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

A new device has been developed for the detection of low NO2 concentrations in air. The structure consists of a p+-Si substrate, an n-Si epitaxial layer, a thin tunnel SiO2 layer and a thin SnO2 sputtered film. Some of the sensors have been catalyzed with a thin Al sputtered layer to improve the sensitivity and response rate to NO2. The electrical I-V characteristics are those of a tunnel diode, which shows a bi-stable (low impedance, high impedance) behaviour. The switch may be accounted 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 with the ionosorption of the electronegative NO2 molecules. The possibility of detecting NO2 concentrations as low as 50 ppb in air has been demonstrated.