Capacitive-type sensors for the selective detection of nitrogen oxides

Abstract Since the capacitance of an oxide mixture consiting of two kinds of semiconducting oxides depends on the NO concentration, these mixed-oxide capacitors can be applied for a capacitive type of NO x sensor. Among the examined oxides, NiO mixed with ZnO was the most promising in terms of the sensitivity and response characteristics. A temperature slightly higher than 300°C was desirable as the operating temperature of the NiO-ZnO element, and a linear relationship between capacitance and NO x concentration exists below 30 ppm. Furthermore, the capacitance of NiO-ZnO is highly selective to NO x . As a result, the binary oxide of NiO-ZnO has a great potential as a new type of NO x sensor based on a capacitance change.