Improved long-term stability of MOS gas sensors using on-chip switched-capacitorreadout techniques

Despite a long period of more than one decade MOS gas sensors are still suffering from long-term instabilities. We present a new way of overcoming some of the problems by incorporating on-chip analog switched-capacitor circuitry. With this method the DC operating of the sensing devices is avoided and, hence, the sensors exhibit much higherstability. As heating elements and a temperature sensor are included, an external control circuit can maintain a constant operation temperature. Furthermore, the analog switched-capacitor circuits, which are also fully compatible with digital circuit techniques, offer the possibility of providing highly sophisticated signal conditioning and processing on the same silicon chip gas sensing.