This letter produces a bifacial SnO2 thin-film ethanol gas sensor using micro-electro mechanical systems technology. A 1-μm-thick SnO2 film (290 μm × 290 μm) is deposited as the lower sensing layer, and a square (625 μm × 625 μm) 2-μm SnO2 is deposited as the upper sensing layer. For the interdigital transducer electrode and micro-heater, Cr is deposited at a thickness of 50-nm-thick Cr and Ni is deposited at a thickness of 250 nm. The measurement results show that with respect to the ethanol sensitivity, the bifacial structure has a much better ability to sense SnO2 than a single-sided sensing layer, at an optimum working temperature of 200°C.
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