FET-like silicon sensor with a porous layer for NO2 detection

A new porous silicon-based sensor for detection of low level NO(2) concentrations (100 ppb) is presented. The sensor is an integrated p-channel JFET, provided with a porous adsorbing layer as sensing element. Adsorbed molecules by the porous silicon layer modulate the electrical current flowing through the crystalline p-channel below, in a similar way as the gate voltage in a FET. As a matter of fact, the device current increases as the NO(2) concentration increases. The effect of different NO(2) concentrations on the sensor current is investigated at different relative humidity levels and using ethanol as interfering gas. The sensor is highly selective for NO(2) with respect to ethanol. In fact, while 100 ppb of NO(2) produce a significant current variation (more that one order of magnitude), exposure to 500 ppm of ethanol does not produce appreciable changes. The relative humidity shows a screen effect, that is the current variation decreases as the relative humidity increases.