silicon nitride membrane, 200 nm thick, has been obtained using the micromachining of silicon. The thin SnO2 based sensing layers have been deposited on top of the integrated microstructure using the reotaxial growth and thermal oxidation technique. Outputs of three sensors are processed by a mixed analog-digital electronic interface to compensate effects of relative humidity (RH) and of the C2H5OH interfering gas. Sigma-delta (Sigma Delta) signal processing and low-frequency noise reduction techniques are used to minimise silicon area and to meet required performance in a standard CMOS technology.