AN SNO(2) BASED SWITCHING TUNNEL DEVICE FOR THE DETECTION OF NO(2) INAIR AT THE SUB PPM LEVEL

A new device has been developed for the detection of low NO2 concentra tions in air. The structure consists of a p+-Si substrate, an n-Si epi taxial layer, a thin tunnel SiO2 layer and a thin SnO2 sputtered film. Some of the sensors have been catalyzed with a thin Al sputtered laye r to improve the sensitivity and response rate to NO2. The electrical I-V characteristics are those of a tunnel diode, which shows a bi-stab le (low impedance, high impedance) behaviour. The switch may be accoun ted for by punchthrough and avalanche multiplication at the n-Si layer . It was found that the switching voltage is an increasing function of the NO2 concentration, as the work function of the SnO2 increases wit h the ionosorption of the electronegative NO2 molecules. The possibili ty of detecting NO2 concentrations as low as 50 ppb in air has been de monstrated.