Development of a miniaturized NO2 gas sensor based on nanoparticles WO3 thin film on interdigitated electrodes

A miniaturized semiconducting metal oxide NO₂ gas sensor with integrated micro heater is reported in this paper. The sensor has the size of 1×1×0.4 mm³ and detects NO₂ based on the electrical conductance change of porous nanoparticles WO₃ thin film, which is deposited on the interdigitated Pt electrodes. Integrated micro heater designed to provide the operating temperature above 200°C for the sensing material WO₃. In this work, a 2 μm-thick Si diaphragm is suspended on four surrounding beams and separated from the substrate, therefore, the thermal isolation is very efficient. Furthermore, the thermal stress is also reduced in the diaphragm, because it could expand or contract easily in all directions when the temperature changed. The fabrication is simple since the heater and electrode are fabricated in the same process. The sensor can detect dilute NO₂ gas as low as 0.05 ppm with high sensitivity up to 13. The design and electro-thermo-structural coupled field simulation as well as the fabrication and testing of the sensor are presented.