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 NO₂ concentration increases. The effect of different NO₂ concentrations on the sensor current is investigated at different relative humidity levels and using ethanol as interfering gas. The sensor is highly selective for NO₂ with respect to ethanol. In fact, while 100 ppb of NO₂ 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